Monitor Battery Voltage on bot

Since I use standard 7.2v RC battery packs on my bot can I use one of the analog inputs to monitor the battery voltage?

Or is 7.2 volts to high?


7.2V is too high, but use a voltage divider to measure, say, half the voltage.


Since I have the Mega board and it has a 3.3 v terminal

Could I use that?

I would assume as the battery drains i loose voltage at the 3.3 v terminal?

I would just have to figure out the relationship between 7.2 and 3.3


I would imagine that the 3.3 line is pretty well regulated, such that it won't drop until the supply voltage is under 4-ish volts...

Another idea is to use the voltage drop of a zener diode to lop a chunk off the voltage. With a 5.6V zener between the positive and your voltage divider, you would only see the last 1.6V at the A-D sensor. Once the battery dips below 5.6V you'll see 0V, but the state-of-charge when the voltage drops that low is "totally exhausted".

My plan is to display the battery voltage on my 2x16 lcd

thats mounted on the bot chassis

Note that the reference voltage needs to stay constant to get accurate readings.