@hhalibo said in 
4-channel switcher/dimmer:
is 220v
My English not so good, sorry. I say about low voltage on Atmega. There should be not less than 3.3v. If it is less then may not be enough current to open the optocoupler.
D1 i not problem. The zero crossing detect works correctly. You see it on LEDs.
@hhalibo
What supply voltage? 3.3V?..
Usually if properly assembled, there should be no problems.
@Andrea-Boarino
Hi! It is Sanhe enclosure. I have bought it in Ukraine.
@hhalibo
Check for neutral and phase connected right. I can see only one wire of load connected to X1. Other one must be connected to neutral if on X4.1 is phase. Otherwise try to reduce down to zero R5,7,9,11. May be not open the optocouplers.
@Samuel235, It is just my first project and it has some weaknesses. But thanks for the comment, I will use it in future.
@tonnerre33,
Thank you for your interest to my device.
The fuse installed to protect the mains 220V from short circuit in the device. Phase need to be connected to the device through a circuit breaker. It will protect from dangerous potential and this allows the lamps to be served safely. But you're right. It would be properly to put the fuse on the phase.
Looking at my experience I can say that never had a problem without varistor. But probably in the future I will add it to the board.
Updated description and been added the source code.
@esawyja,
No, triacs used without radiators and under severe conditions for a long time can not work. In practice, I have loaded a maximum of 360W.
@tbowmo said in 4-channel switcher/dimmer:
Would you mind adding the schematics as a PDF file
Yes, I add it soon.