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PICList Thread
'battery backed RAM'
1996\06\06@105511 by Wireless Scientific

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Folks,

I was reading last night that RAM is maintained if VDD is at least 1.5V. On
my last 80C188 design I used a NVRAM controller which managed sensing,
RESET, addressing and battery/VDD switch over for the RAM. So I'm familiar
with that but I'm having some problems thinking about battery backed
operation with a PIC.

Let's say that I found a battery controller chip that sensed VDD, worked
with MCLR and switched VDD to battery to maintain the 1.5V needed for RAM.
Here's my question, which I couldn't find the answer to in data sheets,
when MCLR is taken low as in circuit above, what happens to the I/O pins?
If they are output, are they going to still draw current? Something I don't
want because I'm battery powered now, only to save the RAM registers.
There's a initialization table that states the registers aren't affected
using MCLR like this (kind of like sleep mode). If this is the case, the
section on sleep might point me somewhere except my PIC is not really
sleeping, I'm holding it in reset until power is restored.


Does this make any sense? Any suggestions?

craig

1996\06\07@004811 by Steve Hardy

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{Quote hidden}

According to the datasheets, TIOZ is the time from asserting !MCLR low
to ports going Hi-Z, about 100ns.

Thus the I/O pins go HI-Z and no, they don't sink or source significant
current in this condition, even if their TRIS state is output.

Regards,
SJH
Canberra, Australia

1996\06\07@025724 by engmessi

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What info do you guys have about Parallax's 8051-like assembler for PICs ?

Is it time-saving ?
How about the final size of the program ?

Also, have any of you heard about embedding JAVA programs in PICs ?


Regards,

Pedro Drummond
__________________________________________________________________

   .-.
  /   \           .-.                                 .-.
 /     \         /   \       .-.     _     .-.       /   \
-/-------\-------/-----\-----/---\---/-\---/---\-----/-----
         \     /       \   /     `-'   `-'     \   /
          \   /         `-'                     `-'
Pedro Drummond
Engenharia Mestra de Sistemas / SP / Brasil
Tel: 55-11-883.4799  Fax: 55-11-883.4926
http://www.geocities.com/SiliconValley/4364
e-mail: .....mestraKILLspamspam@spam@u-netsys.com.br
_________________________________________________________________


'Battery Charger'
1996\11\15@064125 by ang (Chee Foon Tiang)
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Hi,
   Any PIC-ers have every done a
   Multi-battery (NiMH,NiCD & Li-ion) or
   Smart Battery charger?
   Would like to share notes.
Rgds,
Peter Tiang
tiangcfoonspamKILLspamhitachi.com.my

1996\11\15@085835 by Brian Hackett

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>    Any PIC-ers have every done a
>    Multi-battery (NiMH,NiCD & Li-ion) or
>    Smart Battery charger?
>    Would like to share notes.

Dear Peter,

I you do hear about anything, please let me know.  I am trying to use 4 NiMH
batteries in a pack and need a battery charger.  Thanks.  Brian.

'Battery Chargers'
1996\11\15@092438 by Harrison Cooper

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If I remember correctly, doesn't microchip have a special
little module using a PIC as a battery charger? I thought
it was based on the PIC14000 part.Could be wrong..

1996\11\15@093243 by Larry G. Nelson Sr.

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I just finished a smart charger with a benchmarq BQ2003 chip. Not fancy and
not as good as can be done with the Microchip part but the design was quick
and works well. No gas gauge or anything like that but charge before
discharge is supported as well as a large variety of charge termination
parameters.




At 09:09 AM 11/15/96 -0500, Brian Hackett wrote:
{Quote hidden}

Larry G. Nelson Sr.
.....L.NelsonKILLspamspam.....ieee.org
http://www.ultranet.com/~nr

1996\11\15@100135 by Ray Gardiner

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EDN ran a few articles last year on battery charging methods,I seem to recall
that the key was to look at the first derivitive of the battery volts and
look for inflections, you could try http://www.ednmag.com and do a search
of their back issues archives. If you already have a pic doing other stuff
then you will want it to look after the battery management. It is a complex
task and when the battery management fails the system as a whole fails!

If cost is not an issue then a solution like the microchip/zilog/benchmarq
parts may be a better solution.


{Quote hidden}

                                        regards,

Ray Gardiner, Shepparton, Victoria 3630,  Australia,   EraseMErayspam_OUTspamTakeThisOuTnetspace.net.au

1996\11\15@192706 by Jeff Otterson/N1KDO

picon face
Look at Maxim's MAX712 (NiMH) and MAX713 (NiCd) chips.  No PIC involved,
sorry.  I hava a schematic for a NiCd charger based on the MAX713 at my
website: http://www.mindspring.com/otterson/ham.htm


Jeff
Jeff Otterson
-------------
ottersonspamspam_OUTmindspring.com
Maker and user of tools
PGP key available at http://www.mindspring.com/~otterson/pgp.htm

1996\11\15@202544 by ang (Chee Foon Tiang)

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>Hi,
>I'm just inside this topic for my proper use. I fly some electric glider and
>now i'm studying a Hi-Tech charger with trickle mode, peak detection, charge
>with pulse and controlled current. But this project is waiting in my mind now.
>I'm thinking using a 8031 instead a PIC, because 8031 need only an EPROM and I
>can just program 16C84, 71 , 54..57, and EPROM that's all.
>As these chip seems to have not enought I/O and RAM, (means no RAM extension
>except trought I2C), my design will certainly use a 8031. In addition, most of
>A/D and D/A converter need a data bus sequence and 8031 have already a built
>in one.
>But nothing is fixed yet.
>
>The charger must do:
>        - delta-V charge,

   The charge termination method that is usually employed in the
   industry are:
   i.   minus delta V  - This is applicable to NiCD and NiMH batteries
                         although the NiMH has a smaller drop in
                         its terminal voltage upon full charge
                         Resolution required : -8mV/cell (for normal 6V
                         cellular batteries would be around -20~-40 mV)
                         This method is not applicable to the Li-Ion
                         battery
   ii.  dT/dt          - This method monitors the rate of change in
                         temperature and is very suitable for NiMH
                         batteries with termination at 0.8C/min.
   iii. const V, min I - This method is used for the Li-Ion batteries
                         which requires a constant V charge (you can
                         start as const I but must end with const V) as
                         oppose to constant I charge for the NiMH/NiCD.
                         Method is to charge at the rated voltage and
                         monitors the drop in I until a minimum cutoff.
   iv.  max V, max T & timer cutoff
                       - these are provided as a backup in the event of
                         i, ii & iii termination failure.

>        - pulse charge/measurement

   Pulse charge are suggested to prevent large crystals formation
   in batteries with continuous charge.

>        - cycling a batterie,

   Cycling basically discharges a battery follow by full charge.
   Discharging eliminates "memory effect" which are basically battery
   hysteresis. This is really important only for NiCD batteries.
   Newer batteries like NiMH and Li-Ion does not require discharge before
   charge

>        - discharge with controlled current/voltage

   This is a bit tricky, pulsed discharge (unless you have other method of
   controlling I/V) is not recommend as I heard somewhere that it
   damages the cell materials.

>        - trickle mode
>        - allows to charge more than 16 elements with a car batterie

   Car batteries are made of Lead acids elements, don't have much experience.

>        - allow to charge a minimum of 2 pack simultaneously with different
>        parameter,
>        - record the curve of charge/discharge, (EEPROM or RAM)
>        - be able to comunicate with a PC

   I would recommend that you build a big-banged RS-232-C interface to the
   PC and any data collected on the charge/discharge curve be store on it.

>        - have a LCD panel, some buttons
>
   LCD based on the Hitachi 44780 are quite good, especially if you
   use the 4-bit data interface (which saves you 4 I/Os, only 7 required)

>As you see, I just begin to think it. Seems to need a minimum:
>        - 16K RAM/or EEPROM

   If a PC is used you don't really need that much RAM or EEPROM.

>        - a 12 bit A/D

   For NiMH/NiCD charging, I don't think you require this kind of
   resolution. However, if you plan to charge Li-Ion batteries,
   it is highly recommended, as a difference in 100mV makes a lot of
   difference in the full charge capacity of the Li-Ion.

>        - two 8 bit D/A
   Why would you need a D/A?

>        - a PWM power
   Step down DC-DC convertor under PWM control would be recommended.
   However, check the maximum frequency of the microcontroller PWM
   that you are using as it ultimately dictates the size of your
   filtering components.
>        - an LCD panel
>        - a RS232 interface,
   As above.

>About Ni-Mh and Li-Ion, I don't have any documentation and I don't know what
>are the
>requierment to charge it in the better way.

   For all "normal" purpose, NiMH/NiCD can be charged in the same way.
   This is because NiMH batteries are designed to mimic the characteristic
   of the NiCD. However take note that it has a smaller -delta V termination
   point.
   Li-Ion is a totally type of battery. It can take const I charge but
   must be charged at const V finally. Accuracy of the charging V is
   crucial.

   Hope this gives a brief introduction to battery charging technology.

Regards,

Peter Tiang
@spam@tiangcfoonKILLspamspamhitachi.com.my

'Battery Charger -Reply'
1996\11\15@203210 by Chee Foon Tiang

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>Dear Peter,
>
>I you do hear about anything, please let me know.  I am trying to use 4 NiMH
>batteries in a pack and need a battery charger.  Thanks.  Brian.

   If you specifically used only NiMH batteries, then your
   life is much easier.
   Charge termination method:
   i.    dT/dt   - monitor the rate of change in temperature, normally
                   you would terminate at 0.8C/min
   ii.   -deltaV - monitor the drop in battery terminal voltage during
                   charging. Normally -8mV/cell. 1 cell = 1.2V
   iii.  Max V, Max T and timer cutoff thrown in for good measure.

   In your case of 4 battery packs, is it in series or parallel?

Regards,
Peter

1996\11\16@112103 by Brian Hackett

picon face
>Look at Maxim's MAX712 (NiMH) and MAX713 (NiCd) chips.  No PIC involved,
>sorry.  I hava a schematic for a NiCd charger based on the MAX713 at my
>website: http://www.mindspring.com/otterson/ham.htm

Hi Jeff,

Thanks for the info on the MAX713.  I tried to access your site and got a
"URL not found" error.  I can find Mindspring but can't find you on it.  Pse
advise.  Thanks.

Brian

1996\11\16@114829 by Chuck Kirk

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At 07:40 PM 11/15/96 +0800, Peter Tiang (Chee Foon Tiang)

Peter;

Check out the Maxim 2003. Look at the data sheets, app notes etc at:

http://www.maxim-ic.com/

and ask for a sample.

Regards.

1996\11\16@143258 by Jeff Otterson/N1KDO

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oooops...  I left the all-important tilde off...

 try

   http://www.mindspring.com/~otterson/ham.htm

there is a *postscript* copy of the schematic for the max713 based nicad
charger there.  If you don't have access to a postscript printer, then I
guess you could try GhostScript, which is freeware...

Jeff



At 11:20 AM 11/16/96 -0500, you wrote:
{Quote hidden}

Jeff Otterson
-------------
KILLspamottersonKILLspamspammindspring.com
Maker and user of tools
PGP key available at http://www.mindspring.com/~otterson/pgp.htm


'Battery Backup'
1997\01\21@184849 by James Ruxton
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I was wondering if anyone has any simple solutions for battery backup. I'm
using a 16C74 that is displaying info. on an alphanumeric led display.
There are times when I'll have to change the main battery , or turn off the
main battery for one or two days. My problem is I don't want to lose the
data in the PIC .  What would people reccomend in this case. Should I add
eeprom? Should I turn off the display  put the pic to sleep and run off a
cap or small battery? What is the simplest way to detect the main battery
being removed from the system and still have time to save important data?
If anyone has any thoughts on this issue I'd love to hear them. Thanks
--
Jim Ruxton              (416)927-7679
Cinematronics
Toronto Canada
RemoveMEcinetronTakeThisOuTspampassport.ca

1997\01\21@190934 by TONY NIXON 54964

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The simplest way is to have a diode in series with a backup battery
connected to the supply rail to the PIC.

If external components are controlled by the PIC which draw unwanted
current then the PIC can monitor the main supply rail with an IO pin.
When power is turned off, the backup battery takes over, and because
of the low input, the PIC can disable all external devices. The IO
pin may need a resistor to ground.

Memory backup caps (SuperCaps) can also be diode isolated and feed
the PIC power pins when the main supply is disconnected. The PIC
should then be put to sleep to minimise current draw. The PIC may not
function properly at voltages lower than 5V, but the RAM holds its
data OK. (1.5V RAM retention specified).

If the project is mains powered, then this power can charge a NiCad
or similay battery via a resistor in parallel with the supply
regulator.

More sophisticated ways can be employed using supply rail monitors
(from Maxim for example). These will automatically connect a backup
battery in the event of a power failure.

Regards
Tony


Just when I thought I knew it all,
I learned that I didn't.

1997\01\22@083947 by Mark A. Corio

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In a message dated 97-01-21 18:50:59 EST, you write:

>I was wondering if anyone has any simple solutions for battery backup. I'm
>using a 16C74 that is displaying info. on an alphanumeric led display.
>There are times when I'll have to change the main battery , or turn off the
>main battery for one or two days. My problem is I don't want to lose the
>data in the PIC .  What would people reccomend in this case. Should I add
>eeprom? Should I turn off the display  put the pic to sleep and run off a
>cap or small battery? What is the simplest way to detect the main battery
>being removed from the system and still have time to save important data?
>If anyone has any thoughts on this issue I'd love to hear them. Thanks
>--
>Jim Ruxton

Jim,
If your data that you want to maintain is not changing too often, eeprom
works well.  We are currently building a product where we want to power up
with the configurations that were set when the unit was powered down.  We
save the configuration to eeprom each time the user changes any settings.
This way they are always available at power up.

Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY  14624
Tel:  (716) 328-5850 --- Fax:  (716) 328-1144
http://www.frontiernet.net/~rmi/

***** Designing Electronics For Research & Industry *****


'Battery Isolators (Totally Unrelated to PIC)'
1997\02\05@185456 by Brian Boles
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    Does anyone know what is in a battery isolator, the devices that let
    one alternator charge 2 batteries on seperate circuits in a truck or
    boat.  Is it low forward drop diodes or some kind of relay???

    I would go for a newsgroup but our IS dept. won't set us up for that.

    Rgds, Brian.                    spamBeGonebbolesspamBeGonespammicrochip.com

1997\02\05@194133 by bigb

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Brian Boles wrote:
>
>      Does anyone know what is in a battery isolator, the devices that let
>      one alternator charge 2 batteries on seperate circuits in a truck or
>      boat.  Is it low forward drop diodes or some kind of relay???
>
>      I would go for a newsgroup but our IS dept. won't set us up for that.
>
>      Rgds, Brian.                    TakeThisOuTbbolesEraseMEspamspam_OUTmicrochip.com
The only ones i've seen contain 2 low forward drop diodes.
Brian Hurst

1997\02\05@195346 by Tony Matthews

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Brian Boles wrote:
>
>      Does anyone know what is in a battery isolator, the devices that let
>      one alternator charge 2 batteries on seperate circuits in a truck or
>      boat.  Is it low forward drop diodes or some kind of relay???
>
>      I would go for a newsgroup but our IS dept. won't set us up for that.
>
>      Rgds, Brian.                    RemoveMEbbolesspamTakeThisOuTmicrochip.com
Two diodes is my experience in the maritime buis. Tony m.

1997\02\05@230517 by Bob Blick

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At 04:47 PM 2/5/97 -0700, you wrote:
>     Does anyone know what is in a battery isolator, the devices that let
>     one alternator charge 2 batteries on seperate circuits in a truck or
>     boat.  Is it low forward drop diodes or some kind of relay???

The diodes are not low drop. The voltage regulator monitors the actual
battery voltage and the alternator just produces a little more voltage. The
secondary battery is not directly regulated, just regulated because of its
similar connection.

-Bob

1997\02\06@090213 by William Sadler

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On  5 Feb 97 at 16:47, Brian Boles wrote:

>     Does anyone know what is in a battery isolator, the devices that let
>     one alternator charge 2 batteries on seperate circuits in a truck or
>     boat.  Is it low forward drop diodes or some kind of relay???
>
>     I would go for a newsgroup but our IS dept. won't set us up for that.
>
>     Rgds, Brian.                    bbolesEraseMEspam.....microchip.com
>

In the UK for a second battery in a towed caravan a relay is usually
used. The relay is switched on when the ignition of the vehicle is
switched on, (ie. when the engine is running).

William Sadler

1997\02\06@105520 by Martin McCormick

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       I privately wrote Bryan, but one of the replies to the group makes
me a bit curious.  I told Bryan that one would need a voltage regulator
for each path since the batteries might be in different states of discharge.
If one battery sulphated or was, for some reason, discharged more than the
other, the one that was most charged would get an overcharge while the
deader battery was trying to catch up.  Is this possible or am I just mistaken?
The battery with the highest voltage will totally carry the system since the
diodes won't let current flow any other direction.

Martin McCormick

'Thanks for Battery Isolator Info'
1997\02\06@111145 by Brian Boles

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    Again, this list is a wealth of info.  I figured that if I just bought
    one, I would be paying too much for a metal box with some diodes in
    it.

    Thanks, Brian.

'Battery Isolators (Totally Unrelated to PIC)'
1997\02\06@112229 by Bradley, Larry

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Except that in a lot of standard marine alternators, the voltage
regulator is built into the alternator directly, and only can monitor
the alternator output voltage, not the battery voltage.

West Marine sells a device (which would be easy to build) that is a
relay that parallels the two batteries when the voltage is "high",
indicating that the alternator is charging the batteries. When the
voltage drops to a level that suggests discharge, the relay opens and
the two batteries are disconnected form one another.

Larry

{Quote hidden}

1997\02\06@182736 by William Chops Westfield

face picon face
   I privately wrote Bryan, but one of the replies to the group makes me a
   bit curious.  I told Bryan that one would need a voltage regulator for
   each path since the batteries might be in different states of discharge.

Lead acid batteries, unlike NiCd's/etc, are usually charged from a
constant-volatge supply (ie same voltage regardless of charge state.)

BillW

1997\02\06@201600 by Bob Blick

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At 11:21 AM 2/6/97 -0500, you wrote:
>Except that in a lot of standard marine alternators, the voltage
>regulator is built into the alternator directly, and only can monitor
>the alternator output voltage, not the battery voltage.
>

Yes and no. The regulator is built into many alternators, but that does not
mean it can't monitor the battery voltage.

I don't want to contradict you, but if you check with alternator
manufacturers, you will find that the alternator output wire is "never"
used for sensing the battery voltage. There is always another wire used to
sense the battery voltage, even if it does not appear that way, ie the
"idiot light" wire serves two purposes, both sensing(input) and
indicating(output)(Mercury Capri among others).

Alternators can be incorrectly connected, and monitor their output voltage
rather than the battery voltage, but no boat or automobile manufacturer
will do it that way. Mechanics and do-it-yourselfers, on the other hand,
will do whatever they want, whether it's right or not, and it might "work"
sort of.

Cheers, Bob

1997\02\06@215204 by Tony Matthews

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Bradley, Larry wrote:
{Quote hidden}

It's only .7 volt and I have used the two diode method to charge and
maintain starter motor battery /lighting electronics battery many times
in commercial enviroments.

1997\02\07@001539 by *optoeng

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Bob Blick wrote:
>
> At 11:21 AM 2/6/97 -0500, you wrote:
> >Except that in a lot of standard marine alternators, the voltage
> >regulator is built into the alternator directly, and only can monitor
> >the alternator output voltage, not the battery voltage.
> >
>
> Yes and no. The regulator is built into many alternators, but that does not
> mean it can't monitor the battery voltage.
>
> I don't want to contradict you, but if you check with alternator
> manufacturers, you will find that the alternator output wire is "never"
> used for sensing the battery voltage. There is always another wire used to
> sense the battery voltage, even if it does not appear that way, ie the
> "idiot light" wire serves two purposes, both sensing(input) and
> indicating(output)(Mercury Capri among others).


Never say 'never'.  There are definitely alternators that have only 2
external electrical connections.

>
> Alternators can be incorrectly connected, and monitor their output voltage
> rather than the battery voltage, but no boat or automobile manufacturer
> will do it that way. Mechanics and do-it-yourselfers, on the other hand,
> will do whatever they want, whether it's right or not, and it might "work"
> sort of.
>
> Cheers, Bob

--
NOTE: remove asterisks from email address to reply directly

Paul Mathews, consulting engineer
AEngineering Co.

email: RemoveMEoptoengspam_OUTspamKILLspamwhidbey.com
non-contact sensing and optoelectronics specialists

1997\02\07@035433 by Bob Blick

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At 09:06 PM 2/6/97 -0800, you wrote:

>Never say 'never'.

