LEDC Dimmer Example

This example demonstrates how to generate TRIAC gate trigger pulses that are synchronized to the mains zero‑cross using LEDC and ETM. As a simplified demonstration, it simulates the 50 Hz zero‑cross AC mains detector input using a GPIO that toggles at 50 Hz, and uses ETM to reset the LEDC timer on each edge (every half-cycle) for synchronization. By shifting the LEDC hpoint (phase angle) after each reset, the gate pulse moves within the half‑cycle, achieving dimming.

How to use example

Hardware Required

• A development board with any Espressif SoC that has ETM functionality (e.g., ESP32C61-DevKitC etc.)
• A USB cable for power supply and programming

Signals and pins

Expected observation if connect an oscilloscope or logic analyzer:

• A 50 Hz square wave on GPIO3.
• Short pulses on GPIO2 that occur once each half‑cycle, moving left/right (earlier/later) every 2 seconds as the brightness ramps down and up.

Build and flash

Build the project and flash it to the board, then run monitor tool to view serial output:

idf.py build
idf.py -p PORT flash monitor

(Replace PORT with the name of the serial port to use.)

(To exit the serial monitor, type Ctrl-].)

See the ESP‑IDF Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Adapting to real mains dimming (advanced)

If you want to control a real TRIAC load (lamp):

1. Replace the simulated reference wave with a proper zero‑cross detector feeding an isolated input GPIO.
   • Configure REFERENCE_WAVE_IO as input only, remove the toggling task, and ensure ETM still triggers on both edges. Or to normalize the AC mains to some analog signal, and use analog comparator to trigger a ETM event.
2. Drive the TRIAC gate through an opto‑triac from the LEDC output GPIO with proper current‑limit resistor.

Here shows a simplified schematic for reference:

And here is an actual timing diagrams (AC mains + dimmer output waveforms with phase angle):

Troubleshooting

• Pulse timing not updating on C6/C5/H2/P4/H4/H21 → Check the notes in the example source file. For such targets, LEDC timer period should be shorter than the half-cycle of the mains, so that timer overflow could happen to update the duty parameters.
• Please make sure (hpoint + duty) is always less than (2 ** timer_resolution), otherwise, behavior is unexpected.

For any technical queries, please open an issue on GitHub. We will get back to you soon.