Jon Titus
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Re: Part V: Tricks With PIC: Using the Trusty PIC Microcontroller
Jon Titus   1/20/2012 5:36:05 PM
Q: What would be your recommendation for measuring Battery voltage thru a micro A/D, say a 9-volt battery?  Simply using a voltage divider causes current draw while the micro is shut down.


A:  Yes, if you use two resistors to create a voltage divider you continue to draw current all the time.  Use a small NPN transistor between the resistors and ground and turn it on with an output pin at logic 0.  Then current will flow through the resistors and you can measure the voltage.  Just account for the voltage drop across the NPN transistor when you calculate the resistor values needed to get a voltage you can measure.

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