I didn't. I intentionally said "never" :-)

Cheers, Bob

1997\02\07@150259 by peter

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Anyone interested in alternators read on
if not delete

Before I start I would like to say that I am talking
about the type of alternator found on most European cars
and I'm sure there are exceptions

The alternator is a three phase AC generator
the three windings are connected in delta( triangle )
The three corners each go to two diodes (one to earth called D-
the other to 12V called D+ )

Now we come to the first variation
some alternators have three more diodes
which are connected to each corner to give a second
+ V.  These diodes are small (5amps)
This second + V. source powers, via the regulator,
the field ( also called DF )
This source is also connected to the ignition + via a
charge warning light, this has a double function,
first it powers the field (lamp lit) when the engine first starts
and indicates that the alternator is not charging

Regulators are normaly combinded with the brushes
but some are external normaly connected to the alternator
via a three pin plug, similar to a headlight bulb,
marked D-, D+ and DF

Regulators normaly use two transistors a Zener diode
one small cap (22n) and a few resistors
and the output is set to 13.8V
though a few are made for 14 or 14.2

Anyone want a circuit for a car regulator
email me direct and I'll send it to you
--
Peter Cousens
email: RemoveMEpeterTakeThisOuTspamspamcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem

1997\02\10@131527 by Bradley, Larry

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The regulator on the Motorola alternator on my boat (>25 years old)
appears to use pulse width modulation to control the field current ...
at least, that's what it looks like on a 'scope
Larry
{Quote hidden}

1997\02\10@164903 by peter

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Bradley, Larry wrote:
>
> The regulator on the Motorola alternator on my boat (>25 years old)
> appears to use pulse width modulation to control the field current ...
> at least, that's what it looks like on a 'scope
> Larry
> >----------
> >From:  Peter Cousens[SMTP:peterSTOPspamspamspam_OUTcousens.her.forthnet.gr]
> >Sent:  Saturday, February 08, 1997 12:56 AM
> >To:    spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU
> >Subject:       Re: Battery Isolators (Totally Unrelated to PIC)
> >
> >(SNIP)
> >Regulators normaly use two transistors a Zener diode
> >one small cap (22n) and a few resistors
> >and the output is set to 13.8V
> >though a few are made for 14 or 14.2

Yes they do work in switchmode
thats what the 22n cap is for

--
Peter Cousens
email: KILLspampeterspamBeGonespamcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem


'Battery Charge'
1997\06\02@013028 by Pablo
flavicon
face
Hi
I'm looking for an IC, or app note about charging a lead-acid
battery. I must use the less components I can and to make it
really cheap. I'm using a 68HC68 RTC that can control and manage
switching betwen VCC and battery because it has a Power Sense
circuit. Can I use this feature of the RTC for this application?.
I'll appreciate any help.
Thanks in advance,
Pablo Mochcovsky

1997\06\02@040706 by tjaart

flavicon
face
Pablo wrote:
>
> Hi
> I'm looking for an IC, or app note about charging a lead-acid
> battery. I must use the less components I can and to make it
> really cheap. I'm using a 68HC68 RTC that can control and manage
> switching betwen VCC and battery because it has a Power Sense
> circuit. Can I use this feature of the RTC for this application?.
> I'll appreciate any help.
> Thanks in advance,
> Pablo Mochcovsky

AN626 has both lead-acid and NiCd. Very good app-note.

--
Friendly Regards

Tjaart van der Walt
EraseMEtjaartspamEraseMEwasp.co.za
_____________________________________________________________
| Another sun-deprived R&D Engineer slaving away in a dungeon |
|             WASP International  http://wasp.co.za           |
|             GSM and GPS value-added applications            |
|  Voice : +27-(0)11-622-8686   |   Fax : +27-(0)11-622-8973  |
|_____________________________________________________________|

1997\06\02@050250 by Keith Dowsett

flavicon
face
At 02:26 02/06/94 ARG, you wrote:
>Hi
>I'm looking for an IC, or app note about charging a lead-acid
>battery. I must use the less components I can and to make it
>really cheap. I'm using a 68HC68 RTC that can control and manage
>switching betwen VCC and battery because it has a Power Sense
>circuit. Can I use this feature of the RTC for this application?.
>I'll appreciate any help.
>Thanks in advance,
>Pablo Mochcovsky

Float charging or cyclic charging?

So far as using the minimum number of components I read somewhere on the
Microchip site about a new 12C67x series chip with an ADC on board. Add a
few resistors, 78L05, and a high current FET (or two) and off you go.

Perhaps someone from Microchip can enlighten us about when the 12C671 & 672
will be hitting the streets?

Keith.


==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: @spam@kdowsett@spam@spamspam_OUTrpms.ac.uk
  WWW: http://kd.rpms.ac.uk/index.htm

1997\06\02@100838 by Ben J. Dasher III

picon face
Unitrode makes an IC (UC3906) which is a very good lead acid / gelcell
smart
battery charger. This IC requires a minimum of parts, and takes care of all
of
the battery charging functions. My ham radio club is currently using this
IC in
an on-line charger for our club repeater. I do not know what unitrode's web
site
address is, but  their telephone number is 603-429-8725, they are located
in
Merrimack, NH USA. Hope this helps.

Ben Dasher
Micro Computer Consultants
Atlanta, GA
Email spamBeGonebendasherspamKILLspamcompuserve.com

1997\06\02@150922 by Daniel

flavicon
face
-----Original Message-----
From:   Ben J. Dasher III [SMTP:.....BenDasherspam_OUTspamCOMPUSERVE.COM]
Sent:   Monday, June 02, 1997 6:56 AM
To:     TakeThisOuTPICLIST.....spamTakeThisOuTMITVMA.MIT.EDU
Subject:        Battery Charge

Unitrode makes an IC (UC3906) which is a very good lead acid / gelcell
smart
battery charger. This IC requires a minimum of parts, and takes care of all
of
the battery charging functions. My ham radio club is currently using this
IC in
an on-line charger for our club repeater. I do not know what unitrode's web
site
address is, but  their telephone number is 603-429-8725, they are located
in
Merrimack, NH USA. Hope this helps.

Ben Dasher
Micro Computer Consultants
Atlanta, GA
Email TakeThisOuTbendasherKILLspamspamspamcompuserve.com


Unitrode www page:

       http://www.unitrode.com

They have a new set of databooks coming out in a few weeks.


Daniel
Eagle Designs Corporation
Tel 503 492 2370    Fax 503 667 9613
.....infospamRemoveMEeagledesigns.com


'battery-operated pics...'
1997\07\29@165613 by William Chops Westfield
face picon face
A couple question on the LP pics and other PICs operated from batteries.

1) For the PIC rated to operate on 3-6V, do they work reliably when powered
  from a 3V lithium battery (ie Duracell DL123?)

2) The LP parts are rated for a max clock freqeuncy of 40kHz.  I find it
  difficult to believe that a drastically different process is used for
  these, and assume tha 40kHz is just as fast as they'll go and still stay
  under then 18uA current consumption limit.  Is that correct?  If I'm
  willing to put up with higher current drain, will they run reliably at
  1 to 4 MHz?

Thanks
BillW

1997\07\29@171638 by Miller, Steve

flavicon
face
>1) For the PIC rated to operate on 3-6V, do they work reliablywhen powered
>   from a 3V lithium battery (ie Duracell DL123?)
<snip>

My experience with the 16LC622 is that they cannot reliably be operated from a
3V lithium battery at 4MHZ.  (The data sheet claims that they will work down to
2V at a max clock of 40KHZ., but I needed a minimum clock of 4MZ.)  With a 4MHZ
crystal some parts will not even startup with a fresh lithium battery (3.3V to
3.6 V).  My local FAE stated that the parts are speced at 4MHZ and 3.0 V.  Other
parts, will work fine at 2.4 V with a 4MHZ crystal.  I ended up using two 3V
lithiums in series to get any sort of reliable operation from the 16LC622.
Remember to test at the voltages you expect with a weak battery.  Good Luck.

----- Steve Miller

1997\07\29@181200 by Matt Bonner

flavicon
face
> 2) The LP parts are rated for a max clock freqeuncy of 40kHz.  I find it
>    difficult to believe that a drastically different process is used for
>    these, and assume tha 40kHz is just as fast as they'll go and still stay
>    under then 18uA current consumption limit.  Is that correct?  If I'm
>    willing to put up with higher current drain, will they run reliably at
>    1 to 4 MHz?
AFAIK, _running_ reliably is not the problem - starting up is.  I
believe LP versus XT versus HS establishes the value of the internal
feedback resistor between OSC1 and OSC2: higher frequency crystals need
more feedback current.

--Matt

1997\07\29@223811 by David W. Duley

picon face
In a message dated 97-07-29 18:19:34 EDT, you write:

<<
My experience with the 16LC622 is that they cannot reliably be operated from
a
3V lithium battery at 4MHZ.  (The data sheet claims that they will work down
to
2V at a max clock of 40KHZ., but I needed a minimum clock of 4MZ.)  With a
4MHZ
crystal some parts will not even startup with a fresh lithium battery (3.3V
to
3.6 V).  My local FAE stated that the parts are speced at 4MHZ and 3.0 V.
Other
parts, will work fine at 2.4 V with a 4MHZ crystal.  I ended up using two 3V
lithiums in series to get any sort of reliable operation from the 16LC622.
Remember to test at the voltages you expect with a weak battery.  Good Luck.

----- Steve Miller >>
Hello Steve and all,
I did a project a while ago that was faced with the same problem.  I solved
it by using a MAX859 (I think that was the part#) Switching mode regulator.
It accepts down to 1V in and provides 3.6 volts out at 50ma.  It is a 8 pin
SO8 package and all you need is a 47mh inductor (This was about a 1206 SMD).
The device had to be small because it is wrist worn by astronauts.  It also
has a battery low output that can be monitored by the PIC.  We used a 1600mah
lithium primary cell that was 1" X .7" X .4".  The device had to run for 5
days on a single battery.
Hope this helps
Dave Duley
V.P. DreiTek Inc.


'Battery Charging Techniques'
1997\08\06@081902 by Scott Walsh
flavicon
face
    Guys,

    I know this is off topic, so please repsond via email.

    I need to implement a battery charger for NiMH cells, the battery has
    three cells.

    The battery needs to be fast charged in about 1 hour, the obvious
    thinsg I need to know are how do I determine when the battery has been
    charged. What time period did people take a measurement of the battery
    voltage ... 30secs, 1min maybe 2mins? Do I need to wait that long for
    the battery voltage to have change enough to be detected by an 8bit
    ADC. That of course raises the question as to whether 8bit ADC is
    enough ... I may be able to get a 10bit one.

    I am in the process of buidling a test rig with GPIB equipment to
    collate the data I need, but if anybody would care to enlighten me
    form their own experiences I would be very grateful.

    kind regards,
    Scott.

'Battery Charging Techniques - Reply'
1997\08\06@095417 by ang (Chee Foon Tiang)

flavicon
face
NiMH batteries requires constant current charge.
Typical fast charge is at 1C, where C is the capacity of the battery.

e.g If you have a 800mAH 3-cell NiMH battery, you charge them at
   a constant 800mA

End of charge condition:

i.   -dV    - small drop in battery voltage at full charge
ii.  0dV    - consequtive zero increment in battery voltage over a
             period of time at full charge
iii. dT/dt  - Sharp increase in the rate of change of temperature
             at full charge, typically 0.8 C / min.
iv.  timer  - fail safe timer cut-off
v.   max V  - fail safe absolute maximum voltage cut-off
vi.  max T  - fail safe absolute maximum (charger) temperature
             cut-off

Any one of the above would be satisfactory, but typically used
in combination. Fail-safe cut-off are required in commercial
charger to prevent possible fire hazard.

Normally 8-bit ADC would be sufficient but do note that the
the resolution, with a Vref of 5V, is around 20mV / bit.
And the -dV drop is in that region.

Furthermore, NiMH have a smaller -dV drop as compared to NiCD and
typical commercial charger uses a combination of at least two
end-of-charge detection.

Hope this helps,

Peter Tiang

====================================================================

    Guys,

    I know this is off topic, so please repsond via email.

    I need to implement a battery charger for NiMH cells, the
battery has
    three cells.

    The battery needs to be fast charged in about 1 hour, the
obvious
    thinsg I need to know are how do I determine when the battery
has been
    charged. What time period did people take a measurement of the
battery
    voltage ... 30secs, 1min maybe 2mins? Do I need to wait that
long for
    the battery voltage to have change enough to be detected by an
8bit
    ADC. That of course raises the question as to whether 8bit ADC
is
    enough ... I may be able to get a 10bit one.

    I am in the process of buidling a test rig with GPIB equipment
to
    collate the data I need, but if anybody would care to enlighten
me
    form their own experiences I would be very grateful.

    kind regards,
    Scott.

1997\08\06@101436 by Garrick A Kremesec

flavicon
face
I'm attempting to use a LTC1325 microprocessor-controlled battery
management system from Linear with a PIC.  It appears to be a versitile
chip and can be used to charge just about any type of battery you desire.
It requires several external components to drive the charging/discharging
of the battery, but the devices suggested are fairly common IRF devices.
It also has a "gas gauge" mode which measures the average voltage accross
a sense resistor to determine the average battery load current.  Or so
goes the advertisement.

Has anyone else used/attempted this controller?  How accurate is the "gas
gauge"?  Oh, it does a a 10 bit deep ADC to perform all of the various
measurements required during charging as measuring load current.

--
Garrick Kremesec
Beckman Institute - RA
http://www.cen.uiuc.edu/~gkremese
RemoveMEgkremesespamspamBeGoneuiuc.edu

1997\08\06@121416 by Harold Hallikainen

picon face
       There are, of course, chips just for this purpose.  I think they
generally watch for either a zero or negative dV/dt, depending on battery
chemistry.  They will also often watch battery temperature, since there
is a rapid rise in cell temperature on continued charging after the
battery reaches full charge.  Each of these techniques assume a constant
current charge.
       Comapnies that come to mind are Maxim and maybe Linear
Technology.  You could, in the interest of reducing chip count, do
soemething similar with a PIC.


Harold

1997\08\06@132230 by Scott Walsh

flavicon
face
    Harold,

    I am trying to design out a Benchmarq device we are currently using,
    yes we have a microcontroller on board and so I am going to get it to
    do the work.


______________________________ Reply Separator _________________________________
Subject: Re: Battery Charging Techniques
Author:  pic microcontroller discussion list <spamBeGonePICLIST@spam@spamspam_OUTMITVMA.MIT.EDU> at
INTERNET
Date:    06/08/97 12:11


       There are, of course, chips just for this purpose.  I think they
generally watch for either a zero or negative dV/dt, depending on battery
chemistry.  They will also often watch battery temperature, since there
is a rapid rise in cell temperature on continued charging after the
battery reaches full charge.  Each of these techniques assume a constant
current charge.
       Comapnies that come to mind are Maxim and maybe Linear
Technology.  You could, in the interest of reducing chip count, do
soemething similar with a PIC.


Harold


'Sensing Low Battery Condition'
1997\10\13@140426 by Ricardo Seixas
flavicon
face
Hi PICers

       Does anyone know a quick and dirty way (no Op Amp) to measure a low
battery condition ?
       Let's me explain:
       I've built a portable camber meter using a 16F84 that's powered by
a 9V battery and regulated down to 5V with a 7805, now I'm thinking to
implement a simple low voltage indicator that drives a pin (High or Low)
when battery reachs 5.5V.
       This pin must be shared, since all pins are already used :(
       It's no funny when you're in the middle of a camber adjustment and
the battery dies ...
       Any sugestions ?

Thanks


Ricardo Seixas

-------------------------------------------------------------------------
Ricardo Seixas
Mechanical Engineer
TakeThisOuTrseixasspamspamciclone.com.br

... Smile, tomorrow will be worst ...

-------------------------------------------------------------------------

1997\10\13@142914 by Jean Mercier

flavicon
face
Your 7805 regulator needs at least 7 volts to operate properly !
Use a low drop out regulator with an on board low input indicator. See
Maxim !
Jean

Ricardo Seixas wrote:
{Quote hidden}

1997\10\13@162205 by Roger L Stevens

picon face
Try the MAXIM MAX 666. It is an adjustable low drop out
regulator with a low battery indicator output  (LBO).
The LBO is open drain, low for low battery, thus may
be shared with another function.

Thanks to those who posted the HOLTEK info for me.

Roger
-----------------------------------------
What is a JOWETT JUPITER ?
Are there really Jowett Nuts ?
RemoveMErogerlstevensEraseMEspamspam_OUTjuno.com
-----------------------------------------

1997\10\14@013025 by Mike Keitz

picon face
On Mon, 13 Oct 1997 16:02:14 -0300 Ricardo Seixas
<@spam@rseixasRemoveMEspamEraseMECICLONE.COM.BR> writes:
>Hi PICers
>
>        Does anyone know a quick and dirty way (no Op Amp) to measure
>a low
>battery condition ?

Use one of the Panasonic voltage detectors in the Digi-Key catalog with a
voltage divider on the supply pin.  The current drawn from this pin is
only 5uA or so so the voltage divider resistors can be large.


>        This pin must be shared, since all pins are already used :(

It depends on what sheme you're using for pin sharing.  They have 3 kinds
of outputs, I think CMOS, inverted CMOS, and open-drain.  You want the
open-drain one so the output current doesn't flow through the voltage
divider and upset the comparison.  If you cut the power to the open-drain
one (pull Vdd pin low through a diode), the output should stay at
high-impedance.

1997\10\14@015048 by tjaart

flavicon
face
Ricardo Seixas wrote:
>
> Hi PICers
>
>         Does anyone know a quick and dirty way (no Op Amp) to measure a low
> battery condition ?
>         Let's me explain:
>         I've built a portable camber meter using a 16F84 that's powered by
> a 9V battery and regulated down to 5V with a 7805, now I'm thinking to
> implement a simple low voltage indicator that drives a pin (High or Low)
> when battery reachs 5.5V.
>         This pin must be shared, since all pins are already used :(
>         It's no funny when you're in the middle of a camber adjustment and
> the battery dies ...
>         Any sugestions ?
>
> Thanks
>
> Ricardo Seixas
>

Two resistors as a voltage divider on an input. Choose the values so the
input will 'trip' from high to low when the battery goes low. It won't
be
very accurate, but it will be cheap & simple.

--
Friendly Regards

Tjaart van der Walt
EraseMEtjaartspam@spam@wasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
|    Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973    |
|              WGS-84 : 26010.52'S 28006.19'E                 |
|_____________________________________________________________|

1997\10\14@054507 by Mike Smith

flavicon
face
-----Original Message-----
From: Ricardo Seixas <@spam@rseixasspam_OUTspam.....CICLONE.COM.BR>
To: spamBeGonePICLISTEraseMEspamMITVMA.MIT.EDU <PICLISTspamBeGonespamMITVMA.MIT.EDU>
Date: Tuesday, 14 October 1997 3:35
Subject: Sensing Low Battery Condition


{Quote hidden}

Measuring terminal volts may not be a good way of indicating low battery,
becuase you will get so little warning of impending dead battery that it is
meaningless (nicads are a good example).
How about storing 'battery used' time?  This works well with rechargables.
Microchip make a dedicated chip for battery management that includes this -
you interrogate it for battery life.

MikeS
<RemoveMEmikesmith_oz@spam@spamspamBeGonerelaymail.net>

1997\10\14@084214 by Larry G. Nelson Sr.

flavicon
face
You can use a comparitor. Set the input voltages using a divider network on
the raw DC and  the other side off the regulated DC. When the raw DC
divided value goes below the regulated value the comparitor will change
state and you will know the battery is below the threshold. I use a similar
technique with a 16C73 using an A/D channel to monitor battery voltage. Set
the divider networks so the output voltage from each is equal when the
battery voltage is at the minimum you find acceptable.


At 04:02 PM 10/13/97 -0300, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
.....L.NelsonRemoveMEspamieee.org
http://www.ultranet.com/~nr

1997\10\14@140004 by Steve Smith

picon face
Use a TL431CLP programable zener needs 2.5v ref therefore can set to turn on
at 4.8V with just 2 resistors and a cap output is low when voltage is ok any
port b line with pull ups turned on works fine. Using a 4k7 it can be twined
with something like an LCD enable line (active high) set to output read pin
as input the TL431 takes over cost about #0.30 total.

ascii circuit (poor)

5v-----2k7-----I      TL431,o----4k7-------pic port
0v-----3k0-----I-----TL431,c
0v--------------------TL431,g

Pic port pin may need a pull up r depending on use (use on an output active
high pin)

Cheers Steve.....

'Sensing Low Battery Condition (Thanks!!)'
1997\10\14@155957 by Ricardo Seixas

flavicon
face


       I'd like to thanks all that replyed to my question.
       In this circuit I'll use the method described by Mike Smith
to store "battery used time" since I'm using nicad.
       Using one or two EEPROM locations I can create a counter that
increment every minute and, when a determined count (time) is reached
I can display a message with a safety margin to recycle the battery.
       When the battery is recharged I can press a button before turn-on
the device then, at power-up the start routine check the button and if
pressed reset the counter.
       Another thing that flashed my mind is to use the EEPROM counter as a
safety device so, when a preset used time (or number of power-up's)is
reached the user at the next power-up MUST press a pre-determined sequence
in the buttons, otherwise the device becomes useless.
       To increment the counter on EEPROM every minute is no problem since
1x10^6 cycles (EEPROM safety margin)  = 694 days, 24 hours a day and, the
circuit is used 2 or 3 times a day (one hour max.).
       Note, this is note a comercial device.
       Now, another question ...

       Do nicads self-discharge when not in use ?
               If yes Then
                       this method becomes half useless
               End If
       Loop

Thanks again.

Ricardo Seixas

1997\10\14@163705 by WF AUTOMA‚̀O

flavicon
face
Ricardo Seixas wrote:
{Quote hidden}

Seixas,

O gravador PICgrammer vai indo bem? Qual m‡quina voc est‡ utilizando? Um Pentium?

Miguel.

1997\10\14@172432 by Steve Baldwin

flavicon
face
>         Do nicads self-discharge when not in use ?
>                 If yes Then
>                         this method becomes half useless
>                 End If
>         Loop

Just happen to have the right book next to me.

"Nicads have a self discharge rate of about 0.5% per day at 23 deg C when
near full charge and retain 20% to 40% capacity after 5 months. At 30 deg
C, 505 to 80% of
the charge is retained after 30 days."

Steve.

'Battery self discharge....'
1997\10\14@172439 by Steve Smith

picon face
In a message dated 14/10/97  20:03:55, you write:

<<   Now, another question ...

