• 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

• 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/

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/

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