I wrote a bash script to turn GPIO on/off to control a fan, but it's causing high CPU usage and I cant figure out why.
It works but whenever it changes state from off to on or vice versa , the script freezes causing high CPU usage and after about 5 min it changes state and CPU usage returns back to normal. And the problem repeats again after about 20-60 seconds.
Can someone please help me understand what's wrong with my script?
[Raspberry Pi 4 running Ubuntu 20.04]
#!/bin/bash
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin"
gpio -g mode 3 out
on=48000
off=44000
while true; do
cpu=$(</sys/class/thermal/thermal_zone0/temp) # get CPU temperature
if (( "$cpu" > "$on" )); then
gpio -g write 3 1 # turn fan ON
echo "CPU Hot"
sleep 60
fi
if (( "$off" > "$cpu" )); then
echo "CPU Cool."
gpio -g write 3 0 # turn fan OFF
sleep 5
fi
done
Okay so I was able to solve the problem, thanks to @shellter...
The problem was that the script did not have any condition to handle when the CPU temperature was between 4800 and 4400
The basic idea of the solution is:
if (CPU is Hot); then
turn fan ON
set boolean = true
sleep 60 sec
else if (CPU is Cool); then
turn fan OFF
set boolean = false
sleep 5 sec
else (when CPU is neither Hot OR Cool.. somewhere between 4400 && 4800)
if (boolean is true.. meaning CPU didn't go below 4400); then
sleep 60 sec
else (boolean is false.. meaning CPU didn't go above 4800); then
sleep 5 sec
The working code is:
#!/bin/bash
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin"
gpio -g mode 3 out
on=48000
off=44000
hot=false
while true; do
cpu=$(</sys/class/thermal/thermal_zone0/temp)
if (( "$cpu" > "$on" )); then
echo "CPU Hot"
hot=true
gpio -g write 3 1 # turn fan ON
sleep 60
elif (( "$off" > "$cpu" )); then
echo "CPU Cool."
hot=false
gpio -g write 3 0 # turn fan OFF
sleep 5
else
if [ "$hot" = true ]; then
echo "CPU still Hot"
sleep 60
else
echo "CPU Cool"
sleep 5
fi
fi
done