        Do nicads self-discharge when not in use ?
                If yes Then
                        this method becomes half useless
                End If
        Loop
 >>
Yes all secondary cells have a self discharge rate found in the battery data
sheets and generally expressed as n/C where C is the capacity in AH uasally
at the 10 hour rate and n the percentage of self discharge over a giiven time
eg .001 per day ect.
Nicads have lower self discharge rates than NiMh battries but are prone to
develop a 'memory' if only charged and discharged to part of their capacity
by far the best soulition to self discharge is a sealed lead acid battery but
the power to weight raito is much lower than Nicads very useful in stationary
aplications but not so good in portable equipment. (remember the old Luagable
telephones) lead acid battries.
Charging methods can be optimised to reduce cell memory in Nicads by using a
discharge cycle to ensure the battery is flat before commencing a charge
cycle.
It may be worth taking a look at Cyclon battries sealed lead acid but with a
very high discharge rate and very good power to weight raito made by Gates
energy products in US. These can be opperated in any orientation and give a
life expectancy in excess of a sealed Nicad the self discharge values are
very low on this product also.


Cheers Steve.........

'Sensing Low Battery Condition (Thanks!!)'
1997\10\15@012712 by tjaart

flavicon
face
Steve Baldwin wrote:
>
> >         Do nicads self-discharge when not in use ?
> >                 If yes Then
> >                         this method becomes half useless
> >                 End If
> >         Loop
>
> Just happen to have the right book next to me.
>
> "Nicads have a self discharge rate of about 0.5% per day at 23 deg C when
> near full charge and retain 20% to 40% capacity after 5 months. At 30 deg
> C, 505 to 80% of
> the charge is retained after 30 days."

This is true. We also use NiCds and have found the only way of getting
any meaningful indication is to measure the voltage difference between
discharging the battery for 10s at around 0.1C The voltage means
*nothing*.
Even the ambient temperature affects the discharge rate quite a bit.

--
Friendly Regards

Tjaart van der Walt
.....tjaartSTOPspamspam@spam@wasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
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1997\10\15@040713 by Scott Walsh

flavicon
face
    Ahhhh!

    I am also trying to define a way of implementing a 'low battery'
    detector.

    I have set up a GPIB system to make LOTS of measurements on a battery
    discharging, and it is becoming clear that just measuring an absoulte
    voltage to determine that the battery is about to fail is pretty bad.
    The behaviour of one battery pack to the next means that if using a
    voltage threshold as the decision for sensing the battery low
    condition that I will get from 1.5 minutes to 10minutes difference.

    I have come to the conclusion that meauring the rate of change of
    voltage drop is a MUCH better way. And is this what you are saying?
    Measure the voltage every 10 or 20 seconds or so and look at the
    difference between samples. This way you are going to 'quite' reliably
    going to find the 'knee' in the discharge curve of the battery just
    before it starts plumeting and your supply voltage becomes
    unregulated.

    regards,
    SW.


______________________________ Reply Separator _________________________________
Subject: Re: Sensing Low Battery Condition (Thanks!!)
Author:  tjaartEraseMEspam@spam@wasp.co.za at INTERNET
Date:    15/10/97 07:28


Steve Baldwin wrote:
{Quote hidden}

This is true. We also use NiCds and have found the only way of getting
any meaningful indication is to measure the voltage difference between
discharging the battery for 10s at around 0.1C The voltage means
*nothing*.
Even the ambient temperature affects the discharge rate quite a bit.

--
Friendly Regards

Tjaart van der Walt
RemoveMEtjaartspamspamBeGonewasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
|    Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973    |
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1997\10\15@042552 by tjaart

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Scott Walsh wrote:
{Quote hidden}

That is also a possibillity (the negative dV/dT method). This is a good
way
to decide when to stop fast charging. However, if you just need to know
the
current charge, do the following :
1) Measure V
2) Discharge for 10s at 0.1C
3) Measure V
The difference voltage as a percentage of 1) is a good indication of
current
charge level. (not perfect by any means, but good)

Don't do this often though, because you loose charge, and you may
deteriorate
the capacity through the 'memory' effect. This memory effect is claimed
to be
something of the past, but it is not (anyone with a cellphone should
know this).

The two greatest enemies of NiCd's :
1) Heat (ambient or from charging) - permanent loss of capacity
2) Cold - charge loss

--
Friendly Regards

Tjaart van der Walt
spamBeGonetjaartKILLspamspam@spam@wasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
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1997\10\15@074059 by Mike Smith

flavicon
face
-----Original Message-----
From: Ricardo Seixas <rseixasspam_OUTspam@spam@CICLONE.COM.BR>
To: spamBeGonePICLIST@spam@spamMITVMA.MIT.EDU <RemoveMEPICLISTEraseMEspamKILLspamMITVMA.MIT.EDU>
Date: Wednesday, 15 October 1997 5:35
Subject: Sensing Low Battery Condition (Thanks!!)


{Quote hidden}

Yes, somewhat, but the specs sheets should give you enough data to include
this effect.  Use a sleep system / RTC to keep track of time.

MikeS
<spamBeGonemikesmith_ozspam_OUTspamRemoveMErelaymail.net>

1997\10\15@080617 by Scott Walsh

flavicon
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    Doing the measurement every 10s or so at 0.1C discharge, is not a
    problem for me. I have a 650mAh battery pack being discharged at 60mA
    is this 0.09C ?

    So if you do use this method, what is the change in voltage between
    each 10s sample that you use to indicate a battery that is failing?
    Eeek, hold on, I know this depends on the number of cells in your
    battery, but hit me with the info anyway? I have three NiMH cells!

    kind regards,
    SW.


______________________________ Reply Separator _________________________________
Subject: Re: Sensing Low Battery Condition (Thanks!!)
Author:  .....tjaartspamRemoveMEwasp.co.za at INTERNET
Date:    15/10/97 10:25


Scott Walsh wrote:
{Quote hidden}

That is also a possibillity (the negative dV/dT method). This is a good
way
to decide when to stop fast charging. However, if you just need to know
the
current charge, do the following :
1) Measure V
2) Discharge for 10s at 0.1C
3) Measure V
The difference voltage as a percentage of 1) is a good indication of
current
charge level. (not perfect by any means, but good)

Don't do this often though, because you loose charge, and you may
deteriorate
the capacity through the 'memory' effect. This memory effect is claimed
to be
something of the past, but it is not (anyone with a cellphone should
know this).

The two greatest enemies of NiCd's :
1) Heat (ambient or from charging) - permanent loss of capacity
2) Cold - charge loss

--
Friendly Regards

Tjaart van der Walt
tjaartspam@spam@wasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
|    Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973    |
|              WGS-84 : 26010.52'S 28006.19'E                 |
|_____________________________________________________________|

1997\10\15@082910 by tjaart

flavicon
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Scott Walsh wrote:
>
>      Doing the measurement every 10s or so at 0.1C discharge, is not a
>      problem for me. I have a 650mAh battery pack being discharged at 60mA
>      is this 0.09C ?
>
>      So if you do use this method, what is the change in voltage between
>      each 10s sample that you use to indicate a battery that is failing?
>      Eeek, hold on, I know this depends on the number of cells in your
>      battery, but hit me with the info anyway? I have three NiMH cells!
>
>      kind regards,
>      SW.

Whoa! NiMH is not NiCd! Therefore the charge/discharge curves are not
the
same.

To give you some indication for NiCds, if you take the difference as a
percentage of the starting voltage, over 95% is full, and below 50%
becomes dicey.

I haven't tried it on NiMH cells, but it would be interesting to see how
well it works.

--
Friendly Regards

Tjaart van der Walt
EraseMEtjaartRemoveMEspamSTOPspamwasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
|    Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973    |
|              WGS-84 : 26010.52'S 28006.19'E                 |
|_____________________________________________________________|

'Battery self discharge....'
1997\10\15@105019 by Matt Bonner

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Steve Smith wrote:
>
> In a message dated 14/10/97  20:03:55, you write:
>
> <<   Now, another question ...
>
>          Do nicads self-discharge when not in use ?
>                  If yes Then
>                          this method becomes half useless
>                  End If
>          Loop
>   >>
> Yes all secondary cells have a self discharge rate
..snip..
> It may be worth taking a look at Cyclon battries sealed lead acid but with a
> very high discharge rate and very good power to weight raito made by Gates
> energy products in US. These can be opperated in any orientation and give a
> life expectancy in excess of a sealed Nicad the self discharge values are
> very low on this product also.
I've recently been playing with rechargable alkaline.  Apparently they
have a low self-discharge (they're already charged off-the-shelf), have
no memory problems, can be recharged up to 150 times.  I don't know
their energy density, but it's at least as good as NiCad.  Need their
own type of charger, though.
--Matt

'Sensing Low Battery Condition (Thanks!!)'
1997\10\15@120628 by Mike Keitz

picon face
On Tue, 14 Oct 1997 17:58:00 -0300 Ricardo Seixas
<RemoveMErseixasKILLspamspamTakeThisOuTCICLONE.COM.BR> writes:
>
>        I'd like to thanks all that replyed to my question.
>        In this circuit I'll use the method described by Mike Smith
>to store "battery used time" since I'm using nicad.

I believe in the original post you said the project was a portable
measuring device.  What does your device do as the battery runs down?
Does it (a) just quit all of a sudden, or (b) give inaccurate readings
when the battery voltage is low?  The latter condition is very bad.
Others have proposed schemes to give an early warning that the battery is
failing.  This is somewhat difficult on NiCds and may not be of much use
anyway.  Users will correctly deduce that a mode (a) condition is a dead
battery.  But you need the circuit designed to guarantee that
mis-operation in mode (b) will not happen.  Regardless of the battery
type, this is done with a simple absolute voltage detector or design of
the circuit so it always goes to mode (a) first.

>        Using one or two EEPROM locations I can create a counter that
>increment every minute and, when a determined count (time) is reached
>I can display a message with a safety margin to recycle the battery.
>        When the battery is recharged I can press a button before
>turn-on
>the device then, at power-up the start routine check the button and if
>pressed reset the counter.

This assumes that the battery will be fully recharged every time.  The
time needs to be decreased as the battery loses capacity due to age, or
you could set it rather short from the outset so significant capacity
will be sure to remain.  This will lead users to ignore the warning
though.

Users often only charge enough to get a little more use.  This is rough
on the battery, but what do they know?  Also they may have to if they
can't afford the time to take the device out of service for a full
recharge.  They may ignore the warning and continue using until the
battery is dead.  That's why it needs to be designed to stop gracefully
when the battery expires.

1997\10\16@022625 by Dwayne Reid

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face
>        Does anyone know a quick and dirty way (no Op Amp) to measure a low
>battery condition ?
>        Let's me explain:
>        I've built a portable camber meter using a 16F84 that's powered by
>a 9V battery and regulated down to 5V with a 7805, now I'm thinking to
>implement a simple low voltage indicator that drives a pin (High or Low)
>when battery reachs 5.5V.
>        This pin must be shared, since all pins are already used :(

I have a simple circuit using a few resistors and almost any PNP transistor.
It works well only when you are using a low dropout regulator however.

I generally use a National LP2950 regulator (0.2 V dropout, loads less than
50 mA) or a LM2931 (similar dropout, good for several hundred mA, but a real
pig for current when the battery gets low).  My best recomendation is the
LP2950 if your current requirements will allow it.  NOTE: any of these low
dropout regulators MUST have a large output filter cap (10 uF) or they will
oscillate.

The actual low V dropout detect is based upon the 0.6 V emitter-base turn on
voltage of the transistor.  When the battery voltage drops to less than
about 5.7V, the transistor turns off.  The dropout voltage of the regulators
mentioned earlier is about 0.2V, well below the turn on voltage of the
transistor.  It gives solid, reliable low voltage warning from while the
battery is still able to keep the regulator in regulation down to the point
where the micro won't function any more.



           -----------    ------/\/----+----  to PIC pin
          |         E \  / C    47K    |      HI=batt OK
          |          ------            \      LO=batt low
          |             |              /
          |             /         100K \
          |             \ 47K          |
          |             /             gnd
          |   -------   |
  from ---+---| reg |---+-- +5v to circuit
  batt    |   ---+---   |
     i/p ---     |     --- o/p
     cap ---     |     --- cap
          |      |      |
         gnd    gnd    gnd


notes:
1) the voltage at the collector of the transistor nearly the same as the
battery voltage while the battery is above the dropout voltage.  The 47K
series resistor at collector limits the current into the port pin protection
diodes.  The 100K pulldown resistor pull the port pin to gnd when the
transistor turns off.  Note that the port pin must be configured for TTL
input levels (don't use pin RA4 unless you change the 47K resistor).

2) The circuit that you are powering with this must draw a certain minimum
amount of current or the regulated voltage will rise above the desired
value.  This is because both 47K resistors are supplying current from the
unregulated input to the regulated output.  For example, if using a 9V
battery, the minimum current the circuit must draw is (9-5) / 47K + (9-5) /
47K = 0.17 mA.  Note that almost none of the current is wasted - most of it
goes to the 5 V rail.

3) I have used this when I am really short of IO pins by using the output
from the transitor as a pullup for a data line or pushbutton input and
adding a 1 uF cap from the collector to gnd.  Software then checks to see if
the line is low for a longer period than normal; if it is, then the battery
is too low and I can warn the user of the fact.  The added cap at the
collector ensures that short "blips" of current that might pull a weak
battery below the dropout threshold do not corrupt the normal function of
the IO line.

If you don't need to warn the user of a low battery and just want the PIC to
play dead, then use the output to drive MCLR.  You'll need to change the
output series resistor to about 10K, the pulldown resistor to about 39K, add
a signal diode from MCLR to VDD (anode to MCLR), and another 1 uF cap from
MCLR to either VDD or gnd.  The diode ensures that MCLR stays within
allowable limits (it doesn't have a protect diode to VDD), the cap keeps
noise from resetting the PIC inadvertantly.  I personally don't use this
method for user operated devices, however, a variation of this is what I use
for all unattended (embedded) type projects.

I hope this helps.

Dwayne Reid   <spamBeGonedwaynerspam@spam@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, Alberta, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1997\10\16@072953 by Mike Smith

flavicon
face
-----Original Message-----
From: Mike Keitz <RemoveMEmkeitzspam_OUTspamJUNO.COM>
To: PICLISTspamspamMITVMA.MIT.EDU <spam_OUTPICLISTspam_OUTspamspam_OUTMITVMA.MIT.EDU>
Date: Thursday, 16 October 1997 1:37
Subject: Re: Sensing Low Battery Condition (Thanks!!)


{Quote hidden}

My suggestion was to use a dedicated battery minder chip - these monitor
degradation of battery with time, and measure discharge via a series
resistor temp transducer.  (they also keep battery charged nicely:)

MikeS
<RemoveMEmikesmith_ozKILLspamspam@spam@relaymail.net>

1997\10\16@130423 by Mike Keitz

picon face
On Thu, 16 Oct 1997 00:30:11 -0600 Dwayne Reid <dwaynerspamBeGonespam.....PLANET.EON.NET>
writes:

>I have a simple circuit using a few resistors and almost any PNP
>transistor.

 When the battery voltage drops to less
{Quote hidden}

Rearrange the circuit so the resistor in series with the emitter instead,
and connect the base directly to the 5V line.  The collector voltage will
then rise only to about 5.6V regardless of the battery voltage.   A 100K
resistor from the collector to the PIC pin will limit flow into the
protection diode to a very small amount.

The circuit becomes a common-base voltage amplifier then.  When the
transistor comes out of saturation (because the input voltage is
falling), the emitter and collector currents are essentially the same.
If you use a 1M load resistor, 2.5 uA of collector current are needed to
reach 2.5V on the PIC pin.  For a 6V minimum input (1V minimum difference
across regulator), the emitter resistor would need to be (1 - 0.7) / 2.5u
= 120K.  With this setup the PIC pin will reach 5V when the input voltage
rises to 6.3V.  When the input voltage is well above the threshold, 5.6
uA of the emitter current goes to ground through the load resitor, and
the rest into the 5V line through the base.  Also, it is safe to short
the transistor's collector to ground.  This may be useful driving MCLR
for example and providing a manual reset button.

The sensing threshold could be raised more predictably by putting diodes,
Zeners, etc. in the emitter circuit.  This could be useful if the
regulator is not the low-dropout type, or advance warning of power-off is
required to backup into EEPROM, etc.

 Note that the port pin must be configured for
>TTL
>input levels (don't use pin RA4 unless you change the 47K resistor).

Don't use RA4 with the original circuit (unless adding a diode), since
the open-circuit voltage can rise above 5V (changing the 47K resistor to
prevent this would make the PIC pin voltage go below 2.5V even when the
battery was well above 6V).  But, using the emitter-resistor circuit, RA4
may be the best choice, since it can withstand 5.6V without flowing any
current.  Applying significantly more than 5V to RA4 could put the PIC in
a test mode.  The emitter-resistor circuit should also be suitable to
drive MCLR directly.

>
>2) The circuit that you are powering with this must draw a certain
>minimum
>amount of current or the regulated voltage will rise above the desired
>value.  This is because both 47K resistors are supplying current from
>the
>unregulated input to the regulated output.

True.  If the circuit is to go to sleep, the 5V line will rise above 5V.
There doesn't seem to be a simple way to disable the voltage-detector
circuit to prevent it from leaking current into the 5V line.

1997\10\16@160744 by Dwayne Reid

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 <snip>
>>
>>            -----------    ------/\/----+----  to PIC pin
>>           |         E \  / C    47K    |      HI=batt OK
>>           |          ------            \      LO=batt low
>>           |             |              /
>>           |             /         100K \
>>           |             \ 47K          |
>>           |             /             gnd
>>           |   -------   |
>>   from ---+---| reg |---+-- +5v to circuit
>>   batt    |   ---+---   |
>>      i/p ---     |     --- o/p
>>      cap ---     |     --- cap
>>           |      |      |
>>          gnd    gnd    gnd
>>
>>

Mile Keitz suggested:

>Rearrange the circuit so the resistor in series with the emitter instead,
>and connect the base directly to the 5V line.  The collector voltage will
>then rise only to about 5.6V regardless of the battery voltage.   A 100K
>resistor from the collector to the PIC pin will limit flow into the
>protection diode to a very small amount.

good point, good call.  There was a good reason that I didn't do that on my
original version (but I can't think of it right now, dammit), and inertia
just kept me using the circuit.  Another circuit that I posted here a couple
of years back used a 4.3V zener and the Vbe drop to make a simple 5V zener
regulator.  The output of that one directly drives MCLR, and the transistor
for that one IS used in common base configuration.  Many thousands of that
one out there so far (part of a furnace controller).

<more snip>

>The sensing threshold could be raised more predictably by putting diodes,
>Zeners, etc. in the emitter circuit.  This could be useful if the
>regulator is not the low-dropout type, or advance warning of power-off is
>required to backup into EEPROM, etc.

I suppose . . . but would you really want to?

Personally, I want to get as much life out of the battery as possible.  That
means using the low dropout reg.  If I have to worry about updating EEPROM,
I use a port pin into the PIC (not MCLR, which would shut the PIC down
immediately) and power the product with alkaline batteries.  So far, the
0.4V difference between signalling a low battery and the regulator reaching
dropout voltage has allowed enough time to complete any pending writes
(usually just a single byte).

<more snip>

But, using the emitter-resistor circuit, RA4
>may be the best choice, since it can withstand 5.6V without flowing any
>current.  Applying significantly more than 5V to RA4 could put the PIC in
>a test mode.  The emitter-resistor circuit should also be suitable to
>drive MCLR directly.

Your suggested change means that RA4 is indeed the optimal input pin.  Only
3 components implements the dropout detector: the transistor, with B tied
directly to VDD, the emitter resistor to Vin, and the pulldown resistor from
C to gnd.

<more snip>

>True.  If the circuit is to go to sleep, the 5V line will rise above 5V.
>There doesn't seem to be a simple way to disable the voltage-detector
>circuit to prevent it from leaking current into the 5V line.

I haven't done any projects where I have had to put the PIC to sleep yet.
The most that I have done is power down things like displays, sensors, etc
while still leaving the PIC operating.

Dwayne Reid   <KILLspamdwaynerspam.....planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, Alberta, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

'Battery self discharge....'
1997\10\16@214825 by Dave Mullenix

flavicon
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Matt wrote:

>I've recently been playing with rechargable alkaline.  Apparently they
>have a low self-discharge (they're already charged off-the-shelf), have
>no memory problems, can be recharged up to 150 times.  I don't know
>their energy density, but it's at least as good as NiCad.  Need their
>own type of charger, though.

I did some experiments with these batteries when they first came out.  I
used a set of four penlights to power a pocket LCD TV.  I'd turn the TV on
and let it run until it turned itself off and note the time.

After 25 discharge/charge cycles, their capacity was down to that of a set
of NiCads.  This seems to be consistent with what the manufacturer claims
for their lifetime.

They'll do better if they're recharged before they's run completely down.
NiCads are the only batteries that thrive on deep discharge cycles.

Dave

1997\10\17@090210 by Jack Warren

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>
> NiCads are the only batteries that thrive on deep discharge cycles.
>
> Dave

Careful.  I know you mean 1 volt per cell when you say "thrive on deep
discharge cycles".  You can discharge a single Ni-CD cell to 0 volts, but to
do that with a battery (2 or more cells) WILL reverse charge the weakest one.
After that, the pack is rather worthless...


Jack Warren
(I REALLY like the Rayovac Renewals!!!)

1997\10\17@090411 by Andy Kunz

flavicon
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>They'll do better if they're recharged before they's run completely down.
>NiCads are the only batteries that thrive on deep discharge cycles.

There's a lot to getting the most from NiCd's (NiCad is a Sanyo TM, btw).
Anybody interested should ask on newsgroup rec.models.rc.land and see the
flurry of confusion it generates.

Andy

==================================================================
Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
         Hardware & Software for Industry & R/C Hobbies
       "Go fast, turn right, and keep the wet side down!"
==================================================================

1997\10\17@090830 by Andy Kunz

flavicon
face
>Careful.  I know you mean 1 volt per cell when you say "thrive on deep
>discharge cycles".  You can discharge a single Ni-CD cell to 0 volts, but to
>do that with a battery (2 or more cells) WILL reverse charge the weakest one.
>After that, the pack is rather worthless...

R/C Car racers (including pros) will discharge their packs to 0V per cell,
and connect the + to - terminals (multiple cells) together for storage.
NiCd's do not like to be stored with a charge.

