Monday, April 30, 2012

Voltage Monitor

Now that we have the current monitor working, the next step is to build the voltage monitor circuit. I built a voltage divider that will break down the highest voltage my battery can possibly see, into a 0-5v input for the Arduino. Here is a great tutorial explaining the math behind determining the resister values,, and a schematic of our version:

Here is a screen shot of the monitor showing both current and voltage being monitored.

Now the trick is to multiply the current with the voltage to get watts.

The next step is to sample over time to display the amp hour and watt hour values. Still working on that. I've posted a spreadsheet for calculating the resistor values (and amp hour formulas) at

There's a good discussion of this project at


  1. Hello can you put the code for the last image attached on your post? Thanks very much

  2. Code is listed at

    just replace the lcd print statements with Serial.print().

  3. Thanks very much ! I will reply if my project works.

  4. Hello again, I have some problems with the readings. I have done with this exemple to read a 5v. What I'm doing wrong ? Here is an image with the readings .

  5. The example you posted is a current sensor, not a voltage sensor.


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