INMP441 Integration with Raspberry Pi CM5

[danic85]

As part of the proposed changes for Cody, the Raspberry Pi 5 will be replaced with a Pi Compute Module 5. This will allow a carrier board to be created that can house the core modules needed for the robot in a much smaller package.

This discussion details the potential use of the INMP441 I2S MEMS microphone as an alternative to the Adafruit SPH0645 module currently used in buddy, and will hopefully allow the module to be embedded on the carrier board directly as discrete components.

The module allows for a simple connection to the Raspberry Pi and even supports L/R feeds with two modules connected:

Pins 12, 35 and 38 are used in this example (GPIO 18, 19 & 20).

Datasheet is available here: https://www.digikey.com/htmldatasheets/production/1431884/0/0/1/inmp441-datasheet.html

[danic85]

It has taken a while to get this component to play nicely with the MAX98357 amp, but I have an installer script (or three) that should work. I will keep testing as the installation modifies the same files which can cause conflicts.

The installers need to be executed in the following order, with multiple restarts during the process (which is why they are not a single install):

• install-mics.sh
• install-speech-recognition.sh
• install-amp.sh

The scripts may require re-running after restart, so I'll try to make that clear from the debug output.

Full commit showing changes: fbe3eae

More information

It seems as though the adafruit i2s installer scripts are a good baseline for this, and I have created my own bash scripts to do the following:

1. Install the INMP441 microphones
2. Configure the microphones to support speech recognition
3. Install the MAX98357A amplifier.

The original mic installer attempts to make and install Raspberry-Pi-Installer-Scripts/i2s_mic_module, but this resulted in a number of errors I couldn't resolve. Fortunately excluding this step hasn't caused any problems. Reference of error here

There is a line added to /etc/asound.conf dtoverlay=max98357a on the original install script, but this appears to block the microphones so they no longer appear in arecord -l. Removing this line resolves this and doesn't appear to impact the amplifier.

Testing

I have tested the speakers using speaker-test -l5 -c2 -t wav -D plughw:0 where plughw is the card number from aplay -l. Occasionally after install the card number is shown as 2, but a restart will reset it to the default of 0.

cm5@cm5:~/modular-biped $ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: sndrpigooglevoi [snd_rpi_googlevoicehat_soundcar], device 0: Google voiceHAT SoundCard HiFi voicehat-hifi-0 [Google voiceHAT SoundCard HiFi voicehat-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: vc4hdmi0 [vc4-hdmi-0], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: vc4hdmi1 [vc4-hdmi-1], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Testing the microphones and speech recognition can be done by enabling the speechinput module in the yaml and enabling run-on-boot in that same file's config. You can also quickly check that the microphones are accessible using arecord- l

cm5@cm5:~/modular-biped $ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: sndrpigooglevoi [snd_rpi_googlevoicehat_soundcar], device 0: Google voiceHAT SoundCard HiFi voicehat-hifi-0 [Google voiceHAT SoundCard HiFi voicehat-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0