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'[PICLIST] Battery life in sleep mode (PIC16F84)'
2000\08\06@131053 by John Mullan

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I have a countdown timer (seconds only) with 7 segment displays (4).
Basically, after it reaches zero and sounds the piezo, I have it go to
sleep.

I plan to power this with 3 AA cells.  The current draw in sleep mode is
9ma.

How long will the batteries last in sleep mode??

What do I look for to get the sleep current as low as possible??

The PIC is 16F84

John Mullan

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2000\08\06@181922 by Bob Ammerman

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I built a circuit with a 16C84 powered by 4 AAs. Current in sleep mode was
measured at about 30 microamps.

I'm not sure why your getting 9 milliamps draw.

Things to look for:

TRIS all pins to be inputs, and make sure they are driven by a signal at or
very near the ground or power rail.

Alternatively, a pin can be set to be an output, but make sure that it isn't
'bucking' any internal or external pull-up/pull-down.

If you are periodically waking up using the watchdog then make sure you use
the largest acceptable prescale value, and minimize the amount of code that
runs each time the watchdog fires.

At 30 microamps I figured I had months of sleep mode run time available.

Bob Ammerman
(contract development of high performance, high function, low-level
software)

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2000\08\06@211830 by Dwayne Reid

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At 01:08 PM 8/6/00 -0400, John Mullan wrote:
>I have a countdown timer (seconds only) with 7 segment displays (4).
>Basically, after it reaches zero and sounds the piezo, I have it go to
>sleep.
>
>I plan to power this with 3 AA cells.  The current draw in sleep mode is
>9ma.

That is VERY high!  You should be able to get down to 100 uA or less.

Look for floating pins.  The quick check for those is to monitor current
drain (in sleep mode) while you touch each lead with a scope or DMM probe -
if the current goes down when you touch that lead, you have found one of
the problems.

One of my products uses a 16c73B, X25043 watchdog / PSU supervisor /
eeprom, a couple of op-amps, LT1298 a/d convertor driving 4 digits of LED 7
segment displays - it sleeps at about 100 uA.  I do shut down the sensors,
op-amps and a/d convertor but everything else remains powered.

Keep looking.

dwayne



Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2000\08\07@045825 by mike

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On Sun, 6 Aug 2000 13:08:12 -0400, you wrote:

>I have a countdown timer (seconds only) with 7 segment displays (4).
>Basically, after it reaches zero and sounds the piezo, I have it go to
>sleep.
>
>I plan to power this with 3 AA cells.  The current draw in sleep mode is
>9ma.
I assume you are still running the LEDs - current draw in sleep mode
should be 5-20 microamps, depending on whether the watchdog is running
or not.
>How long will the batteries last in sleep mode??
Capacity of an AA alkaline is about 2400mAHrs, so a PCI in sleep mode
with no extra drain will last pretty much forever, or at least until
the batteries are leaking goo..
>What do I look for to get the sleep current as low as possible??
Make sure no inputs are floating and outputs are not sourcing current
anywhere.
Oh, yes... and TURN THE LEDs OFF!
>The PIC is 16F84
>
>John Mullan

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2000\08\07@134601 by M. Adam Davis

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Well, it's almost a moot point.  With 3 AA cells, you get about 1260 seconds (21
minutes) until you drain the batteries.

(assuming average 20mA draw for 5 (average) leds in 4 displays)  This also
assumes a good set of batteries at 1400mA/H each.

I can see you wanting to preserve battery power after the count is done, but
unless you are only counting 5 minutes at a time (300 seconds, might as well get
rid of a display..), there really isn't much reason to worry about the batteries
draining after the count is finished, there isn't enough left to perform another
count later.

What are you using this timer for?  Is it expected to wake back up later and
perform another count?  Must the display be lit throughout the count?

As far as your question goes, if your project is given a new set of batteries
(generally 1.4 Amp/Hour for AA Alkaline, IIRC) and the chip goes into sleep
immediately, then at 9mA the chip will drain the batteries in about 155 hours
(6.5 days).

