This is a video of the Gertboard being put through its paces in the Darlington array relay switching tests. There is a Darlington array on the Gertboard that can drive up to six relays. Each can switch 50V and 0.5A. This video shows the program Gert provided to test this functionality (and train us how to use them too).
On the video I talk about relays. In fact I mean relay drivers. My bad.
via RasPi.tv http://raspi.tv/2012/gertboard-relay-testing