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PICList Thread
'Driving sensitive gate triacs directly'
1995\07\28@090937 by Harrison Cooper

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face
There was some discussion on interfacing with a SSR, but I don't remember
reading how it turned out.

How about this one - since the output current is quite hefty from a PIC
(40 mA if I remember right), can you drive a sensitive gate triac directly ?
Data sheet for a MAC228A would indicate 5mA trigger with a 15mA hold.
Anyone done this before ?  Normally, I use a optocoupler but it would be
nice to eliminate another part.

spam_OUThcooperTakeThisOuTspames.com

1995\07\28@094156 by Reg Neale

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face
On Jul 28,  7:09am, Harrison Cooper wrote:
|Subject: Driving sensitive gate triacs directly
| There was some discussion on interfacing with a SSR, but I don't remember
| reading how it turned out.
|
| How about this one - since the output current is quite hefty from a PIC
| (40 mA if I remember right), can you drive a sensitive gate triac directly ?
| Data sheet for a MAC228A would indicate 5mA trigger with a 15mA hold.
| Anyone done this before ?  Normally, I use a optocoupler but it would be
| nice to eliminate another part.
|
| .....hcooperKILLspamspam@spam@es.com
|-- End of excerpt from Harrison Cooper

Depends on how vulnerable you are to getting fried. One of the functions
of SSR's is isolation from the line. Sure, you can do what you suggested,
but be aware that your PIC and whatever circuitry is attached will be
connected to potentially lethal power source.


*Reg Neale=nealespamKILLspamee.rochester.edu ....standard disclaimer applies...*
*..."Ignorance is a renewable resource."....P.J. O'Rourke............*

1995\07\28@102224 by Kevin P. Fleming

picon face
At 07:09 AM 7/28/95 -0600, Harrison Cooper wrote:
>There was some discussion on interfacing with a SSR, but I don't remember
>reading how it turned out.
>
>How about this one - since the output current is quite hefty from a PIC
>(40 mA if I remember right), can you drive a sensitive gate triac directly ?
>Data sheet for a MAC228A would indicate 5mA trigger with a 15mA hold.
>Anyone done this before ?  Normally, I use a optocoupler but it would be
>nice to eliminate another part.
>
>.....hcooperKILLspamspam.....es.com
>
>

I thought about this too, but I wanted zero-crossing, and the triac-output
optocouplers are pretty cheap and reliable (and easy to use).

I think I'd rather pay the extra two bucks per triac than risk blowing up my
PIC and all its attached hardware with 115 VAC...
Kevin Fleming, Reliable Networx, Inc.
Phoenix, AZ
Internet: EraseMEkpfhomespam_OUTspamTakeThisOuTprimenet.com


"Please, don't change colors while I'm talking to you."


'Photosensitive PIC circuit'
1996\07\01@180647 by pic
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picon face
It seemed so simple.  I wanted a yellow LED in my PIC16C84 design, so I
connected it via a 3K3 resistor between RA4 and Vdd.  So far so good.

Then I noticed something odd.  With the PIC spending most of its time in
sleep mode, its quiescent supply current (with the LED off) varied from
30uA to 90uA in sympathy with the ambient light level - disconnection of
the LED removed this variation.  A voltmeter (>1M impedance) showed RA4
to sit at +3.6V relative to Vss when its open-drain output was inactive.

It seems as if the photocurrent injected by the LED is entering RA4 and
affecting the operation of the PIC (maybe via the Schmitt input buffer).

Several questions spring to mind:

1.  What is causing the supply current variations?
2.  Is there any risk of misoperation of the PIC in this configuration?
3.  Would a non open-drain port pin be a better choice to drive an LED?

Any thoughts?

- Ian Chapman

1996\07\02@084057 by Wolfram Liebchen

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Ian Chapman wrote:
{Quote hidden}

Ian,

the inputs of CMOS circuits like the PIC don't like intermediate
input levels, because then you partially enable both of the input
amplifier transistors, making a weak rail-to-rail connection.
The more you come to the center voltage (2.5V) the more current
flows. The PIC datasheets show the input stage of the port pins,
and - as I think - also the current consumption under various
conditions.
If you would use a non open collector output, this effect should
not happen, because you short-circuit the LED
(plus-rail * LED * port-pin at Vdd).

Wolfram


--

+-----------------------------------------------+
! Wolfram Liebchen, liebchenspamspam_OUTipserv.ffo.fgan.de !
!        Forschungsinstitut fuer Optik          !
+-----------------------------------------------+


'windowed PICs sensitive to light??'
1997\07\09@100053 by Tim Drury
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Here is my setup:

PIC14000 acting as I2C master sending 5 bytes to a PIC16C63 acting as I2C slave.
PIC16C63 buffers the I2C data and sends it to a PC via RS-232.  I can look on a
scope and see the 5 I2C bytes followed by the 5 (plus checksum, total 6) bytes
on the RS232 line.

One of the bytes from the PIC14000 indicates how many data bytes are in the
message.  There is a three byte header and two data bytes for this test.
I know the protocol of the I2C doesn't need a "number of bytes" parameter; that
info is used by the RS232 portion of the 16C63, so it has to stay.

Everything works fine until I place my hand between my 100W halogen desk lamp
and the PIC14000.  The PIC14000 still only sends 5 bytes but the PIC16C63 starts
sending lots of data (lots and lots...).  Presumably the 14000 is telling the
16C63
that there are more than 2 data bytes.  This is strange, but what is also
stranger
is that it only works with the light _on_.  When I block the light or turn it
off the
PIC losses its mind.  This doesn't bode well for a dark, windowless OTP 14000.
BTW, the 16C63 doesn't have any problems (that I can detect).

The first think I thought of is the internal 4Mhz clock of the 14000 is
fluctuating
enough that the I2C master clock and data timing are moving outside the limits.
That isn't happening.  I confirmed it on the scope.

Any ideas?  Will the OTP parts exhibit the same behavior?

-tim drury

1997\07\09@130458 by Mike

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At 10:02 AM 7/9/97 -0400, you wrote:
>Here is my setup:

<snip>

Make sure you clear or initiate all RAM variables before use.

The light ON might act to clear those RAM variables you didn't in
software - especially on power up...

We had a couple of MC68705R5S processors on a remote hybrid power station
and had the windows covered with black masking tape.

When we took a photo of the cabinet (with a flash) it went haywire and
relays clicked all over the place - fortunately the hardware safety
interlocks prevented the generators starting...

The point is that opaque masking tape was not opaque the the UV from an
electronic flash. We had to put aluminium foil (doubled over to avoid
pin holes) then cover this with tape to be sure we didn't let any other
light in...

Rgds

Mike


Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.
                                                                      Massen

1997\07\10@053603 by Tom Handley

picon face
re: Errors with 14000/16C63

  Tim, this is probably obvious but are both those parts EPROM versions and did
you run the test with the windows covered up by a suitable opaque cover?

  - Tom

At 10:02 AM 7/9/97 -0400, you wrote:
>Here is my setup:
>
>PIC14000 acting as I2C master sending 5 bytes to a PIC16C63 acting as I2C
slave.
{Quote hidden}

starts
{Quote hidden}

1997\07\10@103052 by Tim Drury

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>Make sure you clear or initiate all RAM variables before use.
>
>The light ON might act to clear those RAM variables you didn't in
>software - especially on power up...
>
>We had a couple of MC68705R5S processors on a remote hybrid power station
>and had the windows covered with black masking tape.
>
>When we took a photo of the cabinet (with a flash) it went haywire and
>relays clicked all over the place - fortunately the hardware safety
>interlocks prevented the generators starting...
>
>The point is that opaque masking tape was not opaque the the UV from an
>electronic flash. We had to put aluminium foil (doubled over to avoid
>pin holes) then cover this with tape to be sure we didn't let any other
>light in...

Mike,

Thanks for the reply.  I read the FAQ regarding uninitialized variables.  I
didn't
think this problem affected me since it wasn't a "boot-up" problem.  This
occurred hours into the test after (I believe) every RAM location had been
accessed.

Anyway, I went through the code in fine detail and found a couple subtle bugs
that didn't relate to the uninitialized RAM problem.  After fixing them, the
problem went away.  I don't really know why.

The question I have is this: once the PIC is powered up, can it be affected
by light.  I would certainly think not, but my earlier problem hints that it
can.  I just don't know the answer.

Did you track your flash-bulb problem down to a specific uninitialized
register?  I can't find mine, and I hate solving a problem without knowing
what the answer was.  It unnerves me.

-tim

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1997\07\10@105724 by John Payson

picon face
> The question I have is this: once the PIC is powered up, can it be affected
> by light.  I would certainly think not, but my earlier problem hints that it
> can.  I just don't know the answer.

From my experience, light has three effects on a 16C622/JW that I've been
able to identify:

[1] It seems to cause the comparators to misread slightly.

[2] If the light gets strong, it can increase current consumption (e.g. when
   the part is sleeping)

[3] If the light gets very strong (e.g. mini-Maglite at 1") the part will start
   to malfunction "randomly" [there's probably some pattern to what it does,
   but I've not identified it; it did cause a program crash].

1997\07\10@144311 by Mike

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At 10:32 AM 7/10/97 -0400, you wrote:

>>When we took a photo of the cabinet (with a flash) it went haywire and
>>relays clicked all over the place - fortunately the hardware safety
>>interlocks prevented the generators starting...
>>
>>The point is that opaque masking tape was not opaque the the UV from an
>>electronic flash. We had to put aluminium foil (doubled over to avoid
>>pin holes) then cover this with tape to be sure we didn't let any other
>>light in...

>Did you track your flash-bulb problem down to a specific uninitialized
>register?  I can't find mine, and I hate solving a problem without knowing
>what the answer was.  It unnerves me.

Both controllers were set up as state machines, so there were negligble
opportunities for uninitialised variables. It seems the direction registers
were momentarily inverted when the UV burst from the flash hit. One thing
we did as a precaution was to refresh the direction registers upon each
state change detected. WHen didn't have time to investigate any further and
found no other software precautions/changes necessary.

As a matter of policy ALL our windowed chips are covered with full opaque
metal tabs to be as sure as possible there is no chance of any light
causing alteration of operation.

It stands to reason that chips will have some susceptibility, especially
with design tolerances getting ever smaller and the energy per gate being
very small indeed.

Prior to the UV flash we noticed no difference in operation from normal
incandescent light bulbs, though these were MC68705R5S dies which were
NMOS and were made around 1988 so die sizes were a bit larger than etc...

Maybe some subtle thing like a flag or set of memory locations are being
changed - it would be quite easy to set up a test - that is a full
RAM XOR to report which RAM locations and/or flags change.

This would be a simple, yet most interesting experiment.

I know of one chap around 1985 that used a 2708 fully programmed and watched
how the bits were slowly erased by exposure to daylight as a possible
means to determine UV strength - I think consistency was a problem...

Rgds

Mike
Perth, Western Australia


Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.
                                                                      Massen

1997\07\10@182906 by Andy Kunz

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>The question I have is this: once the PIC is powered up, can it be affected
>by light.  I would certainly think not, but my earlier problem hints that it
>can.  I just don't know the answer.

Yes.

I have seen all my windowed chips behave slightly differently, from
changing frequency (with the 8-pin devices on internal RC) to losing memory
in RAM.  All kinds of things.

Here's what to do with all those 5" disk write-protect tabs.  Use them as
EPROM window shades!

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\07\14@100622 by Tim Drury

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>> The question I have is this: once the PIC is powered up, can it be affected
>> by light.  I would certainly think not, but my earlier problem hints that it
>> can.  I just don't know the answer.
>
>From my experience, light has three effects on a 16C622/JW that I've been
>able to identify:
>
>[1] It seems to cause the comparators to misread slightly.
>
>[2] If the light gets strong, it can increase current consumption (e.g. when
>    the part is sleeping)
>
>[3] If the light gets very strong (e.g. mini-Maglite at 1") the part will start
>    to malfunction "randomly" [there's probably some pattern to what it does,
>    but I've not identified it; it did cause a program crash].


Thanks for all the responses.  There is obviously a problem with windowed
PICs and light, but nothing that cannot be cured.

Did anyone notice, however, that my problem was NOT a problem with light,
but with _dark_??  My system ran fine with a 100W halogen desk lamp shining
but when I turned the light off, or if I put my hand between the PIC and the
lamp, then the system started to malfunction?

In this case, placing an opaque cover on the PIC made the problem worse.
What I needed to do was tape a light bulb to the PIC!  Kidding, of course.

As Mike stated, this would be an interesting problem to explore, but I don't
have the time.  I have to keep moving forward.

Thanks again, folks.

-tim


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1997\07\14@130245 by Andy Kunz

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>Did anyone notice, however, that my problem was NOT a problem with light,
>but with _dark_??  My system ran fine with a 100W halogen desk lamp shining
>but when I turned the light off, or if I put my hand between the PIC and the
>lamp, then the system started to malfunction?

I noticed that you _saw_ a problem when the chip was operating in the
proper mode.

This implies that the code was wrong.

Since then you fixed the code, I presume, and now the chip works correctly.

Amazing the neat little things you learn on this list!

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\07\15@164255 by Tim Kerby

picon face
Halogen lights give off a load of uv - thats why they need a glass plate
over the bulb and you should be further than a metre away at all times.  It
could be erasing the chip.

Tim


At 10:02 09/07/97 -0400, you wrote:
>Here is my setup:
>
>PIC14000 acting as I2C master sending 5 bytes to a PIC16C63 acting as I2C
slave.
>PIC16C63 buffers the I2C data and sends it to a PC via RS-232.  I can look
on a
>scope and see the 5 I2C bytes followed by the 5 (plus checksum, total 6)
bytes
>on the RS232 line.
>
>One of the bytes from the PIC14000 indicates how many data bytes are in the
>message.  There is a three byte header and two data bytes for this test.
>I know the protocol of the I2C doesn't need a "number of bytes" parameter;
that
>info is used by the RS232 portion of the 16C63, so it has to stay.
>
>Everything works fine until I place my hand between my 100W halogen desk lamp
>and the PIC14000.  The PIC14000 still only sends 5 bytes but the PIC16C63
starts
>sending lots of data (lots and lots...).  Presumably the 14000 is telling the
> 16C63
>that there are more than 2 data bytes.  This is strange, but what is also
> stranger
>is that it only works with the light _on_.  When I block the light or turn it
> off the
>PIC losses its mind.  This doesn't bode well for a dark, windowless OTP
14000.
>BTW, the 16C63 doesn't have any problems (that I can detect).
>
>The first think I thought of is the internal 4Mhz clock of the 14000 is
> fluctuating
>enough that the I2C master clock and data timing are moving outside the
limits.
>That isn't happening.  I confirmed it on the scope.
>
>Any ideas?  Will the OTP parts exhibit the same behavior?
>
>-tim drury
>
>


------------------------------------------------------------------
Personal Web Pages: http://web.ukonline.co.uk/members/tim.kerby/
PIC Site: web.ukonline.co.uk/members/tim.kerby/pic/
The PIC Pages are under construction and I am looking for projects
------------------------------------------------------------------

1997\07\16@034840 by Keith Dowsett

flavicon
face
At 21:25 15/07/97 +0100, you wrote:
>Halogen lights give off a load of uv - thats why they need a glass plate
>over the bulb and you should be further than a metre away at all times.  It
>could be erasing the chip.
>
>Tim
>

Hmm, not all that much u.v. They have a colour temperature around 3200K
(sorry photograpy creeping in) which is similar to a domestic light bulb.
They emit a little more uv because the tube is silica rather than glass.

AFAIK the reason most of them have a glass plate in front is because they
frequently fail with a bang. Being sprayed with lots of red hot quartz
fragments is no fun (been there, done that).

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

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


'Touch sensitive code'
1998\07\15@133401 by John Haggins
picon face
Hi,

Anyone got code to make a PIC input touch sensitive with no external
components?

i.e. if you connect a wire to an input, the PIC "knows" when you touch the
wire.

Thanks!

1998\07\15@144406 by Michael S. Hagberg

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face
i've set one port to an output and sent a pulse train out then looked at the
inputs for the signal.
the output pin is used for all inputs.

michael

-----Original Message-----
From: John Haggins <KILLspamjawgKILLspamspamEARTHLINK.NET>
To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Date: Wednesday, July 15, 1998 12:44 PM
Subject: Touch sensitive code


{Quote hidden}

1998\07\15@151147 by Peter L. Peres

picon face
On Wed, 15 Jul 1998, John Haggins wrote:

> Hi,
>
> Anyone got code to make a PIC input touch sensitive with no external
> components?
>
> i.e. if you connect a wire to an input, the PIC "knows" when you touch the
> wire.
>
> Thanks!

                           R2
                        +-/\/\/\- +Vcc
                 R1     |               |
Touch here O----/\/\/\---*---------------O Pic pin
                                        |

The code simply counts pulses as long as the signal goe LOW. If it gets
over 25 pulses in a second (we have 50Hz here) then it assumes that
something is touching the sensor. The sensor can be painted or under a
paper sticker, however it MUST have low C vs everything else. R1 is 1 Meg
and R2 is as high as you can get (I used a 22 Meg one I think).

The circuit is sensitive to EVERYTHING, including neighboring pins, which
must be set as outputs, and driven LOW. Use a guard ring. Also reacts to
walkie-talkies and cellular phones. Probably also to cats that brush
against one's trouser leg and thunderstorms ANYWHERE.

The circuit is unreliable for production systems. The one where I checked
it out had a 32768 kHz crystal and almost nothing else on it (timer app).
The sensor was made by gluing small pieces of thin copper to a glass board
(bare). Wires were very short (5 cm) and power was 9Volts + 78L05. The
guard ring was a piece of wire-wrap wire that surrounded the outline of
the sensor. The shape does not seem to matter but it won't work at all
outdoors in a quiet spot.

There is a version of this circuit that uses the oscillator output to
drive a capacitive bridge, with the user's finger being the short to
ground over it. It involves etching a certain 3-wire pattern into a
circuit board, that relies on the copper thickness / pattern area ratio to
achieve its effect. This one is reliable but forget about passing any FCC
or CE EMI/RFI test with it. It can be used only for very limited things.
It can be used for less limited things if it is shielded by a conductive
membrane that contains elastic 'cups' to keep the membrane away from the
pattern when not pushed. The cups used in remote controls and membrane
keyboards are just perfect for this. The solution is water-tight and I
suppose that it should last about as long as the polymers in the membrane.

Peter

1998\07\15@154619 by andre

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face
John:
I haven't try it with PIC but this is
what I would do first.
16c71 or any 7X family pic use analog input.
you need at list 1 resistor like 100 k or 1mohm  to ground.


do this

1. make input analog
2. start conversion
3. check for end of conversion
4. load result in w
5. xorlw b'00000001'
6. check z flag
7. if set then party time

Andre Abelian

John Haggins wrote:

> Hi,
>
> Anyone got code to make a PIC input touch sensitive with no external
> components?
>
> i.e. if you connect a wire to an input, the PIC "knows" when you touch the
> wire.
>
> Thanks!

1998\07\15@155600 by Sylvain Bilanger

picon face
I think if you just put the wire on the A/D input of the 16C71 there is
a big enought change of voltage on the wire for the PIC to know that you
touched it... just make a condition in the PIC that says if there is a X
amount of variation something touched it... I dont know if it helps but
i hope so.

Just try it you will see!
Cya! Sylvain


>Hi,
>
>Anyone got code to make a PIC input touch sensitive with no external
>components?
>
>i.e. if you connect a wire to an input, the PIC "knows" when you touch
the
>wire.
>
>Thanks!
>


______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com

1998\07\15@161643 by Harold Hallikainen

picon face
On Wed, 15 Jul 1998 22:01:15 +0000 "Peter L. Peres" <TakeThisOuTplpEraseMEspamspam_OUTACTCOM.CO.IL>
writes:
>On Wed, 15 Jul 1998, John Haggins wrote:
>
>> Hi,
>>
>> Anyone got code to make a PIC input touch sensitive with no external
>> components?
>>


       Probably 20 years ago someone made a chip for this.  I probably
still have the sample buried somewhere.  I imagine it could be simulated
with a PIC.
       Ascii art follows...  Change to monospace type now!



      ||-------- square wave from PIC pin
      ||
      |
      ||
      ||-------- PIC input


       The touch plate is on the left and is insulated from the right
plates by a suitable dielectric (perhaps fiberglass circuit board
material, or a glass panel like on a microwave oven).  The circuit is two
capacitors in series, which passes the square wave from the PIC output
back to the PIC input.  When the left plate is touched, the junction of
the two capacitors is grounded, preventing the square wave from getting
back to the PIC input. Your circuit watches for loss of the input square
wave (perhaps by having an edge reset a timer and having it overflow on
loss of signal).
       I'd probably add a pull-up or pull-down resistor on the PIC input
side (maybe even a port b weak pull-up), though that may not be
necessary.
       Anyway, something to play with.

