led optocoupler circuit diagram

LED Optocoupler Circuit

This LED Optocoupler circuit uses two ordinary LEDs as the optocoupler element. When a voltage of 2V is fed to the input, LED 2 will generate a voltage that is strong enough to switch on transistor T5. The upper frequency limit is around 38 kHz. Very low pulse frequencies are almost meaningless for the circuit.

Eventhough the LEDs are quite intensive to stray light, it is a good idea to enclose them with an opaque box. Resistor R2 must be selected basing on the power supply voltage. It can be between 680Ω and 1KΩ. Resistor R11 must not be lower than 220Ω.
Transistor T6 has an open-collecter character.

Optocoupler Circuit Diagram

led optocoupler circuit diagram

Optocoupler PCB and Parts Placement


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  • shailaja

    actually we put resistor at input side then capacitor in parallel to any circuit…why here kept like that to opto coupler?

  • shailaja

    why capactor kept starting then resistor? is is not possible the resistor at input side then capacitor

  • Jorge

    With this circuit I have the same exact signal between Out+ and Gnd than in In+ and Gnd? thank you.

  • mep

    Hello! Why would we use such a large amount of components when we can do it so much simpler? just two resistors, a transistor and a IR LED for the emitter and an opto-transistor with a pull-up resistor in the collector for the receiver part.. just wondered.


      Maybe because with those 5 transistors working as voltage amplifiers you will get enough voltage at the optocoupler output.

    • mep

      I used the circuit I mentioned for a lab project to connect a telephone line to a PIC and it worked 100% :\


      mep, then maybe you can send me an email with the project you are talking about and with your permission I will publish it on the website. Thank you.

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