I have a solar panel charged battery device I had boards made for and I now need to monitor the battery for low voltage so I can shut down the processor.
The battery is 4v the panel can only produce 4.5V so there is no regulation, the mega48v can run it down to 1.8V, not a good idea.
So, I had 4 extra pins I ran traces too in case I needed them, and no one is not an ADC. They are pins 11,12,13 and 5.
My thought is to put a resistor from 11 to 12 and another resistor from 12 to 13. Then jumper a wire from ADC5 (pin28) to 12 to get a voltage reading using the 1.1V internal reference like I do for the solar panel voltage reading. Pin 12 will stay tristate as I am just using the hole in the board and not the pin. Pin 11 will go high and pin 13 will go low and then I will read the ADC.
The brow-out levels selectable are 1.8 , 2.7 and 4.3 and I want to shut down at 3.5V
Is there a different way to do this with what I have on the board to modify the circuit board in some way that would be easier than the one I described above. The 4 open holes are big enough to get three 1/6th watt resistor wires in so it should not be much of a problem.
By the way I went with the .125 mA regular fuse on the positive side of the battery terminal wire and a reverse diode across the battery terminals on the board to protect reverse battery hookup instead of the resettable fuse because without the holes in the board it just got too messy.