I typically run my packs down to .8V at 60A before recharging.

Andy

==================================================================
Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
         Hardware & Software for Industry & R/C Hobbies
       "Go fast, turn right, and keep the wet side down!"
==================================================================

'Another Battery Monitor Sch'
1997\10\17@123915 by Walter Lenk

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         Subject:   Another Battery Monitor Scheme

On a recent 9 Volt battery powered project, I implemented a battery level
monitor scheme by measuring the voltage drop across the low dropout 5V
regulator (LT1121CZ-5).  This was implemented with a single PNP transistor
(2N4403) and 4 resistors as follows : Q1's emitter was connected to the 5V
regulator's input terminal ; R1 (15K) was connected from Q1's emitter to it's
base ; R2 (33K) was connected from Q1's base to the 5V regulator's output
terminal ; R3 (47K) was connected from Q1's collector to ground ; R4 (100K)
was connected from Q1's collector to the PIC 12C508's GP3 input.  As long as
the battery's voltage is greater than about 6.7 Volts, R4 tries to pull GP3
hi (Gp3 is also connected to the output of a LTC1298 serial A2D convertor).
The software polls GP3 once a second for the battery level information, and
the user is then notified of battery condition by the pilot LED flash pattern
: one 20 mS flash every Second for a good battery, two successive 20 mS
flashes every 2 Seconds for a low battery.
This scheme works pretty well, but it has several restrictions : 1) the post
regulator current drawn by the load must be at least .11 mA to offset the
regulator bypass current sourced by R1 & R2, and 2) the whole circuit needs
to have a mechanical or electrical on/off switch before it (you can't use the
shutdown pin on the regulator and still have the circuit turn completely
off).

I hope this is useful,
Walter Lenk    Cambridge, MA

'Battery self discharge....'
1997\10\17@142035 by Eric van Es

flavicon
face
Andy Kunz wrote:

> >They'll do better if they're recharged before they's run completely down.
> >NiCads are the only batteries that thrive on deep discharge cycles.
>
> There's a lot to getting the most from NiCd's (NiCad is a Sanyo TM, btw).
> Anybody interested should ask on newsgroup rec.models.rc.land and see the
> flurry of confusion it generates.
>
> Andy

Aye - see what its gone and done to this here list!

--
Eric van Es               | Cape Town, South Africa
spam_OUTvanesspamKILLspamilink.nis.za | http://www.nis.za/~vanes
LOOKING FOR TEMPORARY / HOLIDAY ACCOMODATION?
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1997\10\19@201505 by Dave Mullenix

flavicon
face
Just a note on Renewal rechargable alkaline cells:

I live in Madison, Wisconsin, home of Ray-O-Vac, and they provided a speaker
for our local ham club.  He stated that one of the reasons Ray-O-Vac decided
to get into rechargeable alkaline cells is because their research showed
that ham radio operators are almost the only people to ever get anywhere
near rated lifetime from their nicads.  This is because they habitually
carry a spare battery pack and run each pack down to zilch before switching
to a fresh pack.  (We don't discharge to the point where a cell might be
reversed, of course.)

He said that most people buy nicads, use them a few times, grossly
overcharge them between uses or take them out of the charger before they're
fully recharged and consequently find the cells are dead after five or ten
recharge cycles.  They figured that Renewals, which give at least 25
recharge cycles before they're down to nicad energy levels, would give most
users the best buy for their money.

One other tidbit I picked up: the difference between ordinary dry cells and
heavy duty dry cells is that the heavy duty dry cells have slighty purer
chemicals.  I always wondered about that.

Dave, N9LTD


'Battery power for PIC Project'
1997\11\21@055632 by Mark Birks
flavicon
face
Following the thread on batteries et al I have a question :

What is the best way to provide battery power for a PIC circuit which is
'watchdogging' another piece of hardware. I would prefer a lithium cell
or such like or perhaps even a simple re-chargable scheme.

The PIC is controlling a 24x2 LCD but backlight power would not be
required from the battery (unless you know of a simple scheme to reduce
power such as PWM)

Any suggestions ??

      \\\|///
    \\  - -  // "Yes it IS safe
     (  @ @  )   to switch on"
+---oOOo-(_)-oOOo------------------+
| Mark Birks                       |
| Hardware Section Leader          |
| OmniBus Systems, Stanford House, |
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    \_)     ) /
           (_/

1997\11\21@062754 by tjaart

flavicon
face
Mark Birks wrote:
>
> Following the thread on batteries et al I have a question :
>
> What is the best way to provide battery power for a PIC circuit which is
> 'watchdogging' another piece of hardware. I would prefer a lithium cell
> or such like or perhaps even a simple re-chargable scheme.
>
> The PIC is controlling a 24x2 LCD but backlight power would not be
> required from the battery (unless you know of a simple scheme to reduce
> power such as PWM)
>
> Any suggestions ??

You'd have to give more specs. Have a look at my posting
earlier today.

--
Friendly Regards

Tjaart van der Walt
KILLspamtjaartspamspamBeGonewasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
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'Battery charger'
1997\11\26@140444 by Tim Kerby

picon face
Hi
How about an intelligent battery charger someone.  To be able to charge
NiCad, Lead Acid (sealed gel type), NiMH and others using bulk, float and
trickle charging at various voltages to get the best performance all in one
unit would be great.  PIC control with an LCD and mini keypad anyone?


Tim Kerby


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------------------------------------------------------------------

1997\11\26@233447 by Michael S. Hagberg

flavicon
face
check out the maxim site. i recall recently (this year) seeing specs on an
intelligent charging chip. there was also a schematic with the chip.

michael

{Original Message removed}

'Battery charger [OT]'
1997\11\26@235332 by tjaart

flavicon
face
Tim Kerby wrote:
>
> Hi
> How about an intelligent battery charger someone.  To be able to charge
> NiCad, Lead Acid (sealed gel type), NiMH and others using bulk, float and
> trickle charging at various voltages to get the best performance all in one
> unit would be great.  PIC control with an LCD and mini keypad anyone?

I just did one without a micro. I used junkbox components only.
Basically it is a constant current (preset .1C - 1C) charger that
starts to pulse as soon as a predetermined level is reached. A LED
tells you when it is charged. The pulse width decreases when the
voltage still goes up. If you throw the switch, it discharges through
a 22E 5W resistor down to another preset level where a LED will warn
you.
Total component count? One darlington transistor, a dual opamp, two LEDs
8 resistors, a diode and a spdt switch.

--
Friendly Regards

Tjaart van der Walt
RemoveMEtjaartspamBeGonespamRemoveMEwasp.co.za
_____________________________________________________________
| WASP International http://www.wasp.co.za/~tjaart/index.html |
|       R&D Engineer : GSM peripheral services development    |
|   Vehicle tracking | Telemetry systems | GSM data transfer  |
|    Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973    |
|              WGS-84 : 26010.52'S 28006.19'E                 |
|_____________________________________________________________|


'Battery charger'
1997\12\01@081505 by Jason Wolfson
flavicon
face
I'm slowly working on a universal charger with a 20x4 LCD and small key pad,
uses a 16C63 and a 14000, very small, just haven't had time to finish the
code!
also want to be able to charge single cells, i.e. 1.2V......
anyone have some pointers to the latest state of the art charging
algorithms?
Jason

{Original Message removed}


'[OT] ?: LED With only one battery'
1998\01\14@021731 by Pasi T Mustalahti
picon face
Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
possibilities to make a LED to run with only one NiCd that has the output
valtage of about 1.2 V. Led needs about 1.6 V.
The system should not have any fancy IC's and it should fit in the size of
half of an AAA-cell.

Virtual beer for the best idea !

--------------------------------------------------------------------------
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--------------------------------------------------------------------------

1998\01\14@044814 by Steve Baldwin

flavicon
face
> Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
> possibilities to make a LED to run with only one NiCd that has the output
> valtage of about 1.2 V. Led needs about 1.6 V.
> The system should not have any fancy IC's and it should fit in the size
of
> half of an AAA-cell.

A couple of transistors/FETs and a capacitor to make a charge pump doubler.

Steve.

======================================================
 Very funny Scotty.  Now beam down my clothes.
======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680                email: stevebspamBeGonespamspamBeGonekcbbs.gen.nz
New Lynn, Auckland           ph  +64 9 820-2221
New Zealand                  fax +64 9 820-1929
======================================================

1998\01\14@050644 by Keith Howell

flavicon
face
Check out the LM3909 LED flasher chip. 8-pin DIP package.
By National Semiconductor.
Developed for toys flashing a LED from a single cell.
It uses the timing capacitor to increase the voltage to the LED.
Data sheet shows internal circuit.
You may be able to implement it with a few discretes,
but it's not worth the effort unless you're making
many gadgets.

1998\01\14@051726 by William Chops Westfield

face picon face
   Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
   possibilities to make a LED to run with only one NiCd that has the output
   valtage of about 1.2 V. Led needs about 1.6 V.
   The system should not have any fancy IC's and it should fit in the size of
   half of an AAA-cell.

An LM3909 "LED Flasher" charges a cap and then discharges it in series with
the battery to drive an LED from a single cell.  While the "normal"
configuration uses a 300uF cap and flashes once a second, presumably
(haven't tried it) a smaller cap would result in a faster rate, perhaps up
to the "apparently continuously on".  Might be awfully dim, though - it's
none too bright in the original config.  About $1 for the chip - the circuit
would fit in your space if you can find SOIC versions.

You might be able to achieve the same sort of thing with a couple
transistors, some IO pins and some intelligent software (sorta like a
standard AC voltage doubler driven by IO pins, which might work too, for
high efficiency LEDs...)

BillW

1998\01\14@060957 by REMOVE_TO_REPLY_jnlrich

flavicon
face
Try this:

  PIC Output pin
        |
  +-----+------+
  }            |
  |            |
  |           ---
  |           ---    .1 to 2.2 uFd - value depends on drive pulse
  |            |                     rate, use smaller value with
  |            |                     higher rates        
  |            |        
  \            \
  / 1K         /
  \            \      10-100 Ohms - may not even be needed.
  /            /                     Limits peak current
  \            \                     from output pin.
  |            |
  |            |
  |     /------+
  |  | /       | //
  |  |/       ---  
  +--|   LED  / \    
     |\|      ---  
     | \       |      
2N3904  |      |  
        |      |
       ---    ---
       ///    ///

The LED will appear to be on solid when the pulse rate is more
than 30 per second.



On Wed, 14 Jan 1998 09:16:58 +0200, you wrote:

->Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
->possibilities to make a LED to run with only one NiCd that has the
output
->valtage of about 1.2 V. Led needs about 1.6 V.
->The system should not have any fancy IC's and it should fit in the
size of
->half of an AAA-cell.
->
->Virtual beer for the best idea !
->
->--------------------------------------------------------------------------
->PTM, spamBeGonepasi.mustalahtispamutu.fi, spam_OUTptmustaSTOPspamspamutu.fi,
http://www.utu.fi/~ptmusta
->Lab.ins. (mikrotuki) ATK-keskus/Mat.Luon.Tdk
OH1HEK
->Lab.engineer (PC support) Computer Center
OI7234
->Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
->Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577)
->--------------------------------------------------------------------------

1998\01\14@064341 by Ian Stirling

flavicon
picon face
>
> Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
> possibilities to make a LED to run with only one NiCd that has the output
> valtage of about 1.2 V. Led needs about 1.6 V.
> The system should not have any fancy IC's and it should fit in the size of
> half of an AAA-cell.
>
> Virtual beer for the best idea !

Don't know if this mail message will work...
However, I've done this, it's not too hard.
What I did.
Take small pot-core, break/sand to get a toroid of 3mm*1mm*1mm
Wrap with fine wire, to get a reasonable inductance (I picked
200Khz, and 60ma max current).
Then you need a way of switching this coil, at 200Khz or so.
I picked a multivibrator, as it was simplest, and diddn't require
much thinking to get working.
One end of one collector resistor was connected directly (IIRC) to
the base of the switching transistor.
The LED became it's own diode.
IIRC, efficiancy was around 85%.

I posted on this on misc.sirvivalism, dejanews should pick it up.
Final size was around 3mm long, and the diameter of an AAA cell, it
went in space made by extra compression of the spring, in a single
AAA cell light.
Transistors were surface mount, and the other components were mounted
round them, using fine enameled wire, which fluxes when soldered to.
Need a magnifying glass :)

1998\01\14@085456 by Lynn Richardson

flavicon
face
Sorry, guy, my brain misfired this morning.
The ciruit should have been:

  PIC Output pin
        |
  +-----+------+
  |            |
  |            |
  |           ---
  |           ---    .1 to 2.2 uFd - value depends on drive pulse
  |            |                     rate, use smaller value with
  |            |                     higher rates
  |            |
  \            \
  / 1K         /
  \            \      10-100 Ohms - may not even be needed.
  /            /                     Limits peak current
  \            \                     from output pin.
  |            |
  |            |
  |     /------+
  |  | /       | //
  |  |/       ---
  +--|   LED  / \
     |\|      ---
     | \       |
2N3904  |      |
        |      |
       ---   (VCC)
      ///
               ^
Note the LED anode now connects to VCC, instead of VSS.

At 11:01 AM 1/14/98 GMT, in a state of severe coffee deprivation,
Lynn Richardson wrote:
{Quote hidden}

---------------------------------------------------------------------------
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1998\01\14@115003 by John Halleck

flavicon
face
On Wed, 14 Jan 1998, Pasi T Mustalahti wrote:

> Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
> possibilities to make a LED to run with only one NiCd that has the output
> valtage of about 1.2 V. Led needs about 1.6 V.

 I flash a 2.0 LED on a 1.2 V battery all the time.
 The 3909 chip does the job...   And the idea behind it seems quite "Pic"able.
 Just charge a cap, and then put it in series with the battery.

{Quote hidden}

1998\01\15@080609 by Pasi T Mustalahti

picon face
PTM: This was not exactly what I was looking for, but I liked it.
So, here you got some beer from Finland (and some foreign
too)
http://www.hartwall.fi/new/merkit_frameset.html

73 de OH1HEK


On Wed, 14 Jan 1998, Lynn Richardson wrote:

{Quote hidden}

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--------------------------------------------------------------------------

'[OT] ?: LED With only one battery back emf'
1998\01\15@130749 by XYGAX

picon face
> Trying to run a PIC 16F84 with 2V i came to tihnk if there is any
> possibilities to make a LED to run with only one NiCd that has the output
> valtage of about 1.2 V. Led needs about 1.6 V.
> The system should not have any fancy IC's and it should fit in the size
of
> half of an AAA-cell.

A couple of transistors/FETs and a capacitor to make a charge pump doubler.

Steve.

I dismantled a SONY remote that used 1 battery technology and the circuit is
simple a transistor is used to energise a coil and the led is the catch diode
(it comes on as the transistor goes off) try it some time with a relay use a
LED to catch the back emf it flashes small inductors are cheep and cost less
than charge pump but the still need the resiviour cap close to them simple
idea but effictive ..

Cheers Steve (a different one) ..........

1998\01\16@075724 by paulb

flavicon
face
Pasi T Mustalahti wrote:

> PTM: This was not exactly what I was looking for, but I liked it.

 Well, I certainly didn't like the original.  I am still very
suspicious of the circuit published.  Transistors still have some gain
with emitter and collector reversed.  Unless the 2N3904 is somehow
immune to this (and I am SURE I have seen it deliberately used "upside-
down" somewhere to achieve a low saturation votage), when the PIC output
pin having been high and charged the capacitor, goes to ground, will it
not bias the transistor on so as to discharge the capacitor "up" to
ground as soon as the transistor's nominal collector falls 0.7V below
ground?

 Perhaps the LED will conduct first at 1.7V which is only 0.5V below
ground with a Vcc of 1.2V, but this is a bit close.  If the LED requires
2.0V, you are going to lose current through the transistor.

It would be simpler to replace the transistor with a Schottky diode.

 Cheers,
       Paul B.

1998\01\16@075727 by paulb

flavicon
face
William Chops Westfield wrote:

> An LM3909 "LED Flasher" charges a cap and then discharges it in series
> with the battery to drive an LED from a single cell.  While the
> "normal" configuration uses a 300uF cap and flashes once a second,
> presumably (haven't tried it) a smaller cap would result in a faster
> rate, perhaps up to the "apparently continuously on".  Might be
> awfully dim, though - it's none too bright in the original config.

 It can be brightened by shunting the time constant resistors with a
much lower value (original is as I seem to recall, two 5k steps).  The
problem I have with it is that there is no actual "enable" pin; the
series pair of said resistors is internally connected in place so you
can decrease the fixed resistance but not increase or open it.

 Consequently, the only way to switch it on and off is to use the PIC
to feed power to it, adding the PIC I/O resistance to any other losses.

 Cheers,
       Paul B.

'Battery short circuit protection [OT]'
1998\01\21@054803 by David Lions

picon face
Hi,

May I draw on the eternal wisdom of the list?  I have a problem with
battery protection.

Our product uses a 12V 3AHr NiMh battery pack (and 3 PIC's).  The
battery pack is designed for use in rough environments, and for this and
other reasons, the terminals have been left relatively well exposed.
This is a problem if the battery is short circuited.  The batteries are
a small but expensive part of the unit.

Can anyone suggest a way of short circuit proofing the batteries?  The
method has to :

1. Be user-resettable after a short circuit, or self-resetting.

2. Respond very quickly after the current limit is exceeded (batteries
are quickly damaged).  Ideally the current limit will hardly be exceeded
at all, even for an instant.

3. Draw very little or preferably no quiescent current (NiMH
self-discharge automatically :-).

Some "resettable" fuses that we've tried are way too slow.  The current
limit by the way is 9A.

Any ideas?


Thanks.
David Lions
spambjlions.....spamspammagna.com.au.NOSPAM

1998\01\21@073102 by Najemy, Daniel

flavicon
face
Daniel Najemy - Numaliine Power Systems

{Quote hidden}

1998\01\21@073724 by Najemy, Daniel

flavicon
face
Here's a handful of  ideas:

1. Check out Raychems polyswitches - although the SRP series is rated
too low for you application, you may
   be able to use the RUE series (assuming you can put this outside of
the battery pack).

2. Put a mosfet in series with the battery voltage, sense the battery
voltage with a micro/low power voltage
   comparator, and then turn the mosfet off when the voltage begins to
collapse - or sense the current w/ a
   low power shunt and do the same.  You would probably us a p-channel
fet and pull the gate low during normal
   operation, this way you won't need a charge pump to drive the
n-channel above the battery voltage.

3. Unitrode/Linear tech have some ic's that do something similar to 2. I
use the LTC1153 in a similar application.

There aren't too many more solutions out there - I think 2 above is the
slickest way to do it.

Daniel Najemy - Data General Corporation,  Numaliine Power Systems

> {Original Message removed}

1998\01\21@082513 by mike

flavicon
picon face
We use Polyfuses on our power supply.

When we first got samples to play with we connected them directly across
a car battery to see what would happen. It was remarkably unspectacular.


Regards,


Mike Watson

In message  <EraseME34C5D398.4B33E1AC@spam@spam@spam@magna.com.au> @spam@PICLISTspamspamKILLspamMITVMA.MIT.EDU writes:
{Quote hidden}

--
Denison Mayes Group

1998\01\21@132032 by wwl

picon face
On Wed, 21 Jan 1998 21:53:12 +1100, you wrote:

>Hi,
>
>May I draw on the eternal wisdom of the list?  I have a problem with
>battery protection.
>
>Our product uses a 12V 3AHr NiMh battery pack (and 3 PIC's).  The
>battery pack is designed for use in rough environments, and for this and
>other reasons, the terminals have been left relatively well exposed.
>This is a problem if the battery is short circuited.  The batteries are
>a small but expensive part of the unit.
>
>Can anyone suggest a way of short circuit proofing the batteries?  The
>method has to :
>
>1. Be user-resettable after a short circuit, or self-resetting.
>
>2. Respond very quickly after the current limit is exceeded (batteries
>are quickly damaged).  Ideally the current limit will hardly be exceeded
>at all, even for an instant.
How quickly is 'very' ? 1S?, 1mS?, 1uS?
>3. Draw very little or preferably no quiescent current (NiMH
>self-discharge automatically :-).
If they self-discharge anyway, a little extra for a protection cct
won't hurt much, would it?
>Some "resettable" fuses that we've tried are way too slow.  The current
>limit by the way is 9A.
I'd use a polywitch (Raychem/Bourns) - small, reliable & cheap.
Although slow at marginal overloads, they trip fast on larger
overloads, which in this application would be what you'd normally have
(i.e. dead short rather than, say 50% overcurrent). I'd be surprised
if there would be much risk of battery damage within the trip time.
If your batteries are shorted so frequently that you'd be worried
about damage, then change the mechanical design!
Even with current-limit, there may be safety issues - 12V at 9A could
easily set fire to things, or burn someone if shorted. I'm not sure if
any of the electrical safety standards say anything about short
circuit current hazards - it's probably worth a look.

The only other sensible choice would be a mosfet & current sense
circuit, but this would probably be more expensive.
You don't say what the ratio of normal to fault current is - this
would make a difference to how precise the sensing cct needed to be.



    ____                                                           ____
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/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

1998\01\21@132037 by wwl

picon face
On Wed, 21 Jan 1998 07:35:12 -0500, you wrote:

>Here's a handful of  ideas:
>
>1. Check out Raychems polyswitches - although the SRP series is rated
>too low for you application, you may
>    be able to use the RUE series (assuming you can put this outside of
>the battery pack).
>
>2. Put a mosfet in series with the battery voltage, sense the battery
>voltage with a micro/low power voltage
>    comparator, and then turn the mosfet off when the voltage begins to
>collapse - or sense the current w/ a
>    low power shunt and do the same.  You would probably us a p-channel
>fet and pull the gate low during normal
>    operation, this way you won't need a charge pump to drive the
>n-channel above the battery voltage.
No need for P channel or charge pumps - remember that in a battery
pack you could switch the negative rail.