Harold

[back to normal typeface...]

Harold Hallikainen
RemoveMEharoldspamTakeThisOuThallikainen.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\07\15@162300 by Ohtsji, Randie

flavicon
face
Watch out for ESD!  Semtech (http://www.semtech.com) makes some pretty good
protection devices (TVS).

Randie
randie.ohtsjiEraseMEspam.....glenayre.com


> {Original Message removed}

1998\07\15@171409 by John Haggins

picon face
Thanks to everyone for your suggestions!

At 12:54 PM 7/15/98 PDT, you wrote:
{Quote hidden}

1998\07\15@171409 by John Haggins

picon face
Thanks to everyone for your suggestions!

At 12:54 PM 7/15/98 PDT, you wrote:
{Quote hidden}

1998\07\15@175206 by Sean Breheny

face picon face
It would seem to me that this would be very difficult to achieve reliably
with NO external components, but with about 2 or 3 components, it could
be done properly. If you have a pull up resistor of about 2 Meg from
the PIc pin to +5v, then toughing a finger between this input and GND
should pull it low enough to change the state. THe only remaining problem
is that of ESD protection and keeping the circuit from being thrown off
by picking up stray signals. A .01 uF cap from the pin to ground should
help with the stray signals. The input protection diodes might be good
enough for some applications, but you might also add a 6 or 7 volt zener
diode, reverse biased, to ground.At this point, the same software
debouncing routines which work for bushbuttons would probably work on
this, too.

Sean


On Wed, 15 Jul 1998, John Haggins wrote:

{Quote hidden}

1998\07\15@181038 by Sean Breheny

face picon face
In my previous reply, I forgot to mention one thing: It would also be a
good idea to include two 100k resistors, in series with the grounded
touch terminal, and in series with the touch terminal going to the pic
pin. I have not tested the idea, but with these resistors, the pull up
resistor, the zener, and the cap, I think that this would be very robust,
and still cheaper than a pushbutton.

Sean


On Wed, 15 Jul 1998, John Haggins wrote:

{Quote hidden}

1998\07\17@180846 by Walter Banks

picon face
The following  the touch sensitive switch is

                                      -----------
                500K              |
        ----- \/\/\/\/------------|   Pa
       |                             |
       |                             |
       |                             |
        ------------------------|  Pb
       |                             |
    ------                          |
    ------
       |
   Finger separated by an insulator


A port Pa  puts out a step from 0 to Vcc through a 0.5M
resistor (470K or 560K) 5 microseconds later the port art Pb
samples the value on the touch plate (Which is insulated
from the finger).  A sampled 1 indicates nothing touching the
plate. A sampled 0 indicates that the capacitor has not charged
up to the switching threshold of Pb.

The way it works is the number of free electrons in the finger
acts like a virtual ground and the RC time constant of 0.5 M
and the C establishes the 5 microsecond sample time.

I have used these in a variety of ways usually etching the plate
directly on a PC board and using a heat shrink plastic as an
insulator

In simple applications where you need only one or two
switches then the following circuit will also work.
        |
        |
       /
       \  500K                    ------
       /                             |
       |                             |
       |                             |
        ------------------------|  Pb
       |                             |
    ------                          |
    ------
       |
   Finger separated by an insulator

This requires a single port bit that outputs a 0 and discharges the
capacitive switch. The port data direction is changed and sampled
5 microseconds later. A 0 indicates the presence of a finger
and a 1 the absence of a finger.

Walter Banks
http://www.bytecraft.com


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

the
> wire.
>
> Thanks!


'Sensitive RB0...'
1998\11\20@155314 by Dave Johnson
flavicon
face
I've just started experimenting with sleep on a PIC16F84, waking it up on
a low-to-high transition on RB0/INT. It's working fine, but I noticed
something surprising (to me anyway): simply turning on my oscilloscope,
even when it's not connected to the circuit at all, is enough to wake up
the PIC!! Sometimes just turning on the work light over my bench does it
too, but not always. The program quickly realizes that nothing is really
going on and goes back to sleep, of course, but I guess this means my
circuit isn't very tolerant of noise. Or is this normal?

I assume that the fairly long lead going to RB0 (about 2 inches) is
acting like an antenna or something, and my 'scope is an old 80s classic
(Tektronix 2213), maybe EMI rules weren't so strict back then :-) But why
the light?

Anyone else seen similar behavior? And I guess my real question is: what
can I do to make the circuit more immune to outside noise?

Dave Johnson

1998\11\21@211152 by Marc

flavicon
face
> I've just started experimenting with sleep on a PIC16F84, waking it up on
> a low-to-high transition on RB0/INT.

> Anyone else seen similar behavior? And I guess my real question is: what
> can I do to make the circuit more immune to outside noise?

You can add a pulldown resistor on RB0, if you don't have one already. 2k2 is
a good value for many apps.

1998\11\22@172228 by Jurva-Markus Vehasmaa

flavicon
face
Sounds to me like a power glitch. When turning on some equipment on your
bench will generate power spike. That spike could get throw your power
supply that drives the pic.

Had same type of problem whit soldering iron once. It was in lab other side
of room and made prototype to lockup eb'very time solderin iron started to
heat the tip. Good line filter was enough to remove the problem.


Jurva-Markus Vehasmaa

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

1998\11\22@181708 by James Cameron

flavicon
face
Dave Johnson wrote:
> Anyone else seen similar behavior?

Yesterday on a 16F84/4 I was able to use RB0/INT interrupt as a finger
switchable 50Hz oscillator.  If I spread my hand to hover near the caps
on the crystal, I could greatly increase the speed of the interrupts.

Yes, a suitable pulldown resistor fixed it.  I would imagine a small
capacitor would help reduce higher frequency noise.

--
James Cameron                                      (EraseMEcameronspamspamspamBeGonestl.dec.com)

OpenVMS, Linux, Firewalls, Software Engineering, CGI, HTTP, X, C, FORTH,
COBOL, BASIC, DCL, csh, bash, ksh, sh, Electronics, Microcontrollers,
Disability Engineering, Netrek, Bicycles, Pedant, Farming, Home Control,
Remote Area Power, Greek Scholar, Tenor Vocalist, Church Sound, Husband.

"Specialisation is for insects." -- Robert Heinlein.


'[OT] humidity sensitive IC's ??'
1999\08\27@225736 by Nicholas Irias
flavicon
face
I just received some Ramtron FRAM chips (FM25040-P's) from Future
Electronics.  The chips are sealed in a de-aired plastic package along with
what appears to be a dessicant pouch.  And there is a warning that says:

"CAUTION This bag contains moisture sensitive devices"
It goes on to state that shelf life in the bag is 12 months at <40 degrees C
and <90% relative humidity (RH).  It then says that chips not immediately
mounted after removal from the bag must be baked and it has a schedule of
baking options.  There are no instructions suggesting what the life span of
chips are after mounting, which is curious, since merely soldering the leads
on the chip does not protect the chip from moisture.

Is this warning message:
A) the work of prankster
B) some paranoid label that gets put on all bags leaving Future Electronics
C) a real warning, in which case Ramtron is severely misrepresenting its
products.  Ramtron makes no mention of humidity sensitivity on the data
sheet for the chip.

- Nicholas

1999\08\27@232048 by Peter van Hoof

flavicon
face
> "CAUTION This bag contains moisture sensitive devices"
> It goes on to state that shelf life in the bag is 12 months at
> <40 degrees C
> and <90% relative humidity (RH).  It then says that chips not immediately
> mounted after removal from the bag must be baked and it has a schedule of
> baking options.

What chips did you say?  Potato?  :}

Peter van Hoof
-------------
RemoveMEpvhKILLspamspamvertonet.com
http://go.to/pvh

1999\08\28@002505 by Bob Blick

face
flavicon
face
Hi Nicholas,

Automated soldering process can be stressful on the chip, especially when
moisture has crept up the legs. It can cause the case to have little
fractures which are hard to detect, or loosen the leads, or bust the case
open.

If you hand solder the parts you can ignore the warning.

Cheers,
Bob

http://www.bobblick.com/

1999\08\28@045424 by Anne Ogborn

flavicon
face
The issue is NOT the life of the chips after manufacturing - the issue
is that if you let the chips absorb moisture, when you immerse them in
liquid solder they have a tendency to explode, this being what water does
when you heat it to 450 degrees.

The baking instructions are to be done just prior to soldering.

Ramtron isn't 'severely misrepresenting' it's product - any more than
by not mentioning that the chips won't work if you stick them in a reactor
or boil them in aqua regia or whatever.
This is pretty standard for all IC's that are to be immersion or reflow soldered
.
They're just being unusually conscientious by giving you the info to do the
baking, instead of letting you guess for yourself.

--
Anniepoo
Need loco motors?
http://www.idiom.com/~anniepoo/depot/motors.html

1999\08\28@174541 by William K. Borsum

flavicon
face
<x-rich>At 08:00 PM 8/27/99 -0700, you wrote:

>I just received some Ramtron FRAM chips (FM25040-P's) from Future

>Electronics.  The chips are sealed in a de-aired plastic package along
with

>what appears to be a dessicant pouch.  And there is a warning that
says:

>

>"CAUTION This bag contains moisture sensitive devices"

>It goes on to state that shelf life in the bag is 12 months at <<40
degrees C

>and <<90% relative humidity (RH).  It then says that chips not
immediately

>mounted after removal from the bag must be baked and it has a schedule
of

>baking options.  There are no instructions suggesting what the life span
of

>chips are after mounting, which is curious, since merely soldering the
leads

>on the chip does not protect the chip from moisture.

>

>Is this warning message:

>A) the work of prankster

>B) some paranoid label that gets put on all bags leaving Future
Electronics

>C) a real warning, in which case Ramtron is severely misrepresenting
its

>products.  Ramtron makes no mention of humidity sensitivity on the
data

>sheet for the chip.



The plastic encapsulating the chips absorbs water.  With DIP parts this
is usually not a problem since they are wave soldered in production and
the case doesn't get too hot.  It is a REAL problem with tiny SMT
parts--I have seen them explode when the hot air hits the parts and they
get hot.

Its the moisture turning to steam.


This does NOT effect the parts in operation--<underline>only
</underline>during assembly.  Manufactureres always recommend an overnite
bakeout of SMT parts going into automated assembly.  I haven't had a
problem (Knock on wood) yet with hand assembly.  BUT I keep the parts in
the bag with the desiccant any way, and work in an environment with
fairly low humidity to begin with.  It doesn't hurt, and may definitely
help.


Moisture CAN effect systems that are operating on VERY low power or
analog stuff that has very high input impedances--moisture will adsorb or
absorb as the case may be and form leakage paths.  Washing and baking my
PCB's dry after assembly will cut power draw from 50 to 30 uA in many
cases.


Enjoy,

kelly





William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems

<<borsumSTOPspamspamspam_OUTdascor.com> & <<http://www.dascor.com>

</x-rich>


'[OT] developing photosensitive boards'
1999\12\03@072130 by Quentin
flavicon
face
Hi Picsters, it's been a while..

I am experimenting with these kind of boards to see if it is worthwhile
for prototyping.
What can I use for developing and exposing?

Years ago a played with something called Positiv20. It's a spray on
photosensitive (and a pain to use, so don't ask me about it, hehe).
I exposed the board for 30 minutes in the sun and used Caustic Soda to
develop it.

will it work for pre coated boards?

If I have to build an exposure unit, what wattage of lamp must I use?
Will Metal-Hallide lamps work (used for printing plate exposures)?

Oh, and BTW, are the boards positive or negative exposure?

Thanks
Quentin

1999\12\03@075319 by Pavel Korensky

flavicon
face
Hello,

>Years ago a played with something called Positiv20. It's a spray on
>photosensitive (and a pain to use, so don't ask me about it, hehe).
>I exposed the board for 30 minutes in the sun and used Caustic Soda to
>develop it.
>
>will it work for pre coated boards?

Caustic soda is NaOH (natrium hydroxide) ? If so, it will work with
precoated boards, I am using it.

>
>If I have to build an exposure unit, what wattage of lamp must I use?

I am using homebuild unit, made from UV tubes sold in Europe by Conrad and
RS. Those tubes are 8W/230V. I am using two of them.

>Oh, and BTW, are the boards positive or negative exposure?

All boards I saw was positive. But there can be exceptions.

Best regards

PavelK

**************************************************************************
* Pavel KorenskyÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
* DATOR3 LAN Services spol. s r.o.ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
* Styblova 13, 140 00, Prague 4, Czech Republic      ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
*ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
* PGP Key fingerprint:Ê F3 E1 AE BC 34 18 CB A6Ê CC D0 DA 9E 79 03 41 D4 *
*ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ *
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**************************************************************************

1999\12\03@081206 by Graham North

flavicon
face
       >Oh, and BTW, are the boards positive or negative exposure?

       All boards I saw was positive. But there can be exceptions.



       What is the difference between positive and negative exposure?

       What does this mean?

1999\12\03@082034 by Quentin

flavicon
face
Positive, you use a master image exaxtly like you see it. When you
develop, only the areas that were exposed will wash off.
Negative, only the areas that were not exposed will wash of, so you will
have to use a negative master of the image.
Don't worry about it, I don't think I've ever seen negative exposure
stuff for PCB myself, but had to ask to make sure.

Quentin

Graham North wrote:
>
>         >Oh, and BTW, are the boards positive or negative exposure?
>
>         All boards I saw was positive. But there can be exceptions.
>
>         What is the difference between positive and negative exposure?
>
>         What does this mean?

1999\12\03@082244 by Graham North

flavicon
face
Yes, sorry I remember using this stuff at school(!) now.

       ----------
       From:  Quentin [SMTP:spamBeGoneqscSTOPspamspamEraseMEICON.CO.ZA]
       Sent:  03 December 1999 13:24
       To:  KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU
       Subject:  Re: [OT] developing photosensitive boards

       Positive, you use a master image exaxtly like you see it. When you
       develop, only the areas that were exposed will wash off.
       Negative, only the areas that were not exposed will wash of, so you
will
       have to use a negative master of the image.
       Don't worry about it, I don't think I've ever seen negative exposure
       stuff for PCB myself, but had to ask to make sure.

       Quentin

       Graham North wrote:
       >
       >         >Oh, and BTW, are the boards positive or negative
exposure?
       >
       >         All boards I saw was positive. But there can be
exceptions.
       >
       >         What is the difference between positive and negative
exposure?
       >
       >         What does this mean?

1999\12\03@151859 by Brian Aase

flavicon
face
Back in my PCB-making days, I used photoresist coatings
exclusively.  If everything is done just right, you get excellent
resolution and repeatability.  (If not, you get a lot of frustration and
wasted materials.)

In my experience (which is a few years old) there were two
fundamental types of photoresist: Negative-acting (Kodak and
Dynachem), and Positive-acting (Shipley).  These resists are
marketed under various names, so it's sometimes hard to tell
which brand you have. DuPont also makes a laminated-film
type of resist, but that was always beyond my budget.

In general, the negative-acting resists use some type of
hydrocarbon solvent as a developer, such as Xylene.  The positive
ones use variations of sodium hydroxide solutions, as the caustic
soda you mentioned.  Development is kind of an all-or-nothing
process.  The idea is to dissolve the unwanted resist, while leaving
the PCB resist pattern intact.  Both Shipley and Dynachem resists
were colored so you could get a clue when to pull the board out of
the developing solution.

Exposure time is not critical.  To get your process "right on", go to
the camera store and pick up one of those little 14-step gray scale
guides, and expose a few small boards with it using various times
like 5, 10, 15 minutes.  Pick the time that results in the bottom 1/3
of the scale leaving solid resist, and the top 1/3 being cleanly
washed away.  For Kodak KPR4 resist and a No. 2 photoflood bulb
at a distance of 10" from the PCB, six minutes of exposure was
just right for me.  Shipley resist wanted much more time, maybe
20 minutes or so.

Tip: I found it important to use as much of a point-source lamp as
possible for best resolution.  Those exposure frames with banks of
blacklights always blurred things out too much when I tried them.
If you're really serious, you can get *great* results from a carbon
arc lamp.

The final trick is to get an exposure frame that keeps the PCB in
*intimate* contact with the film!  (Yes, this is crucial.)  A vacuum-
back frame will give you perfect results every time, if you can afford
one.  I found those little wood-and-glass things with a spring on the
back never really did an adequate job for me.

email me if you want further useless info  ;-)

Brian Aase

{Quote hidden}

1999\12\06@023606 by ruben

flavicon
face
CAD a layout with horizontal lines of the linewidth You use under
each other, perhaps 15cm wide. Make 10 vertical lines (of the same
width) spaced 1cm apart. Starting from left, write the numbers 15,
14, 13...7, 6, 5 under the vertical lines. Expose Your PCB with this
layout as You normally would except that You start with only the
vertical line numbered 15 visible and the others covered with some UV
blocking material (a non etched PCB perhaps). For every minute that
passes You slide the cover to the right exposing the next vertical
line. When the last vertical line is visible expose for 5 more
minutes. The leftmost part of the PCB is now exposed 15 minutes and
the rightmost part is exposed 5 minutes. Now develop your board and
etch it as You usually would do. At the resulting PCB You should be
able to see what exposure time is the best to use.

Depending on the materials of the film, the type of photoresist and
the type of lamp You use 15 to 5 minutes may not be the best, just
add vertical lines and increase exposure time if You need more.

{Quote hidden}

==============================
Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +4640 142078
FAX INT +4640 947388
EraseMErubenspamEraseME2.sbbs.se
==============================


'Pressure Sensitive Key'
2000\02\21@151726 by brooke
flavicon
face
Hello Lance:

What you are looking for sounds like the type of key that is used on some electronic musical
keyboards.
I am not current this, but you might try out the demo keyboards at a discount store to see
which ones have this feature.
My old Yamaha DX-II had these.

Have Fun,

Brooke

Subject:
       Pressure Sensor
  Date:
       Mon, 21 Feb 2000 09:23:38 +1200
  From:
       Lance Allen <@spam@l.allen@spam@spamspam_OUTAUCKLAND.AC.NZ>



I want to sense an analog response to how hard a button is being
pressed. A small button like any membrane keypad type except
rather than just a close or open an output that is continuous ,
doesn't have to linear or anything.
The PIC A/D will read this and use a lookup table.

I have been examining carbon loaded plastic and capacitance type
sensors but I am unhappy with what I have found so far, an off the
shelf solution would of course be best.

If anyone has any tips, links etc I would be grateful.

2000\02\21@154045 by paulb

flavicon
face
Brooke Clarke wrote:

> What you are looking for sounds like the type of key that is used on
> some electronic musical keyboards.

 Ahh, now this provides a *whole new* slant on the problem.  Musical
keyboards provide not a pressure-sensitive interface, but a velocity-
sensitive one.  Is that what you want after all?  It may be.

 Velocity sensing is dead easy - it just requires two contacts which
operate at different points of the key travel (reliably).  Most
commonly, the two contacts are the end points of a SPDT action and
correspond to the supply rails, so the logic must discriminate between
pulled high, pulled low and tri-state.

 There are ways of doing this with a single PIC I/O.  If you can spare
two I/O per switch, it's even easier.
--
 Cheers,
       Paul B.


'[OT] building PCB with photo sensitive boards'
2000\03\13@020314 by Javier Grijalba
flavicon
face
Hi
Any advice for building photo sensitive PCB«s ??
Time of exposure to the sun??
Whats the finest pad possible?? What about 0.2 mm??
Bye
Javier
{Original Message removed}

2000\03\13@083000 by mike

flavicon
face
On Mon, 13 Mar 2000 03:53:55 -0600, you wrote:

>Hi
>Any advice for building photo sensitive PCB«s ??
>Time of exposure to the sun??
>Whats the finest pad possible?? What about 0.2 mm??
>Bye
>Javier
Check out :
http://www.netcomuk.co.uk/~wwl/pcbs.html
for lots of info on making _GOOD_ homebrew PCBs.

