I have one of these single-relay boards and I am trying to control it with my RasPi's GPIO. (I'm a complete noob).
I am using WiringPi and in this particular case I'm using pin 1 (aka BCM pin 18) as the control pin. From the relay board, I have the + pin wired to the RasPi's 5v, the - pin to RasPi's ground and the S pin to the control pin.
As soon as I connect the wires, the relay clicks and its led turns on. If I run a program that turns it on and off every 3 seconds, the relay's led turns on and off, but the relay stays connected (it doesn't click either). If I disconnect the control pin or gound then it clicks and turns off.
What am I doing wrong? Do I have to ground something else? I thought that by sending a LOW signal to the control pin, I was effectively sending it 0v, which should turn off the relay, but that doesn't seem to be the case.
Closeups of the relay board: Back and Front
Update:
I've gotten it to work by using the 3.3v pin on the RasPi instead of the 5v. Could anyone explain why the 5v + GPIO pin on LOW doesn't go to 0v, but to 1.5? Will having my 5v relay connected to the 3.3v damage it?