4pcs DC 5V Relay Module - 1 Channel Relay Switch Board with Optocoupler Isolation, High or Low Level Trigger

Served my purpose very well.

These are fine set of relays, which trigger reliably from Raspberry Pi. My experience with such boards has been hit or miss because Raspberry Pi’s high pin voltage is not really that high. This board performs beautifully without the need to enhance the trigger voltage.

I am very happy with these small devices. I only tried a few of them and they work great on my bench! Good price for 4 of them. Only negative thought is the screw terminals are not the best, they do work, but not very good. If the screw terminal does fail over time, I will just solder the wire in place and ignore the terminal.Update Mar 03, 2023:My only complaint is the mounting holes on the board. The board is too small and the holes are too close to the edge of the board, and too close to the terminals. Difficult mounting and using screws. They need to make the board "bigger" in size to allow more spacing for mounting.

This function used to be called a "VSER" or voltage-sensitive electronic relay. It has a front-end comparator which measures the voltage of a DC signal, then it energizes a relay when the measured voltage falls within the preset range. We used this device to interface with a Gamewell fire alarm , then used the relay to activate a light and a bell. In the recent past, this function required a small custom circuit, but the relay handles it perfectly. High current capacity in the relay (10A) allows many uses with small computers to drive large loads from voltage outputs.

All of the relays came dead on arrival. None of them worked. Is what I would have said if the pin out was exactly the same as the 12 volt module but it's not. Whoops.

Happily switches US mains voltage. Requires 5v supply but this allows you to control it with an I/O pin, which is handy because You could run the relay module off VBUS of the same controller board.

I use this device to provide a mute circuit in a bias T I made for a remote antenna pre-amplifier. A control line which goes to ground when my transmitter is activated, connected to the low input, triggers the relay. Works well.Edit: I have built two different mute circuits using this device. They work well. But a few learning points have emerged.As other reviewers have noted, the screw terminals merit close attention to ensure they have adequately secured the wires you connect to it.Secondly, there is a voltage present on the sense input equal to the supply voltage. It appears to be a very high impedance source. That phantom voltage may affect the circuit you have it connected to. It did in my case. I solved this by placing a Schottky diode at that input port, which isolated the other equipment.I still recommend this module. Just keep these other two factors in mind. They are easily resolvable.

Once of these modules was intermittently closing the relay with a 4.5V source, fully capable of 300mA+. Sometimes it wouldn't close, and the relay would need to be physically tapped for it to actually close. I measured the current to that whole module at 81mA when closed. Yes, that's not the full 5V, but I found it worrying. I replaced it with another module and the replacement was able to consistently close with a voltage all the way down to 3.8V. The draw on that module was 95mA. So these have a large variance in tolerance. You may want to test each module to see if it can handle small voltage sags.