An Arduino Voltage Meter Serial Interface. Can take a reading from Arduino (to which you must connect a voltage sensor) and display it neatly on the computer. The connection is made via serial on 9600 baud rate. You can adjust these for your needs.
Pretty much you can connect one of those very popular voltage sensors to your Arduino and code it to send the values via serial. The program can detect the COM PORT of most Arduinos automatically but if it doesn't, you can specify it manually. The program can be modified to work with those Serial-ready multimeters if you want too, but that's outside the scope.
Made just for fun. I am sure it can be improved in many ways, I am not a huge fan of coding on Windows (I am a Mac user) so feel free to come with improvements.
It pretty much looks like this:
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