🛠 Son sur CM4 : DAC I2S/PCM (PCM5102) sans prise jack

Objectives

The CM4 has no audio jack (no embedded ADC/DAC), but exposes a PCM (I2S) interface on its pins. This tutorial connects an inexpensive I2S DAC (PCM5102) to the HAT footprint of the IO Board and configures the board as the default audio output via a device tree overlay — the standard approach across the entire BCM2711 ecosystem.

Hardware

• 1 × CM4 on IO Board, running 64-bit Raspberry Pi OS
• 1 × PCM5102 I2S DAC (an "I2S stereo DAC" module, ~€5), powered by 5 V
• HAT wiring: GPIO18=SCLK (bit clock), GPIO19=LRCLK (word clock), GPIO21=BCLK/DIN (data), 5 V and GND — verify the exact pinout of the module (some invert BCLK/LRCLK)
• Amplified speaker or headphones connected to the DAC output

Complete code

# 1) Activer I2S et charger le driver du DAC
sudo raspi-config nonint do_i2s 0        # active device tree I2S
{ echo 'dtparam=i2s=on'; echo 'dtoverlay=hifiberry-dac'; } | sudo tee -a /boot/firmware/config.txt
sudo reboot

# 2) Vérifier la carte audio
aplay -l                                  # attendu : snd_rpi_hifiberry_dac
cat /proc/asound/cards

# 3) En faire la sortie par défaut
cat > /etc/asound.conf <<'EOF'
pcm.!default {
  type plug
  slave.pcm "hw:1,0"}
EOF

# 4) Test sonore
speaker-test -D plughw:1,0 -c 2 -t sin -f 440 --duration 3

Expected verification

aplay -l lists snd_rpi_hifiberry_dac; speaker-test produces a clear 440 Hz tone in the speaker; a wav file plays with aplay music.wav without options. dmesg | grep -i hifiberry shows no probe errors.

Common errors

• Looking for the Pi 4B's jack: the CM4 doesn't have one; without an external DAC, aplay -l only shows HDMI — this is normal.
• SCLK/LRCLK/DIN swapped: the classic symptom is total silence or mono crackling; swap LRCLK and BCLK on the DAC module.
• Missing overlay: without dtoverlay=hifiberry-dac, the I2S bus runs idle and no ALSA card appears.
• Powering the DAC with 3.3 V when it requires 5 V: inaudible or distorted volume; check the pinout of the purchased module.