Monitoring Battery Level
Monitoring Battery Level
(OP)
I need to have my micro-controller monitor the battery level. The CPU runs off of a regulated source, but battery is about 1.5 volts above the regulated voltage and can not be fed directly into the ADC. I do not want to use a simple voltage divider because it would always be drawing power. I have only one general purpose pin available, but I might be able to open up one more if really needed. Suggestions?





RE: Monitoring Battery Level
Keith Cress
kcress - http://www.flaminsystems.com
RE: Monitoring Battery Level
There are many battery monitor chips available. What type of battery are you using?
RE: Monitoring Battery Level
3 AA. The uC runs off of a 2.7V regulator.
RE: Monitoring Battery Level
Another approach would be to use very high value resistors in the voltage divider to minimize leakage, but have a little capacitor in parallel with the sample to give you enough voltage for enough time to measure into your lower impedance input.
Another approach would be a simple serial resistor to divide the voltage with the input Z. And then use software to calibrate it back into reasonable accuracy.
RE: Monitoring Battery Level
If it's not 5 volt compliant, you might end up drawing some small current through the divider resistors and the input protection diode. (It won't cause any damage since the voltage divider resistors will limit the current.) If that's the case you might want to drive an external N channel MOSFET to enable the divider.
Set the GPIO pin to a LOW output to read the divider down battery voltage.
Some processors have this sort of function, with an internal voltage divider built in. Check the documentation.