[geeks] 9v battery meter

[Dave McGuire]

On Friday, January 10, 2003, at 01:27 PM, Kurt Huhn wrote:
>>    So...with that in mind, it might actually be better to get a PIC
>> processor with an on-chip A/D converter and drive a bunch of LEDs from
>> that.  That'd be dead simple (and fun) to build and write the little
>> smidgen of firmware for, and that way you can simply build a
>> translation table in memory to map the incoming A/D values to the LED
>> scale based on the battery chemistry in question.
>
> Way more time than I wanted to devote to this - a project that really 
> has no
> more value than creating blinkenlights (at least to me).
>
> Oh well, maybe just a chaser for the blinky effect unless I could do
> something else.  I recall seeing a meter that used a bunch resistors 
> for
> this, but if what you say about the output of batteries is correct, 
> this
> wouldn't work for most cells.

   Well, not very accurately.  Most such meters will have three or four 
LEDs at most, so the inherent nonlinearity of the discharge profile is 
hidden in the low resolution of the display.

   The resistors were simply a chain of voltage dividers.  The LM3914 
chip I mentioned uses this scheme, with the resistor network driven 
from a voltage reference, and with a comparator at each one...so each 
LED turns either all the way on or all the way off.

   Don't give up on it yet...The PIC circuit really wouldn't be very 
difficult to build, and it would be fun.  And it'd be a great way to 
get into PICs in particular and microcontrollers in general, if you're 
not already.

   A possibly easier alternative might be a Basic Stamp.  They're even 
easier to program, and could do this with ease.

          -Dave

--
Dave McGuire           "She's a cheek pincher.  I have scars."
St. Petersburg, FL                          -Gary Nichols