I'm having a hard time understanding how an optocoupler works. I made a circuit based on example 15 if the Arduino projects book. Instead of trying to hack a button, I'm trying to just light an LED on either side of the optocoupler. I'm misunderstanding how this should work because the LED I'm trying to light doesn't light.

My youtube video shows my circuit. You can see the blue LED which runs from pin 2 of the optocoupler into ground lights up, but the red LED (which works, I verified) which runs from pins 4 to pin 5 of the optocoupler does not. I was under the impression that if I emitted high from the arduino to the pin 1 of the optocoupler through a 220 resistor (mine is 270 actually) and provided a path to ground that the optocoupler would be switched on and I would get current and ground from the pins on the other side.

Any suggestions - what am I missing?

  • \$\begingroup\$ Please write the part number of the optocoupler. A circuit diagram would be good too. \$\endgroup\$
    – Gunnish
    Aug 6, 2013 at 15:33
  • 1
    \$\begingroup\$ Or a link to the "Example 15". Usually there are 2 seperate power and grounds in use with an opto-isolator. It maybe looks like only one is connected? You can't really diagnose with out a schematic like @gunnish said. here is a link to an arduino to an optocoupler example on youtube. youtube.com/watch?v=Gxa5l3gD8bc \$\endgroup\$
    – EE_PCB
    Aug 6, 2013 at 16:29
  • \$\begingroup\$ WHICH Arduino projects book? \$\endgroup\$
    – Passerby
    Aug 6, 2013 at 17:09

1 Answer 1


Re: Comments - the project book is titled the Arduino Project book. It comes with the Arduino Uno starter kit.

Re: Schematic - yea, I'm not quite at making those yet. Next time :(

Re: The answer -

I just figured it out, soooo...silly me. Optocouplers don't supply their own power. They're just a switch. So in the example video above there is nothing powering the 2nd LED.

The working model with both LEDs lit is here: http://www.youtube.com/watch?v=_CF1xPcXGNY&feature=youtube_gdata_player&desktop_uri=%2Fwatch%3Fv%3D_CF1xPcXGNY%26feature%3Dyoutube_gdata_player&nomobile=1

This link was super helpful in case anyone else stumbles on it: http://www.technogumbo.com/projects/Learning-to-Use-an-Optocoupler-or-OptoIsolator/


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.