🛠 Refroidir le CM5 : ventilateur PWM sur le connecteur JST-SH et tachymétrie

Objectives

The CM5 delivers significantly more performance than the CM4 and generates more heat (throttling at 85 °C case temperature); the CM5IO Board provides a 4-pin JST-SH fan connector (5 V, Fan_PWM, tachometer, GND) and the firmware controls the PWM similarly to the Pi 5. This tutorial covers wiring the fan, reading the tachometer on Fan_Tacho (GPIO29), and understanding the documented pitfall: Fan_PWM stops at shutdown, but a fan powered separately with 5 V may continue to spin if the carrier board does not cut its power supply.

Hardware

• 1 × CM5 on a CM5IO Board (or a carrier board featuring the JST-SH connector, ref. JST BM04B-SRSS-TB on the board side)
• 1 × 5 V PWM 4-wire fan (Noctua NF-A4x10 PWM type or equivalent)
• The official IO case has a known v1 defect: it is impossible to mount both the CM5 Cooler and the pre-installed fan (fixed in v2)
• sudo apt install -y python3-gpiozero

Complete Code

#!/usr/bin/env python3
# rpm-ventilateur.py — lit Fan_Tacho (GPIO29) du connecteur ventilateur CM5IO.
from gpiozero import DigitalInputDevice
from time import sleep

compte = 0
def tick(_):
    global compte
    compte += 1

tach = DigitalInputDevice(29, pull_up=True, bounce_time=0.0005)
tach.when_activated = tick
sleep(5)
rpm = compte / 5 / 2 * 60          # 5 s, 2 impulsions par tour (typique)
print(f"~ {rpm:.0f} tr/min")
tach.close

# Température et état de throttle pendant la montée en charge
vcgencmd measure_temp && vcgencmd get_throttled
sudo apt install -y stress-ng && stress-ng --cpu 4 --timeout 90 &
sleep 45; python3 rpm-ventilateur.py; vcgencmd measure_temp

Expected Verification

The script displays a stable speed (e.g., ~2000 RPM); under stress, the temperature rises and the firmware accelerates the fan (the displayed speed increases, get_throttled remains at 0x0). Upon shutdown (sudo systemctl poweroff), the fan connected to the IO Board connector must stop — if it is still spinning, your carrier board does not cut the 5 V supply to the fan.

Common Errors

• Fan spinning after shutdown: documented in the datasheet (§2.11) — share the VBUS_EN line or add a 74LVC1G07 buffer on the carrier board to cut the 5 V supply.
• IO case v1 + CM5 Cooler: the two do not fit together; remove the pre-installed fan or switch to the v2 case.
• Tachometer without pull-up: the open-collector signal of a fan remains floating without pull_up=True — guaranteed zero count.
• Swapping PWM and 5 V in the JST-SH connector: verify the pin order on the fan side before powering up.