Active Noise Cancellation on Raspberry Pi

Project Structure

• src/ - MATLAB source for calibration/ANC plus deploy wrappers (anc_calibrate.m, anc_run.m, anc_calibrate_deploy.m, anc_run_deploy.m).
• host/ - Host-side deployment scripts (deploy_calibration.m, deploy_runtime.m, deploy_calibration_and_runtime.m). They configure the Pi connection, add src/ to the path, and invoke deploy.
• docs/ - Design/requirements references (codex-spec.md, Project Info.txt).
• build/ - Artifacts produced by MATLAB code generation (e.g., ELF binaries). MATLAB may also create a codegen/ folder automatically.
• Assorted Testing Garbage/ - Scratch utilities such as the mic self-test harness.

Prerequisites

1. MATLAB with Audio Toolbox + Raspberry Pi Support Package.
2. Raspberry Pi 4 reachable at 10.42.0.250 (edit the host scripts if your IP/credentials differ).
3. ALSA capture/playback devices configured as described in docs/Project Info.txt (I2S mics + PWM playback).

Workflow

1. Calibrate the secondary path
   • In MATLAB, cd into host/ and run deploy_calibration (or deploy_calibration_and_runtime to do both stages sequentially).
   • The script deploys anc_calibrate_deploy to the Pi; it plays ~20 s of white noise and writes /home/pi/anc/anc_S.bin (consumed by anc_run). A companion /home/pi/anc/anc_S.mat is only produced when you run anc_calibrate directly inside MATLAB for debugging.
2. Run ANC
   • Still in host/, run deploy_runtime (or reuse deploy_calibration_and_runtime after calibration).
   • This builds/deploys anc_run_deploy so the ANC loop executes on the Pi. Stop it via Ctrl+C in MATLAB.
3. Recalibrate when hardware changes
   • Anytime the speaker/mic geometry changes, rerun deploy_calibration before deploy_runtime so anc_S.bin stays in sync.

Audio Bring-up / Mic Self-test

1. Enable the I2S stack (Pi config)
   • Edit /boot/firmware/config.txt and ensure the [all] section contains:

     dtparam=i2s=on
     dtoverlay=googlevoicehat-soundcard
     dtoverlay=audremap,pins_12_13
     

   • Reboot, then run /usr/bin/dtoverlay -l and arecord -l. The capture card should appear as snd_rpi_googlevoicehat_soundcar (typically plughw:1,0).
2. Verify wiring
   • Both INMP441 boards share the same bus: BCLK -> GPIO18 (pin 12), LRCLK -> GPIO19 (pin 35), DIN -> GPIO20 (pin 38), 3V3 -> pin 1/17, GND -> pin 6/9/etc.
   • Strap the reference mic's L/R pin to GND (left channel) and the error mic's L/R pin to 3V3 (right channel).
   • Speaker/amp: PWM left channel on GPIO12 (pin 32) -> 220 ohm -> junction -> 100 ohm -> filtered node -> three 0.01 uF caps to the GND rail; filtered node to PAM8302 A+, A- to GND, VIN to pin 2 (5 V).
3. Run the mic self-test
   • From MATLAB, cd into Assorted Testing Garbage/ and run run_mic_selftest to deploy mic_selftest via deploy.
   • After it finishes, read /home/pi/anc/mic_selftest_report.txt on the Pi. Both channels must report non-zero RMS before proceeding with calibration.

Notes

• Do not call the deploy wrappers (anc_calibrate_deploy, anc_run_deploy) directly from the host MATLAB prompt; they are entry points for deploy(board,...) and expect to run on the Pi.
• anc_run reads the secondary-path taps from /home/pi/anc/anc_S.bin using fopen/fread; the .mat file is only for offline inspection when available.
• All MATLAB source lives under src/; add it to your path if you open files directly outside the host scripts.
• The Assorted Testing Garbage/ folder also contains the generated ELF plus codegen/ artifacts if you need to redeploy manually on the Pi.
• Playback is on the left PWM pin (GPIO12). If your RC filter is on GPIO13, move the wire or adjust the code/device usage back to right channel.
• Keep audio play calls at the same frame size (256) on the Pi; playblocking is not available, and mixing buffer sizes causes size-lock errors.