Raspberry Pi 4 GPIO Fan Control on LineageOS 23 AndroidTV

I made this tutorial to show how I set up a 5V fan controlled by GPIO 23 on my Raspberry Pi 4 running LineageOS 23.

In my setup, the fan turns ON when GPIO 23 is HIGH and OFF when LOW, with an optional automatic fan script running at boot.

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1. Hardware Design

Components

• Raspberry Pi 4 (GPIO output)
• 5V fan (cooler)
• NPN transistor 2N2222
• Optional diode 1N4007 (for protection)
• 330 Ω resistor (for transistor base)

Goal

Control the fan using GPIO 23: ON when HIGH, OFF when LOW.

Hardware Diagram

The following diagram illustrates the wiring setup between the Raspberry Pi 4, the transistor, and the fan:

Step-by-step Wiring

Step 1: Identify transistor pins (2N2222)

Pin	Description
Emitter (E)	Small pin at one end
Base (B)	Middle pin
Collector (C)	Pin at other end

Double-check your transistor datasheet; packages may vary.

Step 2: Connect the fan

• Red wire (+5V) → +5V power supply
• Black wire (−) → Collector (C) of 2N2222

Step 3: Connect transistor emitter

• Emitter (E) → GND (common ground with Raspberry Pi)

Step 4: Connect GPIO to transistor base

• GPIO 23 → 330–470 Ω resistor → Base (B)
• Resistor protects GPIO by limiting current.

Step 5: Optional diode across fan

• Cathode (stripe) → fan +5V
• Anode → fan − / transistor collector
• Prevents voltage spikes from damaging the transistor.

Step 6: Power the fan

• Fan red → +5V
• Fan black → Collector (C)
• Emitter → GND

Step 7: GPIO Logic

• GPIO 23 HIGH (3.3V) → transistor conducts → fan ON
• GPIO 23 LOW (0V) → transistor off → fan OFF

Summary Table

Component	Connect to	Notes
Fan + (red)	+5V	Power supply
Fan − (black)	Collector (C) of 2N2222	NPN transistor switching side
Emitter (E)	GND	Common ground
GPIO 23	Base (B) via 330–470 Ω resistor	Controls transistor
1N4007 diode	Across fan, stripe to +5V	Optional protection

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2. ADB Software Configuration

This section sets up the fan control script to run automatically on boot.

Step 1: Prepare the script

Create fan_control.sh:

#!/system/bin/sh

ON_THRESHOLD=75
OFF_THRESHOLD=60

while true; do
    TEMP=$(( $(cat /sys/class/thermal/thermal_zone0/temp) / 1000 ))

    if [ "$TEMP" -ge "$ON_THRESHOLD" ]; then
        gpioset gpiochip0 23=1
    elif [ "$TEMP" -le "$OFF_THRESHOLD" ]; then
        gpioset gpiochip0 23=0
    fi

    sleep 5
done

Make it executable:

chmod +x fan_control.sh

Step 2: Create init service file

Create fan_control.rc:

service fan_control /data/local/fan_control.sh
    class main
    user root
    group root
    disabled
    seclabel u:r:init:s0

on property:sys.boot_completed=1
    start fan_control

Step 3: Deploy files via ADB

1. Connect to your Pi:

adb connect <YOUR_PI_IP>
adb root
adb remount

2. Push files:

adb push fan_control.sh /data/local/
adb push fan_control.rc /data/local/

3. Set permissions and move RC file:

adb shell
chmod 755 /data/local/fan_control.sh
mv /data/local/fan_control.rc /vendor/etc/init/
chcon u:object_r:vendor_file:s0 /data/local/fan_control.sh
chcon u:object_r:vendor_configs_file:s0 /vendor/etc/init/fan_control.rc
exit

Step 4: Reboot and verify

adb reboot
adb shell
getprop init.svc.fan_control

• Expected output: running
• Your fan will now automatically turn on/off based on CPU temperature at boot.

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Notes

• The script polls CPU temperature every 5 seconds.
• GPIO pin 23 must match your wiring.
• Optional diode protects the transistor from voltage spikes.
• Ensure root access is available, or the script will not control GPIO.

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References

• LineageOS 23 for Raspberry Pi 4 Android TV
• Raspberry Pi GPIO Control Guide