    ____                                                           ____
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/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

1998\01\25@204128 by Larry G. Nelson Sr.

flavicon
face
Take a look at the Raychem Polyswitches. The battery should be able to take
anything they will allow to pass before they trip and after the short is
removed they reset themselves. I have used them on power busses for medical
equipment. The only complaint is they cause a slight voltage drop that you
need to take into account.


At 09:53 PM 1/21/98 +1100, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
EraseMEL.Nelson.....spamKILLspamieee.org
http://www.ultranet.com/~nr


'DRAM with battery backup'
1998\03\11@233135 by Danjel McGougan
flavicon
face
Hi all,

First of all I want to thank everyone who answered my mail concerning
audio compression algorithms. They were really helpful and now I have
a general idea of how to proceed.

For those of you who didn't read the mail: I'm thinking of building a
digital telephone answering machine and needed some help in deciding
what type of memory and software compression to use for storing the
speech.

I'm going the hard way without the use of ISD's chips. I'm
thinking of using a 2M x 4 DRAM chip for storing 4-bit ADPCM codes at
6kHz sampling frequency. This gives me approximately 6 minutes of
speech with reasonable quality which ought to be enough.

I've written ADPCM decoding and encoding routines and found that I
need about 110 program cycles per sample to encode and about 80
program cycles to decode. With overhead I'll probably need a crystal
running at 8MHz.

Now to the problem. I need to use DRAM which I have very little
experience in using (I'm really a software guy, not hardware). How
does one proceed to design a battery backed-up system with a DRAM and
a PIC processor? I understand that the DRAM must go into self-refresh
mode when the power is cut. Also, how do I get the memory to refresh
during normal operation? I understand that I probably need some kind
of external counter and perhaps something else to run the refreshing.
I'd really appreciate ideas and schematics for solving some of these
problems or all of them :-)

Thanks in advance,
Danjel McGougan.

1998\03\12@003207 by Mike Keitz

picon face
On Thu, 12 Mar 1998 05:30:38 +0000 Danjel McGougan
<spamdanmc458spamSTUDENT.LIU.SE> writes:

>Now to the problem. I need to use DRAM which I have very little
>experience in using (I'm really a software guy, not hardware). How
>does one proceed to design a battery backed-up system with a DRAM and
>a PIC processor? I understand that the DRAM must go into self-refresh
>mode when the power is cut. Also, how do I get the memory to refresh
>during normal operation? I understand that I probably need some kind
>of external counter and perhaps something else to run the refreshing.

You really need to RTFM on the RAM chip you intend to use, since there
are several different kinds.  At the very least, it'll support
CAS-before-RAS refreshing.  This means you can keep the data in the DRAM
alive just by holding all the pins except RAS and maybe WE low, and hae
your PIC or an external timer apply periodic (about 30 KHz) short low
pulses to RAS.  The DRAM chip contains an internal counter that will
sequence through all the rows for you.  Maybe "self-refresh" involves an
internal timer as well, I'm not familiar with that.

When power is on, you can do CAS-before-RAS cycles periodically,
interspersed with your data reading or writing cycles if the machine is
active.

_____________________________________________________________________
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1998\03\12@120503 by andre

flavicon
face
Speaking of DRAM what I can recommend you is to use RAM
with EEPROM build in it. every thing is inside when you power it on
it will automatically load data from eeprom when you turn it off
it will automatically load data to eeprom. I played with it it is
very good toy but it is more expensive.
if you need to try I can look for the name. I have a data book.

Andre

Danjel McGougan wrote:

{Quote hidden}

--








==========================================
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= Tel 909-589-5485  Fax 909-598-5695     =
==========================================

1998\03\12@190220 by Chris A Brainerd

picon face
Its kinda expensive, but what about SGS-Thomson Zeropower SRAM. Has a 10
year backup battery built in and you don't have to worry about refreshing
it. Just an idea..

       Chris


_____________________________________________________________________
I'm, like, a product, OK, of american, you know, education, all right?
@spam@DJ_Ramen.....spamspamjuno.com

On Thu, 12 Mar 1998 07:48:18 -0800 Andre Abelian <spamandre.....spam.....compufire.com>
writes:
{Quote hidden}

_____________________________________________________________________
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'LCD's for battery operation'
1998\03\24@152639 by Adi Linden

flavicon
face
I need to use a display on a battery operated device. I've looked at
basic LCD displays (i.e. Varitronix 6 or 8 digit display available
from Digi-Key).

What is required to drive these? I asked for a datasheet but all it
shows is pinouts. What kind of waveforms do they need?

Are there multiplexed LCDs available from other vendors that
eliminate the need of a high pincount PIC or external drivers?

Are there 1 or 2 line alpanumeric displays available with
controllers that have a very low power consumption?

Lots of questions about LCD's...

Regards,
Adi


'Smart battery charger/monitor'
1998\04\28@073837 by HŒvard T¿rring
flavicon
face
Hi,

I am going to build a system based on rechargable batteries (NiCd). At any
time, I need to know for how many minutes can this system run without
charging. The batteries will under normal condition be charged for 2.5
minutes and discharged for 2.5 minutes. This will go on for weeks, so I
need a reliable way to tell when it's time to change batteries. And, I need
to know before the batteries fails.

-To keep On Topic, This will off course be done by a PIC...

Has anybody got any experience with this kind of problems??

Regards,
Haavard
------------------------------------------------
HŒvard T¿rring
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Norway


'Smart battery charger/monitor'
1998\05\19@212903 by Larry G. Nelson Sr.
flavicon
face
I have done this type of project using Benchmarq chips in the past. The
14000 is a good choice for this type of project. By tracking power in vs
power out along with time and temperature you can build a type of gas gauge
for the batteries. A problem comes from the fact there are losses in
efficiency and a memory effect can also limit capacity such that a battery
conditioning cycle should be done every so often.


At 01:37 PM 4/28/98 +0200, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
TakeThisOuTL.NelsonKILLspamspam@spam@ieee.org
http://www.ultranet.com/~nr

'Battery level indicator'
1998\05\22@223830 by Javier Grijalba

flavicon
face
Hi
I would appreciate if somebody could tell me were to find schematics of a
simple and small  battery indicator with leds for  microcontrollers to avoid
a brown
out reset.
Thanks a lot
Javier


'Pull-up in battery powered application'
1998\06\04@064329 by Stuart Allen
flavicon
face
Hello,

I have a battery powered design using 16C84. I need to be able to read a
keypad, this requires 3 inputs. The design will spend a lot of time asleep.
Long battery life isn't critical, but I would like to extend it as much as
possible.

These inputs must be pulled up to 5v. I could use the weak pull-ups, but the
other pins on port B are inputs, and I would rather not pull them up. Also,
I think that it will be more economical (in terms of power consumption) to
just pull those 3 pins.

However, there is no reference of the input current required to pull-up a
input pin in the PICs specification. It mentions that the port B pull-up
current is typically 250uA, so if I divide by 8 pins I get 31.25uA. So
should I pull up each port with 160K (5/31.25uA)? Or is the 250uA per pin,
not for the port? Maybe is it completely wrong to use this value?

Any advice gratefully received,

Regards,

Stuart.

1998\06\04@085313 by Pasi T Mustalahti

picon face
On Thu, 4 Jun 1998, Stuart Allen wrote:

> Hello,
>
> I have a battery powered design using 16C84. I need to be able to read a
> keypad, this requires 3 inputs. The design will spend a lot of time asleep.
> Long battery life isn't critical, but I would like to extend it as much as
> possible.
>
> These inputs must be pulled up to 5v. I could use the weak pull-ups, but the
> other pins on port B are inputs, and I would rather not pull them up. Also,
> I think that it will be more economical (in terms of power consumption) to
> just pull those 3 pins.
>
> However, there is no reference of the input current required to pull-up a
> input pin in the PICs specification. It mentions that the port B pull-up
> current is typically 250uA, so if I divide by 8 pins I get 31.25uA. So
> should I pull up each port with 160K (5/31.25uA)? Or is the 250uA per pin,
> not for the port? Maybe is it completely wrong to use this value?
PTM: It depends..
If you have very capacitive keypad and you try to read it very fast, you
got to use small resistors. The same goes with long cables: they are very
'capacitive'. If you can give some time to the keyput input to stabilise,
you can use large resistors. PIC has inbuildt resistors of about 50k that
you can set active. I have used them to pull up a keyboard with rather
good speed.
Another way is to use these inbuildt resistors and cut them off and set
the port as input when you don't read the keys. It is enough to read keys
about 10..20 times / sec. That leaves enormously time to go and have
a cup of coffee between read periods.
--------------------------------------------------------------------------
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Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014
Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 0400-555577)
--------------------------------------------------------------------------

1998\06\05@121052 by Dennis Plunkett

flavicon
face
At 11:44 AM 4/06/98 +0200, you wrote:
{Quote hidden}

It would be economical to only pull up the three lines if the other port
pins on B spend long periods of time low. As for the current required? I do
think that this is in the Microchip data book, you will find this under
"Input current" As for the size of the resistors? Well it depends on the CR
time constant of the keypad, and the number of times per second that you
sample it. Note that key bounce can exist for periods of up to 50mS,
generally the user will not notice any problems if the keypad is sampled
around 10Hz, any slower and the user may have to think in brain dead mode.
Also if the keypad switches low, then the resistor can be quite small, as
the on time is generally short. Also ensure wetting currents of 50uA
(General rule of thumb type thing) are used to keep the keypad contacts clean.


Dennis


-=====================================================================-

Dennis Plunkett: Embedded Hardware, Software design
NEC Australia DRMASS
ph 03 9264-3867

-=====================================================================-

'selection of battery for power consumption of 300m'
1998\06\08@170010 by David Wong

flavicon
face
Where can I find data or a web site on batteries in general.  I'm looking to
spec in a battery to power a Pic and a bunch of other electronics for about
20 hours.  The current consumption of the parts would be about 300mA/hour.
What would be the ideal battery?  Also can anyone direct me to some
companies that do fast charger IC's as well as gas gauges for batteries.
And any parts that you may recommend.

Thanks
DW

1998\06\08@224850 by Clyde Smith-Stubbs

flavicon
face
On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
> Where can I find data or a web site on batteries in general.  I'm looking to
> spec in a battery to power a Pic and a bunch of other electronics for about
> 20 hours.  The current consumption of the parts would be about 300mA/hour.

A lead-acid gel-cell battery would be the best choice, unless weight is critical
,
in which case you might want to look at Nimh (Nickel-metal hydride) or Lithium-i
on
batteries, but the gel-cell will be cheaper, and can be float charged with const
ant
voltage. The others require fancy charging circuitry. A "gas-gauge" for a gel-ce
ll is
basically a voltmeter.

--
Clyde Smith-Stubbs               |            HI-TECH Software
Email: TakeThisOuTclydespamspam_OUThtsoft.com          |          Phone            Fax
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1998\06\08@234134 by Bob Blick

face
flavicon
face
www.duracellnpt.com/techref.d/refind.html

Has some specs on duracell batteries. Note that in practice what you get
is about 75% of the rating. Also note that they expect you to take the
cells down to something like .8 volts

Cheers,
Bob

1998\06\09@050542 by Mike Keitz

picon face
On Tue, 9 Jun 1998 07:55:36 +1000 Clyde Smith-Stubbs <.....clydeEraseMEspamHTSOFT.COM>
writes:
>On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
>>battery to power a Pic and a bunch of other electronics
>for about
>> 20 hours.  The current consumption of the parts would be about
>300mA/hour.
>
You mean the operating current is 300 mA (at 5V, I assume)?  This is
quite a bit of power.  The battery is going to be rather unweildly.  It
would be advantageous to look at reducing the power by using micropower
techniques or implementing standby/sleep modes.

On the other hand, if the capacity required is 300 mA-hr, (operating
current of 15 mA for 20 hours), just about any sort of medium sized
battery such as 4 "AA" cells will have lots of capacity.  Specify a
battery with plenty of extra capacity, then it will be less necessary to
have a gas gauge or rapid charge.  Also the battery will wear out more
slowly, and it's "useful life" will extend further into the wear-out
phase.


(The rest of this is assuming 300mA * 20 hr = 6 A-hr)
>A lead-acid gel-cell battery would be the best choice, unless weight
>is critical,
>in which case you might want to look at Nimh (Nickel-metal hydride) or
>Lithium-ion
>batteries, but the gel-cell will be cheaper,

I think the lead-acid is about the only practical choice.  If the weight
(about 5 lbs for a 10 A-hr 6V gell-cell) is a problem you will do much
better to reduce the power consumption rather than deal with exotic
batteries.

and can be float charged
>with constant
>voltage. The others require fancy charging circuitry. A "gas-gauge"
>for a gel-cell is
>basically a voltmeter.

Yes, easy to charge with just a constant-voltage, current-limited
arrangement.  However, it is not recommended to charge faster than 4
hours.  Measuring the voltage does give a meaningful indication of the
energy remaining.  Be sure your circuit has a cut-out that will keep the
battery from overdischarging, as this is very bad for them.

_____________________________________________________________________
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1998\06\09@051245 by Dennis Plunkett

flavicon
face
At 02:41 PM 8/06/98 -0700, you wrote:
>http://www.duracellnpt.com/techref.d/refind.html
>
>Has some specs on duracell batteries. Note that in practice what you get
>is about 75% of the rating. Also note that they expect you to take the
>cells down to something like .8 volts
>
>Cheers,
>Bob
>
>

I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
that the capacity tests are done with a light load! Not a huge 1AMP  or
something like that. 0.8V is quite OK for most things, also note the
internal impedance of the cell at this voltage.

Dennis

-=====================================================================-

Dennis Plunkett: Embedded Hardware, Software design
NEC Australia DRMASS
ph 03 9264-3867

-=====================================================================-

1998\06\09@052256 by Dr. Imre Bartfai

flavicon
face
It seems for me as a total capacity of 6Ah theoretically (a small remark:
the measure 300 mA/hour makes no sense; the current is measured in mA). I
would suggest a jelly type lead battery.

Imre


On Mon, 8 Jun 1998, David Wong wrote:

{Quote hidden}

1998\06\09@084020 by Scott Walsh

flavicon
face
    On a similar point, we are evaluating batteries from different
    manufacturers as the moment for a battery powered application.

    And we are discharging Ni-MH batteries down to 1.1V per cell, and seem
    to be getting aound 80% capacity out of the cell when discharging at
    1C ... does that sound reasonable?

    For Ni-MH what volatge per cell do the manufacturers rate the mAh
    capacity of the battery. or is this one of the tricks they play with
    specs to make thier batteries look batter than the competition?

    Does dicscharge rate affect the capacity of the battery to any great
    extent?

    thanks in advance,
    SW.


______________________________ Reply Separator _________________________________
Subject: Re: selection of battery for power consumption of 300mA/hour
Author:  pic microcontroller discussion list <spamBeGonePICLISTspamRemoveMEMITVMA.MIT.EDU> at
INTERNET
Date:    09/06/98 14:57


At 02:41 PM 8/06/98 -0700, you wrote:
{Quote hidden}

I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
that the capacity tests are done with a light load! Not a huge 1AMP  or
something like that. 0.8V is quite OK for most things, also note the
internal impedance of the cell at this voltage.

Dennis

-=====================================================================-

Dennis Plunkett: Embedded Hardware, Software design
NEC Australia DRMASS
ph 03 9264-3867

-=====================================================================-

1998\06\09@084623 by Andy Kunz

flavicon
face
>     And we are discharging Ni-MH batteries down to 1.1V per cell, and seem
>     to be getting aound 80% capacity out of the cell when discharging at
>     1C ... does that sound reasonable?

A lot of other factors come into play, including temperature, charge type
(peak, timed, etc.)

You should get 80%-90% out of what you put in, as a rule of thumb.  I put
2200-2300 mAH into a 2000 mAH cell, and get about 1980 out.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\06\09@105053 by 'Grif' w. keith griffith

flavicon
face
At 07:55 AM 6/9/98 +1000, you wrote:
>On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
>> Where can I find data or a web site on batteries in general.
>A lead-acid gel-cell battery would be the best choice, unless weight is
critical,
>in which case you might want to look at Nimh (Nickel-metal hydride) or
Lithium-ion
>batteries,

snip,hack

Gel cells are great, as long as you get them back on charge after use, if
they are going to be left in a discharged state, use something else.  Oh,
and for the float charger is great mind set, don't forget if you set the
float for 13.6 or so, and don't do anything "fancy" my memory is telling me
you only get about 80% of capacity.  Seems like some of the power one
charger wall warts do a 14.6 volt end point constant current then pop over
to a float.



'Grif' N7IVS

1998\06\09@122516 by tjaart

flavicon
face
'Grif' w. keith griffith wrote:

> At 07:55 AM 6/9/98 +1000, you wrote:
> >On Mon, Jun 08, 1998 at 11:45:16AM -0400, David Wong wrote:
> >> Where can I find data or a web site on batteries in general.
> >A lead-acid gel-cell battery would be the best choice, unless weight is
> critical,
> >in which case you might want to look at Nimh (Nickel-metal hydride) or
> Lithium-ion
> >batteries,
>
> snip,hack
>
> Gel cells are great, as long as you get them back on charge after use, if
> they are going to be left in a discharged state, use something else.

...unless it is a Hawker (Gates) They are the only Pb's that can take it.

--
Friendly Regards

Tjaart van der Walt
.....tjaartEraseMEspamwasp.co.za

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1998\06\09@131929 by Reginald Neale

flavicon
face
Bob said:
>>Has some specs on duracell batteries. Note that in practice what you get
>>is about 75% of the rating. Also note that they expect you to take the
>>cells down to something like .8 volts
>>

and Dennis replied:
>I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
>that the capacity tests are done with a light load! Not a huge 1AMP  or
>something like that. 0.8V is quite OK for most things, also note the
>internal impedance of the cell at this voltage.
>

"Capacity" is meaningful only when both the load current and endpoint
voltage are specified. AFAIK, all batteries give maximum capacity for
lightest possible loads and (obviously) lowest possible endpoint voltages.
The range of capacities for a given battery can be dramatic. Example: an
automotive battery may be rated for 100 ampere-hours, but that rating is by
convention at the 10-hr rate, which makes the numbers look high but is not
useful in trying to determine how long you can crank an engine. You aren't
even going to come close to being able to supply 100 amps for an hour.

Bottom line, determine what endpoint voltage makes sense in your
application, and how much current is required; then make your own
measurements on candidate battery types to get the most useful answers.
Allow a generous fudge factor to take care of unit-to-unit variations. Also
note that capacity varies with temperature range in a manner specific to
each battery technology, generally dropping with temperature. Many types
lose most of their capacity at freezing temperatures.

Good luck with your project!

Reg Neale

1998\06\09@134416 by Bob Blick

face
flavicon
face
On Tue, 9 Jun 1998, Dennis Plunkett wrote:
>
> I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
> that the capacity tests are done with a light load! Not a huge 1AMP  or
> something like that. 0.8V is quite OK for most things, also note the
> internal impedance of the cell at this voltage.

Maybe it's a conversion problem from American to Australian amp-hours :-)
Seriously, though. The specs published by Duracell are the optimum. It is
almost impossible to get what they claim. The original post was from
someone with a 300mA requirement. I had previously done tests of Duracell
D-cells at that exact load, with temperature varying between 50 and 70
degrees F. I got a fraction over 12 amp hours. The cells are rated 15 amp
hours by Duracell. I think I gave a valid answer to his exact question,
and to the majority of users.

Cheerful regards,
Bob

1998\06\09@141418 by Scott Walsh

flavicon
face
    I am aware of most of the thinsg to be aware of 8*) but I am just
    hunting to compare notes with other people that have implemented their
    own battery chargers. With regards to the charge type, I actually use
    a rate of change of temperature for terminating the fast charging of a
    550mAh NI-MH battery. And this appears to work just great and
    terminates at pretty close, to within 30 seconds, where a peak voltage
    (dV/dt < 0) method would terminate. This has been measured by
    attaching a GPIB voltmeter to the battery as it is charged and then
    plotting the data in Excel.

    If the battery has been charged to the point where the 'voltage peaks'
    then how much capacity should I be able to get out of the battery? FYI
    this is charging at a rate of 1C.

    thanks in advance
    SW.


______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: selection of battery for power consumption of 300
Author:  pic microcontroller discussion list <spamPICLIST@spam@spamSTOPspamMITVMA.MIT.EDU> at
INTERNET
Date:    09/06/98 08:45


>     And we are discharging Ni-MH batteries down to 1.1V per cell, and seem
>     to be getting aound 80% capacity out of the cell when discharging at
>     1C ... does that sound reasonable?

A lot of other factors come into play, including temperature, charge type
(peak, timed, etc.)

You should get 80%-90% out of what you put in, as a rule of thumb.  I put
2200-2300 mAH into a 2000 mAH cell, and get about 1980 out.

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\06\10@005956 by tjaart

flavicon
face
Bob Blick wrote:

> On Tue, 9 Jun 1998, Dennis Plunkett wrote:
> >
> > I don't agree with the 75% of capacity, we get 100 to 115% consistntly, note
> > that the capacity tests are done with a light load! Not a huge 1AMP  or
> > something like that. 0.8V is quite OK for most things, also note the
> > internal impedance of the cell at this voltage.
>
> Maybe it's a conversion problem from American to Australian amp-hours :-)
> Seriously, though. The specs published by Duracell are the optimum. It is
> almost impossible to get what they claim. The original post was from
> someone with a 300mA requirement. I had previously done tests of Duracell
> D-cells at that exact load, with temperature varying between 50 and 70
> degrees F. I got a fraction over 12 amp hours. The cells are rated 15 amp
> hours by Duracell. I think I gave a valid answer to his exact question,
> and to the majority of users.

You are right. The 'capacity' quoted by manufacturers are the integralof the current over time for a
really 'light' load. When you slap on your
current guzzlers, you get to experience the rise in internal resistance,
temperature effects and other mysterious properties that make your
life a misery.

This is why you have to check for a discharge curve at the load you
want to work with.

