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'[EE]:monitoring computer voltage with 16F877'
2001\12\12@115126 by Brandon Stewart

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I want to monitor the 5 and 12 volts from my computers power supply.  I had
thought of using the PIC A to D ability.  BUT I WOULDN'T WANT TO JUST BASE
THIS OFF OF A VOLTAGE DIVIDER THAT WAS ALWAYS SINKING CURRENT OFF OF THE
POWER SUPPLY WOULD I??  Anyone know of a good, cheap, high impedance IC that
will do this, maybe even with an 8bit digital output!!???  How would you do
this?  IT IS FOR AN X_MAS PRESENT SO PLEASE RESPOND SOON!!!

Thank You,
Brandon

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2001\12\12@115741 by David VanHorn

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At 11:49 AM 12/12/01 -0500, Brandon Stewart wrote:
>I want to monitor the 5 and 12 volts from my computers power supply.  I had
>thought of using the PIC A to D ability.  BUT I WOULDN'T WANT TO JUST BASE
>THIS OFF OF A VOLTAGE DIVIDER THAT WAS ALWAYS SINKING CURRENT OFF OF THE
>POWER SUPPLY WOULD I??

Why not. It won't notice the extra milliamp, trust me.


>  Anyone know of a good, cheap, high impedance IC that
>will do this, maybe even with an 8bit digital output!!???  How would you do
>this?  IT IS FOR AN X_MAS PRESENT SO PLEASE RESPOND SOON!!!

Either divide it down, or use a zener to trim off the bottom, and give you
better resolution.


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2001\12\12@120159 by Dal Wheeler

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WHY NOT!?!?
----- Original Message -----
From: Brandon Stewart <brandonstewartspamKILLspamMEDIAONE.NET>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Wednesday, December 12, 2001 9:49 AM
Subject: Re: [EE]:monitoring computer voltage with 16F877


> I want to monitor the 5 and 12 volts from my computers power supply.  I
had
> thought of using the PIC A to D ability.  BUT I WOULDN'T WANT TO JUST BASE
> THIS OFF OF A VOLTAGE DIVIDER THAT WAS ALWAYS SINKING CURRENT OFF OF THE
> POWER SUPPLY WOULD I??  Anyone know of a good, cheap, high impedance IC
that
> will do this, maybe even with an 8bit digital output!!???  How would you
do
> this?  IT IS FOR AN X_MAS PRESENT SO PLEASE RESPOND SOON!!!

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2001\12\12@125316 by Mitch Miller

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I think his concern is that if he's using the PC's supply as his
reference, and it begins to sag, the reference will sag with it.  Did I
interpret that right?

-- Mitch


On Wed, 12 Dec 2001, Dal Wheeler wrote:
> WHY NOT!?!?
> {Original Message removed}

2001\12\12@133422 by Andre Abelian

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Brandon,

Why are you worry about a few ms current? you can use any pic with 2
Analog inputs and send the result thru rs232 to hyper terminal to
Display the voltage. I am sure you can find some IC's to do similar
Job too but to me using pic is better, cheaper and smaller.

Andre Abelian


>I want to monitor the 5 and 12 volts from my computers power supply.  I
had
>thought of using the PIC A to D ability.  BUT I WOULDN'T WANT TO JUST
BASE
>THIS OFF OF A VOLTAGE DIVIDER THAT WAS ALWAYS SINKING CURRENT OFF OF
THE
>POWER SUPPLY WOULD I??  Anyone know of a good, cheap, high impedance IC
>that
>will do this, maybe even with an 8bit digital output!!???  How would
you do
>this?  IT IS FOR AN X_MAS PRESENT SO PLEASE RESPOND SOON!!!

>Thank You,
>Brandon

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2001\12\12@140757 by Paul Hutchinson

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That was my impression as well.

The solution is to derive a stable reference voltage from the power supply
being measured.

For me a quick and easy way to get the stable voltage is to use a LT1009
precision 2.5 volt reference. Then feed it's output into a 2X non-inverting
amplifier to get a stable 5V reference for the A/D. You should to power the
op-amp off the 12V (or +/-12V) supply to allow the use of a cheap op-amp.

Paul Hutchinson

{Quote hidden}

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2001\12\12@205413 by Bob Ammerman

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Or just use a 75L05 regulator sourced by the the 12V power rail, and
apporpriate decoupling to provide a solid +5V for both the PIC and its
reference.

Bob Ammerman
RAm Systems

{Original Message removed}

2001\12\13@015740 by dr. Imre Bartfai

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If you want to have a relatively exact reference at low cost, use
LM336-5.0. I agree with another colleagues the some mA's at the
measurement of 12V is no concern (I guess you want to power the PIC from
the PC also). Another remark: I guess 16F877 would an overkill
here. 16F870 would suffice (28 pins also, has an USART, too, costs less
than half of the former one).

