The compact ac light dimmer module with zero-crossing detector described here is ideal for microcontroller-based ac voltage controlling applications and projects.

This light dimmer control has active timing capacitor reset or AC line zero-crossing synchronization. The 13 additional components are garden variety and cost less than $2. Performance at the low end ...

A PIC controls a triac connected across the supply by monitoring power line zero-crossing. The PIC controls dimming by delaying the time the triac fires, which trims the peaks off of the AC waveform.