A simple library for controlling the Freetronics 8-Channel Relay Driver Shield http://tron.cc/r8
To include in your project, clone this repo into /Documents/Arduino/libraries/RelayShield
#include <Wire.h> in your project
#include "RelayShield.h"
Instantiate the library with RelayShield* relay = new RelayShield();
To turn a relay 1 on, use relay->on(1)
To turn it off, use relay->off(1)
Refer to the example to see it in action.
Relays can be used for switching high voltages. Be careful when tinkering. Never touch a live wire and be aware of residual charge from capacitors even after a circuit has been opened!