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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.