Hi Leandro,

Try to fire the Triac from the pulsed out put from your micro. Make a DC flasher from a port of the micro and flash an LED.

The replace the LED with the opto coupler and connect that to the triac according to the proper schematic.

The triac should flash turn on and off.

Now for your dimming:

I have done it the same way, i.e. using zero crossing for the interrupt.

1. make sure the interrupt is transition type.

2. make sure you are not using a zero crossing opto coupler for triac driving.

3. you can use MOC3020 kind of opto of Motorola.

Where you are getting the AC signal for the external interrupt ??

Hope above helps


Simon