Wth care, and the right material you can reliably do 10 mil (0.01",
0.254mm) tracks. 0.2mm would probably be practical if the artwork
quality was good enough.
Forget about using sunlight - build a UV exposure box.

2000\03\13@104845 by jamesnewton

face picon face
I have a bit of collected advice at
http://techref.massmind.org/pcbetch

I'd love to know if I'm missing any.

---
James Newton spamBeGonejamesnewtonspamKILLspamgeocities.com 1-619-652-0593
http://techref.massmind.org NEW! FINALLY A REAL NAME!
Members can add private/public comments/pages ($0 TANSTAAFL web hosting)


{Original Message removed}

'[OT] building PCB with photo sensitive boards (thr'
2000\03\16@065906 by Alan Pearce

face picon face
has anyone used this product known as Press-n-Peel? see http://www.techniks.com/

there is also a UK agent handling it. It sounds very similar to the processes
being discussed in this thread recently, but I am not sure if it is the product
I saw reviewed in a magazine.

2000\03\16@073021 by Andy Baker

flavicon
face
I've used press and peel, it is sold by Maplin in the UK.

I must admit, I didn't find it very convenient to use, although the idea
seems great. On average it took me at least 5 board revisions to get a
decent one.

The critical stage is the ironing. Too hot an iron, and the tracks 'blob'
outwards. Too cold, and you end up with missing patches. To make things
worse, the PCBs I had all had a very subtle bow to them which meant ironing
as a flat surface was very difficult.

When I did get a good result, I got a very good result.

However I got fed up of the low yield, and have now ordered a UV light box,
and photo sensitive PCBs.

What I would say is give it a go, if you crack the ironing technique, it
will do the job nicely. I just couldn't crack it.

Good luck,

Andy


-----Original Message-----
From: Alan Pearce [.....A.B.Pearcespam_OUTspamRL.AC.UK]
Sent: 16 March 2000 11:57
To: TakeThisOuTPICLIST.....spamTakeThisOuTMITVMA.MIT.EDU
Subject: Re: [OT] building PCB with photo sensitive boards (thread
revived)


has anyone used this product known as Press-n-Peel? see
http://www.techniks.com/

there is also a UK agent handling it. It sounds very similar to the
processes
being discussed in this thread recently, but I am not sure if it is the
product
I saw reviewed in a magazine.


'[PICLIST] [EE}: Pressure sensitive box: problem so'
2001\06\01@181557 by Peter L. Peres
picon face
Hi,

Thanks again to all who wrote about this, I have solved the problem. The
pressure sensitive element was a SMT LM324 opamp mounted on 1.6mm FR4
board (away from the glued side). The hot glue was strong enough to bend
it and the board. Not related to the 7106 which is steady now.

Solution: the board is mounted in one point only. This fixed it.

Solution2: The next time I make something accurate to 0.0005 I use an
alumina board and a better (cerdip or TO...) opamp.

Question: Any more recommendations wrt this problem ?

thanks,

Peter

PS: In case you want to say something about building things to 0.0005
with garden variety parts:
a) I will keep trying and succeeding to do these things
b) 0.0005 [V] is the inherent precision of any 7106 DVM set to +/- 2000
counts (vref = 2V).
c) I hate parts with insufficient specs (like mechanical load on plastic
IC cases vs. electrical characteristics).

PS2: This gives me an idea: strain gage made of SMT opamp (quad) on FR4
board which serves as base. The four outputs form a surface gage (reads
four elements in a square probe at the same time).

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads



'[PICLIST] [OT] sensitive inhalation or pressure se'
2002\04\24@182405 by Brian Taylor
flavicon
face
I have an oxygen system for my sailplane that provides a short burst of
oxygen at the start of each inspiration cycle.  The oxygen burst width
varies with altitude and by firing the oxygen in at the start of the breath
intake, the oxygen gets right through the lungs.  The over all system is
extremely frugal with its oxygen use.  The system uses no mask, it has two
tiny cannula that poke 10 mm into the nostrils.

The pressure sensor is a capacitor fabricated on the PCB as a 50 mm
diameter disk of vacuum aluminised plastic (looks like wine cask
material).  This is vented to atmosphere one side.  When you inhale the
small pressure drop in the cannula moves the capacitor plate and a '555
(yep - it should be a PIC) changes frequency. This is sensed and the oxygen
valve is opened for the required milliseconds.

It all runs on one 9v PP9 battery and works to over 25,000 feet.

Hope this helps.

Cheers
Brian

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2002\04\24@184452 by John Dammeyer

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That's cool.  Is this a commercial system or did you build it yourself.

John Dammeyer



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2002\04\24@193943 by A.J. Tufgar

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That's cool!
I'm thinking I might be able to do something like that.  The project is
similair where someone breathes through the cannula, and I need to tell
when they inhale so this would probably work well.  I was thinking of a
rubber membrane that would have a wire or piece of metal attached and
when you breathe in it moves and close a switch.  But I was thinking
there may not be enough movement.  However using capacitance I probably
wouldn't need to move very far to see a big change in freq.  Any
thoughts on this anyone?  Whould a switch or capacitance work better?

Thanks Brian even if this doesn't work it was cool to learn about,
Aaron

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2002\04\24@195740 by Dave King

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face
At 08:28 AM 4/25/02 +1000, you wrote:
>I have an oxygen system for my sailplane that provides a short burst of
>oxygen at the start of each inspiration cycle.
>Cheers
>Brian

Brian

Is this a commercial system ?

We''re going to take a run at one of the FAI C1 records this
summer and anything I can find weighs more than the airframe.

Dave

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'[PICLIST] [OT] Oxygen system - sensitive inspirati'
2002\04\25@020838 by Brian Taylor

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face
For those that want to take the sensitive pressure sensor idea further,
here is the URL of the maker.
The EDS (Electronic Delivery System) is what to look at.

http://www.mhoxygen.com/

www.mhoxygen.com/index.phtml?nav_id=28&product_id=88
shows the PCB and the pressure sensor.


cheers
Brian

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'[PICLIST] [OT] sensitive inhalation or pressure se'
2002\04\25@033937 by Alan B. Pearce

face picon face
>But I was thinking there may not be enough movement.
>However using capacitance I probably wouldn't need to
>move very far to see a big change in freq.  Any thoughts
>on this anyone?  Whould a switch or capacitance work better?

Try using a CD4046 PLL as a capacitance change detector. If the varying
capacitance is the frequency determining C in the PLL you should be able to
set the desired sensitivity by determining the max-min frequency swing for
the control voltage range. You could then measure the control voltage with
an ADC, or if you can get the swing suitable just feed it into a Schmitt
trigger to get a digital signal.

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2002\04\25@145715 by Peter L. Peres

picon face
>The pressure sensor is a capacitor fabricated on the PCB as a 50 mm
>diameter disk of vacuum aluminised plastic (looks like wine cask
>material).  This is vented to atmosphere one side.  When you inhale the
>small pressure drop in the cannula moves the capacitor plate and a '555
>(yep - it should be a PIC) changes frequency. This is sensed and the
>oxygen valve is opened for the required milliseconds.

Imho lose the strange sensor and use a simple capacitive microphone
capsule as is, perhaps in the canula tube on the face using a T joint. It
might work from further away in the tubing. Output voltage (DC coupled)
jumps 0.2V or more under the described conditions.

Peter

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'[AVR]: Static sensitive reset?'
2002\12\14@020246 by Richard Sloan
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part 1 450 bytes content-type:text/plain (decoded quoted-printable)

Atmel recommends a brownout circuit for 4414 and 8515's I think they corrupt the eeprom without it.

Can it be made less sensitive?

Attached is a small schematic of it.

Any other thoughts on static induced resets? It does not take much to do it!


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Richard.

part 2 10080 bytes content-type:image/jpeg; name="reset.jpg" (decode)


part 3 2 bytes
-

2002\12\14@073530 by mark

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--Message-Boundary-28766
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Content-description: Mail message body

On 14 Dec 2002 at 2:00, Richard Sloan wrote:

> Any other thoughts on static induced resets? It does not take much to do it!
>

I have used the attached circuit without problems.

Mark


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--Message-Boundary-28766--

2002\12\14@073553 by Spehro Pefhany

picon face
At 02:00 AM 12/14/02 -0500, you wrote:
>Atmel recommends a brownout circuit for 4414 and 8515's I think they
>corrupt the eeprom without it.
>
>Can it be made less sensitive?
>
>Attached is a small schematic of it.
>
>Any other thoughts on static induced resets? It does not take much to do it!

Suggest you use a proper reset circuit such as Microchip's MCP809/810
(or the TO-92 versions). Similar parts are available from Seiko, Motorola,
and many others. You can make your circuit less sensitive by paralleling
R1/R2 with similar ratio capacitors, but it's still going to be a crummy
temperature-sensitive circuit without timer or hysteresis. Unless you
are building very high volume goods, it just ain't worth it.

Bset regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffEraseMEspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2002\12\14@112736 by Richard Sloan

flavicon
face
They were 182K and 33K I added 0.1 and 0.01 and it seemed to work!

I will keep trying and seeing if I can reset it with a zap!

R.


>>  At 02:00 AM 12/14/02 -0500, you wrote:
>>  >Atmel recommends a brownout circuit for 4414 and 8515's I think they
>>  >corrupt the eeprom without it.
>>  >
>>  >Can it be made less sensitive?
>>  >
>>  >Attached is a small schematic of it.
>>  >
>>  >Any other thoughts on static induced resets? It does not take much to do
>>  it!

>>  Suggest you use a proper reset circuit such as Microchip's MCP809/810
>>  (or the TO-92 versions). Similar parts are available from Seiko, Motorola,
>>  and many others. You can make your circuit less sensitive by paralleling
>>  R1/R2 with similar ratio capacitors, but it's still going to be a crummy
>>  temperature-sensitive circuit without timer or hysteresis. Unless you
>>  are building very high volume goods, it just ain't worth it.

>>  Bset regards,

>>  Spehro Pefhany --"it's the network..."            "The Journey is the
>>  reward"
>>  RemoveMEspeffEraseMEspamspam_OUTinterlog.com             Info for manufacturers:
>>  http://www.trexon.com
>>  Embedded software/hardware/analog  Info for designers:  >>  http://www.speff.com

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Thanks,
Richard Sloan
__________________________________________________________
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'[EE]: Photosensitive chemical.'
2002\12\14@123725 by A.J. Tufgar

flavicon
face
A friend was telling me about a chemical he painted on copper clad to
make photosensitive PCB's, rather then buying the presensitized PCB.
Anyone know where you can buy this?  In Canada preferably.

Thanks in Advance,

Aaron

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2002\12\14@130502 by Tal Bejerano - AMC

flavicon
face
my advice is don't use it
it's too messy.
I have a photosensitive spray from a German company called "KONTAKT CHEMIE"
it's called POSITIV 20
I try to work with it with a little luck.
buying the ready made is better

Regards

Tal Bejerano
AMC - ISRAEL


{Original Message removed}

2002\12\14@132143 by Rick C.

flavicon
face
I have used a chemical called KPR (Kodak Photo Resist). I don't know if
they make it anymore. I bought a quart of it about 30 years ago and have
sensitized over a thousand boards with it and I still have half a bottle
of it. Google shows about 50 hits on it. Apparently it is toxic, but so
is everything.
I'm getting ready to release a new web page this evening showing how to
make excellent circuit boards.
I have not seen any spray on resist that actually works.
Rick

"A.J. Tufgar" wrote:

{Quote hidden}

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2002\12\14@133201 by TIM S

flavicon
face
i use positive  pre sensitize pcb from gc(old general cement)
http://www.gcwaldom.com
do a search at there site for  circuit boards.
there are distributors in canada.
best regards  tim
{Original Message removed}

2002\12\14@144632 by Mike Harrison

flavicon
face
Don't waste your time with this stuff - it's almost impossible to get
a consistent coating thickness and keep the dust off.

On Sat, 14 Dec 2002 12:36:32 -0500, you wrote:

>A friend was telling me about a chemical he painted on copper clad to
>make photosensitive PCB's, rather then buying the presensitized PCB.
> Anyone know where you can buy this?  In Canada preferably.
>
>Thanks in Advance,
>
>Aaron

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2002\12\14@172138 by Josh Koffman

flavicon
face
Next time you head into Toronto, head to Supremetronics on Queen Street
West. They have spray cans of the stuff. Not too expensive, but you may
be getting what you pay for.

Josh
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completely foolproof is to underestimate the ingenuity of complete
fools.
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"A.J. Tufgar" wrote:
> A friend was telling me about a chemical he painted on copper clad to
> make photosensitive PCB's, rather then buying the presensitized PCB.
>  Anyone know where you can buy this?  In Canada preferably.

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2002\12\14@174700 by Peter L. Peres

picon face
On Sat, 14 Dec 2002, Tal Bejerano - AMC wrote:

*>my advice is don't use it
*>it's too messy.
*>I have a photosensitive spray from a German company called "KONTAKT CHEMIE"
*>it's called POSITIV 20
*>I try to work with it with a little luck.

I have used both and P20 is very good once you follow the instructions
EXACTLY (wrt baking and developer and cleaning and dust) and experiment a
little. Two layers on preheated board (60 degrees C) at 5 minutes between
them and following oven bake for 30 minutes at 75C in the dark make
perfect boards every time ... DO NOT BREATHE THE FUMES - USE A BIG FAN TO
MOVE AIR AWAY FROM THE WORK AREA.

Imho the precoated boards sold here are of inferior quality and they
cannot b cut to shape without resist flaking off.

Peter

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2002\12\14@174712 by Peter L. Peres

picon face
You are looking for photoresist. Comes in two kinds: liquid or spray-on.
Make sure you find out the process requirements BEFORE you buy, some of
them require rather special processing, are poisonous, smell bad, and in
general dangerous. One that is much used by amateurs is Photopositiv 20
from Contact Chemie in Europe (but available everywhere afaik - even
here). There are other options, like Kepro, 3M and many others.

Peter

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2002\12\14@213559 by Russell McMahon

face
flavicon
face
> You are looking for photoresist. Comes in two kinds: liquid or spray-on.

Applying your own photoresist is similar to using laser printers to make
your own PCBs - the results are very dependant on method, knack and
attention to details and being a competent craftsman can help a lot. If you
are prepared to work at it you can get good results. If you do it half
heartedly you can expect variable and unacceptable results.

       RM

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2002\12\15@020040 by Alan Shinn

picon face
Wow,
I was recently looking at my ancient bottle of KPR and was wondering if
it still works. Do you use the developer that was sold to work with it
or have you found a substitute?
I used it long ago to photoetch brass jewelry. I used one of thos little
spray thingies with it. Then there was some nasty seeming developer
stuff (some sort of chlorinated hydrocarbon) which I no longer have.
Then there was a nice dye to put on after developing (dissolving off the
unexposed resist) to be able to see the remaining resist to "proof read
it". The system worked very well for me but it did take a bit of doing
to learn how.



Date:    Sat, 14 Dec 2002 13:22:01 -0500
From:    "Rick C." <EraseMErixyspam@spam@VVALLEY.COM>
Subject: Re: [EE]:  Photosensitive chemical.

I have used a chemical called KPR (Kodak Photo Resist). I don't know if
they make it anymore. I bought a quart of it about 30 years ago and have
sensitized over a thousand boards with it and I still have half a bottle
of it. Google shows about 50 hits on it. Apparently it is toxic, but so
is everything.
I'm getting ready to release a new web page this evening showing how to
make excellent circuit boards.
I have not seen any spray on resist that actually works.
Rick
--
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beginnings of microscopy.
Make your own replica
of one of Antony van Leeuwenhoek's microscopes.
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2002\12\15@090611 by Rick C.

flavicon
face
KPR should last your lifetime as long as it is kept in the tightly sealed
brown glass bottle it came in. The stuff should smell something like
fingernail polish. The early developers were/are nasty chemicals.
Carcinogens and the like. I used to use trichlorethelyene 1.1.1 and it
worked great! YOu just could not breathe any vapors. Illegal to purchase
now. I used it in 5 gallon drums to clean hydraulic oil from the floors of
nuclear missile sites underground. Not very much ventilation. We'd come out
after a day of breathing tons of that stuff as high as a kite. Little did we
know our kidneys and liver were being damaged.

Xylene is currently available to use on circuit boards. Go to my new web
page and I explain the whole thing. http://www.pic101.com/pcb

My boards are so consistent I never had to use a dye.

Rick

Alan Shinn wrote:

{Quote hidden}

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2002\12\15@124541 by Olin Lathrop

face picon face
> A friend was telling me about a chemical he painted on copper clad to
> make photosensitive PCB's, rather then buying the presensitized PCB.
>  Anyone know where you can buy this?  In Canada preferably.

I did that sort of thing a bit over 20 years ago.  At that time there were
two basic types.  One was a lacquer-based spray that had to be developed in
a special chemical that appeared to be lacquer thinner with stuff added.
The other were two water soluable chemicals that you mix shortly before use
and paint on the board.  You let them dry, expose, then rinse in water to
get rid of the unexposed areas.  You have to then bake the remaining part
before it works like a resist.  I played around with both methods and
decided I liked the second better.  It was called something like "Resolve"
if I remember right.  I found it in a local electronics store.

I have no idea how things may have changed in the last 22 years.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\12\15@143323 by Peter L. Peres

picon face
On Sun, 15 Dec 2002, Olin Lathrop wrote:

*>I have no idea how things may have changed in the last 22 years.

I'll try to describe the P20 photoresist spray from Kontakt that I used
till recently (1year ago):

It's a small spray can with instructions on it. One component. You clean
the board, preheat it to about 60C and spray one layer from about 20cm in
one pass. The layer will be pale green (the liquid is dark green). This is
done in subdued light.  After 5 minutes (while still keeping the board at
60C) you spray a second layer as above. Then you leave it be at 60C for an
hour or 70C for 30 minutes. That's it. After this the board can be stored
up to a few months in a cool dark box or exposed immediately. Exposure is
about 5 minutes with normal UV exposure lamps (350nm Hg vapor) through 1
sheet of 3mm glass frame and transparency artwork (laser printed). The
developer is 4 grams of lye (NaOH) in 1liter of tap water. The development
is done in 1 minute or less, leaving the green layer only where there was
no light. After this you can etch with FeCl3 or something else. The resist
comes off with acetone or nitro paint thinner. The spray bottle covers
about 10 square feet and keeps for 1 year or more. The chemicals are not
so nasty excepting for the solvent vapor that MUST be fanned away. I have
used a full face mask respirator for this before but a vent is better.

The datasheet and msds sheets are on the web (long line paste carefully):

http://212.166.5.17/csp/web/DSlst.csp?lng=3&country=BE&product=POSITIV 20&brand=KOC&SCAD=208206042541

Kontakt Chemie is a brand name of CRC Industries as you can see. They say
the color is blue but mine is actually bluieish-greenish and the layer on
the board is definitely green. The artwork appears yellowish green
(faintly) on the flatter green of the layer after correct exposure and
before development.

Peter

PS: All the horror stories about this material on the web have to do with
the fact that nobody I heard of uses a preheated board - which is
essential. If the board is not heated then the drying resist will build up
a lot of charge from the departing solvent and will form holes and
mountains on every piece of dust it can attract (and it can attract them
all, even from a completely clean washed plastic food box with a
hermetic lid). With the heat on drying is so fast it has no time to do
stupid things and it works great.

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2002\12\18@174226 by Brian Smith

picon face
Peter L. Peres wrote:
> PS: All the horror stories about this material on the web have to do
with
> the fact that nobody I heard of uses a preheated board - which is
> essential. If the board is not heated then the drying resist will
build up
> a lot of charge from the departing solvent and will form holes and
> mountains on every piece of dust it can attract (and it can attract
them
> all, even from a completely clean washed plastic food box with a
> hermetic lid). With the heat on drying is so fast it has no time to do
> stupid things and it works great.

How do you keep the board at 60C while you are spraying?  That's a tad
warm
for my house.  Is a warm dark oven at 150F (about 63C) acceptable for
before
and after spraying?

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2002\12\20@124205 by Peter L. Peres

picon face
On Wed, 18 Dec 2002, Brian Smith wrote:

*>How do you keep the board at 60C while you are spraying?  That's a tad
*>warm
*>for my house.  Is a warm dark oven at 150F (about 63C) acceptable for
*>before
*>and after spraying?

