I built this circuit but it doesn't seem to work at all. The load is a lamp at 230V, the triac a bt138 and the optocoupler a moc3011. I've tested the zero crossing and microcontroller (5V) portions before it and they both work as planned. Is there anything i am missing here?
thanks

 

You need some current from MT2 to turn on the gate. I suggest a circuit like the one below.

 

So i should just add a resistor from the gate of my schematic to the MT that's connected to my lamp? I did that with a 500Ω resistor but nothing changed. Lamp stays off..

 

If the output of your optocoupler a triac just move the existing 330 ohm resistor to the MT (MT2) that is connected to the lamp so that the 330 ohms and the optocoupler are in series with the gate. Then add another 330 ohm resistor from the gate to MT1 to prevent false triggering.

 

So i should just add a resistor from the gate of my schematic to the MT that's connected to my lamp? I did that with a 500Ω resistor but nothing changed. Lamp stays off..

Move R5 from Mt1 to Mt2 terminal, make sure the lamp is connected to the Live and Mt2, to test the triac, short out the Gate and Mt2 with a 1K resistor the lamp should light up.

 

Ok, i changed the circuit and the lamp does light up but doesn't listen to the dimmer, it stays on even if i don't trigger the triac. Does it matter if i interchange the pins 6 and 4 of the moc3011?

 

Ok, i changed the circuit and the lamp does light up but doesn't listen to the dimmer, it stays on even if i don't trigger the triac. Does it matter if i interchange the pins 6 and 4 of the moc3011?

It might. Most power triacs are not as sensitive in some combinations of input and power line polarities. The MOC3011 may have the similar characteristics.

It is best to stick with the circuit as shown in the data sheet and post #2.

 

When you don't trigger the triac what signal if any is across the input of the coupler?

Also, did you put a resistor between the triac gate and MT1?

 

Here is an example of how to connect it, Note MT2 goes to Hot, MT1 to Neutral, the load can be in either the Hot or Neutral connection.

Ideally can you post your full circuit diagram.

 

Added the resistor between gate and MT1 and it now works.