I bought a single channel relay on eBay and besides the NC/COM/NO, it has six pins and a jumper.


It is not possible to see the labels on the image, but the labels are:

X  X--X  X  X  X
VCC   -IN+   GND

The default jumper position is shown above with a - mark.

Which pins should I use for VCC, GND and ARDUINO? Is the jumper on the correct position?

2 Answers 2


Your module consists of both an optocoupler (large black rectangular device) and a P-channel MOSFET driver circuit for the relay.

VCC and GND are used to power the MOSFET and relay, and so should be connected to a power source suitable for driving the relay (if it's a 5V relay then the +5V and GND pins of the Arduino - if it's a 12V relay then a 12V power supply).

The interface to the Arduino is through the optocoupler. The Arduino sees that as just an LED, so you can wire it up just like any other LED. The circuit contains a current limiting resistor already, so you don't need to worry about that at all. So you connect the - of the input to GND and the + to an IO pin, or connect the + to +5V and the - to the IO pin, depending on which polarity of drive you want to have.

The jumper is optional to allow you to create one of those two links on the board - say connecting - to GND or connecting + to VCC so you don't need the extra wire.

  • I tried it and I was able to control the relay (there is a led to indicate the relay state), but the relay itself apparently didn't active (no sound) and the NC/COM didn't switch to COM/NO. Is this a faulty relay?
    – thiagolr
    Nov 29, 2015 at 12:17
  • 1
    It may be, but unlikely. Be sure that you are providing the right voltage to VCC.
    – Majenko
    Nov 29, 2015 at 12:19

You should do a bit of testing. The Vcc and GND pins will go to power and ground respectively. They are powering the circuitry on the board that protects the Arduino from the relay coil. Then it looks like the IN pins allow you to operate the relay either from an active high or an active low signal.

If you have a DMM check the connections of the pins (see if any of them are common). The thing that is puzzling to me is the jumper, but it may be set up so that you can use only two wires to control the relay by using the IN terminal to also supply either Vcc or ground.

So start out by hooking up to power and ground, and then test by jumping the IN pins to ground and power in turn. I would expect the relay to operate when the IN+ goes to Vcc or when the IN- goes to GND.

  • The two VCC pins and the two GND pins are common. I was able to control it with the other answer.
    – thiagolr
    Nov 29, 2015 at 12:18

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