I built an effects box for use in my performance. It works by switching two inputs into one output. It works for audio, video and would even do 240V mains power if required.
This small board fits on top of the Arduino as a shield. It contains a transistor to drive the switching relay.
This little board contains the relay and has terminals to attach the things you want to switch (left and right). It has two wires that activate the relay (bottom).
I attached three jack sockets to the relay. There are two inputs and one output, or you can use it the other way around with two outputs and one input.
These two pots control the speed the relay switches. As you turn the pots the arduino software adjusts the switching speed. I have experimented with two different ways of doing this. It is nice to be able to change the behavior of the equipment with software, without needing to rewire or solder anything.
I prefer to use these small bits of veroboard rather than breadboard for prototyping, mainly because it feels more like making something, and because veroboard gives a better electrical connection. I broke up the circuits into smaller parts and joined them together with connector blocks and bus wire. Many of the parts used are were recovered from other equipment.
The affect of the switch when used with audio is to create a rhythm out of almost any video or sound input. It can be used with only one input, switching between sound and silence. It can also switch very fast, creating an intense barrage of sound.