There are other factors at work here, which may make it last longer, and I've
made a bunch of assumptions, any of which could be incorrect.  But you need to
know that LEDs are power hogs in the world of embedded design.  You might be
better off going for an LCD display of some type.

-Adam

John Mullan wrote:
{Quote hidden}

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2000\08\07@190752 by Peter L. Peres

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>9mA sleeping

I think that you should look at IO pins that remain high when you go to
sleep, and that you need to put the LCD in sleep mode. If it hasn't got
one then use a PNP to turn it off when sleeping. Sleeping current is in
the 10s of uA range normally.

Peter

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2000\08\09@214732 by John Mullan

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OK, I'm beginning to see that this project may not be what I expected.

This was supposed to be a timeout timer for use when a little 6 year old boy
needs a timeout :)

You press a button and it starts with 5 minutes.  Each successive press adds
5 minutes.  When time runs out it beeps (timeout over).

Now the catch.  It goes into sleep mode when done waiting for the next use.

Obviously it won't work with the current configuration.  I really wanted
something that would be easy for the child to be able to see and watch from
a few feet away.  An LCD wouldn't cut it.  I was hoping to stay away from
using a wall-wart but might have too.

Anybody have other ideas???

John

{Original Message removed}

2000\08\09@221745 by Scott Dattalo

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On Wed, 9 Aug 2000, John Mullan wrote:

> OK, I'm beginning to see that this project may not be what I expected.
>
> This was supposed to be a timeout timer for use when a little 6 year old boy
> needs a timeout :)
>
> You press a button and it starts with 5 minutes.  Each successive press adds
> 5 minutes.  When time runs out it beeps (timeout over).
>
> Now the catch.  It goes into sleep mode when done waiting for the next use.
>
> Obviously it won't work with the current configuration.  I really wanted
> something that would be easy for the child to be able to see and watch from
> a few feet away.  An LCD wouldn't cut it.  I was hoping to stay away from
> using a wall-wart but might have too.
>
> Anybody have other ideas???

Belt? :)

For my 5 yr old the threat of a timeout evokes hysteria. For the 2 yr old (turns
2 on 10aug), we can tell to give herself a timeout and she'll walk to her room,
wait for a while and then come out.

But if you insist on a digital solution, I'd suggest having the `push button'
switch turn the device on and then successive pushes will accumulate longer and
longer times. The initial turn on can latch a MOSFET to provide the initial
power. Then provide a means by which the PIC can switch off the MOSFET. The off
resistance of the MOSFET is very high and consequently you won't have to deal
with the PIC sleep currents.

For a chess clock timer I once used large LCD 7-segment displays. These consume
much less power than their Light Emitting cousins. However, they're much more
difficult to drive. Digikey has several different types to choose from.

Scott

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2000\08\09@233419 by Bob Ammerman

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This should still work. Why can't the display just go black after the
timeout?

If so, then you should be just fine.

What is your 'LEDs on' current?

Battery life (assume 1200 ma hour capacity) will be:
    1200ma hour *60 min/hour / current_draw_in_ma
  = 72000 ma min / on_current_in_ma

Using relatively efficient multiplexed displays you should be able to work
with an on_current of under 100 ma.
If your on-current is 100 ma, you will have 720 minutes of on-time

720 min / (5 min/timeout) = 144 timeouts.

Now assuming your 6-year-old is rated at 6 timeouts / day, we have:

   144 timeouts / (6 timeouts / day) = 24 days.

Not too bad. If you can find a better quality 6-year-old your battery life
will be even better. :-)

Bob Ammerman
RAm Systems
(contract development of high performance, high-function, low-level
software)



----- Original Message -----
From: John Mullan <jmullanspamKILLspamHOME.COM>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Wednesday, August 09, 2000 9:37 PM
Subject: Re: [PIC]: Battery life in sleep mode (PIC16F84)

> OK, I'm beginning to see that this project may not be what I expected.
>
> This was supposed to be a timeout timer for use when a little 6 year old
boy
> needs a timeout :)
>
> You press a button and it starts with 5 minutes.  Each successive press
adds
> 5 minutes.  When time runs out it beeps (timeout over).
>
> Now the catch.  It goes into sleep mode when done waiting for the next
use.
>
> Obviously it won't work with the current configuration.  I really wanted
> something that would be easy for the child to be able to see and watch
from
> a few feet away.  An LCD wouldn't cut it.  I was hoping to stay away from
> using a wall-wart but might have too.
>
> Anybody have other ideas???
>
> John
>
>  {Original Message removed}

2000\08\10@090623 by Olin Lathrop

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> Obviously it won't work with the current configuration.  I really wanted
> something that would be easy for the child to be able to see and watch
from
> a few feet away.  An LCD wouldn't cut it. ...

