Controlling a DC fan using PWM (Pulse Width Modulation) is an easy and cost-effective way to cool network cabinets, 3D printer enclosures, AV racks, routers, amplifiers, or any electronics that require temperature-activated airflow.

This guide explains how to use an ESP32 to control the speed of a 5V, 12V, or 24V DC fan using:

• ESPHome (automatic Home Assistant integration)
• MQTT (manual integration for advanced users)

PWM fans offer quiet operation, reduced energy consumption, and dynamic speed control based on temperature sensors such as DS18B20, SHT45, BME280, or any MQTT/ESPHome sensor.

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1. Hardware Required

For 5V–12V DC PWM fan control:

• ESP32 DevKit
• 12V DC fan (e.g., PC fan)
• NPN transistor (2N2222) or N-Channel MOSFET (IRLZ44N recommended)
• Flyback diode (1N4007 or 1N4148)
• 10k resistor (gate/base resistor)
• 12V DC power supply
• Jumper wires

Recommended (if controlling >1 fan):

• MOSFET module (prebuilt MOSFET driver board)
• RC low-pass filter (optional)

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2. PWM Fan Wiring Diagram

Using NPN Transistor (for fans up to ~300mA)

ESP32 GPIO25 → 10k resistor → Transistor Base  
Transistor Emitter → GND  
Transistor Collector → Fan Negative  
Fan Positive → 12V  
Flyback diode across fan terminals

Using MOSFET (recommended for >300mA fans)

ESP32 GPIO25 → 10k resistor → MOSFET Gate  
MOSFET Source → GND  
MOSFET Drain → Fan Negative  
Fan Positive → 12V  
Diode across fan

ESP32 GND and 12V power GND must be common.

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METHOD 1 — ESPHome PWM Fan Control

ESPHome supports PWM output using the output: and fan: platforms.

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3. ESPHome PWM Fan Control YAML

esphome:
  name: esp32-fan
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "YOUR_WIFI"
  password: "YOUR_PASSWORD"

logger:
api:
ota:

output:
  - platform: ledc
    pin: 25
    id: fan_pwm
    frequency: 25000 Hz    # above audible range

fan:
  - platform: speed
    output: fan_pwm
    name: "Cabinet Fan"
    speed_count: 100

Notes:

• 25 kHz PWM avoids fan whining noise
• speed_count: 100 gives a 0–100% speed slider in Home Assistant
• GPIO25 is recommended but any PWM-capable pin works

After upload, Home Assistant automatically shows:

fan.cabinet_fan

with a speed slider.

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METHOD 2 — MQTT Fan Control (Your Style)

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4. Home Assistant configuration.yaml – MQTT Fan Entity

Add under:

mqtt:
  fan:

MQTT Fan YAML

mqtt:
  fan:
    - name: "Cabinet Fan"
      command_topic: "home/fan/set"
      percentage_command_topic: "home/fan/speed"
      state_topic: "home/fan/state"
      percentage_state_topic: "home/fan/speed_state"

This creates a fan with speed control in the UI.

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5. ESP32 Arduino MQTT Code (PWM Fan Control)

#include <WiFi.h>
#include <PubSubClient.h>

#define FAN_PIN 25
#define WIFI_SSID "YOUR_WIFI"
#define WIFI_PASS "YOUR_PASSWORD"
#define MQTT_SERVER "192.168.0.10"

WiFiClient espClient;
PubSubClient client(espClient);

int currentSpeed = 0;

void callback(char* topic, byte* payload, unsigned int length) {
  String cmd;

  for (int i = 0; i < length; i++) cmd += (char)payload[i];

  if (String(topic) == "home/fan/speed") {
    int speed = cmd.toInt();               // 0–100
    currentSpeed = speed;
    ledcWrite(0, (speed * 255) / 100);     // convert to 0–255 PWM
    client.publish("home/fan/speed_state", String(speed).c_str());
  }
}

void setup() {
  ledcAttachPin(FAN_PIN, 0);
  ledcSetup(0, 25000, 8);

  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) delay(500);

  client.setServer(MQTT_SERVER, 1883);
  client.setCallback(callback);
}

void loop() {
  if (!client.connected()) {
    while (!client.connected()) client.connect("ESP32_Fan");
    client.subscribe("home/fan/speed");
  }

  client.loop();
}

Now the fan supports percentage-based speed control from Home Assistant.

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6. Temperature-Based Fan Automation

This works with any temperature sensor:

• DS18B20
• SHT45
• BME280
• SCD30 / SCD41 temperature value

Fan speed curve automation example

automation:
  - alias: "Dynamic Fan Cooling"
    trigger:
      - platform: state
        entity_id: sensor.network_cabinet_temperature
    action:
      - choose:
          - conditions: "{{ states('sensor.network_cabinet_temperature') | float > 35 }}"
            sequence:
              - service: fan.set_percentage
                target:
                  entity_id: fan.cabinet_fan
                data:
                  percentage: 100
          - conditions: "{{ states('sensor.network_cabinet_temperature') | float > 30 }}"
            sequence:
              - service: fan.set_percentage
                target:
                  entity_id: fan.cabinet_fan
                data:
                  percentage: 70
          - conditions: "{{ states('sensor.network_cabinet_temperature') | float > 25 }}"
            sequence:
              - service: fan.set_percentage
                target:
                  entity_id: fan.cabinet_fan
                data:
                  percentage: 40
        default:
          - service: fan.turn_off
            target:
              entity_id: fan.cabinet_fan

This makes the fan behave like a smart cooling system.

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7. Common Use Cases

• Network cabinet cooling
• Router/modem active cooling
• Media cabinet airflow
• Closet server cooling
• 3D printer chamber ventilation
• Projectors, amplifiers, and other electronics

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8. Troubleshooting

Fan always runs at full speed

• Transistor wired incorrectly
• No common GND between ESP32 and PSU
• MOSFET needs logic-level variant (IRLZ44N)

Fan does not move at low PWM

• Increase minimum duty cycle to ~20%
• Add a “kickstart pulse” at 100% for 200 ms

Fan makes buzzing noise

• Raise frequency to 25–30 kHz
• Use MOSFET instead of NPN transistor

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Keywords

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