It's always interesting to see people make their own test equipment based on the Arduino platform, and the following example by Milen Penev is a great workable example. Milen's shield allows for measurement of not only voltage and current, it also includes resistance, transistor beta and more.
Even if you're not interested in making your own, this is an interesting tutorial that explains some theory behind test and measurement - and if you do wish to make your own, Milen has provided the EAGLE files to download and have your own shield PCB manufactured. Finally a quick demonstration is shown in the following video:
Kudos to Milen for such an great Instructable, which can be found here. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.
If you need to add external hardware or devices to your next Arduino project, you'll need a protoshield to mount the external circuitry. In doing so, consider our range of ProtoShields. From the tiny LeoStick to the Mega.