Description: This Relay Shield from Evil Mad Scientist is a simple Arduino add-on that gives your Arduino the ability to control a single electromechanical relay for switching loads of up to 24VDC or 40VAC. Each Relay Shield comes equipped with a single pole - double throw (SPDT) sealed relay which can handle a current load of up to 5A. This means that when current is applied to the coil it throws a simple changeover switch, terminating the connection from the NC (Normally Closed) contact to ground and closing the NO (Normally Open) contact. Use them to switch high voltage/high current devices. As this is a shield, it is powered straight from the 5V power supplied by your Arduino, simply slide it into your Arduino or shield-compatible board (like the RedBoard) and you will be good to go!
The relay shield is controlled through pin Digital 4 on your Arduino via a transistor labeled "Q1". When output Digital 4 on your Arduino is low, the relay shield will connect the NC pin to the "Common" pin of the screw terminal. When output Digital 4 goes high, the “Coil On?” LED will light up and the relay shield will instead connect the NO pin to the "Common" pin of the screw terminal.
The Relay Shield is sold as an easy-to-assemble kit and includes everything listed below with clear assembly instructions listed in the documents section.