AVR-Chat

Thank you, gentlemen.

I was afraid the information was hiding in the datasheet despite my search.  Yes, Table 18-7 is included in my copy as well.

A 10 Mohm divider indicated would put my standing current at a tolerable 1.x uA.  I like the idea of a FET switch to turn the divider "on"; I have a pin and code space to spare.  I do want to keep the circuit simple as well.

I am including a calibration routine to set response thresholds (2 led status indicators), so I have convinced myself that variations of the internal reference voltage from chip to chip shouldn't matter.  If however, internal Vref is influenced greatly by environment, I may have to rethink that point.

I also like the idea of "floating" the ground of the monitor circuit, compressing the readable range and giving better resolution.  I am only a hobbyist, so I have to put some thought into the implications of presenting a voltage below Vgnd to the A/D pin, even with the chip un-powered.

I plan to average four conversion values (easy math) before comparing with the calibration values in EEPROM.  Slow is fine for this application.  Is this method ill advised?

Thanks again for the warm welcome.

Stu