I made this dimmer circuit:


simulate this circuit – Schematic created using CircuitLab

And it does not work (no light). I have looked up other circuits that serve the same purpose and they seem to be different on a few points:

  • There's a capacitor C1 (can't really tell its purpose)
  • They use another TRIAC (BT136)
  • The resistance at the optocoupler is less than 1kOhm

moc3021 opto isolator triac circuit

Another thing I could think of is that I wired the TRIAC wrong: I connected the optoisolator to T1 and G of the BTA16 800B


Several suggestions have been given in the answers. I removed the red LED, changed R2 to 500Ohm and I rewired the TRIAC. I tested the circuit with a 3.3V battery. It work, can't tell which part was the crucial solution.

  • \$\begingroup\$ you have not posted all of the available information. i do not see any mention of the status of the red LED. \$\endgroup\$ – jsotola Dec 19 '17 at 18:09
  • \$\begingroup\$ What's the output voltage from the PI? \$\endgroup\$ – winny Dec 19 '17 at 18:18
  • \$\begingroup\$ The LED gets turned on/off at 100Hz 3.3V, I can see the led being turned on \$\endgroup\$ – Mehdi Nellen Dec 19 '17 at 18:40
  • \$\begingroup\$ Your two Vf in series is much too close to your Vcc. If you see the red LED flashing, you are supplying current and it's unlikely to be your problem here but you can't put it into mass production like that. \$\endgroup\$ – winny Dec 19 '17 at 20:43
  • \$\begingroup\$ Test the triac with a 1k resistor from A1 to G \$\endgroup\$ – τεκ Dec 19 '17 at 21:29

Your Opto-Triac needs to be connected between G and A2.

More likely the reason your lamp does not light is you are placing two LEDs in series on a DIO pin that only provides 3.3 V.

Run the two LEDs in parallel with separate resistors fed by the DIO pin.

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  • \$\begingroup\$ tried both, problem got solved, but also tried the suggestion of @drtechno \$\endgroup\$ – Mehdi Nellen Dec 19 '17 at 22:13

Ihe indicator diode in your circuit should be in parallel instead of series. Also, the 1K should be sized value wise for proper gate current.

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  • \$\begingroup\$ I used a 500Ohm resistor \$\endgroup\$ – Mehdi Nellen Dec 19 '17 at 22:14

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