I bought this 1 channel relay module but the board doesn't have any marking on it. Can someone tell me which pins are power, ground, relay on/off signal etc?
Photograph of module:
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If I see it correctly you have a JQC-3FC/T73.
You can see the pinout here. Use this pinout to know which contact of the relay's the NC NO and Coil. Now follow the lines where it's headed to and what connector the NC NO and Coil are.
Relay has three connections - Common - C, Normally Open-NO, Normally Closed-NC brought out to 3 pin screw terminals which makes it easy to make and remove connections.
Determining NO and NC is something you must do using a continuity tester or ohmmeter. I guess the middle terminal is common.
relay control signals are brought to header pins on the board.
The two remaining 2 pin screw terminals are used for powering the module. However, from the photo you made I can't figure which is +12V and which is GND. If you trace the PCB, you'll see that those terminals are connected, so you can apply power on the one you want. It is possible that the lower terminal of each connector is +12V because it seems that it goes to the anode of the LED.
This should be the schematic:
Note that D1 should be reverse biased. It seems to me (I'm not sure) that it is connected the other way in your PCB. Look here for relay driver examples.