AVR-Chat

thanks, kat. i already figured this out. got a computer from an internet site. i would prefer 100 ohms for the upper resistor and 125 ohm for the lower resistor. would this be alright? i'll use this as the analog input to the ADC to monitor the batter voltage. i'll use the VCC as the reference voltage. i just saw in the datasheet how to conenct the VCC as the reference voltage.
 
-jay

Kathy Quinlan <kat-yahoo@kaqelectronics.dyndns.org> wrote:
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.

-- 
---------------------------------------------------------------
K.A.Q. Electronics      Website: www.kaqelectronics.dyndns.org
IM: Yahoo: PinkyDwaggy  MSN: katinka@kaqelectronics.dyndns.org
For Everything Electronics     Phone: 0419 923 731
---------------------------------------------------------------      

Yahoo! Groups SponsorADVERTISEMENT


---------------------------------
Yahoo! Groups Links

   To visit your group on the web, go to:
http://groups.yahoo.com/group/AVR-Chat/
  
   To unsubscribe from this group, send an email to:
AVR-Chat-unsubscribe@yahoogroups.com
  
   Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. 


		
---------------------------------
Do you Yahoo!?
Yahoo! Domains - Claim yours for only $14.70/year