Little shell script that reads the temperature of a raspberry pi cpu and a connected harddrive using smartctl and controls a GPIO pin where a fan should be connected.

fan_control.sh

#!/bin/bash

c_FAN=26                        # gpio pin the fan is connected to
c_MIN_TEMPERATURE=45            # temperature in degrees c when fan should turn on
c_TEMPERATURE_OFFSET=2          # temperarute offset in degrees c when fan should turn off
c_HARDDRIVE="sda"               # name of your harddrive

temperature_offset=$(( $c_MIN_TEMPERATURE - $c_TEMPERATURE_OFFSET ))
fan_state=0

echo "$c_FAN" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio$c_FAN/direction

while [ 1 ]; do
        cpu_temperature=$(cat /sys/class/thermal/thermal_zone0/temp)
        cpu_temperature=$(( $cpu_temperature / 1000 ))
        hdd_temperature=$(sudo smartctl -d sat --all /dev/$c_HARDDRIVE | grep Temperature_Celsius | awk '{print $10}')
        if [ !fan_state ] && ([ $cpu_temperature -gt $c_MIN_TEMPERATURE ] || [ $hdd_temperature -gt $c_MIN_TEMPERATURE ])
        then
                fan_state=1
                echo "1" > /sys/class/gpio/gpio$c_FAN/value
        elif [ fan_state ] && [ $cpu_temperature -lt $temperature_offset ] && [ $hdd_temperature -lt $temperature_offset ]
        then
                fan_state=0
                echo "0" > /sys/class/gpio/gpio$c_FAN/value
        fi
        /bin/sleep 5
done