Yes. Maybe get a large floor or roof tile or a half height brick and put
the board on it (in the oven). The brick will keep the heat while you
remove it from the oven for spraying but it will take longer to heat up
(an hour or more). A small metal ashtray upside down could serve the same
purpose but work faster.

I use a forced hot air box that is used only for this purpose. At 60-70C
you only need a cardboard box and a thermostated fan. As I said, the
preheating removes the dust problem. The mist is essentially tack dry the
moment it touches the preheated board.

Peter

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'[EE]: Sensitive micro-ammeter?'
2003\11\22@183346 by Philip Pemberton
face picon face
Hi,
 I'm trying to get some power consumption figures for a PIC-based
battery-operated (CR2032s believe it or not) device. The problem is, although
I have a PSU that can provide the 3V-5V Vcc voltage, the built-in ammeter is
useless for low-current circuits. I've pulled out my Fluke 25 DMM and it
doesn't register ANYTHING when the PIC is sleeping - it just sits there
reading "0.00 uA".
 Has anyone here found a way to measure the current of a PIC in sleep mode?
I need better figures than zero to work out how long the batteries will last.

Thanks.
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2003\11\22@205310 by steve

flavicon
face
On 22 Nov 2003 at 23:30, Philip Pemberton wrote:

> Hi,
>   I'm trying to get some power consumption figures for a PIC-based
> battery-operated (CR2032s believe it or not) device.

Put a 1k (or more) resistor in series with the battery. Measuring a few
millivolts is easy and the voltage drop is inconsquential in operation,
except that it will limit the current if there is a short circuit.

Steve.


==========================================
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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: stevespamBeGonespamtla.co.nz                      fax +64 9 820-1929
=========================================

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2003\11\22@215900 by Russell McMahon

face
flavicon
face
> I need better figures than zero to work out how long the batteries will
last.

You possibly don't:-)
If you have a meter that will resolve 1 uA and it doesn't read then you
presumably have less than 1 uA drain.
A 1 uAs drain is 8765 uAh/year or 8.8 mAh per year. If long life is the
issue and the PIC quiescent current then even a modest cell is going to give
you many years so it MUST be a Lithium one. A CR2025 = 20mm x 1.6mm and 150
mAH odd. At even 10 mAh/yr that's 15 years battery life, or in excess of the
10 years off shelf life.

My point is that IF quiescent current is < 1uA and IF it predominates in the
power consumption then almost any battery you can think of will last for
about its shelf life.

>   Has anyone here found a way to measure the current of a PIC in sleep
mode?

So, the trick is to see what the quiescent current is. I'm not sure what the
bottom range is on the Fluke 25, but I'll assume it really can resolve 0.1
uA (let alone 0.01) as you suggest. Sounds like your processor is comatose,
not sleeping :-).

Why not try a capacitor as a power source and measure it's voltage drop with
time.
1st set meter to a suitable VOLTAGE range, charge the capacitor to Vdd (3.6v
or whatever), disconnect power source and note voltage drop from meter load
over say 5 minutes. You can approximate the result with a linear solution or
solve the very simple exponential decay equation.

Rule of thumb linear an amp drawn from a  farad will drop a volt in a
second.
A uA drawn from a 1 uF will drop a volt in a second.

Use a good quality non polar capacitor (mylar or similar).
Start with 1 uF.

A meter with a  100Mohm input resistance will drop a uF by a volt in about
100/V seconds.
Reversing the meter leads and repeating would be wise at this sort of
currents as offset current, even with a fluke, is potentially significant.

Do that a few times with both polarities.

Now connect the PIC and try again.

Where current varies and you get substantial occasional peaks and long
period of quiescent current you can feed the system through a largish
resistor with a suitable filter cap on the equipment side. If RC time
constant is long compared to peak current pulses repetition rate then the
resistor will tend to supply the average current and the capacitor will
supply the current peaks. With a similar filter cap this is something like
the current the battery will tend to see in use.


       Russell McMahon

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2003\11\22@215902 by Bob Ammerman

picon face
Place a 1K resistor in series with the power supply.

Every mV you see across that resistor corresponds to 1 uA of current.

A 10K resistor will give you 10mV per uA

A 100K resistor will give you 100mV per uA

Of course, you must be aware of the reduced voltage seen by your circuit.

Bob Ammerman
RAm Systems

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2003\11\22@220943 by David VanHorn

flavicon
face
At 09:55 PM 11/22/2003 -0500, Bob Ammerman wrote:

>Place a 1K resistor in series with the power supply.
>
>Every mV you see across that resistor corresponds to 1 uA of current.
>
>A 10K resistor will give you 10mV per uA
>
>A 100K resistor will give you 100mV per uA

I'm pretty sure you can wrap that resistor with an op-amp, such that there's no drop, and the opamp output gives you a voltage per uA

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2003\11\23@001206 by Richard Graziano

picon face
And don't forget that you need a very high impedance measuring device...

----- Original Message -----
From: "Bob Ammerman" <rammermanEraseMEspam@spam@ADELPHIA.NET>
To: <RemoveMEPICLISTspamspamBeGoneMITVMA.MIT.EDU>
Sent: Saturday, November 22, 2003 9:55 PM
Subject: Re: Sensitive micro-ammeter?


{Quote hidden}

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2003\11\23@085524 by Bob Ammerman

picon face
> And don't forget that you need a very high impedance measuring device...

Actually you don't. What is 10M or 1M in parallel with 1K....
Just about 1K.

> {Original Message removed}


'[PIC]: Touch sensitive switches?'
2004\09\06@173524 by Philip Pemberton
face picon face
Hi,
 I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
anyone tried out the circuit on that page? Does it work?
 Even better - does anyone know if there's a way to reduce the number of I/O
lines in a similar way to a matrix of pushbuttons? I want something small,
with at least 12 keys, hooked up to a 16F628A (eventually). The whole
device - including the 3x4 keypad array - is going to be around the size of a
credit card.
 Am I stuck with normal mechanical switches?

Thanks.
--
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
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2004\09\06@180209 by Engineering Info

picon face
I wouldn't recomend it for what you need.  The whole idea of that is
that you change the capacitance of the capacitor.  Just putting it in
your shirt pocket will probally trigger things.  Try membrane switches
instead.

Philip Pemberton wrote:

{Quote hidden}

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2004\09\06@180718 by mmynsted_news

picon face
Did you see (Touch Switch) on
http://members.cox.net/berniekm/tricks.html

Sounds like the guy has done something like what you want.
http://members.cox.net/berniekm/

On Monday 06 September 2004 4:35 pm, Philip Pemberton wrote:
{Quote hidden}

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2004\09\06@180751 by Support - KF4HAZ

flavicon
face
We use a 3x4 matrixed keypad that has 8 pins,
pin8 is grounded, 1 - 7 are pulled high through 10k resistors (sip).
When any one key is pressed the row and column read low.
This is read in as an 8 bit value, the 8th bit is stripped of by anding with
$7F,
then the key is read by using a lookup table, even got fancy and included a
couple of 2-key combinations.

KF4HAZ - Lonnie

----- From: "Philip Pemberton" <philpem@
> Hi,
>   I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
> anyone tried out the circuit on that page? Does it work?
>   Even better - does anyone know if there's a way to reduce the number of
I/O
> lines in a similar way to a matrix of pushbuttons? I want something small,
> with at least 12 keys, hooked up to a 16F628A (eventually). The whole
> device - including the 3x4 keypad array - is going to be around the size
of a
> credit card.
>   Am I stuck with normal mechanical switches?
>
> Thanks.
> --
> Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB,
6GB,
> spamBeGonephilpem@spam@spamdsl.pipex.com              | ViewFinder, 10BaseT Ethernet,
2-slice,
> http://www.philpem.dsl.pipex.com/  | 48xCD, ARCINv6c IDE, SCSI
> ... The current limits placed are based on resistance

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2004\09\06@185909 by Bob Axtell

face picon face
One of the best ways to connect switches to minimize PIC pins is to wire
the switches so that when pressed, they present a different voltage
level on a
PIC analog input pin. I've sucessfully used 8 switches on a single PIC
analog input. Just hook 'em up so that a each different resistor value
causes the
voltage at the analog pin to be 1/8FS, 1/4FS, 3/8FS, etc etc. A reading
of FS means NO switch is pressed. If I had 12 switches, I'd connect them to
2 PIC A/D pins, 6 on each pin.

I've tried those touch switches. The reliability changes quite a bit
with temperature. They are NOT  a workable solution.

--Bob

Philip Pemberton wrote:

{Quote hidden}

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2004\09\06@205435 by Cwebber

flavicon
face
At 05:59 PM 9/6/2004, you wrote:
>One of the best ways to connect switches to minimize PIC pins is to wire
>the switches so that when pressed, they present a different voltage level on a
>PIC analog input pin. I've sucessfully used 8 switches on a single PIC
>analog input. Just hook 'em up so that a each different resistor value
>causes the
>voltage at the analog pin to be 1/8FS, 1/4FS, 3/8FS, etc etc. A reading of
>FS means NO switch is pressed. If I had 12 switches, I'd connect them to
>2 PIC A/D pins, 6 on each pin.

If I remember correctly microchip has an appnote called "trick's and tips"
for the 12F628 that includes the method that Bob describes above.  It gives
a schematic and maybe a little bit more detail.  It has a handful of other
techniques to maximize the usefulness of low pin count PIC's.  You should
be able to find it on the product page for the 16F628 or other 8pin PICs.

Chip


>I've tried those touch switches. The reliability changes quite a bit with
>temperature. They are NOT  a workable solution.
>
>--Bob
>
>Philip Pemberton wrote:


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2004\09\07@021947 by Robert Rolf

picon face
Philip Pemberton wrote:
> Hi,
>   I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
> anyone tried out the circuit on that page? Does it work?

I haven't used that specific circuit but I see no reason why it
wouldn't work as described.

I think the 2nd version (500k pullup to Vcc) is the more pin
efficient. Just idle the pin high to minimize power waste.

Don't forget to add clamp diodes to Vcc and Gnd for EACH input pad
since the pin is capacitively couple to a huge static source (finger).

The 10k pullups or the mondo cct will only work if directly
connected to pads (thumbtacks) but there really should be 1k
series protection resistors and clamp diodes.

>   Even better - does anyone know if there's a way to reduce the number of I/O
> lines in a similar way to a matrix of pushbuttons? I want something small,

Use a pair of 4051 analog muxes for the finger pads.
You'll need 5 or 6 pins (4 address using an inverter to handle *E line
and 1 I/O or 3 address and 2 muxed I/O with *E grounded).

You should have a pullup resistor for each mux input, rather than
just one on the uP side since you don't want the inputs floating
particularly with external inputs.

> with at least 12 keys, hooked up to a 16F628A (eventually). The whole
> device - including the 3x4 keypad array - is going to be around the size of a
> credit card.
>   Am I stuck with normal mechanical switches?

No, but I'd make the touch pads interdigitated (two comb traces
interleaved) to ensure that you have a reliable ground.
I have found that you cannot rely on 'virtual ground' of a
human when they're not holding the case of something so small.

I would also suggest you look at snaptron
http://www.snaptron.com/
domes that can mount directly to your board. They are mechanical, but
they are very low profile (0.2mm) and give a nice tactile feedback.

Been using them for years, and as long as you gold plate the pads,
you get great reliability and life.

You'd use the usual key pad matrix scan cct's with them.

12 keys on a credit card? What the heck are you designing?

Robert



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2004\09\07@023231 by Jan-Erik Soderholm

face picon face
Cwebber wrote :

> If I remember correctly microchip has an appnote called
> "trick's and tips"  for the 12F628 that includes the
> method that Bob describes above.

Hi.
Maybe this one :

DS40040B, "Tips ‘n Tricks, 8-pin FLASH"

http://ww1.microchip.com/downloads/en/DeviceDoc/40040b.pdf

"TIP #7, 4x4 Keyboard with 1 Input"

Regards,
Jan-Erik.
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2004\09\07@054834 by Philip Pemberton

face picon face
In message <spamBeGone200409070632.i876WUq21213spam_OUTspamRemoveMEd1o270.telia.com>>          "Jan-Erik Soderholm" <.....jan-erik.soderholmspamRemoveMEtelia.com> wrote:

> DS40040B, "Tips ‘n Tricks, 8-pin FLASH"
>
> ww1.microchip.com/downloads/en/DeviceDoc/40040b.pdf
>
> "TIP #7, 4x4 Keyboard with 1 Input"

Thanks for posting the link, Jan-Erik - certainly beats digging around
Mchip's website :)

Now I need to find 16 switches and select the resistor values. I've been
thinking about ways to prototype the switches, too, and I found something in
one of the RadioShack "Engineer's Mini Notebook" books ("Electronic Sensor
Circuits and Projects", part number 620-5034, page 14) that seems to be quite
similar in concept to a membrane switch.
Basically, you've got a PCB with "fingers" etched into it, like this ('scuse
the ASCII art)
  ____
 | ___
 |___ |
--| ___|---
 |___
 Next you have a piece of plastic with holes cut into it - one per switch.
Finally, you have a piece of plastic with tinfoil squares stuck on the bottom
and your labelling on the top. It looks like it might work - making flat
solder joints to link up the matrix will probably be pretty difficult though.
OTOH, RoadRunner (wiring pencil) wire might work...

Later.
-- Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpemspam@spam@dsl.pipex.com              | ViewFinder, 10BaseT Ethernet, 2-slice,
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2004\09\07@062752 by Jan-Erik Soderholm

face picon face
Philip Pemberton wrote :

> Basically, you've got a PCB with "fingers" etched into it,
> like this ('scuse  the ASCII art)
>    ____
>   | ___
>   |___ |
> --| ___|---
>   |___
>  
> Next you have a piece of plastic with holes cut into it - one
> per switch.
> Finally, you have a piece of plastic with tinfoil squares
> stuck on the bottom and your labelling on the top.

Maybe some of the 0.05 mm double sided copper laminate I have
would work ? It's a 0.05 mm fiber glass core with one 18 mu (1/2 oz)
copper layer on each side. One could etch the "keys" directly from
the copper and put a plastic sheet in between. The "wiring" would be
etched directly from the laminat at the same time, of course.

Send me your address off-list and I'll send you a couple of
sheets (6" x 9"). I have a few uncut 18" x 24" sheets of the
same material also if you'd like to make some *large*
keyboards :-) :-)

Regards,
Jan-Erik.

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2004\09\07@070915 by olin_piclist

face picon face
Cwebber wrote:
>> One of the best ways to connect switches to minimize PIC pins is to
>> wire
>> the switches so that when pressed, they present a different voltage
>> level on a PIC analog input pin.
>
> If I remember correctly microchip has an appnote called "trick's and
> tips"
> for the 12F628 that includes the method that Bob describes above.

That would be a good trick, considering that there is no 12F628 in the first
place, and neither the 12F629 nor 16F628 have A/D inputs anyway.


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2004\09\07@084230 by hael Rigby-Jones

picon face


{Quote hidden}

Nothing to stop you using a homebrew single slope ADC with an R and a C and
a port pin.  Granted the 12F628 is something of a rarity :)

Mike

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2004\09\07@091755 by Russell McMahon

face
flavicon
face
> Nothing to stop you using a homebrew single slope ADC with an R and a C
and
> a port pin.  Granted the 12F628 is something of a rarity :)

Is that the one they are bringing out in TO92 ?
(Power version in TO220 with 2 amp I/O)



       RM


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2004\09\07@095511 by Cwebber

flavicon
face

At 06:09 AM 9/7/2004, you wrote:
>Cwebber wrote:
> >> One of the best ways to connect switches to minimize PIC pins is to
> >> wire
> >> the switches so that when pressed, they present a different voltage
> >> level on a PIC analog input pin.
> >
> > If I remember correctly microchip has an appnote called "trick's and
> > tips"
> > for the 12F628 that includes the method that Bob describes above.
>
>That would be a good trick, considering that there is no 12F628 in the first
>place, and neither the 12F629 nor 16F628 have A/D inputs anyway.

That would be pretty impressive, in the meantime i'll just use an existing
PIC - no need to re-invent the wheel.  I confused the 12F675 (which has
A/D) with the 12F629 (which does not).  Thanks for catching my mistake:)

Chip



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2004\09\07@105110 by Philip Pemberton

face picon face
In message <009c01c494dd$148e7460$7c01a8c0@y2k>
         Russell McMahon <RemoveMEapptechspam_OUTspamparadise.net.nz> wrote:

> > Nothing to stop you using a homebrew single slope ADC with an R and a C
> and
> > a port pin.  Granted the 12F628 is something of a rarity :)
>
> Is that the one they are bringing out in TO92 ?
> (Power version in TO220 with 2 amp I/O)

Sounds nice, but how are you supposed to program it if it only has one I/O
pin? :)
No, wait, how about a PIC in a "Pentawatt" (5-pin TO220) package, similar to
the L200CV voltage regulator? Three usable I/Os, INTRC-only, PIC16 core,
FLASH program memory, 64 bytes of E2PROM, all outputs capable of 1A or more
:)

Later.
--
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2004\09\07@105110 by Philip Pemberton

face picon face
In message <spam_OUT200409071027.i87ARiO10498spam_OUTspamspam_OUTd1o270.telia.com>>          "Jan-Erik Soderholm" <jan-erik.soderholmspam_OUTspamtelia.com> wrote:

> Maybe some of the 0.05 mm double sided copper laminate I have
> would work ? It's a 0.05 mm fiber glass core with one 18 mu (1/2 oz)
> copper layer on each side. One could etch the "keys" directly from
> the copper and put a plastic sheet in between. The "wiring" would be
> etched directly from the laminat at the same time, of course.

Right - I've got the designs sorted. The PCBs are etching now - one
0.05mm-thick PCB with the "coins" on it and one 0.8mm-thick PCB with the
fingers.
I hope 3M PhotoMount spray adhesive isn't electrically conductive :-/

Later.
--
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2004\09\07@121137 by Engineering Info

picon face


Philip Pemberton wrote:

{Quote hidden}

Please refer to the detailed discussion on I-Buttons from about 2 weeks
ago.  Dallas has been doing this for YEARS!!!!!!

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'[PIC]: Touch sensitive switches? cat skins'
2004\09\07@122349 by Robert Rolf

picon face
Bob Axtell wrote:

> One of the best ways to connect switches to minimize PIC pins is to wire
> the switches so that when pressed, they present a different voltage
> level on a
> PIC analog input pin. I've sucessfully used 8 switches on a single PIC
> analog input. Just hook 'em up so that a each different resistor value
> causes the
> voltage at the analog pin to be 1/8FS, 1/4FS, 3/8FS, etc etc. A reading
> of FS means NO switch is pressed. If I had 12 switches, I'd connect them to
> 2 PIC A/D pins, 6 on each pin.

Detecting 12 different levels is not THAT hard for an RC PIC A/D.
(e.g. digital input measuring time to cross threshold).
The trick is deciding what to do about simultaneous presses.

Using a series R chain, where each switch bypasses all resistors
farther away from the pin, is one way to avoid the ambiguity of
the suggested 1/N*R method. e.g.

             Vcc
              R
+R+R+R+R+R+R+R++-PIC
S S S S S S S  C
+-+-+-+-+-+-+--+ Gnd

> I've tried those touch switches. The reliability changes quite a bit
> with temperature. They are NOT  a workable solution.

Temperature???
More likely moisture as that more directly affects capacitance.
And one can also have a 'reference' touch pad with a known
fixed capacitance to calibrate the varying pin leakage currents.

The interdigitated (comb) finger method works quite well,
as long as the users' hand's are not so cold that they have gloves
on. Use wide fingers with minimal separation to maximize the
capacitance change seen. Look at an old PC capacitance keyboard
to see how it's laid out.

If pin count is the big issue, I'd suggest the resistor ladder with
Snaptron domes as most 'user proof'.

R

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2004\09\07@135127 by Dwayne Reid

flavicon
face
At 03:35 PM 9/6/2004, Philip Pemberton wrote:
>Hi,
>   I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
>anyone tried out the circuit on that page? Does it work?
>   Even better - does anyone know if there's a way to reduce the number of I/O
>lines in a similar way to a matrix of pushbuttons? I want something small,
>with at least 12 keys, hooked up to a 16F628A (eventually). The whole
>device - including the 3x4 keypad array - is going to be around the size of a
>credit card.

