Review on 💡 SainSmart 4-Channel Relay Module: Versatile Control for Your Electrical Devices by Aaron Parish

This is a very well made relay module. Diodes are installed on the relay to protect the microcontroller from back EMF. There is a jumper on the VCC that can be used to create a kill switch. Each relay has a status LED. Each relay has three terminals: common, normally open, and normally closed. As others have noted, the instructions for use are poor at best, but to control a specific relay with a microcontroller one simply has to pull the relay pin low to turn it on and high to turn the relay off. I would have preferred screw terminals for connecting the microcontroller to the module instead of a straight 6 pin header