int AC_LOAD = 3; // Output to Opto Triac pin
int dimming = 128; // Dimming level (0-128) 0 = ON, 128 = OFF

void setup()
{
pinMode(AC_LOAD, OUTPUT);// Set AC Load pin as output
attachInterrupt(0, zero_crosss_int, RISING); // Choose the zero cross interrupt # from the table above
}

void zero_crosss_int() //function to be fired at the zero crossing to dim the light
{
int dimtime = (75*dimming); // For 60Hz =>65
delayMicroseconds(dimtime); // Wait till firing the TRIAC
digitalWrite(AC_LOAD, HIGH); // Fire the TRIAC
delayMicroseconds(10); // triac On propogation delay (for 60Hz use 8.33)
digitalWrite(AC_LOAD, LOW); // No longer trigger the TRIAC (the next zero crossing will swith it off) TRIAC
}

void loop() {
for (int i=5; i <= 128; i++){
dimming=i;
delay(10);
}
}