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How to Control Fan on VOXL

Table of contents

  1. Connect the Fan
  2. Control the Fan with the voxl-fan utility
  3. Control the Fan PWM driver directly

Connect the Fan

Connect the cooling fan rated for 5V to J6 (see VOXL Connectors)

Control the Fan with the voxl-fan utility

[voxl-cpu-monitor/(voxl-cpu-monitor) monitors the CPU temperature and adjust the fan control accordingly.

The voxl-utils package (>= v0.5.8) includes a utility voxl-fan to control the fan speed.

yocto:/# voxl-fan --help
General Usage:

voxl-fan on
voxl-fan slow
voxl-fan off

The fan is on at full speed when voxl boots. It can be slowed down to half speed with voxl-fan slow or turned off completely with voxl-fan off.

Control the Fan PWM driver directly

# Spin the fan using 25kHz PWM, 50% duty cycle
echo 0 >     ${PWM_DEVICE}/export
echo 40000 > ${PWM_DEVICE}/pwm0/period
echo 20000 > ${PWM_DEVICE}/pwm0/duty_cycle
echo 1 >     ${PWM_DEVICE}/pwm0/enable


  • The fan turns on at full power when the board is turned on
  • The period and duty_cycle numbers are in microseconds
  • PWM Switching Frequency (kHz) = 1000000 / period
  • PWM duty_cycle should be in the range of [0..period]
  • Only several discrete frequencies are possible : 12.5khz, 15.00khz 18.75khz, 25khz, 30.00khz, 37.5khz, 50khz
  • The requested period gets rounded off or truncated to pick one of these frequencies

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