Have you looked at Motorola's "e-field" sensing chips?  They might do what
you need.  In addition, Qprox has touch sensitive matrix keypad chips that
work well.  I haven't used the Motorola stuff yet but I think highly of Qprox.

I've been using a couple of different approaches for most of my touch stuff
- one is loosely based upon Don Lancaster's touch switch as described in
his "CMOS Cookbook", the other uses a CMOS 555 timer in free-running
astable mode.  Both techniques have worked very well in many public
displays (museums and interpretive centres) that we've built controls for
over the past 20 years.

The 555 timer version works particularly well - there is no direct contact
to the circuit, allowing for pretty darned good ESD protection.  Our
standard demo involves getting the client to try destroying the unit with
anything he can think of - we give him the largest piezo sparker I've been
able to find - it easily generates 1" sparks.  The unit glitches when hit
with that nasty fellow but recovers all by itself.  No units have ever
failed in the field.

The downside of the '555 version is the relatively large footprint required
- the touch switches I've been building have pads that are almost 0.75"
square.  I'd think the smallest size that would work is about 0.5" square.

dwayne

--
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Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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2004\09\07@140641 by hilip Stortz

picon face
i see a couple of problems with all those circuits for your'
application.  first, ESD!  it would be terribly easy to fry the pic with
static electricity even with a thin insulator.  a nice demonstration
idea, but bringing pic pins out where they can be touched, even with a
thin piece of insulation is begging for problems.  second, those
circuits rely on the other plate of the capacitor as well, i.e. the
power supply etc. that the pic is connected to are the other plate when
you touch the switch, if it's all on a credit card, that could be a
problem unless the bottom of it is mostly solid metal protected by
insulation so that your other hand and the circuit metal form part of
the capacitor.  
if you really want touch switches, motorola makes a very nice chip that
reads 10 or 12 keys and can easily be expanded, they call it an "e
field" sensor and it uses a fairly high frequency oscillator so very
little capacitance is required but it will work over a wide range. circuit cellar ran a design contest based on them and there were a
couple of clever ways to scan more keys, and it can be done through as
much as 1/2" of insulating material or more.  the ic normally uses 2
pads to compensate the sensitivity (which you set, but this way it
tracks changes due to temperature etc. ).  it's very slick and very
flexible, it's also great for sensing fluid level, up to 10 fixed levels
with no contact, you put the sensors in a piece of pvc or other plastic
pipe.  if you want it really thin, touch switches are probably the way
to go, or a membrane keyboard if you can find one surplus that's the
right size.  you said about the size of a credit card, but didn't
mention if it had to be thin like a credit card (or a "smart" card) or
how rigid that size spec was.  obviously to keep it thin you'll need
surface mount parts, and either external power of one of those flat
batteries like in polaroid film packs etc. (i forget who makes them, but
they are available).

Philip Pemberton wrote:
>
> Hi,
>   I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
> anyone tried out the circuit on that page? Does it work?
>   Even better - does anyone know if there's a way to reduce the number of I/O
> lines in a similar way to a matrix of pushbuttons? I want something small,
> with at least 12 keys, hooked up to a 16F628A (eventually). The whole
> device - including the 3x4 keypad array - is going to be around the size of a
> credit card.
>   Am I stuck with normal mechanical switches?
------

-- Philip Stortz--"In Germany they came first for the Communists, and I
didn't speak up because I wasn't a Communist. Then they came for the Jews, and I didn't speak up because I wasn't a
Jew. Then they came for the trade unionists, and I didn't speak up because I
wasn't a trade unionist. Then they came for the Catholics, and I didn't speak up because I was a
Protestant. Then they came for me, and by that time no one was left to speak up."
-- Martin Niemöller, 1892-1984 (German Lutheran Pastor), on the Nazi
Holocaust, Congressional Record 14th October 1968 p31636.

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2004\09\07@143916 by Harold Hallikainen

face picon face
The circuit at the provided URL seems like it'd have ESD sensitivity
problems. I imagine a big resistor could be put between the sensing plate
and the input pin to help reduce problems.

Many years ago, I got samples of a chip from someone that did touch
sensitive switches. It was a clever technique. On the "outside" of the box
was the touch plate. On the "inside" of the box were two plates behind the
outside plate, each taking about half the area (with a small gap between
them). This could easily be done with a double sided circuit board. A
square wave drove one of the inside touch plates. The square wave would be
sensed on the other touch plate. The circuit appears to be two capacitors
in series. Touching the outside touch plate grounds the junction of the
two capacitors, preventing the signal from getting to the inside sense
plate.

I never got to use it for anything, but I thought it was pretty clever.

Harold


{Quote hidden}

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2004\09\07@153442 by Dave Tweed

face
flavicon
face
Philip Pemberton <spam_OUTphilpemspamKILLspamdsl.pipex.com> wrote:
> [A 3-pin PIC] Sounds nice, but how are you supposed to program it if it
> only has one I/O pin? :)

The same way you program any other "1wire" (Dallas/Maxim) device.

In fact, there's no reason that a 1wire device couldn't be a master on
the 1wire bus, as long as it's operating power can be supplied by the bus
pullup resistor.

Perhaps the pullup voltage could be raised to force it into slave mode
for programming, then reduced to 5V for normal operation in master mode.

Or it could poll a particular slave address at power-up and reprogram
itself from that slave if it contains a valid image (something like a
serial bootloader).

So there's really no reason you couldn't have a true 2-pin PIC!

-- Dave Tweed
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2004\09\07@154246 by Philip Pemberton

face picon face
In message <RemoveME413DF8E5.88AF111ERemoveMEspamEraseMEearthlink.net>
         Philip Stortz <KILLspammadscientist.at.largespamspamBeGoneearthlink.net> wrote:

> you said about the size of a credit card, but didn't
> mention if it had to be thin like a credit card (or a "smart" card) or
> how rigid that size spec was.

Thickness can be up to around 5mm, but thinner is better (for obvious
reasons).

> obviously to keep it thin you'll need surface mount parts,

Not a problem :)

> and either external power of one of those flat
> batteries like in polaroid film packs etc. (i forget who makes them, but
> they are available).

I was going to use a pair of tagged CR2032s in parallel.

Later.
--
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpemspamspamdsl.pipex.com              | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.dsl.pipex.com/  | 48xCD, ARCINv6c IDE, SCSI
.... Documentation is for people who can't read.
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2004\09\07@155825 by Walter Banks

picon face
There are some potential ESD problems. I don't know of any failures due to ESD.
The key plates in most of our implementations were isolated by Mylar film. It
provides some isolation as does input protection diodes and the resistor.

Some of our applications would have been ESD prone. One was a security keypad
on a chain of secure storage of storage lockers where the entry was done from
arriving cars.

When we first started using this approach to switching I built a QWERTY
keyboard that would work with the glass TTY's we were using. The sensors
were CMOS gates. It had a keypress clicker inside. I used it for a few
months including over a Canadian winter where the relative humidity is
low and the static sparks are long.



w..



Harold Hallikainen wrote:
{Quote hidden}

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2004\09\07@173510 by Bob Japundza

picon face
On Mon, 06 Sep 2004 15:59:11 -0700, Bob Axtell <RemoveMEengineerspamBeGonespamRemoveMEcotse.net> wrote:
> One of the best ways to connect switches to minimize PIC pins is to wire
> the switches so that when pressed, they present a different voltage
> level on a
> PIC analog input pin. I've sucessfully used 8 switches on a single PIC
> analog input. Just hook 'em up so that a each different resistor value
> causes the
> voltage at the analog pin to be 1/8FS, 1/4FS, 3/8FS, etc etc. A reading
> of FS means NO switch is pressed. If I had 12 switches, I'd connect them to
> 2 PIC A/D pins, 6 on each pin.

Bob, can you explain how you handle simultaneous keypresses?

Regards,
another Bob
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2004\09\07@175501 by Support - KF4HAZ

flavicon
face
Or an R2R network (if you can get 250 ohm 500 ohm 1K 2K 4K 8K 16K 32K 64K
128K 256K 512K) you could theoretically read any number of buttons down at
the same time.
For example All pressed would yield Zero none=4095 or vise versa.
(this is assuming ADC of at least 12bit resolution)
But in practice the cheapest way is to use a matrix if you have the pin
space.
Next best solution is a pic coprocessor that reads keys and feeds serial
codes, there are serial keypads outhere, or it is not that complex to use an
8 I/O pic to do the keypad polling.
KF4HAZ - Lonnie

----- From: "Robert Rolf" <Robert.Rolf@
> Bob Axtell wrote:
>
> > One of the best ways to connect switches to minimize PIC pins is to wire
> > the switches so that when pressed, they present a different voltage
> > level on a
> > PIC analog input pin. I've sucessfully used 8 switches on a single PIC
> > analog input. Just hook 'em up so that a each different resistor value
> > causes the
> > voltage at the analog pin to be 1/8FS, 1/4FS, 3/8FS, etc etc. A reading
> > of FS means NO switch is pressed. If I had 12 switches, I'd connect them
to
{Quote hidden}

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2004\09\07@191600 by Bob Axtell

face picon face
Hi, Bob!

Ever been to the "Bob Convention" in Iowa every summer? Gotta be a "Bob"
to get in...

Multiple keypresses are a problem on any multiplex scheme. If I catch a
voltage value between proper
values, I ignore it. If you have a "shift" function (can be down while
others are pressed)  I'd put that on
another pin. Ideally, you should make read the pin several times before
deciding to act on the voltage
value, too.

Of course you have to allow tolerance, but if you use 1% resistors of
high enough value, the
limits are very close (2% or so). If you use low ohm resistors, they
might self-heat (and change value slightly)
from the current through the switch; also some switches measure 100 ohms
when pressed!

BTW, this scheme is used by high-end surveillance cameras to control the
camera settings by the PIC. For that,
I used a  74HC4051 for the 8 different settings, with a precise resistor
on each leg. The digital signals from the
PIC control the camera.

--Bob

Bob Japundza wrote:

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'[EE] Moisture Sensitive Chips was Re: [EE]TSSOP f'
2004\10\17@120604 by Bob Axtell
face picon face
In earlier days, the plastic covering of the chip was quite thick, and
would provide
protection from fairly high external pressure. In other words, water
pressure would have to be
very high to get through to the device inside.

But these very thin packages do not have the level of protection that
thick packages have.
If you clean with water, you should bake the PCB to ensure the removal
of any trapped water.
I consider TSSOP to fall into this catagory.

What I do is to clean with paint thinner first, then use hot soapy
water, then clean water, then
a small 125F bakeout in the oven (make sure temp is reached then turn
the oven off and let everything
slowly dry out and cool down at the same time). bakeout lasts for about
1 hr.

If I believe moisture is going to be a problem, I will dipcoat the final
PCB with an RTV coating.

F

Philip Stortz wrote:

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2004\10\17@134511 by Anthony Toft

flavicon
face
> If I believe moisture is going to be a problem, I will dipcoat the final
> PCB with an RTV coating.

Is there any source for RTV readily available to the hobbiest, other
than the tubes of locktite available in Autoparts stores? I have a
circuit that will need to be coated for short protection.

Anthony
--
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    I'm Anton, and I approve this message

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2004\10\17@140725 by Bob Axtell

face picon face
There more to this than first meets the eye. Lets say you design
something that goes into aviation
equipment, flying at 50000'. Small amounts of pressure trapped inside
the thin case might crack the
case. High vibration levels might also crack a thin case. The device
might work fine until the plane
sits on the ground for a few days in a humid place (like central
America) and moisture becomes
trapped in the cracked case.

The solution is to coat the devices with a semi-hard RTV coating. The
flexibility of the coating ensures
that moisture can't get it whether the case cracks or not. Hard coatings
will eventually crack due to
vibration.

--Bob

Bob Axtell wrote:

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2004\10\17@140958 by Bob Axtell

face picon face
Check the internet for "electronic encapsulants". They are usually two-part
compounds. GE makes electronic coatings, as do DuPont and many others.

--Bob

Anthony Toft wrote:

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2004\10\17@141800 by Marc Nicholas

flavicon
face
Or "conforming coatings". I recall there's one that comes in a spray can.

Nasty stuff, however.


-marc

On Sun, 17 Oct 2004, Bob Axtell wrote:

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2004\10\17@142101 by Bob Axtell

face picon face
There IS one wonderful compound made by Rustoleum, used to make rubberized
handles for pliers, etc. The stuff is expensive but works very well - I used
it for 220VAC circuits on a PCB with low level circuits-

"GRIP & GUARD  Texturized Rubber Coating", comes in a 14.5 fl oz dip
can, in many
colors (I like baby blue best), sold in all ACE hardware stores. It has
a very high dielectric
strength, and is NOT rubber (its a new plastic resin in xylene/acetone
cure). It never hardens,
chips, or cracks.

--Bob

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2004\10\17@151240 by Roland

flavicon
face
At 02:12 PM 17/10/2004 -0400, you wrote:
>Or "conforming coatings". I recall there's one that comes in a spray can.
>
>Nasty stuff, however.
>

Does anyone use 'clear laquer'(in a can) as a conformal coating. Basically
clear automotive paint.
I have, but it's not the best if you need to do repairs afterwards, but is
tolerable.
Very cheap, and seems to work well enough on cars as an anti-moisture:)


Regards
Roland Jollivet

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2004\10\17@152000 by Marc Nicholas

flavicon
face
Clear lacquer isn't a conforming coating....it's not flexible, it won't
build up in a thick enough layer to get into everything, and it'll likely
crack over time, IMHO.


-marc

On Sun, 17 Oct 2004, Roland wrote:

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2004\10\17@153746 by Bob Axtell

face picon face
I used to use it, but found out that it cracks and chips.
Lets moisture in eventually.

Unless they have changed the formula...

--Bob

Roland wrote:

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2004\10\17@191009 by hilip Stortz

picon face
sure, allied, newark, and most other distributors carry non-corrosive
rtv (you want to make sure it's non-corrosive, most rtv is corrosive and
will damage circuitry).  mcm.com may also have it, i haven't checked.
there are also spray conformal coatings that are silicone or other
materials.  miller-stephenson is my preferred source for aerosol
chemicals.  they are good about sample's (for a reduced price) though
they do have a substantial minimum order requirement.

Anthony Toft wrote:
>
> > If I believe moisture is going to be a problem, I will dipcoat the final
> > PCB with an RTV coating.
>
> Is there any source for RTV readily available to the hobbiest, other
> than the tubes of locktite available in Autoparts stores? I have a
> circuit that will need to be coated for short protection.
------

--
President George W. Bush, Vice President Richard B. Cheney, Secretary of
Defense Donald H. Rumsfeld,
and Attorney General John D. Ashcroft have committed violations and
subversions of the Constitution
of the United States of America.  <http://www.VoteToImpeach.org>  They should
be charged with high treason
and as leaders deserve the highest penalty.  If there is no rule of law
there can be no civilization.
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2004\10\17@191553 by hilip Stortz

picon face
i'm glad i asked!  most of what i've seen is more concerned with damage
done during soldering when trapped moisture gets rapidly heated and
expands, creating a crack (or damaging a bond wire even i'd think).
it's good to know it's an ongoing problem and necessitates a conformal
coating.  i know i've seen chips in packages that are thinner than the
naked chips once were!  it's my understanding that some of them have the
back surface ground down after the rest of the manufacturing but before
packaging.  amazing infrastructure there, all industries could learn a
lot from how chips are made (in terms of reliability and quality, as
well as management of a very complex manufacturing process).  then
again, according to dentist i've had people who work in those clean
rooms have a very high incidence of TMJ, not surprising, i can see a lot
of stress in one of those jobs (and it can't help that you can't see all
of other people's faces, making it hard to understand their facial
expression and whether they are joking or deadly serious).

Bob Axtell wrote:
>
> There more to this than first meets the eye. Lets say you design
> something that goes into aviation
> equipment, flying at 50000'. Small amounts of pressure trapped inside
> the thin case might crack the
> case. High vibration levels might also crack a thin case. The device
> might work fine until the plane
> sits on the ground for a few days in a humid place (like central
> America) and moisture becomes
> trapped in the cracked case.
------

--
President George W. Bush, Vice President Richard B. Cheney, Secretary of
Defense Donald H. Rumsfeld,
and Attorney General John D. Ashcroft have committed violations and
subversions of the Constitution
of the United States of America.  <http://www.VoteToImpeach.org>  They should
be charged with high treason
and as leaders deserve the highest penalty.  If there is no rule of law
there can be no civilization.
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2004\10\19@055145 by jsand

flavicon
face
Hello Roland & PIC.ers,

>Does anyone use 'clear laquer'(in a can) as a conformal coating. Basically
>clear automotive paint.
>I have, but it's not the best if you need to do repairs afterwards, but is
>tolerable.
>Very cheap, and seems to work well enough on cars as an anti-moisture:)
>
>
>Regards
>Roland Jollivet

I've been using CRC clear Urethane Seal Coat
'Motor & Generator Winding Coating Insulator'  
Manufacturer's code 2049.

Available from Waco Industries, Johannesburg
tel   011 677 2500
costs about R30 a can in case qtys.

It's acetone soluble, for when you need to do board repairs.
Sprays on THICK, doesn't crack off or cause other unwanted
effects - as the household stuff will do to you.
Superb insulator. Some headers on a pcb here were recently coated
with it (in error) and the pins became completely impervious to 240vac.


           best regards,   John



email from the desk of John Sanderson.
JS Controls, PO Box 1887, Boksburg 1460, Rep. of S. Africa.
Tel/Fax 011 893 4154,
Cell 082 741 6275,
web    http://www.jscontrols.co.za
Manufacturer & purveyor of laboratory force testing apparatus &
related products & services.
email from the desk of John Sanderson.
JS Controls, PO Box 1887, Boksburg 1460, Rep. of S. Africa.
Tel/Fax 011 893 4154,
Cell 082 741 6275,
web    http://www.jscontrols.co.za
Manufacturer & purveyor of laboratory force testing apparatus &
related products & services.

____________________________________________


'[PIC]: Is 628A more sensitive to noise than 628?'
2004\12\23@013712 by Bala Chandar
flavicon
face
A year back, I built a remote control project using 16F628 that receives X10 codes on the power line and controls 5 different 240V devices through 5 relays. This circuit is powered up 24 hours a day and 7 days a week and has been working flawlessly for over a year now.

Recently, I bought a 16F628A (priced slightly less than 628), compiled the same code for this PIC and used it in the circuit in place of the old 16F628. The operation was found to be OK. But, I found that when the fluorescent lamp was switched on, the remaining 4 devices would also get switched on; this would happen at least 3 out of 5 times. When an incandescent lamp was turned on, this problem was not observed. My guess is that the noise generated by the fluorescent lamp is the main reason for the odd behavior. So, in addition to the 0.1uf cap already soldered across the power pins of the PIC, I added two more caps for the ICs (74HC595 & UCN5841A). But this doesn't seem to have made any improvement and the problem persists.

Would appreciate suggestions and guidance to resolve this issue.

Thanks & Regards,
Bala

____________________________________________

2004\12\23@023625 by Jose Da Silva

flavicon
face
On Wednesday 22 December 2004 10:36 pm, EraseMEBala.ChandarSTOPspamspamRemoveMEaventis.com wrote:
> A year back, I built a remote control project using 16F628 that receives
> X10 codes on the power line and controls 5 different 240V devices through
> 5 relays. This circuit is powered up 24 hours a day and 7 days a week and
> has been working flawlessly for over a year now.
>
> Recently, I bought a 16F628A (priced slightly less than 628), compiled the
> same code for this PIC and used it in the circuit in place of the old
> 16F628. The operation was found to be OK. But, I found that when the
> fluorescent lamp was switched on, the remaining 4 devices would also get
> switched on; this would happen at least 3 out of 5 times.

I have a computer which has a power supply that does that too. The computer,
or in your case fluorescent lights are creating random noise at
approximately the right frequency to imitate an ON code. You need to insert
something there to block the noise from the light. Your other option is
since you built the circuit, you may be able to create a narrower bandpass
so noises such as fluorescents (approx 90khz) don't get through.

> When an
> incandescent lamp was turned on, this problem was not observed.

Turning on the incandescent added a 500ohm across the AC lines so it reduced
the power level of the fluorescent noise below the threshold of your
circuit.