A very important thing about batteries : *NEVER* believe the reps.
Check it out for yourself. We've seen really cheap no-name NiCd
batteries outperform (and outlast) all the NiCd brand makes. I've
heard such crap comming from these reps that I went the mile and
made a bit of a study. It is really worth it.

Three weeks ago one of these a**holes told me that the Hawker
batteries aren't very good because they don't do well in temp extremes.
Bull!! They are the *only* batteries to still work (and charge) well
from -20DC to +80DC.

So, bottom line, do your homework. Study all the types, and then
choose a Hawker Pb gel. ;) I think there is a link on my home page
to Hawker.

--
Friendly Regards

Tjaart van der Walt
spamBeGonetjaartspamBeGonespam@spam@wasp.co.za

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'PICs and battery-backup SRAM'
1998\07\08@174444 by Gary Patterson
picon face
Hi,

I've got an application where I want to use a large capacity, low power
SRAM along with a PIC controller.  The SRAM will be used to hold data
and I want to use battery backup to protect the contents of the SRAM,
should someone accidentally disconnect the power supply from the circuit
etc.

Can somebody help me with 2 questions?

1.  What circuitry is necessary to implement battery backup for an SRAM?
2.  If the PIC is writing to SRAM when the power goes off, how do I
ensure that invalid data isn't advertently written to the SRAM?

I am using PIC I/O lines to directly control the address/data/control
lines of the SRAM.

Thanks for your help!

Regards,
Gary Patterson

e-mail: nukepepKILLspamspamspamhotmail.com

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1998\07\08@202945 by David Lions

picon face
Hi,  I did this recently.  I used an ICL7673 from Harris (if memory is
correct) to switch the Vcc for the SRAM between the PIC supply and the
backup battery.  It selects the greater of two input voltages and
directs it to SRAM Vcc.

The CS\ of the SRAM has to be tied up to it's Vcc.  That way when the
power is off it is still unselected by battery power.  Unfortunately, if
a PIC pin is controlling the SRAM cs\ directly, then when the PIC's
power is off, battery power is drained through the PIC's internal
protection diodes.  I used a mosfet (can't remember how exactly)  so
that battery current wouldn't leak through cs\ pull-up and through PIC
pin.

This should isolate the SRAM from the PIC.  I used Hitachi
something-something-256 but it had "SLP" or "ULP" markings (for
super/ultra low power).  I used 2032 lithium coin cell and the only time
it drained was when I accidentally short circuited it.

I didn't bother with data getting corrupted because it powered itself
down so can't suggest anything from experience here. :)

Gary Patterson wrote:
{Quote hidden}

1998\07\08@204010 by Ron Fial

flavicon
face
Dallas Semiconductor is the primary supplier of chips and intellegent sockets an
d battery-RAM modules.  These devices control the power, chip select and write l
ines of static ram, and provide power from a backup battery, and can also contro
l the switching from the main power to backup power without losing data in the s
tatic ram.  See this link for more info.  Other companies make power control chi
ps.  These devices work better and are cheaper most any circuit you can make you
rself.  The 'battery socket' devices are neat (you supply your own RAM chip, up
to 128K).

http://www.dalsemi.com/Prod_info/Memory/index.html

As far as keeping data integrity while writing, and while power is failing, a go
od way is to use a big enough capacitor across the 5 volts, and monitor the powe
r with the PIC.  Check if you have over 4.8 volts, then do one short static RAM
operation (write one byte, or shift one byte to serial eEPROMs). If the power fa
ils, it cannot drop fast enough to corrupt the operation because of the power su
pplied by the capacitor.

You can use logical methods to make sure you never read data corrupted by a powe
r failure:

You can write a 'note' into the ram that you are going to do a write to a certai
n address block, then write the address, then erase the 'note".  When you boot u
p, always check for the note, and you will know if an operation stopped in the m
iddle.  In addition, take each block of data (perhaps each 256 bytes) and add up
the data to form a 16-bit checksum, which you also write into the RAM.  Test th
e checksums when you boot up, and you will likely detect any data corruption.  Y
ou can also write redundant  blocks in two separate writes, say write data, data
again.  Both blocks should have checksums.  Later if block 1 reads bad, read bl
ock 2.  If block 1 is good, then re-use block 2 the next time you write.
 Regards
   Ron Fial

==========================================
At 02:33 PM 7/8/98 PDT, you wrote:
{Quote hidden}

1998\07\08@223847 by Mike Keitz

picon face
Since the original poster said the battery would be used "in case someone
accidentally disconnected the power," long periods of battery operation
are unlikely.  I'd be tempted to connect the PIC to the battery supply as
well and make it SLEEP while the power is off.  If both the PIC and SRAM
will operate over a range of 3-5.5V, just use diodes to route in either
battery or main power.  You'll need a voltage detector connected to a
port to tell when to go to sleep.

Holding the PIC idle by holding MCLR low won't work because the
oscillator will stay on and use a lot of current from the battery.  If
you connect the voltage detector to RB0/INT, it can wake the PIC up with
an interrupt when power comes back on.  But you probably want to poll the
detector with software to decide when to sleep so a RAM write isn't
interrupted.

Also put a pull-up resistor on the CS pin to be sure the RAM is not
activated when the PIC ports are forced to input during a reset.  Coming
out of reset, be sure the software writes the pin to 1 before making it
an output.

On Wed, 8 Jul 1998 17:31:18 -0700 Ron Fial <KILLspamron.....spamTakeThisOuTFIAL.COM> writes:

>Dallas Semiconductor is the primary supplier of chips and intellegent
>sockets and battery-RAM modules.  These devices control the power,
>chip select and write lines of static ram, and provide power from a
>backup battery, and can also control the switching from the main power
>to backup power without losing data in the static ram.

I agree with Ron, the Dallas chips especially are really "trick".  They
integrate the voltage detection, power switching, and forcing the chip
select idle.  The only real reason not to use one is if you can't afford
the cost.

If you want to go with a rock-cheap implementation and must cut power to
the PIC, be prepeared for some headaches.  Here's a few hints.  Some
SRAM's (64K bit and 1M bit) have an active-high chip select pin which can
be used to force the SRAM inactive without messing with the other chip
select.

The active-low chip select can be isolated with a transistor (NPN) or
FET.  The collector or drain goes to the RAM chip select, also to a
pull-up resistor to battery backed Vdd.  The base or gate goes to
non-batery Vdd.  If it's a bipolar a beas resistor is needed.  The
emitter or source goes to the PIC output.  If power is on, when the PIC
pin goes low, the transistor turns on and pulls the RAM pin low.  If
power is off, the transistor can't come on so it is OK for the PIC pin to
go low.


>As far as keeping data integrity while writing, and while power is
>failing, a good way is to use a big enough capacitor across the 5
>volts, and monitor the power with the PIC.  Check if you have over 4.8
>volts, then do one short static RAM operation (write one byte, or
>shift one byte to serial eEPROMs). If the power fails, it cannot drop
>fast enough to corrupt the operation because of the power supplied by
>the capacitor.

This is a sound practice.  Since RAM writing is so fast, the "big
capacitor" doesn't need to be very big at all.  I don't think more exotic
methods will be needed unless the structure of the data requires writing
a large number of bytes to accomplish each update.

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'WARNING:BATTERY-POWERED PIC USERS'
1998\07\12@105458 by Dave Miga

flavicon
face
I've just found out from the Microchip rep here that I am partially the
reason for the programming alert on PIC16cXX devices. If you run the PIC
from battery power, read this completely.

About seven months ago, we ran into a batch of C54As that had an
incredible 100% defect rate. We ran extensive tests and found out that
the PICs were somehow out of spec concerning VCC (supposed to be OK up
to 6.25VDC). In fact, the equipment we have been making for over a year
has had no returns at all, and the original protos are still working
happily.

The defective chips worked fine at 5VDC, but if operated from anything
more than 5.9 volts (such as four fresh AAAs), they were dazed and
confused, sometimes aimlessly blinking leds, running in wierd loops,
etc. Amazingly, if powered up at 5V and then voltage was run up to 6.5V,
they worked perfectly! Weird.

The microchip factory support engineer explained that they actually
sawed the top off of samples that we sent them, and determined the
problem to be in the EPROM section. What was happening was that the
programming was only bringing the bits down partially, not completely.
That's why they worked at lower voltages...the bits were just low enough
to make the product work.

The new specs call for more hits to bring down the bit lower.
Interestingly, the new batch (now called PIC16C54B) does not have the
problem (or at least the samples I was given checked fine at 6.5V).

The problem is most noted with programmers that appear to program very
quickly, such as the Parallax.    -Dave, EDS, Inc.

'12c508 fed by 9V battery'
1998\07\16@035217 by Leo van Loon

flavicon
face
Dear friends,

I am producing an electronic dice with a PIC12C508 as a kit for children.
For simplicity I must use a 9V block battery, but the PIC does not like 9V.
How can I reduce 9V to 5V with a minimum of components?
Does only a serial 4,7 V zener work?
I feed the seven LED's of the display directly from the battery, that can be
no problem.

Leo van Loon
SBB simpeltronics
Netherlands
tel +31 (0481) 450034
fax+31 (0481) 450051
mail TakeThisOuTsbb.simpeltronEraseMEspamRemoveMEtip.nl
url http://www.sbb-simpeltronics.nl
SBB simpeltronics ontwikkelt technische projecten voor basisschool en
basisvorming.
SBB simpeltronics develops technical projects for children in primary and
secondary education.

1998\07\16@035637 by David BALDWIN

flavicon
face
Leo van Loon wrote:
{Quote hidden}

--
       Use 78L05 instead of zener

 _____________
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  \ ALCATEL /               Design engineer
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1998\07\16@090344 by paulb

flavicon
face
Leo van Loon wrote:

> For simplicity I must use a 9V block battery, but the PIC does not
> like 9V.

 Dead right there, recently mentioned on this list.

> How can I reduce 9V to 5V with a minimum of components?
> Does only a serial 4,7 V zener work?

 As I see it, you go either of two ways.  For robustness, you use a
78L05 (as previously advised), because this allows you to maintain
optimum performance over a wide battery voltage.  Preferably use a low-
dropout regulator version.  And these are almost as cheap as
transistors.

 Alternately, consider the range of workable voltage of the PIC (about
3 to 6V is it not?) as a resource.  Connect the two LEDs which must
operate together (the diagonal ones) in series and use them to feed the
PIC and simultaneously drop 3V from the battery.  To drop another 0.6V
just to get it within ratings, use a series diode.

 These LEDs may barely light (but not in sleep mode) especially if you
use high- efficiency ones (but you wouldn«t, would you?).  To truly
light them, switch a resistor across the PIC using one of its outputs.

 Similarly the other two pairs are in series plus a silicon diode, from
the +9V supply to a PIC output each but *via* a resistor of the same
size.  The single LED must needs be driven separately, either by a
transistor or using a series "ballast" LED and diode as the others.

 The big concern with electronic dice (you meant you were producing an
electronic "die") is that switching the display LED current can warp the
randomisation algorithm.  With a PIC you have the opportunity to
actually run the randomisation very quickly (timing the button press in
µS, mod 6) then knowing the desired result, implement a "run-down"
display which eventually stops on the already-determined value!

 Actually, on reflection, a single silicon power diode in series with
all three LED pairs will both reduce the voltage to bring it into the 6V
rating and provide reverse-battery protection.

 Cheers,
       Paul B.

1998\07\16@113132 by Peter L. Peres

picon face
On Thu, 16 Jul 1998, Leo van Loon wrote:

> Dear friends,
>
> I am producing an electronic dice with a PIC12C508 as a kit for children.
> For simplicity I must use a 9V block battery, but the PIC does not like 9V.
> How can I reduce 9V to 5V with a minimum of components?
> Does only a serial 4,7 V zener work?
> I feed the seven LED's of the display directly from the battery, that can be
> no problem.

If the PIC does not do anything peculiarly complex, a simple series
resistor should be enough, once you know how much current it needs when
working, and making sure that this is fairly constant. Of course you get
to decouple the PIC. Also, make sure that the PIC does not sleep. A power
switch is mandatory.

hope this helps,

       Peter

1998\07\16@162218 by Luis Gonzalez

picon face
Leo van Loon wrote:
>
> Dear friends,
>
> I am producing an electronic dice with a PIC12C508 as a kit for
children.
> For simplicity I must use a 9V block battery, but the PIC does not
like 9V.
> How can I reduce 9V to 5V with a minimum of components?
> Does only a serial 4,7 V zener work?
> I feed the seven LED's of the display directly from the battery, that
can be
> no problem.
>
> Leo

Hello Leo:
There are many aspects that affects the choice for DC-regulation needs
such as:
- the voltage range within your circuit must operate (I4m used 9v
batteries as low as 7 volts for some applications and here all linear
regulators as the 78L05 fails because the dropout can be 2volts or more)
- the quisquent current that you can (loss( in the regulator (I4m
actually working in telephone digital circuits and here the zener
regulator is the worst solution for regulate 5v to one PIC16C65 and some
peripherals because they need some apreciable amount of current trough
it to give the specified voltage drop)
- the operation current of your circuit because many parameters depend
on it (dropout of linear regulators, time response of Low-Dropout
Regulators LDOs, load and line regulation of zener regulators and many
others.

My actual application includes PIC16C65A, LCD display 2*16, I2C memory,
tone encoder and decoder and RS-485 interface taking all the supply
voltage from the telephone line that can vary from 5 to 15 volts
depending on the tipe of line, the RENs connected, the weather, etc. and
finally I decide design a transistor-zener based regulator with 2 BJTs,
1 zener and 3 resistors, and this solution was better than the 78L05 and
simple zener option.

If you have more details about your needs please don4t doubt in say it
to me.


Luis Gonzalez
Bogota, COLOMBIA
spamlucho554spam_OUTspamhotmail.com

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1998\07\16@190423 by Russell McMahon

picon face
Note that when you turn the displays off they will rise to the
voltage that they are supplied from - this will be 9 volts if
you feed them directly and the PIC may not like it. If you use
drive resistors (as you should) then the PIC protection diodes
will conduct and MAY save you. Better design is to run the
displays from the 5 volt supply that the PIC is using.

A 7805 regulator in a TO220 package will supply the PIC and a
display happily and costs very little more than a 78L05 - the
78L05 is capable of lower power and will probably not have
enough capacity for a bright LED display.

LM7805s (same as LM340T5) or similar can be purchased from most
electronic suppliers who will also be able to supply a simple
circuit to use them.

----------
> From: Leo van Loon <STOPspamsbb.simpeltronspam_OUTspamspamBeGoneTIP.NL>
> To: spam_OUTPICLISTspamspamBeGoneMITVMA.MIT.EDU
> Subject: 12c508 fed by 9V battery
> Date: Thursday, 16 July 1998 19:47
>
> Dear friends,
>
> I am producing an electronic dice with a PIC12C508 as a kit
for children.
> For simplicity I must use a 9V block battery, but the PIC does
not like 9V.
> How can I reduce 9V to 5V with a minimum of components?
> Does only a serial 4,7 V zener work?
> I feed the seven LED's of the display directly from the
battery, that can be
> no problem.
>
> Leo van Loon
> SBB simpeltronics
> Netherlands
> tel +31 (0481) 450034
> fax+31 (0481) 450051
> mail EraseMEsbb.simpeltronspamKILLspamtip.nl
> url http://www.sbb-simpeltronics.nl
> SBB simpeltronics ontwikkelt technische projecten voor
basisschool en
> basisvorming.
> SBB simpeltronics develops technical projects for children in
primary and
> secondary education.

1998\07\17@005417 by tjaart

flavicon
face
Luis Gonzalez wrote:

> Leo van Loon wrote:
> >
> > Dear friends,
> >
> > I am producing an electronic dice with a PIC12C508 as a kit for
> children.
> > For simplicity I must use a 9V block battery, but the PIC does not
> like 9V.
> > How can I reduce 9V to 5V with a minimum of components?
> > Does only a serial 4,7 V zener work?
> > I feed the seven LED's of the display directly from the battery, that
> can be
> > no problem.
> >
> > Leo

Your enemies are drop-out and quiescent current.

Use a low-drop regulator for starters. JRC makes a cheap range.

To solve the second problem, use some mechanical contact that
will give some sort of a pulse when the die is activated (I suppose
it could be a pushbutton), and a 4011 flip-flip to switch the
regulator on. The PIC can switch the regulator off again.

--
Friendly Regards

Tjaart van der Walt
EraseMEtjaartRemoveMEspamwasp.co.za

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1998\07\17@034528 by William Chops Westfield

face picon face
Doesn't the 12C50x run down to 3.something volts?  Increase your
"battery life" by using a 3.something + epsilon regulator instead
of aiming at 5V.  Of course, that'll be more expensive than the
ubiquitous 5V regulators (which tend to be cheaper in the 1A TO220
cases than in the Lower power to-92 cases, anyway, at least from
many of the "hobbyist" suppliers.  A similar argument applies to
zener regulators (of the parallel sort, anyway.)

BillW

1998\07\17@231608 by J Nagy

flavicon
face
>Dear friends,
>
>I am producing an electronic dice with a PIC12C508 as a kit for children.
>For simplicity I must use a 9V block battery, but the PIC does not like 9V.
>How can I reduce 9V to 5V with a minimum of components?
>Does only a serial 4,7 V zener work?
>I feed the seven LED's of the display directly from the battery, that can be
>no problem.
>

I've been quite successful at driving LEDs directly from a '508 with a 3V
supply, and no series resistor. The LED current is typically about 10mA.
Food for thought...

       Jim

1998\07\19@045043 by paulb

flavicon
face
Russell McMahon wrote:

> Note that when you turn the displays off they will rise to the
> voltage that they are supplied from - this will be 9 volts if
> you feed them directly and the PIC may not like it.

 Hmmm.  Why would they do that?  Are they not diodes with a certain
threshold voltage, about 1.3 to 1.4 Volts?  It is true that Zeners have
a soft "knee", but that is not to say they have outright leakage, else
all our rectification circuits would have bad problems!  A LED is a
different device, but AFAIK it does not leak appreciably.

> A 7805 regulator in a TO220 package will supply the PIC and a
> display happily and costs very little more than a 78L05 - the
> 78L05 is capable of lower power and will probably not have
> enough capacity for a bright LED display.

 The TO-220 package 7805 has a typical quiescent current of 3mA.
Probably more than a running PIC and enough to light a LED on its own
(very nicely - standard method of "adjusting" regulators in 1.4V steps
is to put a LED in the "ground" line and you get a free pilot that also
indicates shutdown!

--
 Cheers,
       Paul B.

'Battery regulation'
1998\07\20@060035 by Stuart Allen

flavicon
face
Hello,

I have a battery powered 16F84 based project; a universal remote control.
There are 3 core components; the 16F84, a 24C65 EEPROM and a 44780 LCD
module.

The problem is how do I power this lot from batteries...

The EEPROM, LCD and all associated pull-ups/LCD contrast voltage are powered
from a PIC output pin. This works fine and drops the IPD to a uA when its
all turned off.

But when it comes to running it from batteries (4 Alkaline AAA's) I am not
sure what to do.
The LCD needs 5v (+/-5% or there abouts), the PIC and EEPROM etc are more
flexible. So here is my idea;

The PIC and IR LED run directly from the batteries, EEPROM runs directly
from the PIC. The LCD is powered through a low dropout regulator with a
standby input controlled by the PIC (same pin that powers the EEPROM) to
switch it on and off. This prevents the regulators quiescent current (which
is _relatively_ large) draining the batteries.

I think this is a pretty good solution, but what do you think and what have
you one?? Minimal component count is important as the case is very small. Is
it wise to run uC/EPROMs directly fom batteries?

Thanks for any help/advise you can give,

Stuart.

'12c508 fed by 9V battery'
1998\07\20@091233 by RHS Linux User

flavicon
face
On Thu, 16 Jul 1998, Leo van Loon wrote:

> I am producing an electronic dice with a PIC12C508 as a kit for children.
> For simplicity I must use a 9V block battery, but the PIC does not like 9V.
> How can I reduce 9V to 5V with a minimum of components?

 LM2931Z-5.0  -- a low-dropout voltage regulator specifically made for
battery-powered applications.  (National Semiconductor, if the 'LM' wasn't
a dead giveaway)

 --Crow

/**/

'Battery regulation'
1998\07\20@174550 by Russell McMahon

picon face
Your 4 cells would start off at about 6 volts but have an end point voltage
of under 4 volts (possibly as low as 3.2v if you want to wring every last
mAH out of the cells. Chances are your LCD will not tolerate either extreme
of this range. A low power PIC will run at 3v but the 16F84 will
theoretically not do so at full clock speed.

As LCD current is liable to be minimal you could possibly use the PIC to
provide a simple voltage multiplier (very compact) to allow operation off v
low battery voltages. (1 PIC pin, 2 diodes, 2 capacitors, 1 x 5v, TO92
regulator (eg LM2936 which has very low quiesecent current & dropout
voltage)).

If size is more important than price you could consider using one of the
many 2 cells to "X" volts converters available. Linear Technology and Maxim
both make a range of these. Nat Semis 'simple switchers" could also be
useful. You can even get 1 cell to 5 volt converters but will get better
efficiency off 2 cells. 2 (0r 3?) x AAA plus converter could be no larger
than 4 x AAA and give superior results.

Batteries could perhaps be 2 x AA depending on the shape of your housing.
This solution has the advantage of giving you a wide usable battery voltage
range.

An AA cell has slightly more than twice the volume of an AAA cell (216% for
one brand) so the battery volume and energy is similar. for 2 AA or 4 AAA
cells. A single AA and converter would have half the nominal energy content
available but the increased usable battery voltage range MAY be enough to
offset this depending on the voltage range you LCD will tolerate.
((Only real reason to use AA over AAA is probably the much better price and
availability of AA (at least tis so in NZ)))

A 9 volt "PP3" transistor battery may be a usable solution - especially
with an inverter.
No problem with low voltage at end of battery life :-).



