Fan speed control using PWM inside BASH script

Question

Is there a way to run some kind of PWM for fan speed control inside bash script?

Here is my current script

#!/bin/bash
### BEGIN INIT INFO
# Provides: rpipwm
# Required-Start: $local_fs 
# Required-Stop: $local_fs
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: rpipwm
### END INIT INFO
 a="echo 20 > /sys/class/gpio/unexport;"
 a=$a"echo 20 > /sys/class/gpio/export;"
 a=$a"echo out > /sys/class/gpio/gpio20/direction"
 eval $a
#start loop script
while true;
do
 #Read temp
 cpuTemp0=$(cat /sys/class/thermal/thermal_zone0/temp)
 cpuTemp1=$(($cpuTemp0/1000))
 temp=$cpuTemp1
 a=""
 #If temperature is equal or lower than 39, the fan will stop spinning
 if [[ $(bc <<< "$temp <= 39") == 1 ]] ;
 then
 a=$a"echo 0 > /sys/class/gpio/gpio20/value"
 fi
 #If temperature is between 40 and 42.99, the fan will start with 2 second burst and 1 second sleep
 if [[ $(bc <<< "$temp >= 40 && $temp <= 43") == 1 ]] ;
 then
 a=$a"echo 1 > /sys/class/gpio/gpio20/value; sleep 2; echo 0 > /sys/class/gpio/gpio20/value; sleep 1 "
 fi
 #If temperature is between 44 and 48.99, the fan will start with 5 second burst and 1 second sleep
 if [[ $(bc <<< "$temp > 44 && $temp <= 49") == 1 ]] ;
 then
 a=$a"echo 1 > /sys/class/gpio/gpio20/value; sleep 5; echo 0 > /sys/class/gpio/gpio20/value; sleep 1" 
 fi
 #If temperature is equal or higher than 50, the fan will start spinning constantly
 if [[ $(bc <<< "$temp >= 50") == 1 ]] ;
 then
 a=$a"echo 1 > /sys/class/gpio/gpio20/value" 
 fi
 eval $a
 sleep 0.1
done

I want to avoid sleep or somehow simulate PWM to my fan have real speed control instand of ON/OFF in defined intervals.

Can someone help me?

Thanks!

• joan: What PWM are you trying to generate? We need to know the frequency and the number of steps between on and off.
• Ivijan Stefan Stipić: I need to experiment that yet. Currently script just on/off fan in certein time my fan what is not good for me.
• joan: I don't see how to help without knowing the sort of PWM you need to control the fan.
• Ivijan Stefan Stipić: Let's try something like this: 100Hz - 50% duty cycle. On this example I can build other things. Thanks!

Answer 1

Personally I'd use one of the many libraries and/or daemons available to you to do the PWM.

Have a look at servoblaster and its clones which provide daemons to provide dedicated PWM.

Or perhaps have a look at the PWM features provided by wiringPi with the bundled gpio utility.

Another alternative is my pigpio daemon and the pigs utility which provides multiple ways of generating PWM.

All of these can be called by a bash script.

Answer 2

BASH script for PWM

function gpiopwm() {
 sleep_low=$(awk -v freq="2ドル" -v duty="3ドル" 'BEGIN{print (1/freq)*((100-duty)/100)}')
 sleep_high=$(awk -v freq="2ドル" -v duty="3ドル" 'BEGIN{print (1/freq)*((100-(100-duty))/100)}')
 var_count=0
 repeat=1000
 while [ $var_count -lt $repeat ]
 do
 echo 1 > /sys/class/gpio/gpio1ドル/value
 sleep $sleep_high
 echo 0 > /sys/class/gpio/gpio1ドル/value
 let var_count=var_count+1
 if [ $var_count -le $repeat ]
 then
 sleep $sleep_low
 fi
 done
}

Based on the frequency & duty cycle parameter, this function 'on' and 'off' the GPIO in different wavelength

Full script for PWM based on CPU temperature using BASH is @ https://github.com/mohdismailj/fancontrol

Refer my implementation

• Darth Vader: Could you please provide a full description of all of the code here. Also, please stop linking to the same YouTube video without disclosing your affiliation.
• Ivijan Stefan Stipić: This is cool code