I was thinking worst case would be it needs an op amp to drive the input. But really a pull down/voltage divider resistor should work fine. I drove it home with the scope running the whole time and the voltages never changed, so once I get a balance point above/below 2.5V it should be fine long term I figure.
Having to divide the voltage between 14 and 11V should not be that hard though really. The zener can protect the AVR from over voltages and the two resistors as a voltage divider should be all that is needed. I will try out this weekend first with a 100k pot pulldown and a lcd scope I have that will be good enough to see the voltages now that we know what we are looking for.
Code:
R1
___
to AVR ---+------+---|___|-- Inj Input
| |
.-. |
| | z
R2 | | A 5.1V Zener
'-' |
| |
GND GND
One of these days I will quit making you add stuff to the schematic
