ESP32-C3 Fan Controller

An automatic server fan controller built on the ESP32-C3. Drives a 5 V fan over PWM through an IRLZ44N MOSFET, auto-selects fan speed from a temperature table with hysteresis, shows live status on an OLED, and publishes sensor/fan state to Home Assistant over MQTT.

Features

• Temperature-driven PWM fan control — 5 discrete speed levels, selected automatically from the current temperature
• Hysteresis — 1 °C drop-down margin prevents level flapping
• DHT22 sensor — reads temperature and humidity every 3 s
• SSD1306 OLED — displays live temp, humidity, fan state, and level
• MQTT publishing — streams sensor and fan data for Home Assistant
• WiFi — connects on boot, auto-reconnects WiFi and MQTT if they drop

Hardware

Component	Details
Microcontroller	ESP32-C3
Sensor	DHT22 (temperature + humidity)
Driver	IRLZ44N N-channel MOSFET (logic-level)
Fan	2-wire 5 V fan
Display	SSD1306 128×64 OLED (I²C)

Wiring

ESP32-C3 Pin	Connected To
GPIO2	DHT22 DATA (+ 4.7 kΩ pullup to 3V3)
GPIO3	MOSFET gate (via ~150 Ω) + 100 kΩ gate→GND pulldown
GPIO5 (SDA)	OLED SDA
GPIO6 (SCL)	OLED SCL
3V3	DHT22 VCC, OLED VCC
GND	DHT22 GND, OLED GND, MOSFET source, fan −

Fan wiring:

• Fan + → USB 5 V
• Fan − → MOSFET drain
• MOSFET source → GND
• MOSFET gate → GPIO3

Configuration

Copy main/secrets.h.example to main/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"
#define MQTT_PORT     1883
#define MQTT_USER     "mqtt_user"
#define MQTT_PASS     "mqtt_password"
#define MQTT_CLIENT   "esp32c3_fan"

secrets.h is gitignored.

Fan Level Table

Fan speed is selected from a table of (temperature threshold → PWM duty) in main/main.ino:

Level	Temp ≥	PWM duty (0–255)
0 (off)	—	0
1	28 °C	230
2	30 °C	236
3	32 °C	242
4	34 °C	249
5	36 °C	255

TEMP_HYST (default 1.0 °C) controls the drop-down margin: the fan only drops a level once temperature falls this much below that level's threshold. Below level 1's threshold minus hysteresis, the fan turns off.

Tune LEVELS[] and TEMP_HYST in main/main.ino to match your thermal setup.

MQTT Topics

All topics are publish-only (the firmware does not accept remote commands).

Topic	Payload	Notes
esp32c3_fan/temperature	23.5	°C, every loop
esp32c3_fan/humidity	41	%, every loop
esp32c3_fan/fan/state	ON / OFF	retained
esp32c3_fan/fan/speed	0..5	current level, retained

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

    - name: "Server Fan Level"
      unique_id: "esp32c3_fan_level"
      state_topic: "esp32c3_fan/fan/speed"

  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

fan4life/
├── main/
│   ├── main.ino            # Main sketch
│   ├── secrets.h           # WiFi & MQTT credentials (gitignored)
│   └── secrets.h.example   # Credentials template
├── cad/                    # Mechanical / enclosure files
├── .gitignore
└── README.md

License

MIT