----------
{Quote hidden}

powered
> from a PIC output pin. This works fine and drops the IPD to a uA when its
> all turned off.
>
> But when it comes to running it from batteries (4 Alkaline AAA's) I am
not
> sure what to do.
> The LCD needs 5v (+/-5% or there abouts), the PIC and EEPROM etc are more
> flexible. So here is my idea;
>
> The PIC and IR LED run directly from the batteries, EEPROM runs directly
> from the PIC. The LCD is powered through a low dropout regulator with a
> standby input controlled by the PIC (same pin that powers the EEPROM) to
> switch it on and off. This prevents the regulators quiescent current
(which
> is _relatively_ large) draining the batteries.
>
> I think this is a pretty good solution, but what do you think and what
have
> you one?? Minimal component count is important as the case is very small.
Is
> it wise to run uC/EPROMs directly fom batteries?
>
> Thanks for any help/advise you can give,
>
> Stuart.

'12c508 fed by 9V battery'
1998\07\21@003031 by Mike Hamilton

picon face
You could use a low drop out regulator from Maxim part number Max667.  This
has a nice feature that can tell the pic when the battery is too low.  Two
of these chips can be obtained for free as samples if you want. Just connect
to their web site. I think it is http://www.maxim.com.
{Original Message removed}

1998\07\21@004135 by Eric Fixler

flavicon
face
actually, http://www.maxim-ic.com

I use them fairly frequently; they have a wide input range and source 250 mA.

e






>You could use a low drop out regulator from Maxim part number Max667.  This
>has a nice feature that can tell the pic when the battery is too low.  Two
>of these chips can be obtained for free as samples if you want. Just connect
>to their web site. I think it is http://www.maxim.com.
>{Original Message removed}

'Battery regulation'
1998\07\22@040355 by Stuart Allen

flavicon
face
Hello,

Thank for the reply.

This is what I have decided on:

2 x AA, a LT1301 step-up regulator which will output 5v @ 200mA, the EEPROM,
LCD and PIC runs from this 5v.

The LT1301 has a SHUTDOWN input. I'll pull this up to Vbatt through a
resistor. (It's within spec). This can then be pulled to ground through a
NPN when any button (active high) is pressed thus starting the regulator and
the PIC, LCD, EEPROM.

The PIC will then pull the SHUTDOWN input low through the same NPN,
effectively latching it. So instead of SLEEPing, the PIC will just set its
SHUTDOWN output to low, the NPN stops conducting, SHUTDOWN goes high, and
its powered off.

In this configurating I will have a standby current of 17uA. Thats not bad
at all.

So the question is, any problem with this? Any problems with the transient
response of the LT1301?

Thanks,

Stuart.


'Battery consumption & LEDs'
1998\08\06@093246 by freeman.kilpatrick
flavicon
face
Hello All,

I am relatively new to PICs (migrating from STAMPS because I wanted
interrupts), and I did a little experiment to see how much power would be
required for a very small circuit.  I set up the standard "blinking LED"
program, and planned to let it run for a week to see what would happen.  I
had a standard energizer 9V battery driving a PIC 16F84 (through a voltage
regulator, of course), 2 LEDs, and an RC clock circuit.  I was surprised to
see that the battery was dead after only a few days.  I wasn't using
low-power LEDs, just standard Radio Shack stuff, but I still thought the
circuit would last longer.  How can I even make a battery-based application
with a "power on" LED if they drain batteries this fast?

Any advice/education welcome.

Alex

1998\08\06@100246 by Stuart Allen

flavicon
face
> Hello All,
>
> I am relatively new to PICs (migrating from STAMPS because I wanted
> interrupts), and I did a little experiment to see how much power would be
> required for a very small circuit.  I set up the standard "blinking LED"
> program, and planned to let it run for a week to see what would happen.  I
> had a standard energizer 9V battery driving a PIC 16F84 (through a voltage
> regulator, of course), 2 LEDs, and an RC clock circuit.  I was
> surprised to
> see that the battery was dead after only a few days.  I wasn't using
> low-power LEDs, just standard Radio Shack stuff, but I still thought the
> circuit would last longer.  How can I even make a battery-based
> application
> with a "power on" LED if they drain batteries this fast?
>
> Any advice/education welcome.
>
> Alex


Hello Alex,

I would imagine that it was the regulator that caused the battery to run
down so quickly, especially if it was standard 7905 type. The regulator was
probably drawing a large proportion of the total power from the battery;
check its spec and look at quiescent current, thats how much current it
effectively 'wastes'.

Try a special low IQ, drop regulator. MAXIM and Linear Technology have
examples, amongst others.

Also, 9v batteries don't have much capacity at all. Around 550mAH. So you
need to save power in as many places as possible. Does your PIC program go
to sleep at all? Using the watchdog timer to wake itself up? Putting the PIC
to sleep is the key to low power design. It can be asleep whether the LED is
on or off, and will use a fraction of the power it usually does, dropping
from 10s of mA to a few 1uA if you are careful.

What frequency is the clock? The slower the less power it uses. This is
documented in the data sheet.

And last of all, use a low current LED, and use the biggest series resistor
that still keeps it visible.

What else... change the flash duty cycle, ie. on for 2/10s off for 2
seconds.

Hope this helps,

Stuart.

1998\08\06@115840 by Peter L. Peres

picon face
On Thu, 6 Aug 1998, Freeman Kilpatrick wrote:

> required for a very small circuit.  I set up the standard "blinking LED"
> program, and planned to let it run for a week to see what would happen.  I

A standard *low power* blinking LED has Ton = 0.2sec Toff ~= 2 sec. This
alone reduces power consumption from 50% (Ton = Toff) to 10% (5 times).

A LED rigged like this for low power operation, should be driven with a
L/C switching arrangement if one can afford it. A PIC output can do the
chopping (RA4). You will probably use an 'inverted' chopper and connect
the LED A to +Vbatt directly, such that this will be the common rail. Its
current limiting resistor will be calculated for a V = Vleds + 0.3 Volts
(only !) as this is what the chopper supply will output (the duty cycle
will be around 1:2.5 for 9 V input, 3.3 V out = 2 red LEDs and a R for
0.3V@15mA = 20 ohms).

This again reduces the power for the LEDs from the original 9V * 15 mA ~=
0.125W to about 3.3V * 15 mA * 1.2 = 0.06 W, almost twice (assuming
continuous use - but the same factor applies for pulsed operation).

Last, use as low a clock frequency as possible (32 kHz or 500 kHz ceramic
or RC if you can live with the drift), and put the PIC to sleep while the
LED is off by using the watchdog timer. This again induces some time
incertainty.

When you will have done all this, you will have reduced the power
requirements from:

BEFORE:

9V battery
PIC runs all the time @ 4MHz = 1.5 mA (approximate v.)
LEDs run 50% of the time = 7.5 mA
Total: 9 mA
6F22 standard 9V battery will last just 220mAh/9mA ~= 22 hours. An
alkaline will last twice as long, probably.

AFTER:

9V battery
PIC runs 10% of the time @500 kHz, sleeps in between = (a few micro-amperes)
LEDs run 10% of the time at ~ 7mA while on = 0.7 mA over time (d.c. = 10%)
Total: less than 0.8 mA
6F22 standard 9V battery will last about 220mAh/0.8mA = 275 hours, and an
alkaline may last 2.5 times as long under these conditions. The actual
time obtained may be slightly shorter.

So, you can 'lean' your application as much as you please. You can
probably squeeze it down to the power required to run one LED with a 10%
duty cycle at 80% system efficiency, which will lead to about 25
milli-watts for the led, divided by 10, or, at said 6F22
220mAh*9V/2.25milli-watts ~= 880 hours. And this is about as far as you
can go with a 6F22, unless you have patient users who can wait 4 seconds
to see the LED flash, such that you can double the number.

Incidentally, 270 hours is well in excess of 1 week, and 880 hours is just
over a month by almost a week.

hope this helps ;)

       Peter

1998\08\06@120048 by Calvin

flavicon
face
part 0 2457 bytes
<META content=text/html;charset=iso-8859-1 http-equiv=Content-Type>
<META content='"MSHTML 4.72.2106.6"' name=GENERATOR>
</HEAD>
<BODY bgColor=#ffffff>
<DIV>There are several thingsd you can do to save power:<BR>a)Use a low dropout
regulator (NOT! a 7805).<BR>b)Use a large resistor to limit the LED current (not
too large, obviously).<BR>c)Keep the duty-cycle of the LED as low as
possible.<BR>d)Put the PIC to sleep between cycles.<BR>e)Use the lowest clock
speed possible for the PIC.<BR>f)Use a high efficiency LED.<BR>g)Any other
suggestions someone else may have...<BR><BR><BR>Calvin<BR><BR><BR>-----Original
Message-----<BR>From: Freeman Kilpatrick &lt;<A
href="RemoveMEfreeman.kilpatrickTakeThisOuTspamafosr.af.mil">@spam@freeman.kilpatrickSTOPspamspamafosr.af.mil</A>&gt;<BR>To:
<A href="TakeThisOuTPICLISTTakeThisOuTspamRemoveMEMITVMA.MIT.EDU">spam_OUTPICLISTspamspam.....MITVMA.MIT.EDU</A> &lt;<A
href="PICLIST.....spam@spam@MITVMA.MIT.EDU">spamBeGonePICLISTspamspam_OUTMITVMA.MIT.EDU</A>&gt;<BR>Date:
Jueves 6 de Agosto de 1998 8:22 AM<BR>Subject: Battery consumption &amp;
LEDs<BR><BR><BR>&gt;Hello All,<BR>&gt;<BR>&gt;I am relatively new to PICs
(migrating from STAMPS because I wanted<BR>&gt;interrupts), and I did a little
experiment to see how much power would be<BR>&gt;required for a very small
circuit.&nbsp; I set up the standard &quot;blinking LED&quot;<BR>&gt;program,
and planned to let it run for a week to see what would happen.&nbsp;
I<BR>&gt;had a standard energizer 9V battery driving a PIC 16F84 (through a
voltage<BR>&gt;regulator, of course), 2 LEDs, and an RC clock circuit.&nbsp; I
was surprised to<BR>&gt;see that the battery was dead after only a few
days.&nbsp; I wasn't using<BR>&gt;low-power LEDs, just standard Radio Shack
stuff, but I still thought the<BR>&gt;circuit would last longer.&nbsp; How can I
even make a battery-based application<BR>&gt;with a &quot;power on&quot; LED if
they drain batteries this fast?<BR>&gt;<BR>&gt;Any advice/education
welcome.<BR>&gt;<BR>&gt;Alex<BR>&gt;<BR></DIV></BODY></HTML>

</x-html>

1998\08\06@121909 by org Hager

flavicon
face
On Thu, 6 Aug 1998, Stuart Allen wrote:

> > circuit would last longer.  How can I even make a battery-based
> > application
> > with a "power on" LED if they drain batteries this fast?
> >
> > Any advice/education welcome.
> >
> > Alex
>
>
> Hello Alex,
>
> I would imagine that it was the regulator that caused the battery to run
> down so quickly, especially if it was standard 7905 type. The regulator was
> probably drawing a large proportion of the total power from the battery;
> check its spec and look at quiescent current, thats how much current it
> effectively 'wastes'.

I've recently measured the quiescent current of an 78L05, and it was
2.5mA! The LM2936Z-5.0 from NS is much better, but needs 10uF of blocking
capacitance at the output to behave properly.

>
> And last of all, use a low current LED, and use the biggest series resistor
> that still keeps it visible.

You can also drive the LED in its `on' state in a PWM-like fashion, e.g.
at 1kHz with a 1:5 duty cycle at 10mA. You will get 2mA of mean current
flowing through the LED, but it will appear brighter to the human eye than
a LED with 2mA steady current. I don't know what the optimal duty cycle
is, but you can save a lot of power that way.

Georg.

1998\08\06@122936 by Peter L. Peres

picon face
On Thu, 6 Aug 1998, Georg Hager wrote:

> I've recently measured the quiescent current of an 78L05, and it was
> 2.5mA! The LM2936Z-5.0 from NS is much better, but needs 10uF of blocking
> capacitance at the output to behave properly.

Huh ?! There was something wrong, for sure. I see max. 0.8 mA for a 'bad'
L05. A good one is more like 0.1 mA. It's not the quiescent current that
is going to get you, it's the lousy efficiency. Drive current for the o/p
transistor comes from the power supply and is not passed to the load...
the 317L is more predictable with 120 uA quiescent and passes the series
transistor drive c. through the load...

Peter

1998\08\06@131950 by Jan Derogee

flavicon
face
Hello Alex,
If you are using normal led's that draw a 20mA current, then your batt. will
last for 2000mAh (batt capacity) / 20mA = 100 hours (aprox 4 days)
If you blink your led (on period = one tenth of the cycle time) then you
can decrease your power drain. But your led won't burn as bright.
If you want a better efficiency for your total project (this also can reduce
power drain) use a better voltage regulator (a switching regulator (step-down)).
If you connect LED's or other power consuming components then try avoid
connecting them to your voltage regulator. Tie your led directly to the positive
9V leads (don't forget to use a higher resistor-value) and control your led
by pulling your PIC-output-ports down (LED lights-up if output=0).

A lower operating frequency for your PIC may also reduce power drain (but
look this up in your datascheets (it may not be worth the effort)).
Try to put your PIC to sleep when it is not needed (i'm not sure if this
can be done in 100% software, perhaps some hardware is needed (check datasheets)

Good luck with this project. I hope this is of any use.
Let me know what you achief.

Jan Derogee

1998\08\06@140113 by Harold Hallikainen

picon face
       It seems that the problem is that we need to drive the LED with a
current source and all we have is a voltage source.  We convert the
constant voltage to a constant current using a series resistor, which is
not very efficient!  So, how about this?

       To avoid ascii art, here's a description of the circuit...

       From +5V connect an inductor in series with an LED in series with
a diode to +5V.  Connect the junction of the LED and the diode (cathode
of LED, anode of diode) to a PIC output pin.  Pulse the pin low.  The LED
current will ramp up as the inductor current increases.  Set the pin
high.  The LED will continue to glow as the the inductor current ramps
down.  The time the pin is high should be long enough to make absolutely
sure the inductor current has ramped down to zero so we don't start the
next ramp up from some value other than zero, eventually resulting in
infinite current (not good).  Once you've done one ramp up and down, do
it again!  The diode is a catch diode and could possibly be replaced by
the clamp diode in the PIC.  With ideal components, this SHOULD be an
efficient way of getting current thru the LED without drops across
resistors.


Thoughts?


Harold




Harold Hallikainen
EraseMEharold.....spamhallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm


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1998\08\06@144439 by Harold Hallikainen

picon face
       On further thought, to eliminate regulator dissipation due to LED
current, we should connect the "left end" of the inductor to unregulated
+ supply, connect the cathode of the catch diode to unregulated + supply,
and use an open drain output on the PIC to pull the junction of the LED
and the catch diode low.  Also, if the LED can tolerate the unregulated
voltage as a reverse voltage, we can move it over to the catch diode
position, eliminating one part (remember, "the ideal design has zero
parts).
       In this situation, we have +supply going thru an inductor, thru
the LED back to + supply.  No current flows.  The "right side" of the
inductor is pulled low by an open drain PIC output.  Inductor current
ramps up.  The open drain output is released and the inductor current
ramps down through the LED (lighting it).  The process is repeated.


Harold


---------------------------------[previous message
below]---------------------------------

       It seems that the problem is that we need to drive the LED with a
current source and all we have is a voltage source.  We convert the
constant voltage to a constant current using a series resistor, which is
not very efficient!  So, how about this?

       To avoid ascii art, here's a description of the circuit...

       From +5V connect an inductor in series with an LED in series with
a diode to +5V.  Connect the junction of the LED and the diode (cathode
of LED, anode of diode) to a PIC output pin.  Pulse the pin low.  The LED
current will ramp up as the inductor current increases.  Set the pin
high.  The LED will continue to glow as the the inductor current ramps
down.  The time the pin is high should be long enough to make absolutely
sure the inductor current has ramped down to zero so we don't start the
next ramp up from some value other than zero, eventually resulting in
infinite current (not good).  Once you've done one ramp up and down, do
it again!  The diode is a catch diode and could possibly be replaced by
the clamp diode in the PIC.  With ideal components, this SHOULD be an
efficient way of getting current thru the LED without drops across
resistors.


Thoughts?


Harold




Harold Hallikainen
spamharoldKILLspamspam@spam@hallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

--------- End forwarded message ----------

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1998\08\06@145504 by David VanHorn

flavicon
face
>        It seems that the problem is that we need to drive the LED with a
>current source and all we have is a voltage source.  We convert the
>constant voltage to a constant current using a series resistor, which is
>not very efficient!  So, how about this?


Any linear regulation is just as inefficient.
For double bonus points, use the PIC as it's own switching regulator,
controlling a pass transistor in a buck configuration.

(Also a great excersize as to why emulators often suck!)

1998\08\06@170114 by Mike Keitz

picon face
A lot of people have posted a lot about this subject today.  I'll try to
avoid writing a lot.

First, use a high-efficiency LED.  This is a no-brainer, a tremendous
amount of bang/buck.

Second, everyone so far has taken the 9V battery/linear regulator as a
given.  For most PIC work, it isn't best.  Since a PIC can operate from
3V to 5.5V, a regulator isn't necessary unless something about the rest
of the circuit requires a stable voltage.  A set of three "penlight"
batteries such as AA or AAA size in series will put out 4.5V when new,
and be about completely run down when the voltage reaches 3V.  If a
stable voltage is required, consider 4 batteries and a micropower linear
regulator to 3.5 or 4V.  Especially the AA size have much more ma-H
capacity than a 9V, and when it is time to replace them, new ones will
cost less than the 9V.

Of course, also think about the user interface so the LEDs don't have to
be on any more than necessary.  Even if high efficiency, the LEDs can
easily use more power than the rest of the circuit.  Quick bright flashes
are much more noticeable thatn steady dim light.  Driving an LED that's
supposed to be on "constantly" with pulses too fast to see is probably
worthwhile if the processor needs to be running during that time anyway.

Many have mentioned switching techniques, but this definitely isn't a
good idea for a beginner like the original poster.  Moving the battery
voltage closer to the LED voltage will greatly narrow the advantage that
can be obtained (by increasing the efficiency of the non-switching
circuit).

If there is a lot of extra voltage, I think there are dual LEDs of the
same color that can be operated in series to get twice the brightness
from the same current.  But a battery of only 3V won't be enough to light
them.

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1998\08\07@084031 by Peter L. Peres

picon face
On Thu, 6 Aug 1998, David VanHorn wrote:

> >        It seems that the problem is that we need to drive the LED with a
> >current source and all we have is a voltage source.  We convert the
> >constant voltage to a constant current using a series resistor, which is
> >not very efficient!  So, how about this?
>
>
> Any linear regulation is just as inefficient.
> For double bonus points, use the PIC as it's own switching regulator,
> controlling a pass transistor in a buck configuration.
>
> (Also a great excersize as to why emulators often suck!)

Good point ! But, from the previous postings, I would way that my posting
did not make it ! I had suggested a switching regulator to drive the 2
LEDs with RA4, using the + unreg rail as common rail for the switching
regulator ! Almost all follow-ups suggest the same ideas, but no-one
refers to my posting ?! Maybe it did not make it ?

Peter

1998\08\07@095743 by Claudio Rachiele IW0DZG

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1998\08\07@095956 by David VanHorn

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>> Any linear regulation is just as inefficient.
>> For double bonus points, use the PIC as it's own switching regulator,
>> controlling a pass transistor in a buck configuration.
>>
>> (Also a great excersize as to why emulators often suck!)
>
>Good point ! But, from the previous postings, I would way that my posting
>did not make it ! I had suggested a switching regulator to drive the 2
>LEDs with RA4, using the + unreg rail as common rail for the switching
>regulator ! Almost all follow-ups suggest the same ideas, but no-one
>refers to my posting ?! Maybe it did not make it ?
>
>Peter

It made it here, and yes, that woks.  The thing to note is that any time you
are limiting current with a resistor, you are wasting power.  In low power
apps, you learn to think in terms of Joules, rather than amps or volts.

1998\08\07@101413 by Claudio Rachiele IW0DZG

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1998\08\07@142415 by Claudio Rachiele IW0DZG

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1998\08\07@155425 by Don

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Claudio Rachiele IW0DZG wrote:
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1998\08\09@104613 by Peter L. Peres

picon face
On Fri, 7 Aug 1998, David VanHorn wrote:

> It made it here, and yes, that woks.  The thing to note is that any time you
> are limiting current with a resistor, you are wasting power.  In low power
> apps, you learn to think in terms of Joules, rather than amps or volts.

The point is, that I fried a 2 mA LED while testing, and I did not manage
to fry it with the R ;) So, one can remove it later...

Peter

'(OT) Sping Loaded Battery Contacts Anyone?'
1998\08\31@130942 by Lewis H. Cobb

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face
Ok, I know this is way off topic on first glance, but the project involves
a PIC in a hand-held instrument so I figured it kind-of applies here.

I'm designing a small hand-held instrument that is going to be
re-chargable.  Rather than spending a bzillion dollars on an industrial
design I have found a suitable off the shelf enclosure that the
manufacturer will modify at a small cost.  There will be two "contact" pads
on the unit that are about .2" (5mm) diameter.  I have been looking around
for spring loaded pins that I can use to design into the mating
charger-holder unit but all I can find are the test point probes that are
used in the bed-of-nails testing jigs that are used in production and these
are far too small.

Years ago I remember seeing exactly what I am looking for in the holder of
a cordless phone.  The pins were stainless and 0.250" diameter, tapering to
a reasonable point, and sping loaded.  That phone can be found nowhere at
this point and web searches have been fruitless.

Can anyone pass along any suggestions on where I might go to find a
manufacturer of these things or something similar?  I have already checked
out the IDI (interconection devices) web site and they have battery
contacts but again, they are more suited to smaller battery packs and not
really what I am looking for.

