Triac-Based AC Light Dimmer with Zero-Crossing Detection and Remote Control

The Triac-Based AC Light Dimmer with Zero-Crossing Detection and Remote Control changes lamp brightness by switching mains power on for only part of each half-cycle, rather than wasting energy as heat in a series resistor. Ordinary wall dimmers hide this mechanism inside a sealed unit, so students rarely see the timing relationship between the mains waveform, the zero-crossing pulse, and the triac firing instant. A laboratory bench that only switches a lamp on and off also misses the point, because it never shows how conduction angle sets average power. The result is a gap between textbook phase-control diagrams and a working circuit that a student can measure, adjust, and explain. The dimmer built here closes that gap with a timed firing circuit, an isolated gate drive, and a remote control that makes each brightness step visible on a real lamp load.

This is a built-to-order hardware project: the assembled dimmer prototype, firmware, circuit and wiring documentation, and the complete documentation kit are prepared fresh for you.

Concept
A triac stays off until its gate receives a trigger pulse, then conducts for the remainder of that mains half-cycle until the load current falls below its holding current near the next zero crossing. Delaying the trigger pulse therefore shortens conduction and dims the lamp, while an early pulse lengthens conduction and brightens it. The zero-crossing detector gives the controller a fresh timing reference at every half-cycle, so the delay is measured from a known point instead of drifting against the mains waveform. Builder note from the actual build: the first prototype flickered at low brightness because the zero-crossing sense wiring ran alongside the gate-drive wiring and picked up switching noise, and the fix was to route the sense and gate-drive wiring apart and keep the low-voltage and mains sections physically separated on the board. First-principles line: firing angle and conduction angle are complementary within one half-cycle, so a longer firing delay always means a shorter conduction slice and therefore lower average power to the lamp.

Mains power enters the dimmer through a fuse and terminal blocks, while a zero-crossing detector watches the mains waveform and pulses each time the voltage passes through zero. An Arduino Nano measures the delay from that pulse, waits for the selected firing delay, and then sends a short gate pulse through the MOC3021 optoisolated driver to the BT136 triac. The triac then conducts for the rest of that half-cycle and switches off naturally near the next zero crossing, so the lamp receives only the chosen slice of each half-cycle and the average power falls as the delay grows. Changing the delay changes the conduction slice and therefore the brightness, and the infrared remote changes the delay value the controller uses for the next cycle. A snubber damps switching transients, a heatsink carries heat from the triac, and the enclosure stays closed throughout, so the whole chain from mains input to lamp output runs as one timed, isolated, and protected sequence.

1. Mains supply at 230 V AC and 50 Hz enters through a fuse and clearly labelled terminal blocks into the enclosed mains section of the board.
2. The zero-crossing detector, built from a bridge rectifier and a PC817 optocoupler, produces a pulse each time the mains waveform crosses zero volts.
3. The Arduino Nano receives that pulse as an interrupt and starts a timer for the firing delay selected by the remote control.
4. When the timer expires, the controller drives the MOC3021 optoisolator, which passes a gate pulse to the BT136 triac by light with no direct electrical connection to the controller.
5. The triac conducts for the remainder of that half-cycle, delivering power to the incandescent lamp load, then turns off naturally as the load current falls near the next zero crossing.
6. The remote receiver decodes each infrared command and updates the firing delay, the on-off state, or the preset brightness level for the next half-cycle.
7. A resistor-capacitor snubber across the triac damps voltage transients at switching, while the heatsink carries heat away from the triac during sustained operation.

Tech stack:

• Arduino Nano
• Arduino IDE · C firmware
• BT136 triac · heatsink
• MOC3021 optoisolated triac driver
• PC817 zero-crossing detector
• Infrared remote · TSOP receiver
• Incandescent lamp load
• Enclosed mains terminal block · fuse

The Triac-Based AC Light Dimmer with Zero-Crossing Detection and Remote Control offers phase-angle dimming, mains-synchronised timing, optoisolated gate drive, and infrared remote control in a single bench prototype. Phase-angle dimming gives smooth brightness steps instead of a simple on-off switch, while zero-crossing detection anchors every firing delay to the mains waveform so brightness stays steady from cycle to cycle. Optoisolation keeps the low-voltage controller electrically separate from the mains switching stage, and the remote lets a demonstrator change brightness without touching the board. Snubber protection and a fused, enclosed mains section complete the build, so the timing, the power stage, and the safety separation are all visible and testable in one prototype that a reviewer can follow step by step. A reviewer can therefore trace one remote press through timing, isolation, and conduction to the lamp in a single demonstration.

• [Phase-angle dimming] The controller delays the triac gate pulse by a controlled amount after each zero crossing, so the lamp receives a shorter or longer conduction slice and visibly changes brightness in steps.
• [Zero-crossing detection] A bridge-rectifier and optocoupler detector produces a timing pulse at each mains half-cycle, giving the firmware a stable reference from which every firing delay is measured.
• [Optoisolated triac drive] The MOC3021 driver couples the gate signal by light, not by a copper connection, so the Arduino Nano side stays electrically separated from the mains side of the circuit.
• [Infrared remote control] A handheld infrared remote with an IR receiver sets brightness up and down, switches the lamp on and off, and selects preset brightness levels without touching the live board.
• [On-board brightness indication] Indicator LEDs and the lamp itself show the selected level during a demonstration, so a reviewer can follow each remote command to its visible effect on the load.
• [Snubber and fuse protection] A resistor-capacitor snubber across the triac damps switching transients, and a mains fuse in series with the load limits fault current in the prototype.
• [Enclosed mains section] The mains wiring, triac, and terminal blocks are housed in an enclosure with the board closed before power is applied, so no live conductor is exposed during normal demonstration.
  Optional customization: a potentiometer for manual brightness control can be added on request, and a second lamp channel can be developed as a separate extension; neither is part of the base single-channel build. Future scope: power measurement display, fan-speed control mode, and wireless control are possible extensions and are not included in the base build.

• Assembled triac dimmer prototype with Arduino Nano, triac and heatsink, optoisolated driver, zero-crossing detector, infrared receiver, and enclosed mains section
• Infrared remote control and incandescent lamp load for demonstration
• Firmware source code with firing-delay and remote-decoding logic
• Circuit diagram, wiring documentation, and component list
• Project report PDF covering phase control, zero-crossing timing, isolation, and safety procedure
• Abstract PDF matching the project page
• PPT presentation for final review
• Demonstration guidance and a safe power-on checklist