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

This board *does not *work* reliably with Raspberry Pi. It is designed for 5V control inputs like those on the Arduino, while the Raspberry Pi 3, 3V used on its GPIO pins. There is a jumper on the board that can be removed to allow the input side of the optocouplers and 5V to be applied to the relay side, but I found that 3.3V was not enough to reliably trigger the relay. But there is a solution: just short-circuit the four LEDs. When they're on, they drop about 1.7V, which happens to be the difference between 5V and 3.3V. The relays then work reliably from the Raspberry Pi, although the displays no longer work, of course. But you still won't see them when the board is in the box.