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'[PIC]: Operation of PICs from low voltage'
2000\06\06@231614 by Russell McMahon

picon face
Still coming to grips with this new fangled system - gotta put : after PIC
they tell me to ensure all the pure PIC people see it .... mumble, mumble
... try again.


QUESTION

Based on actual experience. - What is the lowest Vdd at which a 16F84 will
operate (including occasional EEROM read/write) reliably using an RC clock
at about 1 MHz?

Yes. I know what the data sheets say.
Yes, I know the answer is try it and see.
Yes, I know the results will vary.
No - I don't (yet) know what other people have tried and found works.

BACKGROUND:

Based on random aged 16F84 data sheet:

- The std 16F84 is specified to operate at a minimum Vdd of 4.5 V
- The 16LF84 is specified down to 2 volts

I am building a small 16F84 device where portability and battery life is
important (wearable aid for a disabled person), Essential aim is to drive a
beeper subject to certain constraints - irrelevant to following. Device will
be carried in top pocket / worn on cord around neck / clipped to clothing so
user but hopefully few others can hear the occasional beep. Another variant
may drive a pager vibrator instead.

I am running a 16F84-10 (10M parts happened to be in parts drawer)  .

This runs happily with physically small 3.6V 80 mAH NiMH battery and RC
clock (33K, 18pF) at 1MHz osc = 25o KHz PIC basic instruction rate.
This is very adequate for my task.

At 3.8V it draws 250 uA
At 2 volts it is still running and clock frequency has not moved markedly
and draws 100uA
At 1 volt it is STILL running but clock is MUCH slower (~ factor of 10?) and
draws under 10uA (!)

I don't need to run at 1 V but ability to run at 2V is interesting.
I haven't tried eerom read/writes yet at 2V.

What have other people found about low voltage operation of "standard"
parts.
Is this perhaps another example of Microchip 'select on test"ing parts and
many std parts are in fact capable of low voltage operation?

Yep - I could (try to) buy some 16LF84's but ...



TIA

       Russell McMahon

2000\06\07@024802 by William Chops Westfield

face picon face
A somewhat related question: Are the "low voltage" PICS generally similar to
the "high speed" parts?  Ie, identical execpt for testing?  That is, are the
chances pretty good that a standard 5V part will run at 3V or so?

BillW

2000\06\07@111937 by Bob Blick

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Only experience I've had is running a PIC16F84 on two alkaline C cells at
4 MHz. Ran fine down to 2.6 or 2.7 volts, whereupon it had trouble
starting the oscillator, but I didn't spend any time tweaking the
oscillator, because by that time the batteries were low enough that the
rest of the circuit wanted fresh batteries(not pic-related).

This was crystal controlled, likely RC oscillator will run at lower
voltages with no tweaking just like your experience showed.

Also it was not the low-voltage part, don't know if there's any real
difference in silicon.

For those interested, it was a radio-controlled remote "talkback" switch
that generated MIDI for a Yamaha O2R mixer. I used a wireless doorbell and
disabled the boinger. Put a 16F84 in the receiver to generate MIDI note-on
and note-off(the Yamaha mixer accepted all sorts of commands through MIDI
and talkback was one of them). Then the "producer" got to hold the
doorbell button and could push it whenever he wanted to talk to the
"talent", saving him from having to ask the engineer to push the talkback
button on the mixer. heh. Birthday gift for my nephew the engineer.

-Bob

2000\06\07@121455 by stouchton

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At the old company, we were running PIC's @ 2V and below before anything was
spec'd that low.  The xtal oscillators were very finnicky(?), but the RC
would always get up and fly (pretty much it has too by design).  We did see
RAM problems when the processor was cold (<32F).  Basically, bits flipped on
their own accord.

Processors we were using were the C54, L84, and the LF84.  Had success with
all of these (>85% yield).  LV parts are what is standardized on now, 100%
yield.

