• https://www.raspberrypi.org/products/raspberry-pi-4-model-b/

• https://www.prusaprinters.org/prints/4645-raspberry-pi-4b-box-noctua-fan-variable
• https://www.thingiverse.com/thing:3774560

Source: https://www.domoticz.com/wiki/Raspberry_pi_fan_control_and_monitoring_with_bash

• N-channel MOSFET (e.g. 2N7000/BS170)
  • https://www.tme.eu/cz/details/2n7000-dio/tranzistory-s-kanalem-n-tht/diotec-semiconductor/2n7000/
  • https://www.tme.eu/cz/details/bs170d26z/tranzistory-s-kanalem-n-tht/on-semiconductor-fairchild/
• 0.1 uF electrolytic capacitor
  • https://www.tme.eu/cz/details/rc1h104m04005vr/elektrolyticke-kondenzatory-smd-105degc/samwha/
• 10K resistor
  • https://www.tme.eu/cz/details/1w-10k-1%25/metalizovane-rezistory-tht-1w/royal-ohm/mf01sff1002a10/

PIN PWM: BCM 18 (PWM 0) https://pinout.xyz/

Specific fan speed and temperature breakpoints for Noctua NF-A4x10 5V

fan-noctua.sh

#!/bin/bash
 
# Device references
dev_temp=/sys/class/thermal/thermal_zone0/temp
dev_pwm=/sys/class/pwm/pwmchip0/pwm0
dev_enable=$dev_pwm/enable
dev_duty=$dev_pwm/duty_cycle
dev_period=$dev_pwm/period
 
# Export pwm0 if it's not available
if [ ! -e $dev_pwm ]; then
    echo 0 > /sys/class/pwm/pwmchip0/export
    sleep 2
fi
 
# PWM frequency (nanoseconds)
period=1000000
 
# temperature breakpoints (millidegrees)
off_low=45000
low_off=40000
low_high=52000
high_low=48000
 
# fan-speed (nanoseconds)
low=930000
high=999999
 
# on/off values
off=0
on=1
 
# update interval (seconds)
interval=10
 
# initialise the fan
next=($off $low)
echo $period > $dev_period
echo ${next[0]} > $dev_enable
echo ${next[1]} > $dev_duty
 
update_status() {
    if [[ $(cat $dev_enable) == 1 ]]; then
        if [[ $(cat $dev_duty) == $high ]]; then
            nvalue=3
            svalue="High"
        else
            nvalue=2
            svalue="Low"
        fi
    else
        nvalue=1
        svalue="Off"
    fi
    logger "Fan $svalue"
}
 
while [ : ]
do
    temp=$(cat $dev_temp)
    current=($(cat $dev_enable) $(cat $dev_duty))
    if [ $temp -gt $off_low ]; then
        next[0]=$on
        if [ $temp -gt $low_high ]; then
            next[1]=$high
        elif [ $temp -lt $high_low ]; then
            next[1]=$low
        fi
    elif [ $temp -lt $low_off ]; then
        next[0]=$off
    fi
 
    if [ "${next[*]}" != "${current[*]}" ]; then
        echo ${next[1]} > $dev_duty
        echo ${next[0]} > $dev_enable
        update_status
    fi
    sleep $interval
done

• https://www.instructables.com/id/PWM-Regulated-Fan-Based-on-CPU-Temperature-for-Ras/

• NPN transistor 2N2222A
  • https://www.tme.eu/cz/details/2n2222a-dio/tranzistory-npn-tht/diotec-semiconductor/2n2222a/
• diode 1N4001
  • https://www.tme.eu/cz/details/1n4001-dco/univerzalni-diody-tht/daco-semiconductor/1n4001/
• resistor 1K
  • https://www.tme.eu/cz/details/1w-1k-1%25/metalizovane-rezistory-tht-1w/royal-ohm/mf01sff1001a10/

Install sysbench

shell# apt-get install sysbench

CPU stress test

shell# sysbench --test=cpu --cpu-max-prime=1000000 --num-threads=4 run

Without Fan

shell# vcgencmd measure_temp
shell# temp=78.0'C

With Fan

shell# vcgencmd measure_temp
shell# temp=54.0'C