As the name suggests the CANADUINO MEGA 2560 PLC 500 is based on an Arduino MEGA 2560 compatible computing module and comes in two versions for 100-240V AC line power (model 500 AC) or 12-24V DC ...

They are designed to operate at 24V. He wanted to use these with common ... After working the bugs out of the design he was able to control the relay using 3.3V, 5V, or 12V.