> My guess
> is that the noise generated by the fluorescent lamp is the main reason for
> the odd behavior. So, in addition to the 0.1uf cap already soldered across
> the power pins of the PIC, I added two more caps for the ICs (74HC595 &
> UCN5841A). But this doesn't seem to have made any improvement and the
> problem persists.

I think you want to improve your input circuit so it has a better bandpass
that rejects noises below or above 120khz (narrower bandpass).

>
> Would appreciate suggestions and guidance to resolve this issue.

I'm guessing you replaced a dead 628 with a 628a in which case you probably
did not have enough protection from spikes and noise towards the 628.
You mention you inserted bypass caps, but have you also thought of putting
blocking inductors? Using L and C in the right combinations should work.

Hope the above suggestions help.
____________________________________________

2004\12\23@034218 by Bala Chandar

flavicon
face
Hi Jose,

Thanks for your suggestions.

> I'm guessing you replaced a dead 628 with a 628a in which
> case you probably
> did not have enough protection from spikes and noise towards the 628.
> You mention you inserted bypass caps, but have you also
> thought of putting
> blocking inductors? Using L and C in the right combinations
> should work.
>
> Hope the above suggestions help.

I think, I should clarify a few points. I replaced the PIC, not because the old 628 was dead. I merely wanted to try out the newly bought 628A. Since I found it highly sensitive to noise resulting in unsatisfactory operation, I put the original 628 back and now the circuit is working perfectly, as before.

In my circuit, two of the five devices controlled are fluorescent lamps. When one of these two lamps is switched on, the noise creates the problems mentioned earlier. I have used only .1uF caps so far. I will try out your suggestion of using L and C in the right combination.

At present, it is very easy to resolve the issue by using 628 instead of 628A. But I feel, my circuit design should ensure that it works flawlessly even with a PIC that is more vulnerable to noise.

Regards,
Bala

____________________________________________

2004\12\23@070836 by William Chops Westfield

face picon face

On Dec 23, 2004, at 12:42 AM, spam_OUTBala.ChandarRemoveMEspamEraseMEaventis.com wrote:

> I should clarify a few points. I replaced the PIC, not because the old
> 628
> was dead. I merely wanted to try out the newly bought 628A. Since I
> found
> it highly sensitive to noise resulting in unsatisfactory operation, I
> put
> the original 628 back and now the circuit is working perfectly, as
> before.

Have you tried OTHER 628s?  Perhaps the one you are using happens to be
particularly insensitive...

BillW
____________________________________________

2004\12\23@100008 by Bala Chandar

flavicon
face
{Quote hidden}

Hi BillW,

My guess is that 16F628 is inherently more immune to noise than 16F628A is. (Does the die size have anything to do with this?) I would like to know others's experience with 628A. But, you have a point. I will use the other 628s I have for the same circuit and report my finding.

Regards,
Bala


2004\12\23@105439 by Spehro Pefhany

picon face
At 08:30 PM 12/23/2004 +0530, you wrote:


>Hi BillW,
>
>My guess is that 16F628 is inherently more immune to noise than 16F628A
>is. (Does the die size have anything to do with this?) I would like to
>know others's experience with 628A. But, you have a point. I will use the
>other 628s I have for the same circuit and report my finding.
>
>Regards,
>Bala

Decreased EMI immunity is a common side-effect of die shrinks.

Since no microcontroller manufacturer specs it (even indirectly), there's
no way to tell in advance.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspam_OUTspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2004\12\23@154723 by Robert Rolf

picon face
But doesn't this misbehaviour reveal a flawed circuit
design? Something like a transient getting into the substrate
from the protection diodes, something that should NOT happen.

R

Spehro Pefhany wrote:

{Quote hidden}

2004\12\23@170044 by Spehro Pefhany

picon face
At 01:47 PM 12/23/2004 -0700, you wrote:
>But doesn't this misbehaviour reveal a flawed circuit
>design? Something like a transient getting into the substrate
>from the protection diodes, something that should NOT happen.
>R

Oh, absolutely. Or, just as often, flawed layout or packaging. It's always
the designer's fault when the parts are used outside of the data sheet
limits.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2004\12\27@005249 by Bala Chandar

flavicon
face

Spehro Pefhany wrote:

> Decreased EMI immunity is a common side-effect of die shrinks.

Thanks, Spehro. Your reply specifically answers my question.

I used two other 628s for the circuit I had mentioned earlier. The circuit works quite satisfactorily. That confirms that the 628A which has a smaller die size is more prone to being affected by EMI. So, if I plan to use 628A, my circuit design should incorporate adequate EMI filtering.

Regards,
Bala




2004\12\31@152619 by dr. Imre Bartfai

flavicon
face

> Decreased EMI immunity is a common side-effect of die shrinks.

Interesting. Approx. 10+ years ago, parity was widely used in PC dynamic
RAM memories as I was told the cosmic radiation may induce random parity
errors. Today I heard there is no need of parity bits due to die shrink.

Is not here a contradiction?

Imre

2004\12\31@165828 by Spehro Pefhany

picon face
At 09:26 PM 12/31/2004 +0100, you wrote:

>>Decreased EMI immunity is a common side-effect of die shrinks.
>
>Interesting. Approx. 10+ years ago, parity was widely used in PC dynamic
>RAM memories as I was told the cosmic radiation may induce random parity
>errors. Today I heard there is no need of parity bits due to die shrink.
>
>Is not here a contradiction?
>
>Imre

Do you know that cosmic rays are not EMI? And gamma rays are higher (in
frequency) above typical industrial EMI than *daylight* is above power
line frequency.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffKILLspamspamEraseMEinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com





'[PIC]: Is 628A more sensitive to noise than 628?'
2005\01\04@052102 by dr. Imre Bartfai
flavicon
face
Hi,

of course I do know the difference. However, I was interesing for me a
bit, that EMI susceptibility increases, and radiation susceptibility
decreases the same way. I simply did not believe the latter one and I
sought for additional arguments whether pro or con.

Imre

On Fri, 31 Dec 2004, Spehro Pefhany wrote:

{Quote hidden}

> --

2005\01\04@063837 by Alan B. Pearce

face picon face
>> Decreased EMI immunity is a common side-effect of die shrinks.

>Interesting. Approx. 10+ years ago, parity was widely used in

>PC dynamic RAM memories as I was told the cosmic radiation may

>induce random parity errors. Today I heard there is no need of

>parity bits due to die shrink.

>Is not here a contradiction?



No it is not a contradiction. Also cosmic radiation is not what generates
the EMI that upsets the chips.



As far as cosmic radiation goes, my understanding is that chips with
geometries smaller than 250u are inherently radiation resistant, and so are
preferred for use in space instrumentation applications.

2005\01\04@075343 by Russell McMahon

face
flavicon
face
>>PC dynamic RAM memories as I was told the cosmic radiation may
>>induce random parity errors.

>Also cosmic radiation is not what generates the EMI that upsets the
>chips.

Parity errors were largely caused by radiation for the packaging
material !!!
Significant levels of background radiation can't hep though.


       RM



'[EE] nite lites with light sensitive switch 75 ce'
2006\05\21@142229 by Gus Salavatore Calabrese
face picon face
I found these at Lowe's Hardware.
They have all sorts of possibilities

see http://nope9.com/projects-axxx/tiki-index.php?page=A321

POD

2006\05\21@151539 by Dave Lag

picon face
Gus Salavatore Calabrese wrote:
> I found these at Lowe's Hardware.
> They have all sorts of possibilities
>
> see nope9.com/projects-axxx/tiki-index.php?page=A321
>
> POD
The Cds cells would cost you that much alone.
SCR = half wave? part number?
D

2006\05\21@180806 by Gus S Calabrese

face picon face
It is labeled as an SCR on the PCB,
there is no part number.


On 2006-May 21, at 1:16 PM, Dave Lag wrote:

Gus Salavatore Calabrese wrote:
> I found these at Lowe's Hardware.
> They have all sorts of possibilities
>
> see http://nope9.com/projects-axxx/tiki-index.php?page=A321
>
> POD
The Cds cells would cost you that much alone.
SCR = half wave? part number?
D

2006\05\21@182401 by Steve Smith

flavicon
face
2n5064,2n4444,tic106 should be 400v for 110v line or 600v for 240 line about
1A min for 40w to allow for cold filament current
Half wave yes
Bottom terminal is cathode middle is gate top is anode (from drawing) made
in china by the M

Steve

{Original Message removed}

2006\05\21@183235 by Spehro Pefhany

picon face
At 04:08 PM 5/21/2006 -0600, you wrote:
>It is labeled as an SCR on the PCB,
>there is no part number.

Probably similar to 2N5064 (sensitive gate SCR). Half wave is better
for a nightlight- the bulb life is extended greatly.

But an LED or EL lamp would be better from an energy pov.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
@spam@speffspamspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


'[EE] nite lites with light sensitive switch 75 cen'
2006\05\21@184556 by Richard Prosser

picon face
Is half wave permitted in the wiring regs? It seems to me it is more
likely to cause problems than inefficient wall-warts perminantly
connected. I'm pretty sure that the wiring regs here only allow a very
small DC component.

RP

On 22/05/06, Spehro Pefhany <spamBeGonespeffRemoveMEspamEraseMEinterlog.com> wrote:
{Quote hidden}

> -

2006\05\21@184634 by Gus S Calabrese

face picon face
Who or what is "M" ?

2N4444  600V / 5.1A
2N5064 - 200 V, 800 mA, Plastic SCR.
TIC106  5A 400V SCR
00000000000000000000000000000000000000000000000

On 2006-May 21, at 4:24 PM, Steve Smith wrote:

2n5064,2n4444,tic106 should be 400v for 110v line or 600v for 240  
line about
1A min for 40w to allow for cold filament current
Half wave yes
Bottom terminal is cathode middle is gate top is anode (from drawing)  
made
in china by the M

Steve

{Original Message removed}


'[EE] About capacitance sensitive schematic'
2007\07\17@114415 by Andre Abelian
flavicon
face
Hi to all,

last night some one stole my 2 security cameras by going on the roof.
Since there is an alley I put cameras just in case. now after 7 years
of living there without seeing any problem this is our first problem
seen. no thing got lost but this could be sign of some thing else.
My plane is:
any time some one goes on the roof turn alarm on

My question is:
around the roof there is 24 square feet metal that is isolated
thinking to add capacitance sensitive circuit if any once wants to
go on the roof it will trigger the alarm or any kind of sound.
The reason for capacitance sensitive is if they wear gloves it still
will sense it.

I know cypress PsOC does this but I am not good at PsOC and my
choice is PIC so far. Does any one have any capacitance sensitive schematic
that I can add to pic?

I can only see hand how he is removing the camera by bending the camera around
but what purpose I do not know.

thanks

Andre

2007\07\17@115652 by Xiaofan Chen

face picon face
On 7/17/07, Andre Abelian <TakeThisOuTaabelianspammason-electric.com> wrote:
>
> I know cypress PsOC does this but I am not good at PsOC and my
> choice is PIC so far. Does any one have any capacitance sensitive schematic
> that I can add to pic?
>

Check with Microchip and they should have already application notes
for the cap-sense application.

Xiaofan

2007\07\17@121325 by Bob Blick

face picon face
--- Andre Abelian <spamBeGoneaabelianKILLspamspamTakeThisOuTmason-electric.com> wrote:

> last night some one stole my 2 security cameras by
> going on the roof.

Ouch! On the bright side, at least they didn't break
into your house afterwards, but that really sucks.
It's hard to sleep when you know people consider you a
target 24 hours a day.

> around the roof there is 24 square feet metal that
> is isolated
> thinking to add capacitance sensitive circuit if any
> once wants to
> go on the roof it will trigger the alarm or any kind
> of sound.

Capacitive sensing works because the sensor is
dramatically smaller than the object being sensed. So
I don't think it'll be easy to get it to work.

Cheerful regards,

Bob


2007\07\17@122051 by Walter Banks

picon face
www.bytecraft.com/Touch_Sensitive_Switch

This is a starting point.
I would want to isolate the port pin from the roof.
A local cat could easily destroy a PIC.

w..


Andre Abelian wrote:

{Quote hidden}

> -

2007\07\17@132115 by David VanHorn

picon face
I'd suggest a simpler sensor, like loss of video or breaking a loop
(with known resistor inside the camera housing)

2007\07\17@134106 by Timothy J. Weber

face picon face
David VanHorn wrote:
> I'd suggest a simpler sensor, like loss of video or breaking a loop
> (with known resistor inside the camera housing)

And: put that inside a cheap "dummy," obvious-looking security camera;
use a small, hidden camera trained on the decoy.  That way you may get a
better shot of the person removing the dummy one!
--
Timothy J. Weber
http://timothyweber.org

2007\07\17@140415 by Bob Blick

face picon face

--- Andre Abelian <EraseMEaabelian.....spamKILLspammason-electric.com> wrote:

> if any
> one wants to
> go on the roof it will trigger the alarm or any kind
> of sound.

A friend of mine had problems with people jumping over
his fence. He solved it by putting two strips of
carpet tackstrip on the top of his fence. Not only was
it a repellant, he also got a loud audible signal each
time it got used :)

Cheerful regards,

Bob

2007\07\17@145539 by Recon

picon face
Bob Blick wrote:

> A friend of mine had problems with people jumping overhis fence. He
> solved it by putting two strips ofcarpet tackstrip on the top of his
> fence. Not only wasit a repellant, he also got a loud audible signal each
>
>time it got used :)
>
>Cheerful regards,
>
>Bob
>  
>
Unfortunately You can get sued for damages in alot of states for doing
that.  You have to get the crook after he has done the dirty deed and is
trying to get away.

Recon

2007\07\17@165419 by Andre Abelian

flavicon
face
Hi Bob, every body

I like to thank all of you for giving ideas, suggestions
I will let you know the update later.

once again thanks

Andre






{Original Message removed}

2007\07\17@174806 by Walter Banks

picon face
Theives have been known to take the replacements
in a week or so.

w..


Andre Abelian wrote:

{Quote hidden}

> -

2007\07\17@184821 by Robert Rolf

picon face
Just use a pair of PIR (passive infra red) motions sensors on the ends of the
roof. The only way they'll see any 'motion' in the roof plane is if someone
is trying to steal the cameras.

As for capacitance sensing, just drive the roof with a high frequency (400kHz)
AC signal though a high value (1k) resistor (and coax). Any loading by a human will
cause the amplitude to drop. There will also be a phase shift so you could
use the PIC PWM to generate the AC drive, and the CCP to measure the delay across
the series resistor. Any load change will change the delay by enough uSec that
you can detect it. And with long term averaging for the threshold,
you can account for changes caused by rain, drying or temperature.

Just be sure to put clamp diodes/MOV on the cable sufficient to handle a lightening
strike <G>.

Robert

Walter Banks wrote:

{Quote hidden}

>>-

2007\07\17@190535 by David VanHorn

picon face
On 7/17/07, Robert Rolf <spamRobert.Rolfspamualberta.ca> wrote:
> Just use a pair of PIR (passive infra red) motions sensors on the ends of the
> roof. The only way they'll see any 'motion' in the roof plane is if someone
> is trying to steal the cameras.

Or birds, or bugs, or sunrise/sunset, or heating/cooling of machinery
and vents..


> As for capacitance sensing, just drive the roof with a high frequency (400kHz)
> AC signal though a high value (1k) resistor (and coax).

And apply for that international broadcasting permit!  :)
What happens when it rains?

2007\07\17@202017 by Russell McMahon

face
flavicon
face
> around the roof there is 24 square feet metal that is isolated

100 or 230 VAC on the isolated metal ? :-)


       Russell


2007\07\17@214754 by Richard Prosser

picon face
Or, if it really is isolated, then it could build up a significant
static charge - even more so "with a bit of help" - say from an
ignition coil  or TV tripler. Current linited of coarse. Might help
any stray cat problem also,

RP



On 18/07/07, Russell McMahon <apptechSTOPspamspamparadise.net.nz> wrote:
> > around the roof there is 24 square feet metal that is isolated
>
> 100 or 230 VAC on the isolated metal ? :-)
>
>
>        Russell
>
>
> -

2007\07\17@220937 by Roger, in Bangkok

face
flavicon
face
Souped up fence charger that can "jump" through the gloves, etc.

Augment that with a couple of flat runs of razor wire around the
eaves/gutters and you may well be able to collect some DNA samples :-)

Regards/Roger, in Bangkok

On 7/17/07, Russell McMahon <apptechSTOPspamspamKILLspamparadise.net.nz> wrote:
>
> > around the roof there is 24 square feet metal that is isolated
>
> 100 or 230 VAC on the isolated metal ? :-)
>
>
>         Russell
>
>

2007\07\18@015244 by Yigit Turgut

picon face
     Hi all,

     Assuming you do not have detailed knowledge about capacitors,
their nature consists of (plate-plate capacitors) by fixed distances
of any 90 degree linear line (lets say X) from a plate to the
other.Guy walking on your roof might or not trigger your capsense
alarm but not the way you think.When he stepped on the roof he will
break the length ratios of X's resulting your capsense application to
malfunction.And depending on your capacitance, it's possible for him
to end up dead.Also I haven't mentioned about rainy days, variable air
moisture and density.Meantime covering your roof with a metal plate is
not a good idea at all,  trust me.On the other hand (if you don't want
to kill the man) this technique makes no sense.Say everything written
above is handled somehow, you noticed there is a guy up, it's not wise
to get out and while your children and wife are at home.

What you need is a precisely calibrated action sensor triggering an
alarm or a siren.You can use PSoC for designing a module for
automatically calling the local cops, easy as making a cup of tea.

Cheers

Yigit

2007\07\18@080650 by Master Yager

picon face
*Motion Detectors* – Use these awesome Motion Detectors inside your house to
be alerted of any movement. When someone walks by, your alarm will sound!
Wireless, cheap and will not hurt anyone.
http://www.x10.com



On 7/18/07, Yigit Turgut <@spam@y.turgut.....spamspamgmail.com> wrote:
{Quote hidden}

>


'[EE] Propper storage of static sensitive items.'
2008\04\12@112018 by piclist
flavicon
face
I have a fairly large collection of IC's and other electronic parts
(although most are several states away from me at the moment) and was
wondering how most of you store your stuff?

IC's stuck into anti-static foam is good and I try to do that as much as
possible, but often the foam is stored in a plastic container which is NOT
conductive and so builds up static which can still be dangerous.

Are there any clear anti-static sprays one could use to coat storage
containers to help with this?  anti-static foam doesn't help much with
lots of loose items either which makes storing them a pain as well.

I have a lot of plastic hobby-type boxes with subdivisions inside that
work great for passive parts, and it would be nice to use them for
sensitive ones as well.

What I would love is more containers like this Microchip sample box I
picked up at a Hamfest:

www.ian.org/Remote/MicrochipStorage1.jpg
http://www.ian.org/Remote/MicrochipStorage2.jpg

I have tried things like this.. but I find it annoying to work with.

http://www.ian.org/Remote/BugBox.jpg

Also... is there a way with a multimeter to test anti-static properties?  
Conductive foam is easy, and the black boxes above have very low
resistance too.  But anti-static bags don't test as conductive at all.
I have a 5Kv leak tester (again, not HERE) but I am not clear if that
would test if a charge is building up or not.

A test I just tried was the old plastic bar rubbed on rabits fur trick.
Rubbing the black boxes (whout chips inside!) then testing them showed
they collected no charge.  Same with a silver EST bag.  Pink anti-static
bags hold a small charge, and the Bug Boxes become highly charged, making
me wonder if I should use them at all.  They are supposted to be made with
anti-static properties.

So.. just what am I to make of all this?  I defer to actual electrical
engineers here. :-)

--
ian SMith
http://www.ian.org

2008\04\12@120103 by Bob Axtell

face picon face
piclist@ian.org wrote:
{Quote hidden}

There is a spray compound called "cling free" that women use to reduce
static electricity when they
wear nylon stockings and hose. It works wonders on carpet, desktops, and
plastic trays and boxes.
But when it dries, the effect is mostly lost. There is also a carpet
spray that does the same thing, and
it takes a while for the chemical to dry out.

One thing that works for us is to use empty anti-static bags inside the
drawers. Just place the parts on top
of the anti-static bags.

But the best solution to ESD problems is a properly-grounded work
station, with an antistatic wrist clip.

--Bob A  


'[EE] Moisture sensitive devices'
2011\07\09@174920 by David
flavicon
face
I bought a number of through hole IR receivers, which I used to test a simple device.  Subsequently I have designed a board and ordered up some SMD versions of the same thing (http://tinyurl.com/665gafn).

