Review on 🔴 Highly Effective 8 Channel 5V Relay Module with Optocoupler Isolation for High/Low Level Trigger Relay Support – Red Board by Kim Aguilar

It's useful to have this 4 channel relay board because it works equally well with 3.3V and 5V logic (although the power supply itself has to be 5V). Also, you can configure each channel individually to trigger the relay either high or low. With the jumper in the L (low) position, the input line rises to around 4.3V, allowing for an open collector driver, while at 5V only 2mA is required to activate the relay. In the jumper position H (high) the relay pulls in at 1.7V and drops out again when the voltage drops below 1.5V like the fact that the board has been relocated around an air gap around the common terminal of the relay to provide additional isolation between the high voltage and logic parts of the circuit.