Before i really left my home,

Is 60Hz is your AC line frequency? In this case, use this frequency to generate interrupt and then play with timing.

One another thought, i don't know if your PIC have a PWM module. Case yes, Use this pin an let it run @ 120 HZ at whatever duty cycle. Connect this PWM pin to another pin who can give you interrupt. When you jump to the interrupt routine, play with the duty cycle you need. This is the easyest i can figure now.

Now i really go