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AC Dimmer via MQTT with ESP32 and ESP8266

Control AC load brightness over MQTT — subscribe to a topic, receive 0–100 values, set the dimmer. Works with Home Assistant, Node-RED, AWS IoT, and any MQTT broker.

TL;DR: Install rbdimmerESP32 (for ESP32) or RBDdimmer (for ESP8266) plus PubSubClient. Connect to your MQTT broker, subscribe to a brightness topic, and call rbdimmer_set_level() in the callback. Publish back the current level as the state topic.



How It Works

text
ESP32  ──WiFi──►  MQTT broker  ◄──────  Home Assistant / Node-RED
  │                   │
  │  subscribe: dimmer/level/set
  │  publish:   dimmer/level/state
  │
  └──ISR──►  TRIAC gate  ──►  Load (lamp, heater…)

The ESP32 subscribes to a command topic. When HA publishes a value (0–100), the callback applies it to the dimmer. The ESP32 also publishes its current level so HA stays in sync.



Hardware

Part Example
MCU ESP32 (dual-core) or ESP8266
Dimmer Any 1CH/2CH/4CH rbdimmer module
ZC pin GPIO 5 (any GPIO on ESP32)
DIM pin GPIO 4 (any GPIO on ESP32)
VCC 3.3V

⚠️ Use rbdimmerESP32 on dual-core ESP32. The older RBDdimmer library has no IRAM_ATTR on its ISR — it crashes when WiFi is active. rbdimmerESP32 pins the ISR to Core 0; WiFi runs on Core 1. See: Wrong Library: RBDdimmer vs rbdimmerESP32



Required Libraries

Install via Arduino Library Manager or PlatformIO:

Library Purpose Board
rbdimmerESP32 AC dimmer ISR control ESP32 only
RBDdimmer AC dimmer ISR control Arduino, ESP8266
PubSubClient MQTT client Any
WiFi.h WiFi (built-in) ESP32
ESP8266WiFi.h WiFi (built-in) ESP8266

PlatformIO (platformio.ini):

ini
lib_deps =
  https://github.com/robotdyn-dimmer/rbdimmerESP32
  knolleary/PubSubClient @ ^2.8



Full Code — ESP32

cpp
// AC Dimmer + MQTT on ESP32 (dual-core)
// Library: rbdimmerESP32 + PubSubClient
// IMPORTANT: use rbdimmerESP32, NOT RBDdimmer, on ESP32
#include <WiFi.h>
#include <PubSubClient.h>
#include "rbdimmerESP32.h"
// ── Configuration ─────────────────────────────────────────────
const char* WIFI_SSID     = "YourSSID";
const char* WIFI_PASS     = "YourPassword";
const char* MQTT_SERVER   = "192.168.1.100"; // broker IP
const int   MQTT_PORT     = 1883;
const char* DEVICE_ID     = "dimmer_esp32_01"; // unique per device
// MQTT topics
const char* TOPIC_SET     = "dimmer/level/set";   // receive command
const char* TOPIC_STATE   = "dimmer/level/state"; // publish state
// Dimmer pins
#define ZC_PIN   5
#define DIM_PIN  4
// ── Globals ───────────────────────────────────────────────────
WiFiClient   wifiClient;
PubSubClient mqtt(wifiClient);
rbdimmer_channel_t dimmerCh;
int currentLevel = 0;
// ── MQTT callback ─────────────────────────────────────────────
void onMessage(char* topic, byte* payload, unsigned int length) {
    char buf[8];
    int len = min((int)length, 7);
    memcpy(buf, payload, len);
    buf[len] = '\0';
    int level = atoi(buf);
    level = constrain(level, 0, 100);
    rbdimmer_set_level(dimmerCh, level);
    currentLevel = level;
    // Publish confirmed state
    char stateStr[8];
    itoa(level, stateStr, 10);
    mqtt.publish(TOPIC_STATE, stateStr, true); // retained
}
// ── MQTT reconnect ────────────────────────────────────────────
void mqttReconnect() {
    while (!mqtt.connected()) {
        Serial.print("Connecting to MQTT…");
        if (mqtt.connect(DEVICE_ID)) {
            Serial.println(" connected.");
            mqtt.subscribe(TOPIC_SET);
            // Republish retained state on reconnect
            char stateStr[8];
            itoa(currentLevel, stateStr, 10);
            mqtt.publish(TOPIC_STATE, stateStr, true);
        } else {
            Serial.print(" failed, rc=");
            Serial.println(mqtt.state());
            delay(5000);
        }
    }
}
// ── Setup ─────────────────────────────────────────────────────
void setup() {
    Serial.begin(115200);
    // Connect WiFi
    WiFi.begin(WIFI_SSID, WIFI_PASS);
    while (WiFi.status() != WL_CONNECTED) {
        delay(500); Serial.print(".");
    }
    Serial.println("\nWiFi connected: " + WiFi.localIP().toString());
    // Init dimmer
    rbdimmer_init();
    rbdimmer_register_zero_cross(ZC_PIN, RBDIMMER_PHASE_DEFAULT);
    rbdimmer_config_t cfg = {
        .gpio_pin      = DIM_PIN,
        .phase         = RBDIMMER_PHASE_DEFAULT,
        .initial_level = 0,
        .curve_type    = RBDIMMER_CURVE_RMS
    };
    rbdimmer_create_channel(&cfg, &dimmerCh);
    // Setup MQTT
    mqtt.setServer(MQTT_SERVER, MQTT_PORT);
    mqtt.setCallback(onMessage);
}
// ── Loop ──────────────────────────────────────────────────────
void loop() {
    if (!mqtt.connected()) mqttReconnect();
    mqtt.loop();
}