LP oscillator leaves alot to be desired at 5 volts in term of startup,
wouldn't even try it at 2 volts!!!

Most parts listed above would fly down to 1.8V, but I would be nervous about
the bit flipping issue.

2000\06\08@034239 by JP.BROWN
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One surprising experience I had was to find that the 16F84 would run
happily with a supply voltage of zero volts!, yes thats right zero volts,
on further inspection of the circuit I found that the 16F84 was leaching a
supply from the I/O pins (the external circuit was independently supplied)
Even though I have had years of experience with other microcontrollers the
PIC chip still surprises me with it's flexibility, robustness and other
unexpected qualities (I am amazed to hear that it will run down at 1V).

On Wed, 7 Jun 2000, Bob Blick wrote:

{Quote hidden}

         -----  John P. Brown      spam_OUTJ.P.BrownTakeThisOuTspambradford.ac.uk ----
          \            --- Witty remark goes here ---         /
           --------------------------------------------------

2000\06\08@040023 by James Wilson

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Of course it's not the IO input circiut leaking - it's the pair of static
protection diodes. One conducts from 0V to IO pin, the other from IO pin to
Vcc. These diodes can be used for other things like putting mains directly
into a PIC simply by current limiting. You can tie 240VAC (UK) into a pic
that's battery powered. Tie Neutral to 0V and LIVE to IO pin  via a 10M
resistor. This can be used to synchronise the PIC with the phase of the AC
and to derive an accurate 50Hz time base (very accurate over a period, less
so over short times). The 10M resistor limits the current and the static
prtection diodes leak the small current through to the battery. First time
you rig it up take a deep breath before switching on!

| -----Original Message-----
| From: JP.BROWN [.....J.P.BrownKILLspamspam@spam@BRADFORD.AC.UK]
| Sent: 08 June 2000 08:48
| To: PICLISTspamKILLspamMITVMA.MIT.EDU
| Subject: Re: [PIC]: Operation of PICs from low voltage

| on further inspection of the circuit I found that the 16F84
| was leaching a
| supply from the I/O pins (the external circuit was
| independently supplied)

2000\06\08@040621 by Mike Witherden

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Yup I had one running with no supply as well. I was watching
what happened to the output on a scope when I removed the battery
supply. The signal just kept on going! (way off freq and greatly
attenuated) but still measurable.

MikeW

>>> .....J.P.BrownKILLspamspam.....BRADFORD.AC.UK 06/08/00 09:47AM >>>
One surprising experience I had was to find that the 16F84 would run
happily with a supply voltage of zero volts!, yes thats right zero volts,
on further inspection of the circuit I found that the 16F84 was leaching a
supply from the I/O pins (the external circuit was independently supplied)
Even though I have had years of experience with other microcontrollers the
PIC chip still surprises me with it's flexibility, robustness and other
unexpected qualities (I am amazed to hear that it will run down at 1V).

2000\06\08@131118 by Jilles Oldenbeuving

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>First time
>you rig it up take a deep breath before switching on!


Where i work they let pic's run off 220V AC, trough a couple of
resistors and an X2-type capacitor, or capacitive power supply.

Jilles

2000\06\08@131732 by Andrew Kunz

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Any relation of this one with your previous note about blowing up the JW part?

Andy










Jilles Oldenbeuving <EraseMEjillesspam_OUTspamTakeThisOuTRENDO.DEKOOI.NL> on 06/08/2000 01:12:25 PM

Please respond to pic microcontroller discussion list <PICLISTspamspam_OUTMITVMA.MIT.EDU>








To:      @spam@PICLISTKILLspamspamMITVMA.MIT.EDU

cc:      (bcc: Andrew Kunz/TDI_NOTES)



Subject: Re: [PIC]: Operation of PICs from low voltage








>First time
>you rig it up take a deep breath before switching on!


Where i work they let pic's run off 220V AC, trough a couple of
resistors and an X2-type capacitor, or capacitive power supply.

Jilles

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