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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:


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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


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2 years ago

Just an FYI. Your link to a spreadsheet is broken.

“I’ve posted a spreadsheet for calculating the resistor values (and amp hour formulas) at

Hmm. We’re having trouble finding that site.

We can’t connect to the server at

If that address is correct, here are three other things you can try:

   Try again later.
   Check your network connection.
   If you are connected but behind a firewall, check that Firefox has permission to access the Web.
Reply to  B.A.T.Man

Sorry, but Yahoo shut down groups a year or 2 ago, so the link won’t work.

11 years ago

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

Steve Spence
11 years ago

Code is listed at

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

11 years ago

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

11 years ago

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 .

Steve Spence
11 years ago

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

samia hussain
7 years ago

nice post


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