Monitoring Battery Condition

[bdickens]

Anyone got a simple ( ie beginner level) way to measure the volt/amp condition of a set of nicads with a microcontroller ? I need to make sure that the batteries driving my tethered robot are ok and have it return if they drop below a certain point. 7X1400mah cells.

[Faulkner]

One simple way is to connect a voltage regulator like a 7812 or 7809 and a potentiometer to the battery. The output of the regulator will be constant despite the batteries' voltage, but the voltage over the resistor will drop as the battery dies. By wiring the two to an op amp, you can compare the voltages; when the potentiometer's voltage drops below the regulator's, the op amp will change its output, which your microprocesor can register.<p>You could also try putting a zener diode reverse-biased from the battery. When the voltage drops below the ZD's threshold, it will stop allowing current through. Hook it to a transistor, and you have a voltage- controlled switch.
ZD N---- 5volts (collector)
+ ------- ]<------P (base)
(emitter) N----- to microprocessor