Why not?  This sounds like an almost perfect match for a 16C923 running with
a slow crystal, driving the LCD directly.  That will take very little power
when running, and even less in sleep mode.  I haven't done the calculation,
but I bet battery life would be quite satifactory.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, EraseMEolinspam_OUTspamTakeThisOuTcognivis.com, http://www.cognivis.com

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2000\08\10@092114 by mike

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On Wed, 9 Aug 2000 21:18:26 -0500, you wrote:

{Quote hidden}

Pic sleep current is not the issue - it should be <20uA and therefore
negligible for AA batteries. There is no need to switch power to the
PIC, only the things it drives.

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2000\08\10@092117 by mike

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On Wed, 9 Aug 2000 21:37:23 -0400, you wrote:

>OK, I'm beginning to see that this project may not be what I expected.
>
>This was supposed to be a timeout timer for use when a little 6 year old boy
>needs a timeout :)
>
>You press a button and it starts with 5 minutes.  Each successive press adds
>5 minutes.  When time runs out it beeps (timeout over).
>
>Now the catch.  It goes into sleep mode when done waiting for the next use.
>
>Obviously it won't work with the current configuration.  I really wanted
>something that would be easy for the child to be able to see and watch from
>a few feet away.  An LCD wouldn't cut it.  I was hoping to stay away from
>using a wall-wart but might have too.
>
>Anybody have other ideas???
Instead of having the LEDS on continuously, blink them. Use
low-current displays as well - current would typically be about 1mA
per segment, so say 10ma avarage for a 2-digit display. Flash for say
200mS every second and you have 2mA avarage power draw, which is more
sensible.

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2000\08\10@134240 by acampbell

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another approach might be to use a piezo instead of a display,
and code the time using a minutes/ quarter minutes beep pattern,
with a different pattern at the end.  then its down to something a 12c509 can
handle.

however, if you want a  "Get back in that
corner or its another 5 minutes' option,  you will need a pair
of ultrasonic detector/emitters and a voice chip....

alice
6-year-old owner

{Quote hidden}

>  {Original Message removed}

2000\08\10@180046 by Peter L. Peres

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idea: use a stepping motor to move a needle or scale disc with time. You
will need 5 PIC outputs for 4 phases and a zero switch. You can use a
ULN2003 as driver and a motor scrapped from a floppy drive (head
actuator). The motor takes very little current to move and nothing to stay
put (use single phase drive and no holding torque). You need no gears,
just move the motor every X seconds where X depends on the number of
seconds. Thus put a needle on the axle and use a scale. A stepper will run
off 5V (4.5V, 4.8V) or 9V. Use a 32 kHz crystal and do not sleep for
easier programming ;).

Peter

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2000\08\11@204410 by John Mullan

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OK.  I am running at 20-50 ma (dependant on how many digits are on and
number of segments).

I'm pretty happy with this.  It's the sleep current of 9ma that worries me.

I am thinking of trying the suggestion of latching in the power and have the
PIC cut that power.  But I want to try getting the sleep current down first.
I need to know what state to leave the pins at (again, I know somebody
already said).  I believe it was said that they should all be inputs and
0volts on the pins.

I could always just put in a toggle power switch and hope somebody remembers
to turn it off.

If anybody has a plan for the power latching idea I'd love to hear it.

John


{Original Message removed}

2000\08\11@214446 by John Mullan

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Had the LEDs.  How much for a good sized 7 segment LCD (with drivers, don't
want the added headache)??


{Original Message removed}

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