Several battery manufacturers specify the EOL (End Of Life) point of
their batteries in their documentation. Eveready ("Energizer Bunny"
folks have published several books on the subject; Duracell does too.

Google for 'em.

--

I too have had extremely good luck with a 0.01uF to 0.1uF cap right on
the ADC input, but keeping the the analog input enabled for aquisition
all the time places the input impedance error into the calculation.

To use this correctly: turn on the analog input only a few uS ahead of
the sample time, then read it, then turn it off immediately. You will
notice a tiny movement on the scope at the acquisition time when the
0.1uF charges the ADC input cap. You'll obtain a very accurate reading
this way.

--Bob




fred jones wrote:
> ===================================
> I don't need a lot of
> accuracy, just a ballpark figure (say, tenths of a volt,
> +/- 50 mV) to let the user know when to change the
> battery.
> ==================================
>
> I have a question.  At what voltage do you read from the 9v battery do you
> determine that it should be changed?  I am building a device using some 9v
> alkaline batteries and I am putting a low battery indicator circuit to
> light
> an LED but not really sure at what point you should have it trip and light
> the LED to tell the customer it's time to change the battery.
> Thanks,
> FJ
>
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--

Replier: Most attachments rejected
       --------------
         Bob Axtell
PIC Hardware & Firmware Dev
   http://beam.to/baxtell
       1-520-219-2363

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