Full Code — ESP8266

For ESP8266, swap the library and WiFi header. The MQTT logic is identical.

cpp
// AC Dimmer + MQTT on ESP8266 — complete sketch
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <RBDdimmer.h>
const char* WIFI_SSID   = "YourSSID";
const char* WIFI_PASS   = "YourPassword";
const char* MQTT_SERVER = "192.168.1.100";
const int   MQTT_PORT   = 1883;
const char* DEVICE_ID   = "dimmer_esp8266_01";
const char* TOPIC_SET   = "dimmer/level/set";
const char* TOPIC_STATE = "dimmer/level/state";
#define ZC_PIN  5   // D1 (NodeMCU)
#define DIM_PIN 4   // D2
WiFiClient   wifiClient;
PubSubClient mqtt(wifiClient);
dimmerLamp   dimmer(DIM_PIN, ZC_PIN);
int currentLevel = 0;
void onMessage(char* topic, byte* payload, unsigned int length) {
    char buf[8];
    int len = min((int)length, 7);
    memcpy(buf, payload, len);
    buf[len] = '\0';
    int level = constrain(atoi(buf), 0, 100);
    dimmer.setPower(level);
    currentLevel = level;
    char stateStr[8];
    itoa(level, stateStr, 10);
    mqtt.publish(TOPIC_STATE, stateStr, true);
}
void mqttReconnect() {
    while (!mqtt.connected()) {
        if (mqtt.connect(DEVICE_ID)) {
            mqtt.subscribe(TOPIC_SET);
        } else {
            delay(5000);
        }
    }
}
void setup() {
    WiFi.begin(WIFI_SSID, WIFI_PASS);
    while (WiFi.status() != WL_CONNECTED) delay(500);
    dimmer.begin(NORMAL_MODE, ON);
    dimmer.setPower(0);
    mqtt.setServer(MQTT_SERVER, MQTT_PORT);
    mqtt.setCallback(onMessage);
}
void loop() {
    if (!mqtt.connected()) mqttReconnect();
    mqtt.loop();
}



MQTT Topic Structure

Topic Direction Value Example
dimmer/level/set → ESP32 0–100 75
dimmer/level/state ← ESP32 0–100 75

For multiple dimmers, use unique topic prefixes per device:

text
dimmer/kitchen/level/set
dimmer/bedroom/level/set



Home Assistant Configuration

Add a MQTT light to configuration.yaml (or use MQTT Discovery):

yaml
mqtt:
  light:
    - name: "Living Room Dimmer"
      unique_id: "dimmer_esp32_01"
      command_topic: "dimmer/level/set"
      state_topic: "dimmer/level/state"
      brightness_command_topic: "dimmer/level/set"
      brightness_state_topic: "dimmer/level/state"
      brightness_scale: 100
      on_command_type: "brightness"
      retain: true
      optimistic: false

on_command_type: "brightness" — when you turn the light on from HA, it sends the brightness value as the MQTT payload (e.g., 75) instead of the string "ON". The firmware receives a number directly and applies it to the dimmer.

After adding, restart HA. The dimmer appears as a dimmable light entity with a 0–100% brightness slider.



Multi-Channel MQTT

For 2CH or 4CH modules, create additional topic pairs and channel handles. Each channel gets its own subscribe/publish pair:

cpp
// Additional channel
rbdimmer_channel_t ch2;
const char* TOPIC_SET2   = "dimmer/ch2/level/set";
const char* TOPIC_STATE2 = "dimmer/ch2/level/state";
// In onMessage(): check topic, route to correct channel
if (strcmp(topic, TOPIC_SET) == 0) {
    rbdimmer_set_level(dimmerCh, level);
} else if (strcmp(topic, TOPIC_SET2) == 0) {
    rbdimmer_set_level(ch2, level);
}



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