However, the bag comes with a rather nice sticker explaining how these are moisture sensitive.  In the bag is a humidity sensing patch and a lot of warnings.

This is a hobby board and I'll only make one or two, but I'm wondering how moisture sensitive these things are.  In general, are moisture sensitive parts a pain?  Or am I going to be OK once I've soldered them up?

Davi

2011\07\09@183328 by Oli Glaser

flavicon
face
On 09/07/2011 22:49, David wrote:
> I bought a number of through hole IR receivers, which I used to test a
> simple device.  Subsequently I have designed a board and ordered up some
> SMD versions of the same thing (http://tinyurl.com/665gafn).
>
> However, the bag comes with a rather nice sticker explaining how these
> are moisture sensitive.  In the bag is a humidity sensing patch and a
> lot of warnings.
>
> This is a hobby board and I'll only make one or two, but I'm wondering
> how moisture sensitive these things are.  In general, are moisture
> sensitive parts a pain?  Or am I going to be OK once I've soldered them up?
>
> David

For a hobby board I wouldn't worry - generally the moisture warnings are for reflow, where the package can crack during reflow if it carries excess moisture.
If you check the datasheet it says to reflow within 72hrs of opening the dry pack, and gives information regarding storage conditions and what to do if the devices have absorbed too much moisture.
Since I assume you will be hand soldering though, none of this should be relevant to you.
If you are planning to use reflow method though, then follow the instructions mentioned above in the datasheet.


'[EE] Shielding sensitive eletronics: is thickness '
2011\11\06@100304 by Electron
flavicon
face

Hello,
when shielding sensitive eletronics is the thickness of the metal shield important?

As I'm gonna pot my small circuit into epoxy, I'm tempted to use cheap aluminium
foil to shield the circuit (which seems necessary since I increased the clock
speed (PLLx16), and the environment is disturbed, at 1/16s speed it never crashed
although all the EMI).

Greets,
Mario

2011\11\06@115525 by Sean Breheny

face picon face
Hi Mario,

I believe that the thickness does matter to some degree. Also, it
greatly depends on what you are trying to do - prevent radiation FROM
your device, protect your device from external EM radiation, protect
your device from external low-frequency fields, etc. Can you describe
your application further?

Shielding is a tough subject - it is difficult to get it right the
first time. I would suggest that you get your circuit working
properly, including the shielding aspects, before you pot it.

Sean


On Sun, Nov 6, 2011 at 10:02 AM, Electron <spamelectron2k4.....spam.....infinito.it> wrote:
{Quote hidden}

>

2011\11\06@121504 by David VanHorn

picon face
On Sun, Nov 6, 2011 at 8:02 AM, Electron <electron2k4.....spaminfinito.it> wrote:
>
> Hello,
> when shielding sensitive eletronics is the thickness of the metal shield important?


Thickness helps with low frequency magnetics. A good resource for this
would be any of the vendors of Mu-Metal.
They have application notes that discuss where Mu-Metal works, and
where copper/aluminum works, and how thickness impacts things.


I would look for other sources for your problem though.. From what
little you've said, it sounds more like a PLL stability problem

2011\11\06@125015 by Yigit Turgut

picon face
That all depends on the structure you want to protect as well as the
dispersion parameters of the foil you use. When you cover it with
aluminium  foil you simply cover it with a Faraday cage where grid
mesh size goes to limit 0. Thickness will be a problem if you are
running high frequency components in your circuit due to skin effect
(not penetration depth). If frequency of the core is 16 times the
peripherials, it would be an unexpected behavior if one/some of the
peripherials malfunction where core operates flawlessly. Because high
frequency components will be more prone to environmental effects. It
ends up evaluating the operation environment of your gadget. I have
encountered cases where the device works %100 at a location and goes
crazy at another location due to magnetic and electric field
components of those specific locations - even it was shielded. It is
NOT about the amplitude of the EM around -directly-, it is about the
vectoral components of the disturbing field/wave.

Model the structure and expose to random(vector) far fields then you
can extract em response of your system. It is also even possible to
determine the electrical level effects of the environmental em
radiation in your circuit via more advanced approaches.

It all ends up in the digits of your budget (:

On Sun, Nov 6, 2011 at 5:02 PM, Electron <KILLspamelectron2k4spam_OUTspaminfinito.it> wrote:
{Quote hidden}

>

2011\11\06@125605 by Mark Hanchey

flavicon
face
On 11/6/2011 12:15 PM, David VanHorn wrote:
> On Sun, Nov 6, 2011 at 8:02 AM, Electron<spam_OUTelectron2k4spamTakeThisOuTinfinito.it>  wrote:
>> Hello,
>> when shielding sensitive eletronics is the thickness of the metal shield important?
>
> Thickness helps with low frequency magnetics. A good resource for this
> would be any of the vendors of Mu-Metal.
> They have application notes that discuss where Mu-Metal works, and
> where copper/aluminum works, and how thickness impacts things.
>
>
> I would look for other sources for your problem though.. From what
> little you've said, it sounds more like a PLL stability problem.

speaking of Mu-Metal I saw this while browsing the other day. $10 for a sheet of it.
http://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A

Not sure if that is low or high, but seemed an okay price.
Mark

2011\11\06@152601 by Electron

flavicon
face

Dear Sean,
I need to protect my application from the external environment, namely
from the interference caused by a spark plug. It's a motorbike application.

The spark at the oscilloscope looks like an impulse with 1uS rising edge
and 20-25uS falling edge.

With kind regards,
Mario


At 17.55 2011.11.06, you wrote:
{Quote hidden}

>> -

2011\11\06@152601 by Electron

flavicon
face
At 18.15 2011.11.06, you wrote:
>On Sun, Nov 6, 2011 at 8:02 AM, Electron <spam_OUTelectron2k4TakeThisOuTspamEraseMEinfinito.it> wrote:
>>
>> Hello,
>> when shielding sensitive eletronics is the thickness of the metal
>shield important?
>
>
>Thickness helps with low frequency magnetics. A good resource for this
>would be any of the vendors of Mu-Metal.
>They have application notes that discuss where Mu-Metal works, and
>where copper/aluminum works, and how thickness impacts things.
>
>
>I would look for other sources for your problem though.. From what
>little you've said, it sounds more like a PLL stability problem.

Thank you. How can I investigate if it's a PLL issue? I'm using a 7.3728 MHz
crystal in XT mode and and PLLx16. The part can reach 30 MHz.

Cheers,
Mario

2011\11\06@215221 by Sergey Dryga

flavicon
face
Electron <electron2k4 <at> infinito.it> writes:

> Thank you. How can I investigate if it's a PLL issue? I'm using a 7.3728 MHz
> crystal in XT mode and and PLLx16. The part can reach 30 MHz.

Without knowing what part you are using, your crystal frequency X 16 >>>> 30
MHz.  Unless the crystal is divided before PLL, that would be a problem.  
Sergey Dyrga
http://beaglerobotics.com


2011\11\07@133820 by Electron

flavicon
face
At 03.52 2011.11.07, you wrote:
>Electron <electron2k4 <at> infinito.it> writes:
>
>> Thank you. How can I investigate if it's a PLL issue? I'm using a 7.3728 MHz
>> crystal in XT mode and and PLLx16. The part can reach 30 MHz.
>
>Without knowing what part you are using, your crystal frequency X 16 >>>> 30
>MHz.  Unless the crystal is divided before PLL, that would be a problem.  
This is a dsPIC30F2011, very basic PLL (x4 or x8 or x16)

Greets,
Mario

2011\11\07@143348 by Isaac Marino Bavaresco

flavicon
face
Em 7/11/2011 15:18, Electron escreveu:
> At 03.52 2011.11.07, you wrote:
>> Electron <electron2k4 <at> infinito.it> writes:
>>
>>> Thank you. How can I investigate if it's a PLL issue? I'm using a 7.3728 MHz
>>> crystal in XT mode and and PLLx16. The part can reach 30 MHz.
>> Without knowing what part you are using, your crystal frequency X 16 >>>> 30
>> MHz.  Unless the crystal is divided before PLL, that would be a problem.  
> This is a dsPIC30F2011, very basic PLL (x4 or x8 or x16)


Beware, many PLLs accept the input frequency only in a very narrow band
(say, 4MHz to 8MHz).
If your crystal frequency divided by the input divider is outside this
range, the PLL may not work.


Isaac

2011\11\07@155614 by David VanHorn

picon face
> Thank you. How can I investigate if it's a PLL issue? I'm using a 7.3728 MHz
> crystal in XT mode and and PLLx16. The part can reach 30 MHz.


PLL circuits can be very interesting to get working properly, under
all conditions.
If you are taking a 7.3728 Mhz clock and multiplying by 16, then you
are trying to run the part at 118 MHz, which seems like it's going to
be a problem. :)

What I would do:

First, get the basic system up on direct crystal oscillator, and
provide an output pin that indicates clock speed by using a timer or
pin toggle, or whatever you can easily diagnose with the tools at
hand.

Then read very carefully the PLL section of the data sheet, including
the step-by-step sequence to transition from the crystal to the PLL.
Implement per data sheet with NO shortcuts.  You may need to implement
an analog PLL filter depending on the particular part you're using.

Verify that the system is now running correctly at the proper speed.


Given that you're working in an automotive environment, are you using
regulation and bypassing designed for this?

Don't look for complicated problems when you have simple ones. :

2011\11\08@024825 by Electron

flavicon
face
At 20.03 2011.11.07, you wrote:
>Em 7/11/2011 15:18, Electron escreveu:
>> At 03.52 2011.11.07, you wrote:
>>> Electron <electron2k4 <at> infinito.it> writes:
>>>
>>>> Thank you. How can I investigate if it's a PLL issue? I'm using a
>7.3728 MHz
>>>> crystal in XT mode and and PLLx16. The part can reach 30 MHz.
>>> Without knowing what part you are using, your crystal frequency X 16 >>>> 30
>>> MHz.  Unless the crystal is divided before PLL, that would be a problem..  
>> This is a dsPIC30F2011, very basic PLL (x4 or x8 or x16)
>
>
>Beware, many PLLs accept the input frequency only in a very narrow band
>(say, 4MHz to 8MHz).
>If your crystal frequency divided by the input divider is outside this
>range, the PLL may not work.

Thank you, but this is not the case, I had checked the errata too to make sure
(indeed there're even bugs on the PLL, but only for 4x and 8x modes, while I'm
using the 16x mode).

A futher examination of the errata made me get doubts about this though, do you
think it could be the cause?

---

15. Module: PLL Lock Status Bit

The PLL LOCK Status bit (OSCCON<5>) can occasionally get cleared and generate an
oscillator failure trap even when the PLL is still locked and functioning correctly.

Work around: The user application must include an oscillator failure trap service
routine. In the trap service routine, first inspect the status of the Clock Failure
Status bit (OSCCON<3>). If this bit is clear, return from the trap service routine
immediately and continue program execution.

---

Unfortunately my app is strictly real-time and I cannot enable any interrupt. But
is this possibly causing the malfunction at near full speed?

Greets,
Mario

2011\11\08@035316 by Electron

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face
At 21.56 2011.11.07, you wrote:
>> Thank you. How can I investigate if it's a PLL issue? I'm using a 7.3728 MHz
>> crystal in XT mode and and PLLx16. The part can reach 30 MHz.
>
>
>PLL circuits can be very interesting to get working properly, under
>all conditions.
>If you are taking a 7.3728 Mhz clock and multiplying by 16, then you
>are trying to run the part at 118 MHz, which seems like it's going to
>be a problem. :)

It's within specs, the dsPIC30F2011-30 can run up to 120 MHz, the system
clock (Fcy) runs at only 1/4 of that frequency (i.e. 29.4912 MHz). :-)


{Quote hidden}

Well, yes, but currently it's on my bench, not on the vehicle. However,
when I generate sparks (I got the coil and all on my bench, it's a CDI
that I'm designing) then every n (random) seconds the MPU crashes. If
instead of the spark I use a resistor (~same discharge current of the
coil) then no problems arise, hence I thought it was an EMI problem.


>Don't look for complicated problems when you have simple ones. :)

I don't wish to complicate my life, don't worry. :-) Just to make things
reliable, as I'll race on the woods with my CDI, and a failure is gonna
cause me some problems. I may not become the enduro world champion for
example. :P

:D

2011\11\08@040140 by alan.b.pearce

face picon face
> Without knowing what part you are using, your crystal frequency X 16 >>>> 30 MHz.
> Unless the crystal is divided before PLL, that would be a problem.

The datasheet does say that you can use XT crystal mode with x16 PLL, and crystals over the range of 4 - 7.5MHz, provided the maximum operating frequency of 120MHz is met (ref table 17-1 of the Rev C data sheet). So he is within the operating parameters of the PLL.
-- Scanned by iCritical.

2011\11\08@131528 by David VanHorn

picon face
> Well, yes, but currently it's on my bench, not on the vehicle. However,
> when I generate sparks (I got the coil and all on my bench, it's a CDI
> that I'm designing) then every n (random) seconds the MPU crashes. If
> instead of the spark I use a resistor (~same discharge current of the
> coil) then no problems arise, hence I thought it was an EMI problem.


So now you're down to impedance, decoupling and layout issues.
Have you checked your design to see that all circuits are built with
the lowest practical impedance?
Decoupling can be critical. 0.1uF is not always the best value.

Build a noise probe, using a relay wired as a buzzer and a series LC
across the contacts, with the L being a small (pencil-eraser sized)
coil.  Use this to probe for weak points and evaluate.  Change design
as needed

2011\11\08@184811 by Chris Roper

picon face
> Build a noise probe, using a relay wired as a buzzer and a series LC
> across the contacts, with the L being a small (pencil-eraser sized)
> coil.  Use this to probe for weak points and evaluate.  Change design
> as needed.

Any schematics for a noise probe out there?
It sounds interesting, but I have never heard of one before,  I am
used to working with off the shelf hardware, but we are at the stage
where we need our own boards. The current design has been farmed out
to a hardware house, but it would be great to build up my own test
bench so I can QC their QC.

2011\11\09@054118 by Electron

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face
At 00.48 2011.11.09, you wrote:
>> Build a noise probe, using a relay wired as a buzzer and a series LC
>> across the contacts, with the L being a small (pencil-eraser sized)
>> coil.  Use this to probe for weak points and evaluate.  Change design
>> as needed.

Thanks, but I'm not sure I understand the implementation, nor if this
noise probe should detect EMI or should be connected to various points
in the circuit.

2011\11\09@093027 by David VanHorn

picon face
The noise probe is a small localized source of magnetic noise.

When the contacts open on the buzzer-relay, the coil inductance has
some fair energy stored that MUST go somewhere.  The series RC network
that is the probe itself provides a convenient place.   If you build
it, you can take a thruhole LED, short its leads and bend them into a
hoop, and light the LED from energy radiated up to about an inch away.

I'll try to post a schematic today

2011\11\09@134056 by Electron

flavicon
face
At 15.30 2011.11.09, you wrote:
>The noise probe is a small localized source of magnetic noise.
>
>When the contacts open on the buzzer-relay, the coil inductance has
>some fair energy stored that MUST go somewhere.  The series RC network
>that is the probe itself provides a convenient place.   If you build
>it, you can take a thruhole LED, short its leads and bend them into a
>hoop, and light the LED from energy radiated up to about an inch away.
>
>I'll try to post a schematic today.

Interesting, thanks.

So the purpose of the noise probe (on my circuit at least) would be to
deliberately cause interference, i.e. to test the reliability of my circuit?

2011\11\09@153841 by David VanHorn

picon face
> So the purpose of the noise probe (on my circuit at least) would be to
> deliberately cause interference, i.e. to test the reliability of my circuit?


Yes.  The small probe coil allows you to do this in a targeted manner.
Alternatively, you can spend some serious bucks illuminating your PCB
in a chamber at various frequencies.

I have a PDF that I can email you directly, but I don't have a way to
post it anywhere convenient

2011\11\10@065940 by Electron

flavicon
face
At 21.38 2011.11.09, you wrote:
>> So the purpose of the noise probe (on my circuit at least) would be to
>> deliberately cause interference, i.e. to test the reliability of my circuit?
>
>
>Yes.  The small probe coil allows you to do this in a targeted manner.
>Alternatively, you can spend some serious bucks illuminating your PCB
>in a chamber at various frequencies.
>
>I have a PDF that I can email you directly, but I don't have a way to
>post it anywhere convenient.

Megaupload maybe? I don't know any other free hosting sites.

Meanwhile, thank You for the eMail.. please feel free to send it! :-)

Cheers,
Mario


'[EE] ESD vs touch sensitive kitchen timer'
2014\01\06@183055 by James Cameron
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face
We live in 10% or less relative humidity, where electrostatic
discharge is the most common cause of equipment failure.  We have
exposed grounds everywhere to touch.

Our kitchen timer [1], for $4, has an LCD display and three touch
sensitive areas below it; marked minutes, seconds, and start/stop.  It
is continually powered by a pair of AAA cells.

To program the timer we press minutes or seconds until the right time
is shown, then press start/stop.

We used to be able to press start/stop at any time, but after a recent
electrostatic discharge, start will only work if we recently pressed
minute or seconds.

We used to be able to press start/stop at any time, while the timer is
running, but now we must briefly press seconds first.

Putting it another way, the only time that start/stop works is:

- within a second of pressing minutes or seconds,

- during the end of time alarm condition.

PIC, ARM, and AVR I/O pins often have separate paths for wakeup and
GPIO read.  I don't (yet) know what device this uses; probably a cheap
8051 clone.

Does this sound like an ESD failure of the wakeup path?


--

1.  (the timer is branded "propert", was purchased from Woolworths,
Australia, a sample photograph by someone else:
http://oi46.tinypic.com/5kmvjl.jpg )

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2014\01\07@195140 by David VanHorn

picon face
I don't know what you mean by separate paths for wakeup and GPIO read.
I've worked with touchsense on the AVR, and we simply scan the keys at a
low rate while sleeping.
Over a year on the tiny battery so no complaints.

ESD can definitely kill the I/O pins, especially if they didn't provide
guarding copper.
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2014\01\07@201352 by James Cameron

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On Tue, Jan 07, 2014 at 05:51:38PM -0700, David VanHorn wrote:
> I don't know what you mean by separate paths for wakeup and GPIO
> read.

Happy to explain.

The ARM core that I've most recently worked on shows a schematic for
the infrastructure in the chip that is electrically connected to a pin
on the package.

The schematic is needed because a pin has so many uses; not only GPIO,
but also selectable pullups, pulldowns, wakeup, interrupts, and
various alternate functions.

The schematic shows an input buffer for the GPIO read operation, which
is used when the CPU executes an instruction that reads from the GPIO
port.

Tied to the pin also is a pin change interrupt buffer.

By separate path, I mean that there exists some gates in a chip that
if they fail would render certain functions unavailable.

> I've worked with touchsense on the AVR, and we simply scan the keys at a
> low rate while sleeping.
> Over a year on the tiny battery so no complaints.
>
> ESD can definitely kill the I/O pins, especially if they didn't provide
> guarding copper.

While ESD can completely kill I/O pins, I'm speculating that a low
dose can also degrade certain functions first.

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'[EE]: DIY force sensitive joystick'
2015\07\31@214728 by Mike Hord
picon face
Hi all-

A complaint I've long had about video game joysticks is the relatively high
deflection
they have during use. I'm not much of a gamer, but lately I've been sucked
into the
re-release of the old Star Wars X-Wing series games.

I'd *like* to try and DIY a low-deflection force sensitive (not The Force,
mind you)
joystick, but I'm kind of having a hard time figuring out how to do this.
There are
commercial options but they are $200+.

I've toyed with the idea of strain gauges but they tend to be both pricey
and finicky.
I'm kind of trying to wrap my head around a way to use a force sensitive
resistor <https://www.sparkfun.com/products/9376> to
get a measure of the force being applied, then some other means to
calculate the
vector.

Any ideas? Bonus points if it uses mainly parts from SparkFun.com; I can
use it as
an excuse to write a tutorial or blog post and get the parts for free. ;-)

Mike
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'[EE]: DIY force sensitive joystick'
2015\08\01@044635 by RussellMc
face picon face
You can get some extremely good strain gauges in digital kitchen scales -
and some very poor ones. Odds are even the poor ones will be good enough.
By mechanically biasing one you get two axis (and may be able to use it
over a useful range without biasing.

