ESP32-C3 Fan Controller

An automatic server fan controller built on the ESP32-C3, featuring temperature-based relay control, OLED status display, and Home Assistant integration via MQTT.

Features

Auto fan control — relay switches ON/OFF based on temperature thresholds with hysteresis
DHT22 sensor — reads temperature and humidity every second
SSD1306 OLED — displays live temp, humidity, and fan state
MQTT publishing — streams sensor data and fan state to Home Assistant
WiFi — connects on boot, auto-reconnects if MQTT drops

Hardware

Component	Details
Microcontroller	ESP32-C3 (with onboard OLED)
Sensor	DHT22 (temperature + humidity)
Relay	5V relay module (active-LOW)
Fan	USB 5V fan
Display	SSD1306 128×64 OLED (I2C)

Wiring

ESP32-C3 Pin	Connected To
`GPIO2`	DHT22 DATA (+ 4.7kΩ pullup to 3V3)
`GPIO3`	Relay IN
`GPIO5` (SDA)	OLED SDA
`GPIO6` (SCL)	OLED SCL
`3V3`	DHT22 VCC, OLED VCC
`GND`	DHT22 GND, OLED GND, Relay GND

Relay wiring:

COM → USB 5V
NO → Fan + (red wire)
Fan − (black wire) → GND

Configuration

Copy secrets.h.example to secrets.h and fill in your values:

#define WIFI_SSID  "your_wifi_ssid"
#define WIFI_PASS  "your_wifi_password"
#define MQTT_HOST  "192.168.1.X"   // Home Assistant IP
#define MQTT_USER  "mqtt_user"
#define MQTT_PASS  "mqtt_pass"

Temperature Thresholds

Edit these defines in fan_controller.ino:

#define TEMP_ON   28.0   // Fan turns ON above this (°C)
#define TEMP_OFF  25.0   // Fan turns OFF below this (°C)

MQTT Topics

Topic	Direction	Payload
`esp32c3_fan/temperature`	Publish	`23.5` (°C)
`esp32c3_fan/humidity`	Publish	`41` (%)
`esp32c3_fan/fan/state`	Publish	`ON` / `OFF`

Home Assistant Setup

Add to configuration.yaml:

mqtt:
  sensor:
    - name: "Room Temperature"
      unique_id: "esp32c3_temperature"
      state_topic: "esp32c3_fan/temperature"
      unit_of_measurement: "°C"
      device_class: temperature

    - name: "Room Humidity"
      unique_id: "esp32c3_humidity"
      state_topic: "esp32c3_fan/humidity"
      unit_of_measurement: "%"
      device_class: humidity

  binary_sensor:
    - name: "Server Fan"
      unique_id: "esp32c3_fan"
      state_topic: "esp32c3_fan/fan/state"
      payload_on: "ON"
      payload_off: "OFF"
      device_class: running

Restart HA after saving. Requires the Mosquitto broker add-on installed and running.

Dependencies

Install via Arduino IDE Library Manager:

U8g2 — OLED display
DHT sensor library — DHT22
PubSubClient — MQTT client
WiFi (built-in with ESP32 board package)

Project Structure

esp32c3-fan-controller/
├── fan_controller.ino   # Main sketch
├── secrets.h            # WiFi & MQTT credentials (gitignored)
├── secrets.h.example    # Credentials template
├── .gitignore
└── README.md

License

MIT

README.md Unescape Escape