Voltage Range of Analog Inputs

[Al Skierkiewicz]

Many of the ideas presented here are good ones but there are some potential hazards.
1. (My personal favorite) Measuring battery current on a working robot is best done with a current meter like an AmpProbe or other similar device. These are clamp on meters that will not put your controller (or you) in the presence of the several hundred amps that may be periodically delivered by your battery.
2. I would frown on any resistance you add between the battery and controller. The controller resets at about 8 volts and a resistor will get you close under extreme loads. Feed the controller from the battery side of the resistance.
3. If you are not sure how to do it, don't connect circuitry to the robot controller inputs except as listed in the manual. A bad hit on the analog input is a fatal (i.e. permanent, non warranty) failure.
4. Opening the circuit and inserting a voltmeter would prevent anything from working and should read near the battery terminal voltages. (Open circuit voltage)
5. Much truth about the variable battery internal resistance, it also varies from unit to unit due to production variances. Ironically, it is the internal resistance that ends up dropping the available voltage to the robot during large current draws. When the voltage is so low that it drops below 8 volts (controller dropout) it is because four volts is being dropped across the internal resistance.
Good Luck All,
Al