I have seen various kitchen scales with poor accuracy, poor linearity and
quite often poor temperature sensitivity.

Quite some years ago (10+?) a local supermarket chain endlined some scales
with 2kg max reading and 1 gram resolution.
A test showed that a sample was able to resolve added or removed 2g test
weights (coins) anywhere across the range and that accuracy and resolution
allowed it to be used as a coin counter for as many hundreds of coins as I
has to hand. ie extremely good for what they were. Temperature shift was
essentially zero when heated to well over 50C - again, amazingly good.
AFAIR they have an extra gauge apart from the main bridge quad for
temperature compensation.
They sold for under $10 each as I recall. I and a friend bought the dozen
or so available and I've been 'using them up' ever since. I'll be sad when
I destroy the last one.

If a cheap looking low priced scale can achieve the above performance 10+
years ago a few hours spent in a few Kitchenware departments may reveal a
modern equivalent. (You'll need a source of warm air for likely candidates)..

You may be able to access the amplified analog signal in such devices, but
even if not adding an instrumentation amplifier per channel is affordable.




Russell
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2015\08\01@053546 by Peter

picon face
Precedent: https://en.wikipedia.org/wiki/Pointing_stick
(there are others but 2 orders of magnitude more money, typically LVDT or
resolver based)


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2015\08\01@092824 by alan.b.pearce

face picon face
> If a cheap looking low priced scale can achieve the above performance 10+
> years ago a few hours spent in a few Kitchenware departments may reveal a
> modern equivalent. (You'll need a source of warm air for likely candidates).

They will have been made accurate as they are used for trade, and so will be tested periodically by Weights and Measures (not sure which govt. department they come under in NZ these days), hence the accuracy and linearity. Because they are used for trade purposes they have to be accurate to ensure the customer isn't short changed.

Kitchen scales are a case of 'near enough is good enough' as recipes don't require high accuracy measurement of ingredients, so their accuracy and linearity doesn't need to be so good.

However for the purposes of a force joystick kitchen scale sensors should be good enough. I would have thought they would be repeatable enough when used within the sensors range that they would serve the purpose.

However for the original joystick with too much travel, is there any possibility of lengthening the distance between the hinge point of the joystick, and the point on the joystick that applies pressure to the sensor? Without knowing how these things measure the force I am just pondering the 'how to' possibilities.





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2015\08\01@130036 by Eoin Ross

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Perhaps this might work at the core? http://www.ti.com/product/ldc1614/description
They have a tool on that page for designing a coil on a circuit board.

*------------------------------
The LDC1612 and LDC1614 are 2- and 4-channel, 28-bit inductance to digital converters (LDCs) for inductive sensing solutions. With multiple channels and support for remote sensing, the LDC1612 and LDC1614 enable the performance and reliability benefits of inductive sensing to be realized at minimal cost and power. The products are easy to use, only requiring that the sensor frequency be within 1 kHz and 10 MHz to begin sensing. The wide 1 kHz to 10 MHz sensor frequency range also enables use of very small PCB coils, further reducing sensing solution cost and size.
*------------------------------

On 31/07/2015 9:47 p.m., Mike Hord wrote:
{Quote hidden}

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2015\08\01@141910 by Mike Hord

picon face
General feedback on things that have passed thus far:
1. RE: repurposing a scale. I hadn't considered finding a strain gauge in a
scale.
I expect mainly to find load cells in them BUT now am considering that a
load cell
is just a well-characterized set of strain gauges pre-attached to a bar. I
bet I can
do something with that- and we sell an assortment of load cells and
accessories. <www.sparkfun.com/search/results?term=load+cell>
2. Pointing stick seems equally valid, and maybe I'll try to source
something to
see what I can figure out by disassembly. Also, maybe a good product for us
to
start selling?
3. RE: lengthening the moment arm. Part of the problem I'm having is
finding a
means to actuate against the pressure sensor without destroying it. Also,
most
existing joysticks use either some kind of variation on optical mouse,
optical
encoder, or potentiometer to measure displacement. Force is rarely
considered.
4. Recalibrating the range is possible, but it's going to make delicate
control
even harder. Also, the Alliance upgrade is a thing I intend to use
eventually.
5. Inductance or capacitance based is a good idea.

So, I'm going to experiment with load cells, for now; it'll give me some
excuse to
go into the machine shop!

Mike

On Fri, Jul 31, 2015 at 7:47 PM, Mike Hord <EraseMEmike.hordspamBeGonespamKILLspamgmail.com> wrote:

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2015\08\01@211505 by Brooke Clarke

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face
Hi Mike:

Yesterday I was looking at the Stanford on line classes and found this:
Introduction to Haptics (Self-Paced) <online.stanford.edu/course/introduction-haptics-self-paced>
It has to do with touch sensitive control.

They have a couple of 1-dimensional control kits (one where you glue Acrylic plates together and another that's 3D printed) where a DC motor provides feedback using a custom board from Seeed Studio and a computer or Arduino.
http://hapkit.stanford.edu/
www.seeedstudio.com/depot/hapkit-p-1622.html
The kit includes a Spark Fun pressure sensor as well as an X-Y magnetic sensor to read back the motor shaft position.

You could improve on this be making a 2-axis version.  Not you can program the compliance on the control from a brick wall to very springy.
Also can add feedback like used in commercial jets where the vibrate the control stick to indicate a serious condition.

Touch, engineered: Allison Okamura at TEDxStanford <https://www.youtube.com/watch?v=pPKqW3tdWCQ>
TEDxManhattanBeach - Paulo Blikstein - One Fabrication Lab per School: the FabLab@School project <https://www.youtube.com/watch?v=ylhfpDAniqM>- Big Education Implications
that leads to:
Transformative Learning Technologies Lab <https://tltl.stanford.edu/>& FabLab@School <https://tltl.stanford.edu/project/fablabschool>

Mail_Attachment --
Have Fun,

Brooke Clarke
http://www.PRC68.com
www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html

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2015\08\01@211640 by RussellMc

face picon face

On 2 August 2015 at 01:28, <RemoveMEalan.b.pearcespamBeGonespamspamstfc.ac.uk> wrote:

> > If a cheap looking low priced scale can achieve the above performance 10+
> > years ago a few hours spent in a few Kitchenware departments may reveal a
> > modern equivalent. (You'll need a source of warm air for likely
> candidates).
>
> They will have been made accurate as they are used for trade, and so will
> be tested periodically by Weights and Measures (not sure which govt.
> department they come under in NZ these days), hence the accuracy and
> linearity. Because they are used for trade purposes they have to be
> accurate to ensure the customer isn't short changed.
>
> Kitchen scales are a case of 'near enough is good enough' as recipes don't
> require high accuracy measurement of ingredients, so their accuracy and
> linearity doesn't need to be so good.
>

​The unit I described WAS a "kitchen scale". Typical flat white plastic
type, sloping front panel with on/off and tare buttons. grams/oz switch on
back. 4 x AA cells.
Performance was (and is) well be​yond what I'd have expected - and well
beyond many others. Temperature compensation was a suprise and a joy.

Probably more suitable for trade than many "real" ones, but not intended to
be.


               Russell

Similar to many of these:

www.google.com/search?site=&tbm=isch&source=hp&biw=1280&bih=893&q=kitchen+scale+digital&oq=kitchen+scale+digital&gs_l=img.3..0j0i8i30l6j0i24.3254.9298.0.10023.21.17.0.4.4.0.251.3274.1j0j14.15.0....0...1ac.1.64.img..2.19.3291.XxC69xMFyBQ#tbm=isch&q=kitchen+scale+digital+round+white
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2015\08\02@121031 by Sean Breheny

face picon face
Russell,

What do you mean by "By mechanically biasing one you get two axis"? How can
a single analog signal represent two axes? (I can think of lots of possible
trickery where you encode a digital signal, representing two degrees of
freedom, as an analog signal - but such is inherently non-analog and I
don't think it's what you meant)

Sean


On Sat, Aug 1, 2015 at 4:45 AM, RussellMc <@spam@apptechnzspamspamgmail.com> wrote:

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2015\08\02@194022 by RussellMc

face picon face

On 3 August 2015 at 04:10, Sean Breheny <TakeThisOuTshb7KILLspamspam@spam@cornell.edu> wrote:

> What do you mean by "By mechanically biasing one you get two axis"?


​Sorry - excessively sloppy terminology on my part.
If somebody else had written that I would have taken it to mean what you
thought, so I don't know why I used that word.

What I meant was that the strain gauge is usually set up for positive
(downwards) load operation and while the mecahniical aspect will probably
work with negative (upwards) loads, the electronics may not deal well with
inverted polarity SO by applying a net positive bias you can then get +/-
variations around the zero point.

So I should have said something like "2 of the 4 possible directions"
(poor) or +/- X or Y axis operation (better).
ie 2 load cells needed.


Russell
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2015\08\03@042123 by alan.b.pearce

face picon face
> Perhaps this might work at the core?
> http://www.ti.com/product/ldc1614/description
> They have a tool on that page for designing a coil on a circuit board.
>
> *------------------------------
> The LDC1612 and LDC1614 are 2- and 4-channel, 28-bit inductance to digital
> converters (LDCs) for inductive sensing solutions. With multiple channels and
> support for remote sensing, the LDC1612 and LDC1614 enable the
> performance and reliability benefits of inductive sensing to be realized at
> minimal cost and power. The products are easy to use, only requiring that
> the sensor frequency be within 1 kHz and 10 MHz to begin sensing. The wide
> 1 kHz to 10 MHz sensor frequency range also enables use of very small PCB
> coils, further reducing sensing solution cost and size.
> *------------------------------

Hey, those look like nifty devices, might have a use for them.

Thanks for the pointer.



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'[OT] a method for avoiding oversensitive mail filt'
2016\05\09@215012 by James Cameron
flavicon
face
Here is a method for bypassing filters;

1.  use a mail client that can collapse duplicate messages,

2.  subscribe to mailing list using two or more of your mail
addresses,

As a result, each posting will arrive twice or more in your mail
client.  Enthusiastic or unusual filtering by one of your mail
providers probably won't stop the duplicate from arriving.

If you're not sure if you are being hit by filtering, compare your
incoming mail against the list archives.

On Linux my setup is fetchmail, procmail and mutt, but there are other
mail client programs that can collapse duplicates.  They are very
useful when you are copied on a mail to a list you are also subscribed
to.

-- James Cameron
http://quozl.netrek.org/
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'[EE:] Looking for thin ( & sensitive) force sensor'
2016\10\14@113201 by Joe McCauley
picon face
I'm looking for some planar sensitive force sensors that I can stick onto a flat surface. I found these:

http://www.sensitronics.com/products-1-inch-shunt-mode-fsr.php

and

http://tangio.co/products/force-sensing-resistor-single-zone-thru-mode

I'd like to find something more sensitive in a similar form factor. Ideally I'd like to detect objects impacting on the sensor which exert a force/pressure on the sensor of less than 0.01bar.

Thanks for any insights,

Joe

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2016\10\14@155808 by Jean-Paul Louis

picon face

Joe,

Google is your friend if you use “strain gauge” as a search element.

Just my $0.02,

Jean-Paul
N1JPL



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2016\10\14@160629 by Jean-Paul Louis

picon face

Joe, I forgot to add the link.

http://www.ebay.com/itm/like/261887253339?lpid=82&chn=ps&ul_noapp=true


Just my $0.02,

Jean-Paul
N1JPL



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2016\10\14@211130 by Art

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Can you use a generic/junkbox piezo element? They won't do a constant output as in 'dc', but they do produce spikes. Not sure how much accuracy/repeatability you need.

On 10/14/2016 11:31 AM, Joe McCauley wrote:
> I'm looking for some planar sensitive force sensors that I can stick onto a flat surface. I found these:
>
> http://www.sensitronics.com/products-1-inch-shunt-mode-fsr.php
>
> and
>
> http://tangio.co/products/force-sensing-resistor-single-zone-thru-mode
>
> I'd like to find something more sensitive in a similar form factor. Ideally I'd like to detect objects impacting on the sensor which exert a force/pressure on the sensor of less than 0.01bar.
>
> Thanks for any insights,
>
> Joe
>

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2016\10\17@035053 by Joe McCauley

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The idea was to take a very sensitive commercially available planar sensor and compare to a new sensor material under development. I guess we're looking for accuracy & reputability.

I've never tried piezos for this, though I was aware they could be used for force sensing. I have no feeling if one could be calibrated to do what I want. detecting spikes as a result of a 'hit' is OK as long as the amplitude scales with the force of the strike.

Ideally I'd be wanting a commercial sensor tough.

Thanks,

Joe



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From: RemoveMEpiclist-bouncesspamspamSTOPspammit.edu <.....piclist-bouncesEraseMEspammit.edu> on behalf of Art <spamBeGoneky1kspamRemoveMEmyfairpoint.net>
Sent: 15 October 2016 02:11:24
To: Microcontroller discussion list - Public.
Subject: Re: [EE:] Looking for thin ( & sensitive) force sensors

Can you use a generic/junkbox piezo element? They won't do a constant
output as in 'dc', but they do produce spikes. Not sure how much
accuracy/repeatability you need.

On 10/14/2016 11:31 AM, Joe McCauley wrote:
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2016\10\17@075827 by Andrew Burchill

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Hi Joe,
google 'grain loss sensor'
these have been in use for the agricultural industry for a few decades now.
most of them are constructed in such a way that the sensor is isolated as
much as
possible from the underlying structure that uses them.
output is usually proportional to impact velocity or particle size.


On Mon, Oct 17, 2016 at 5:50 PM, Joe McCauley <.....PMCCULEYEraseMEspamtcd.ie> wrote:

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2016\10\20@033601 by Joe McCauley

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More piezos! Any ideas what a single grain might weigh? I know it depends on the type, but a ballpark number would be good.


Joe

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Sent: 17 October 2016 12:58:25
To: Microcontroller discussion list - Public.
Subject: Re: [EE:] Looking for thin ( & sensitive) force sensors

Hi Joe,
google 'grain loss sensor'
these have been in use for the agricultural industry for a few decades now.
most of them are constructed in such a way that the sensor is isolated as
much as
possible from the underlying structure that uses them.
output is usually proportional to impact velocity or particle size.


On Mon, Oct 17, 2016 at 5:50 PM, Joe McCauley <RemoveMEPMCCULEYRemoveMEspamRemoveMEtcd.ie> wrote:

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2016\10\20@035005 by James Cameron

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On Thu, Oct 20, 2016 at 07:35:56AM +0000, Joe McCauley wrote:
> Any ideas what a single grain might weigh?

65 milligrams.

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2016\10\20@092242 by RussellMc

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On 20 October 2016 at 19:49, James Cameron <quozlKILLspamspamspamlaptop.org> wrote:

> On Thu, Oct 20, 2016 at 07:35:56AM +0000, Joe McCauley wrote:
> > Any ideas what a single grain might weigh?
>
> 65 milligrams.
>

​Almost.
It's
64.79891 milligrams
​ exactly.

That's exactly approximately.
Or approximately exactly.
Or, exactly, on average.
​
.
https://en.wikipedia.org/wiki/Grain_(unit)

http://www.convert-me.com/en/convert/weight/grain.html

____________________________

Wikipedia says:

The grain was the legal foundation of traditional English weight systems
<https://en.wikipedia.org/wiki/English_mass_units>,[5]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-Rowlett2001-5> and is
the only unit that is equal throughout the troy
<https://en.wikipedia.org/wiki/Troy_weight>, avoirdupois
<https://en.wikipedia.org/wiki/Avoirdupois>, and apothecaries' systems
<https://en.wikipedia.org/wiki/Apothecaries%27_system> of mass.[6]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-NIST-6>:C-6 The unit
was based on the weight of a single grain of barley, considered equivalent
to  1 1⁄3 grains of wheat.[5]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-Rowlett2001-5>[7]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-Ridgeway1889-7>:95 The
fundamental unit of the pre-1527 English weight system known as Tower
weights <https://en.wikipedia.org/wiki/English_units#Troy_and_Tower>, was a
different sort of grain known as the "wheat grain".[8]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-8> The Tower wheat
grain was defined as exactly  45⁄64 of a troy grain.[1]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-McDonaldScarre1992-1>
:74

Since the implementation of the international yard and pound
<https://en.wikipedia.org/wiki/International_yard_and_pound> agreement of 1
July 1959, the *grain* or *troy grain* (Symbol: *gr*) measure has been
defined in terms of units of mass in the International System of Units
<https://en.wikipedia.org/wiki/International_System_of_Units> as precisely
64.79891 milligrams <https://en.wikipedia.org/wiki/Milligram>.[6]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-NIST-6>:C-19[9]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-nbs447-9> 1 gram is
approximately 15.43236 grains.[6]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-NIST-6>:C-13 The unit
formerly used by jewellers to measure pearls
<https://en.wikipedia.org/wiki/Pearl>, diamonds
<https://en.wikipedia.org/wiki/Diamond>, or other precious stones, called
the *jeweller's grain* or *pearl grain*, is equal to  1⁄4 of a carat
<https://en.wikipedia.org/wiki/Carat_(unit)>, or 50 mg (~ 0.7716 gr).[5]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-Rowlett2001-5> The
grain was also the name of a traditional French unit
<https://en.wikipedia.org/wiki/Units_of_measurement_in_France> equal to
53.115 mg.[5]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-Rowlett2001-5>

In both British Imperial
<https://en.wikipedia.org/wiki/Imperial_units> and U.S.
customary units
<https://en.wikipedia.org/wiki/United_States_customary_units>, there are
precisely 7,000 grains per avoirdupois pound, and 5,760 grains per troy
pound or apothecaries pound.[6]
<https://en.wikipedia.org/wiki/Grain_(unit)#cite_note-NIST-6>:C-6–C-7

​
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2016\10\20@112025 by Joe McCauley

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Well it seems everyday is still a school day! I had no idea a grain in the sense of the crop was a standardised unit of weight. Then again, why not, its what people dealt in.

I love the "thirty-two grains of wheat, taken from the middle of the ear" part.

Thanks to all who contributed,

Joe

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2016\10\20@114235 by Joe McCauley

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I notice my last two posts to the list come back to me with a header on the message indicating that I may not be who I purport to be " This sender failed our fraud detection checks and may not be who they appear to be. Learn about spoofing at http://aka.ms/LearnAboutSpoofing"

I don't believe that its my PC as the first one was sent from my phone. I did not have that message attached to the message I sent on Monday last.

Anyone have any ideas whats happening? I'm posting from my work account which is usually secure.....

Joe


{Original Message removed}

2016\10\20@115954 by alan.b.pearce

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I think this message is being put on the mail being sent to you from the piclist, as it certainly wasn't on the message that you replied to when your reply reached me.

Maybe your ISP doesn't like the 'piclist-bounces' part of the sender address.



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2016\10\20@162826 by Joe McCauley

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I'll look into the piclist bounces aspect so. I've only seen this on the last couple of messages I've sent to the list though. Never on any other messages I've sent, or indeed messages from others.

Joe
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Sent: 20 October 2016 16:59:50
To: spam_OUTpiclistRemoveMEspam.....mit.edu
Subject: RE: [EE:] Looking for thin ( & sensitive) force sensors

I think this message is being put on the mail being sent to you from the piclist, as it certainly wasn't on the message that you replied to when your reply reached me.

Maybe your ISP doesn't like the 'piclist-bounces' part of the sender address.



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'[PIC] [EE] Internal RC sensitive to PCB flex?'
2017\11\02@170141 by Van Horn, David
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Is there any documentation on sensitivity to PCB flex when using the internal RC?
I have seen this on SAM7 chips and I think it's happening on a 24F chip.

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2017\11\02@184715 by Sean Breheny

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I don't know about documentation but I have seen this before but I cannot
remember whether it was with a 16F88 or dsPIC24. I noticed it only when I
applied pressure directly to the package of the chip, though. I would
suspect that anything which applies pressure to the die will change the
value of resistors and capacitors on the die.



On Thu, Nov 2, 2017 at 5:01 PM, Van Horn, David <
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2017\11\03@111427 by Van Horn, David

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I verified yesterday that it is happening, and that it's not just temperature.  On external crystal a pin toggle based on a timer is dead constant.  On internal RC, applying torque to the board wobbles the oscillator like a theremin.


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