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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.


  • 1x Relay Shield PCB
  • 1x GSLA SPDT 5A Relay
  • 1x Red LED, 3mm
  • 1x 100uF 10V Capacitor
  • 1x 0.1uF 25V Capacitor
  • 1x 2N4401 Transistor
  • 1x Screw Terminal, 3-pos
  • 1x Arduino Header Set
  • 2x 1000 ohm 1/4W Resistor
  • 2x 1N5817 Diode


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What a mess!

Ordered 3 kits. -One came pre-assembled but looked like it had been soldered with a candle. So bad it will almost certainly fail in field, bad soldering, poorly cut wires etc -One came missing one part -One was fine

Who knows how this happened but it was a major disappointment.

Hi, No kits should be pre-assembled. It sounds like a return that managed to get back into our inventory. We would not resell that item intentionally. I’ll be in contact with you directly to help resolve this matter. Thanks