Fan Interface

The Radxa CM4 IO Board features an onboard fan interface for connecting an external fan to cool the board.

Hardware Connection

Connect the fan to the 2-Pin 1.25mm fan header on the Radxa CM4 IO Board.

Fan specifications:

• Interface type: 2-Pin 1.25mm
• Operating voltage: 5V

Interface Location

Refer to the Hardware Information guide to locate the corresponding hardware interface.

Checking Fan Devices

1. Use the ls command to view registered fan devices in the system.

radxa@device$

ls /sys/devices/platform/ | grep fan

Terminal output example:

radxa@device$

pwm-fan

• pwm-fan: Control device for the onboard fan

1. Locate PWM Control Files

The PWM control files for the fan are typically located in the /sys/class/hwmon/ directory. You need to find the hwmon directory corresponding to pwm-fan.

Use the ls command to view the PWM control files for the pwm-fan device:

radxa@device$

ls /sys/class/hwmon/

Terminal output example:

radxa@device$

hwmon0

1. Identify Fan Control Node

Use the ls command to view the PWM control files for the pwm-fan device in the hwmon directory:

radxa@device$

ls -l /sys/class/hwmon/hwmon*/device

Terminal output example:

/sys/class/hwmon/hwmon0/device -> ../../../pwm-fan

Based on the terminal output, we can control the pwm-fan through hwmon0.

Controlling Fan Speed

Use the echo command to set the fan speed. The PWM control range is typically 0~255 (0=stop, 255=full speed).

• Full Speed

radxa@device$

echo 255 | sudo tee /sys/class/hwmon/hwmon0/pwm1

• Half Speed

radxa@device$

echo 128 | sudo tee /sys/class/hwmon/hwmon0/pwm1

• Turn Off Fan

radxa@device$

echo 0 | sudo tee /sys/class/hwmon/hwmon0/pwm1

Interface Pin Definitions

For detailed pin definitions, please refer to the hardware schematics available on the Resource Download page.