Was not aware of the 0.5% reference -- would be nice to find that on=20
larger PIC's, so I'll have to search.  I went with the 12F675 rather=20
than any 10F as IIRC the 10F's only have 8-bit A/D's, so there's another=20
advantage.

Cheers,
-Neil.


On 7/23/2012 3:25 PM, Dwayne Reid wrote:
> I second the choice of 12F675 - its one of my favorite chips. My=20
> current favorite small chip is the 10F322. Its available in both=20
> sot-23-6 and DIP8 packages. Its advantage over the 12F675 is that it=20
> has a built-in voltage reference for use with the a/d converter. Its a=20
> two part measurement - measure the built-in reference, measure the=20
> external battery voltage, then divide the two results to get a=20
> relatively accurate battery voltage reading. Or - you can do what I do=20
> when using a 12F675 - power the chip with a LP2950A low-power 5V=20
> regulator. The "A" variant is specified at 0.5% accuracy. I also like=20
> the idea of the LED flashing when the battery voltage is low - that=20
> makes it stand out when there is a problem. For extra points, make the=20
> flash rate proportional to how low the battery voltage is: rapid=20
> flashing when the battery is approaching the end of run-time. If you=20
> set the low voltage threshold appropriately, the LED will flash while=20
> the engine is starting (typical 10.5V - 11V at battery terminals). If=20
> you really want a good indication while the car is starting, get the=20
> battery sample voltage where the heavy cable connects to the starter=20
> so that you can see the effect of the voltage drop on that cable while=20
> the starter is cranking the engine. dwayne=20


--=20
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