AVR-Chat

Kat, errrr, 9.23uA x 10 ohms = 92uV (9.23e-5), not 10uV.
:)

----- Original Message -----
From: "Kathy Quinlan" <kat-yahoo@kaqelectronics.dyndns.org>
To: <AVR-Chat@yahoogroups.com>
Sent: Friday, May 21, 2004 12:07 AM
Subject: Re: [AVR-Chat] low-battery detection, ADC, and ICP of mega16


> jay marante wrote:
>
> > are you sure you got your formulas right?!
> > that's just a voltage divider and im pretty sure you can't generate
> > 650kV from a 12V battery. im sorry but i can't remember the formula for
> > the voltage divider circuit.
> > maybe someone might confirm that the multisim was right with its output.
> > as far as i know, current can be computed by dividing Vbatt over the
> > total resistance, which is 1,300,010 ohms. pretty low current there!
>
> >      >
> >      >       battery
> >      >          |
> >      >         <
> >      >         > 1.3 Mega ohm
> >      >         <
> >      >          |
> >      >          |------------------- ADC7   ~ 5V as simulated in
multisim
> >      >          |
> >      >         <
> >      >         > 10ohm
> >      >         <
> >      >          |
> >      >      GND
> >      >
>
>
> Work it the other way, I = V/R = 12/1,300,010 =
> 9.2306982253982661671833293590049e-6 A
>
>
> Now we know that V=IxR = 9.2306982253982661671833293590049e-6 x 10 =
> 9.2306982253982661671833293590049e-5V or ~10uV at the ADC7 input...
>
>
> I think the 10 ohm resistor needs to be higher say 10K and the 1.3M
> resistor lower say 13K which would make the ADC voltage 5.21 V now for
> saftey I would use a 15K resistor on the top.
>
>
> All this is hypothetical if you are using the internal Aref as it is
> only 2.56V (haaaaaa why be so presise with the voltage ie to 2 decimal
> places when heat and supply variations make it nowhere near that acurate)
>
> I would use an external Vref something like a 4.096V reference chip.
>
> Regards,
>
> Kat.
>
> --



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.688 / Virus Database: 449 - Release Date: 5/18/2004