ESP32-S2 dimmer not working at all — no response to commands

Help & Support
1

I searched but couldn’t find an answer for this specific case:

ESP32-S2 with rbdimmer 1CH module — dimmer completely unresponsive. No errors during compile or upload, but the lamp does not respond to any commands.

Environment:

  • Board: ESP32-S2 (Wemos S2 Mini)
  • Library: rbdimmerESP32 v1.2
  • IDE: Arduino IDE 2.3.3
  • Module: rbdimmer 1CH 4A
  • Load: 40W incandescent bulb
  • ZC pin: GPIO3, PSM pin: GPIO5

What I tried:

  1. Basic example sketch from library — compiles, uploads, no dimming
  2. Serial.println confirms setPower() values are sent — but no visible change on lamp
  3. Tested same module with standard ESP32 DevKit — works fine
  4. Swapped cables, tested different GPIOs — same result on S2
  5. No crash, no Guru Meditation, no errors in Serial Monitor
#include <rbdimmerESP32.h>

rbdimmer dimmer(5, 3);

void setup() {
  Serial.begin(115200);
  dimmer.begin(NORMAL_MODE, ON);
  Serial.println("Dimmer initialized");
}

void loop() {
  for (int i = 0; i <= 100; i += 10) {
    dimmer.setPower(i);
    Serial.println(i);
    delay(1000);
  }
}

Serial output shows values 0, 10, 20… correctly. Lamp stays off the entire time. Same code and module work on regular ESP32.

Any ideas?

2

Root cause: ESP32-S2 is a single-core chip.

The rbdimmerESP32 library pins its ISR handler and timing task to Core 0 via xTaskCreatePinnedToCore(), and expects your application loop to run on Core 1. On dual-core ESP32 (Xtensa LX6/LX7) this works because the two cores operate independently.

ESP32-S2 has only one core. The FreeRTOS scheduler cannot pin tasks to separate cores, so the library’s interrupt architecture silently fails — no crash, no error, just no TRIAC firing.

Affected chips (all single-core):

  • ESP32-S2 (Xtensa LX7, single-core)
  • ESP32-C3 (RISC-V, single-core)
  • ESP32-H2 (RISC-V, single-core)

Supported chips:

  • ESP32 (Xtensa LX6, dual-core)
  • ESP32-S3 (Xtensa LX7, dual-core)

This explains why the same code works on your regular ESP32 DevKit but not on the S2. The library compiles for both targets because the FreeRTOS API is the same — it just doesn’t function correctly on single-core silicon.

If you must use ESP32-S2, look into the DimmerLink module — it offloads all phase-cut timing to a dedicated MCU and communicates via I2C. Your S2 only sends brightness commands over the bus.

3

Update after two weeks — DimmerLink module arrived today. Thank you Kai and rbdimmer team for the recommendation.

Tested with ESP32-S2 over I2C.

Result: works perfectly. Smooth dimming from 0% to 100%, no issues.

The I2C setup was straightforward — just Wire.begin() and the DimmerLink library handles everything else. Much simpler than the direct TRIAC approach actually.

One note for anyone finding this thread later: the DimmerLink default I2C address is 0x27. If you have other I2C devices on the same bus, check for address conflicts with Wire.beginTransmission() / Wire.endTransmission() scanner sketch.

4

[SOLVED] Root cause: ESP32-S2 is single-core — rbdimmerESP32 library requires dual-core ESP32.

Fix: use DimmerLink module (I2C) instead of direct TRIAC control.

Supported for rbdimmerESP32 library: ESP32 (dual-core), ESP32-S3 (dual-core).
Not supported: ESP32-S2, ESP32-C3, ESP32-H2 (all single-core).