Thanks in advance for any help people can provide.

Lewis
spam_OUTcobbspamspamzeus.ee.unb.ca

1998\08\31@143216 by Mark Willis

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I just bought the girlfriend a couple Pilot "Dr. Grip" pens at Costco
for her to write with (her hands don't close very well.)  These have a
cap (the button you push on to pop the point in & out) that looks JUST
almost like what you're describing to me - This could be chromed brass
or other metal instead of stainless steel, but I think that it, + 2
springs etc. would do the job.

 The top button is 1/4" diameter, sort of a rounded top but with a flat
center, 3/32" diameter, probably at least 1" long;  I imagine it's a
"top hat" shape;  I can't disassemble this pen without wrecking it, and
risking destruction of my self from Robin, but the pens were $6 or so
for a pair.  And you can probably sell me the refills as Robin will use
'em eventually <G>

 There's some sort of brass fitting inside the hand grip that may be
good to base the electrical connection on, even?  If you hit this cap at
a slight angle, you'd have a small 'wiping' contact area & that should
work...

 Also, The local thrift stores, swap meets, flea markets, etc. would be
good places to look for that old cordless.  Or another similar beastie.

 Mark, spammwillisspamspamspamnwlink.com

Lewis H. Cobb wrote:
{Quote hidden}

1998\08\31@154856 by Joe Little

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face
    I saw them once in an EMI shielding catalog.  They were spaced about
every
    four inches around the perimeter of a door so they must have been
    inexpensive.

1998\08\31@163933 by wwl

picon face
On Mon, 31 Aug 1998 14:07:00 -0300, you wrote:

>Ok, I know this is way off topic on first glance, but the project involves
>a PIC in a hand-held instrument so I figured it kind-of applies here.
>
>I'm designing a small hand-held instrument that is going to be
>re-chargable.  Rather than spending a bzillion dollars on an industrial
>design I have found a suitable off the shelf enclosure that the
>manufacturer will modify at a small cost.  There will be two "contact" pads
>on the unit that are about .2" (5mm) diameter.  I have been looking around
>for spring loaded pins that I can use to design into the mating
>charger-holder unit but all I can find are the test point probes that are
>used in the bed-of-nails testing jigs that are used in production and these
>are far too small.
>
Some manufacturers of test-point type probes also make larger stuff
for this type of application - Coda Systems in the UK do a huge range
of this sort of stuff - I'm sure there are many others.
    ____                                                           ____
  _/ L_/  Mike Harrison / White Wing Logic / TakeThisOuTwwlspamspamnetcomuk.co.uk  _/ L_/
_/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

1998\08\31@201831 by David Instone

flavicon
face
       -----Original Message-----
       From:   Mike Harrison [SMTP:spamBeGonewwlspamNETCOMUK.CO.UK]
       Sent:   Tuesday, 1 September 1998 06:41 AM
       To:     EraseMEPICLISTEraseMEspamMITVMA.MIT.EDU
       Subject:        Re: (OT) Sping Loaded Battery Contacts Anyone?

       On Mon, 31 Aug 1998 14:07:00 -0300, you wrote:

       >Ok, I know this is way off topic on first glance, but the project
involves
       >a PIC in a hand-held instrument so I figured it kind-of applies
here.
       >
       >I'm designing a small hand-held instrument that is going to be
       >re-chargable.  Rather than spending a bzillion dollars on an
industrial
       >design I have found a suitable off the shelf enclosure that the
       >manufacturer will modify at a small cost.  There will be two
"contact" pads
       >on the unit that are about .2" (5mm) diameter.  I have been looking
around
       >for spring loaded pins that I can use to design into the mating
       >charger-holder unit but all I can find are the test point probes
that are
       >used in the bed-of-nails testing jigs that are used in production
and these
       >are far too small.
       >
       Some manufacturers of test-point type probes also make larger stuff
       for this type of application - Coda Systems in the UK do a huge
range
       of this sort of stuff - I'm sure there are many others.
            ____
____
          _/ L_/  Mike Harrison / White Wing Logic / spamBeGonewwlspam_OUTspam.....netcomuk.co.uk  _/
L_/
        _/ W_/  Hardware & Software design / PCB Design / Consultancy  _/
W_/
       /_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/

       I had need of something like this once in the past and found my
local spring manufacturer to have or be able to make almost anything I
needed very cheaply
       There should be one in your local phone book. Good luck


'[OT] Op-amp "low battery" detector; female 0.1" he'
1998\09\04@152031 by Brian Scearce
picon face
Amateur electronics question:

I'm working on a battery-powered infrared transmitter, and I'm
concerned by the fact that a working IR LED looks exactly the same as a
non-working IR LED in the visible spectrum, so I'm adding a "battery
low" indicator.

I'm sure that there are a large number of clever ways to do this,  but
I happen to have some LF411 op-amps on hand, and I was planning on
doing something like (sorry, no ASCII art):  divide-by-3 voltage
divider on the 9V supply going to the + input of the op-amp, a
divide-by-2 voltage divider on the 5V regulated supply going to the -
input of op-amp.  Output of the op-amp is "battery above 7.5V".

But I'm haunted by Horowitz and Hill saying "an op-amp is never (well,
almost never) used without feedback".  Am I properly exploiting one of
the "almost never" cases, or am I misusing the op-amp?  I'm aware that
the op-amp will be unstable near the crossover point, and that I could
cure this with feedback; maybe I'll add this later.  I'm only wondering
if this circuit will work without feedback.

Construction questions:

The PCB will have ordinary 0.1" headers for connecting the LEDs.  Where
do you get 1-hole, 2-hole or 3-hole female header plugs to fit these
things?  I know they exist, I've seen them on hobby servos, and for
attaching a PC's panel buttons to its motherboard, but the only ones I
can find in catalogs and surplus places are 20-plus hole plugs for
ribbon cables, not for two or three conductors.  Do I have to keep
cutting up DIP sockets?


I'm also working on an H-bridge motor driver.  I've got a working
prototype, but the MOSFETs are pretty delicate.  I'd like to be able to
easily replace them in the final version.  What do I use for TO-220
sockets?


Thanks,
Brian

1998\09\04@160639 by er

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Put a red LED in series with the IR LED, and
you will have the answer about whether current
is flowing.

On the female header sockets, try Waldom C-Grid
connector housings, which come in single or
dual row, any length, and which are designed
to receive crimp-on Box Crimp Terminals.
Digikey current catalog page 49.  The down side
to this is that the crimp tool is expensive.

On the H Bridge, solder those transistors.  At
the current you are probably running, the sockets
could heat up.

{Original Message removed}

1998\09\04@162134 by Dan Larson

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face
Amatuer electronics answer:

A little "positive" feedback from the output of the op-amp to the
non-inverting input will add hysteresis to the switch over point
and make it less sensitive to noise "jitter".  There is a way to
calculate the hysteresis based on the amount of positive feedback,
but I'll leave that up to you to research.  You could just
determine how much hysteresis you want by experimenting with
different feedback resistors.  Start by making it large compared
to the input resistors.  This will give you a small amount of hysteresis.
Decreasing the feedback ressitor will increase feedback and thus
increase hysteresis.

On Fri, 4 Sep 1998 12:18:39 -0700, Brian Scearce wrote:

{Quote hidden}

Look for "snap off" connectors.  You can snap off the size you want.

>
>I'm also working on an H-bridge motor driver.  I've got a working
>prototype, but the MOSFETs are pretty delicate.  I'd like to be able to
>easily replace them in the final version.  What do I use for TO-220
>sockets?

I wouldn't socket anything driving high current unless you use very
heavy copper or brass lugs and nuts.  Design the H-bridge right and
you won't have to replace the MOSFETS.  I am currently working on an
h-bridge using TO-92 bipolar transistors for a low current motor. A
primary design criteria of mine is "smoke-proofing" the circuit.  It
works very well and doesn't even get warm.  Bipolars are much cheaper.
the only reason I am still working on it is because I want to add
circuitry for using the "back-emf" of the motor for speed measurement.

>
>
>Thanks,
>Brian
>

1998\09\04@164831 by Reginald Neale

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face
Brian asked:

>But I'm haunted by Horowitz and Hill saying "an op-amp is never (well,
>almost never) used without feedback".  Am I properly exploiting one of
>the "almost never" cases, or am I misusing the op-amp?  I'm aware that
>the op-amp will be unstable near the crossover point, and that I could
>cure this with feedback; maybe I'll add this later.  I'm only wondering
>if this circuit will work without feedback.
>
 It probably won't work well enough. The noise near the threshold will
 prevent you from seeing an LED that's reliably ON or OFF.

 The reason for using feedback is to trade gain for stability. You don't
 need the million or so open-loop gain of the op-amp. The negative feedback
 resistor from output to (-) will give you a predictable gain. A positive
 feedback resistor from output to (+) will give you a well-defined threshold
 and a "snap-action" response as you cross it. Books or web references on
 op-amps will show you how to do this.

 Reg Neale

1998\09\04@194859 by Michael Hagberg

flavicon
face
just put a visible LED in series with the IR LED. the advantages of this are
that if you don't use the voltage on the visible LED you will have to waste
the power on a current limiting resistor and there are no additional
components to drain the battery power.

michael

You may leave the list at any time by writing "SIGNOFF PICLIST" in the
   body of a message to spamLISTSERVspamMITVMA.MIT.EDU.


<snip>
>I'm working on a battery-powered infrared transmitter, and I'm
>concerned by the fact that a working IR LED looks exactly the same as a
>non-working IR LED in the visible spectrum, so I'm adding a "battery
>low" indicator.
>
<snip>

1998\09\04@200110 by David VanHorn

flavicon
face
-----Original Message-----
From: Michael Hagberg <RemoveMEmhagbergKILLspamspamKILLspamI1.NET>
To: EraseMEPICLISTspamBeGonespamspamMITVMA.MIT.EDU <KILLspamPICLISTspamMITVMA.MIT.EDU>
Date: Friday, September 04, 1998 6:54 PM
Subject: Re: [OT] Op-amp "low battery" detector; female 0.1" headers; TO-220
sockets


>just put a visible LED in series with the IR LED. the advantages of this
are
>that if you don't use the voltage on the visible LED you will have to waste
>the power on a current limiting resistor and there are no additional
>components to drain the battery power.


As long as you have enough battery voltage to light both, plus some for a
current limiting resistor and VCE for the switching transistor.  Me, I'd put
the visible LED in series between the micro and the switching transistor
base.
It's hard to set the output current accurately when you've only got a few
10ths of a volt to work with.


><snip>
>>I'm working on a battery-powered infrared transmitter, and I'm
>>concerned by the fact that a working IR LED looks exactly the same as a
>>non-working IR LED in the visible spectrum, so I'm adding a "battery
>>low" indicator.


Not in my camcorder they don't :)

I'm not sure what you're talking to, but if it has a display, then you might
send it a code added to each transmission that says "remote battery low"
when applicable.  This saves power on the end that needs it, and uses
whatever display or user interface you've already got on the other end.

1998\09\04@211649 by steve

flavicon
face
> >But I'm haunted by Horowitz and Hill saying "an op-amp is never (well,
> >almost never) used without feedback".

>   It probably won't work well enough. The noise near the threshold will
>   prevent you from seeing an LED that's reliably ON or OFF.

It will work if the LED draws an appreciable current
compared to the normal operation of the circuit. When it reaches the
threshold and turns on the LED (or oscillates) the current
consumption will go up and the battery terminal voltage will drop.
It's positive feedback but not as we know it.

It's always struck me as being a bit odd to have an LED to indicate a
flat battery. If the light is off does that mean that the battery is
OK or that it went flat yesterday ?

In this case, I would pulse a heartbeat LED for 10ms every second
or when it transmits.

Steve.


======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: stevebspam_OUTspamspamtla.co.nz      fax +64 9 820-1929
======================================================

'New Challenge; battery charge'
1998\09\17@121238 by Chris Eddy

flavicon
face
Tjaart;

I didn't read the whole thing, but got the gist.  I am usually a 'put a PIC
in anything' guy, but my current limit was real simple.  A TIP family part
regulated the high side voltage into the battery, and in the low side of the
battery you put a 10 ohm resistor, prepare to try different values.  Then a
small NPN is driven across the 10 ohmer with the base on the high side of the
10 ohm, the emitter going to ground like the low side of the reisistor, and
the collector going to the base of the high side TIP device.  When the
current goes too high, the NPN turns on, and the TIP rolls off.  You get a
close but imperfect box on the VI curve.  Then, the op amp that drives the
base of the TIP device must have some resistance inserted to protect the
opamp.  THEN you have to do one more thing.  When the battery is relied upon
for full current, the 10 ohm resistor will toast.  Place a 1n4001 in reverse
across the 10 ohm, and it will pass the battery load when it is necessary.
Um, that's 3 parts, and it works fairly well, limitting the fast charge then
letting the voltage regulation come into play for float.

Chris Eddy
Pioneer Microsystems, Inc.

Tjaart van der Walt wrote:

> Hi there
>
> I've been playing with all kinds of circuits to limit the current when
> charging a flat lead acid battery. I've been able to construct a 'dumb'

'New PIC Challenge; battery charge'
1998\09\17@123029 by tjaart

flavicon
face
Chris Eddy wrote:

> Tjaart;
>
> I didn't read the whole thing, but got the gist.  I am usually a 'put a PIC
> in anything' guy, but my current limit was real simple.  A TIP family part

The reason I wanted to use a MOSFET and PWM was for (virtually)
zero heat build-up. I've built a jig with TIP122's and opamps to charge
a whole bank of NiCd's a year or so ago. I used positive feedback on the
opamps. The problem remains that  a 10ohm (or a 1 ohm, for that matter)
is going to heat up the whole box at 2A. The MOSFET also offers you a
nifty way of measuring the current (Vds) you don't have on a BJT.

A 17.7A, 50V, SMD, logic gate level MOSFET is around US0.50, which
is dirt cheap too.

I will put a schematic on my web page tomorrow or so.

Hey, it my challenge! I can set the rules! ;)

--
Friendly Regards

Tjaart van der Walt
tjaartspamspam@spam@wasp.co.za

|--------------------------------------------------|
|                WASP International                |
|R&D Engineer : GSM peripheral services development|
|--------------------------------------------------|
|SMS spamBeGonetjaart.....spamsms.wasp.co.za  (160 chars max)|
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'battery specs'
1998\09\21@131025 by goflo

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Anyone got a url for Ray-O-Vac rechargeable alkaline battery specs,
and/or experience with same?

TIA, Jack

1998\09\21@184746 by Mark Willis

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www.rayovac.com has data smattered about, but it's very dilute &
mostly aimed at marketing IMHO (Nowhere near what I'd consider good
solid tech data.)  They do get into the charger a little, but I don't
remember seeing capacity anywhere, just relative capacity vs life cycles
curves, except for AA batteries;  No map to equate the AA curves to C or
D cells, which was what I was interested in.  I may've missed something.

 Mark, .....mwillis@spam@spamnwlink.com

@spam@goflospampacbell.net wrote:
>
> Anyone got a url for Ray-O-Vac rechargeable alkaline battery specs,
> and/or experience with same?
>
> TIA, Jack


'9V battery powered PIC'
1998\10\27@064242 by NCS Products
flavicon
face
>way round and survive, burn your finger and still work or be
>powered direct from a 9V alkaline battery without damage?

Which PICs can be powered from a 9V battery?

1998\10\27@100903 by cousens

flavicon
face
NCS Products wrote:
>
> >way round and survive, burn your finger and still work or be
> >powered direct from a 9V alkaline battery without damage?
>
> Which PICs can be powered from a 9V battery?


This is a reply to my question below on the 3/4/98

Peter Cousens wrote

> Does anyone know the max voltage you can run a 16c84 at ?

I have user PIC16F84-10P 3 month now in my Chistmas melodybox directly
with
9V battery.

I wanted to get more power to speaker ( 4ohm), so I removed 5V
regulator.
Now I drive the speaker directly through 100uF capacitor without
problems.
It is no on continiously, only when I switch device on. Nobody wants to
listen Christmas melodies very long time! Also 9V battery is not
excatcly 9V
volt when programm is runnig, but you aseked can PIC used directly with
9V
battery. the answer is yes ( at least in limeted time).
-----------------------------------------------------------------------
I since then have tried a 16f84 direct from a 9v Alkaline battery
by coincidence on a similar app (a morse code message generator)
but it only runs for 30 secs every hour


--
Peter Cousens
email: cousensRemoveMEspamher.forthnet.gr  phone: + 3081 380534
snailmail:  Folia, Agia Fotini, Karteros, Heraklion  Crete, Greece.

Is it true that they have, on the new version of windows
managed to increase the MTBF from 95 to 98 minutes ?
(That's why they called it 95)

1998\10\28@020032 by Dr. Imre Bartfai

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On Tue, 27 Oct 1998, NCS Products wrote:

> >way round and survive, burn your finger and still work or be
> >powered direct from a 9V alkaline battery without damage?
>
> Which PICs can be powered from a 9V battery?
>
>
PIC16HV540

Imre

1998\10\28@110910 by Craig Lee

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Is this puppy available yet?

Craig

-----Original Message-----
From: Dr. Imre Bartfai <spamrootspamPROF.PMMF.HU>
To: PICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU <spam_OUTPICLIST@spam@spamRemoveMEMITVMA.MIT.EDU>
Date: Tuesday, October 27, 1998 11:47 PM
Subject: Re: 9V battery powered PIC


{Quote hidden}

1998\10\28@125514 by Matt Bonner

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Craig Lee wrote:
>
> Is this puppy available yet?
>
> >PIC16HV540
> >
I'm sitting on two of them.  Funny, the samples got to me before I could
find the data sheet.  Turns out that I can't use them for what I
intended since they're only rated to 85degC.

Also, the part number is no where on the package.  Only:
 76001
 ES/
 REV AX

--Matt

'PIC from 9V battery'
1998\10\30@093757 by scott.list

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Greetings:

I bet this has been covered numerous times before, please excuse the
repititious question if so:

I have a small project where I'd like to incorporate a 16F84 but I need
to power it via a 9v battery.  I'd like to keep the project as
small/light as possible and would like advise on the best way to power
the PIC.

Can someone recommend a specific V-reg (other than the 7805 I've been
using) or perhaps something smaller I can accomplish this with?  Could I
do it with some sort of zener arrangement? Obviously I'm no electroics
wiz :-( .

The PIC will only be monitoring one High/Low input and will be switching
one 2N2222 transistor as output. (I know the '84 is overkill, but it's
what I know how to use).

Thanks in advance for any help.
Scott

1998\10\30@110513 by Peter L. Peres

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On Fri, 30 Oct 1998, Scott Horton wrote:

> The PIC will only be monitoring one High/Low input and will be switching
> one 2N2222 transistor as output. (I know the '84 is overkill, but it's
> what I know how to use).

I suppose that a 4V2 0.3Watt zener in series with the power supply will
get you there. If the zener is not a good quality one you will also need a
resistor of about 10 kOhms between Vdd and Gnd of the PIC to drain the
leakage.

Peter

1998\10\30@170607 by Lynx {Glenn Jones}

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Use a 78L05, only the size of a TO-92 package, so quite small.

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On Fri, 30 Oct 1998, Scott Horton wrote:

{Quote hidden}

1998\10\30@174934 by Craig Lee

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Or an SOIC.  As wide and as high as head of a thumbtack.

Craig

>Use a 78L05, only the size of a TO-92 package, so quite small.

1998\10\30@182243 by Bob Blick

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>
> >Use a 78L05, only the size of a TO-92 package, so quite small.
>
It sounds to me like there must be a lot of Eveready or Duracell
stockholders on this list. A 9v battery will be dead in a couple of days
just powering a 78anything05 regulator.

How about the LM2936-5.0 ? It draws less than the PIC it will power. Or
anything in the TK112 or TK114 line from Toko.

Cheers,
Bob

1998\10\30@185233 by William Chops Westfield

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Switching regulator providers are quick to point out that the current
drain of a simple linear regulator used to provide 5V from a 9V battery
is quite high (compared to typical PIC circuits.)  You can increase your
battery life significantly by going to some sort of swicthing regulator
design (unfortunately increasing your costs and complexity at the same time.)
You can increase it even more by replacing the 9V battery with 2AA cells and
converting to a "boost" switcher configuration - apparently 2AA cells has
considerably more raw power than a 9V battery.  (also, for small current
drain, you can go to a capacitor-only based voltage converter...)

BillW


'PIC from 9V battery'
1998\11\02@121246 by John Payson
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|Switching regulator providers are quick to point out that the current
|drain of a simple linear regulator used to provide 5V from a 9V battery
|is quite high (compared to typical PIC circuits.)  You can increase your
|battery life significantly by going to some sort of swicthing regulator
|design (unfortunately increasing your costs and complexity at the same time.)
|You can increase it even more by replacing the 9V battery with 2AA cells and
|converting to a "boost" switcher configuration - apparently 2AA cells has
|considerably more raw power than a 9V battery.  (also, for small current
|drain, you can go to a capacitor-only based voltage converter...)

Another advantage of the two AA's driving a switcher is that a
boost switcher can operate in "pass-through" mode with zero
quiescent current draw.  If your device only needs the full 5v
when it's really "operating", being able to throttle down to
raw battery may help considerably with current consumption.



Attachment converted: wonderland:WINMAIL.DAT (????/----) (0001C117)

1998\11\02@131722 by Sean Breheny

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Oh oh, John, the attachments from hell are back <G>!

>Attachment Converted: "c:\bawin\winba\eudora\attach\WINMAIL10.DAT"
>

Sean

+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
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1998\11\02@133419 by goflo

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"Simplified Design of Micropower & Battery Circuits",
by John D. Lenk, contains useful discussion and examples...

Jack

John Payson wrote:
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1998\11\02@142555 by Dwayne Reid

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Oh, NO!  Its back!  ;)

<big snip>
>
>begin 600 WINMAIL.DAT
>

dwayne


Dwayne Reid   <@spam@dwaynerspam_OUTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

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