Regards,
Imre


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On Wed, 12 Dec 2001, Bob Ammerman wrote:

> Or just use a 75L05 regulator sourced by the the 12V power rail, and
> apporpriate decoupling to provide a solid +5V for both the PIC and its
> reference.
>
> Bob Ammerman
> RAm Systems
>
> {Original Message removed}

2001\12\13@050159 by Vasile Surducan

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On Thu, 13 Dec 2001, dr. Imre Bartfai wrote:

> If you want to have a relatively exact reference at low cost, use
> LM336-5.0. I agree with another colleagues the some mA's at the
> measurement of 12V is no concern (I guess you want to power the PIC from
> the PC also). Another remark: I guess 16F877 would an overkill
> here. 16F870 would suffice (28 pins also, has an USART, too, costs less
> than half of the former one).
>
 Imre, what do you think about an 627/628 with an extra operational
amplifier chip (with 2 OA inside ) and a simple slope AD converter.
There is an application note ( with 16C622 I think) on Microchip CD.
Will be definitely cheaper than 16F870, but a little dizzy in software.

Vasile

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2001\12\13@052053 by dr. Imre Bartfai

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Hi,

the difference at us between F627/8 and F870 is below $1. I do not think
it is the effort worth (the opamp is about $0.50).

Regards,
Imre


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On Thu, 13 Dec 2001, Vasile Surducan wrote:

{Quote hidden}

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2001\12\13@054735 by Vasile Surducan

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unfortunately not here !
F87x is extremely expensive ( about 13...15 USD )
regards,
Vasile

On Thu, 13 Dec 2001, dr. Imre Bartfai wrote:

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2001\12\13@164323 by Michael Noel

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Hi Vasile,

Try to Ecas srl. Tel: 01 2302550
PIC16F877-04P = 18DM-( USD 7.8  in Ro!)
PIC16F628-04P= 8.3DM-(USD 3.8 in Ro!)

Regards
Miki

Vasile Surducan wrote:

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2001\12\14@020142 by dr. Imre Bartfai

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Incredible! 16F870 costs $3- pro pcs, even 16F877 costs $6. In Hungary
there is a dedicated distributor named ChipCAD. Another resellers have a
markedly higher price level, though.

Regards,
Imre


On Thu, 13 Dec 2001, Vasile Surducan wrote:

{Quote hidden}

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2001\12\14@035745 by Bala Chandar

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It's surprising to see the vast difference in PIC prices!
Here, (Mumbai, India) a 16F877-20 costs around US$7.00 and a 16F870-20 costs
US$3.95 in quantities less than 10!
For volume purchases, the prices will be lower.

Regards,
Bala


> On Thu, 13 Dec 2001, Vasile Surducan wrote:
>
> > unfortunately not here !
> > F87x is extremely expensive ( about 13...15 USD )
> > regards,
> > Vasile

Imre Bartfai wroe:
> Incredible! 16F870 costs $3- pro pcs, even 16F877 costs $6. In Hungary
> there is a dedicated distributor named ChipCAD. Another
> resellers have a
> markedly higher price level, though.

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2001\12\16@220113 by ards, Justin P

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AU$ 19.80 for a 16F877-20

It's surprising to see the vast difference in PIC prices!
Here, (Mumbai, India) a 16F877-20 costs around US$7.00 and a 16F870-20 costs
US$3.95 in quantities less than 10!
For volume purchases, the prices will be lower.

Regards,
Bala


> On Thu, 13 Dec 2001, Vasile Surducan wrote:
>
> > unfortunately not here !
> > F87x is extremely expensive ( about 13...15 USD )
> > regards,
> > Vasile

Imre Bartfai wroe:
> Incredible! 16F870 costs $3- pro pcs, even 16F877 costs $6. In Hungary
> there is a dedicated distributor named ChipCAD. Another
> resellers have a
> markedly higher price level, though.

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2001\12\17@032036 by Vasile Surducan

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SUPER, multumesc mult !
Vasile

On Thu, 13 Dec 2001, Michael Noel wrote:

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2001\12\18@095434 by Cristian C.

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Imre, let me know the address/www/e-mail of ChipCAD, please.
Thanks,
Cristian

At 12/14/2001, you wrote:
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2001\12\19@021226 by dr. Imre Bartfai

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Hi,

very simple: http://www.chipcad.hu
They have integrated address; just dunno.

Regards,
Imre


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On Wed, 19 Dec 2001, Cristian C. wrote:

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2001\12\19@052701 by Vasile Surducan

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Imre, unfortunately these guys which have realy cheapest IC than anywhere
in Romania doesn't sell outside the hungarian border !
I've buy an 877 last year from them and was cheaper than an 16F84 buyed
in Romania ! Here everything has a +VAT to an another VAT and so on...
Regards, Vasile

On Wed, 19 Dec 2001, dr. Imre Bartfai wrote:

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2001\12\19@054703 by dr. Imre Bartfai

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Hi,

just in case u can try Robtron Electronics (http://www.ret.hu) in Szeged. They
are not so cheap and lead only selected PICs, but maybe they sell also
abroad.

Regards,
Imre


On Wed, 19 Dec 2001, Vasile Surducan wrote:

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