Video: Voltmeters aren't terribly expensive, but it's always more fun to build your own devices. YouTube DIYer Educ8s builds a cheap voltmeter for less than $15 using an Arduino and a voltage sensor. A multimeter that measures voltage is one of those devices every electronics tinkerer should have, but sometimes the key to really understanding how to use a device is to make your own. In this case, you'll just need to connect a few cables together, set up the Arduino and be on your way to measuring all the voltage you could possibly want. It's pretty accurate too, but the real fun comes from learning how it all works. Head over to YouTube for the guide.
Arduino Project: DIY Voltmeter [YouTube]