I want to control an LED using a relay.. How to I connect the pins of one channel relay to control and led which is connected to pin 13 of an arduino uno.can you tell me the steps which pin will go to which pin

  • 1
    Unclear. Do you mean to use the Arduino pin 13 LED signal to drive the relay? Or some other LED to be controlled by the relay?
    – Dave X
    Commented Mar 7, 2016 at 8:02
  • I insert an LED on pin 13 ....so I want to control that
    – user18794
    Commented Mar 7, 2016 at 8:59
  • 1
    You need no relay to control a LED. Merely a resistor to limit the current. See the 220 ohm resistor in series with the LED in the tutorial at arduino.cc/en/Tutorial/Blink -- they insert a LED in pin 13 in series with a resistor to Ground.
    – Dave X
    Commented Mar 7, 2016 at 9:04
  • Are you asking which are the outputs and which are the inputs of the relay board? Look at the bottom of the board and compare it to the datasheet of the relay: langir.com/pdf/pcb-relay-T73.pdf
    – Dave X
    Commented Mar 7, 2016 at 15:55
  • But in my relay I don't have any sign like normal connection,command connection and all so I want to know which one is what
    – user18794
    Commented Mar 7, 2016 at 16:03

3 Answers 3


Wiring Diagram to Pin 13 for a single relay? This might help. enter image description here


I believe that the Arduino ground should be common with the 12v source ground. I may be wrong, though that's the way it works for me. Also be aware that some of these relay cards work when the pin is LOW, others when the pin is HIGH. Mine energises when the pin is HIGH, though all tutorials I had read until the last had the relay switching on with a LOW pin.

  • This relay has "Normally Open (NO)" and "Normally Closed (NC)" outputs. Applying voltage would "invert" these.
    – aaa
    Commented May 9, 2016 at 9:53

It looks like http://www.elesof.com/electronics/product/one_6v_spdt_relay_board , http://shop.ciseco.co.uk/jqc-3f-t73-5v-pcb-relay/ and it probably works like http://www.electronics-tutorials.ws/blog/relay-switch-circuit.html

I'd bet that the I/P line connects to the center pin on the transistor through one of those resistors. If so, I'd put a 5V 100mA source on the GND +5 pins on the side, then I'd use a jumper from the +5 on the end to the I/P on the end, and see if it triggers the relay as expected.

If so, I'd siconnect the jumper and I'd connect the end terminal's GND to the arduino GND, and (maybe?) pin 13 to the I/P line and expect the Blink tutorial that blinks the Arduino's LED to click the relay in time.

If you are asking which are the outputs and which are the inputs of the relay board, I can't tell from the pictures. Look at the bottom of the board and compare it to the datasheet of the relay: http://langir.com/pdf/pcb-relay-T73.pdf --

enter image description here

I'd bet that screw terminals are the outputs, connecting to the right hand pair of outputs, and the center of the left hand three inputs. And that the control terminals are the pin connectors, with the I/P conneting through the transistor to one end of the coil, with the other end of the coil going to the +5V/12V pin connector. There are likely two sets of pin connectors to provide for a separate coil/relay supply on the GND,5V12V connector versus a signal or signal plus power on the GND,I/P,5V/12V pin connector. I'd bet the same-named pin connectors are electrically identical. i.e. GND=GND and 5V/12V=5V/12V.

If you are controlling other than low voltage devices with this, I suggest you make certain you are safe before applying potentially dangerous currents.

  • Of course I don't need a relay for led but if I want to control an AC bulb..and can you tell me which one is command,normal connection of relay on that image
    – user18794
    Commented Mar 7, 2016 at 9:50
  • 1
    Common is always in the center, facing the terminals NO will be on the left in most cases and NC on the right.
    – dinotom
    Commented Apr 21, 2016 at 20:34

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