Pico 2 (RP2350) I2S INMP441 Rhythm Pattern Matcher & BPM Estimator

This project implements a real-time, tempo-agnostic rhythm pattern matching system for the INMP441 I2S MEMS Microphone running on the Raspberry Pi Pico 2 (RP2350). It uses the static library driver lf-inmp441 located in the parent directory.

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⚡ Features

• Transient Detector: Isolates the low-to-mid frequency band (62.5 Hz to 375.0 Hz) and triggers on rapid energy attacks (e.g., hand claps or desk taps).
• Tempo-Agnostic Pattern Matching: Uses a rolling 5-interval queue to detect a specific syncopated rhythm template (3:1:2:1:1 relative ratios) corresponding to a 4/4 measure of:
  • Quarter, Eighth Rest, Eighth, Quarter, Two Eighths (Hit step grid: [ x . . x x . x x ])
• Phase Independence: Evaluates all 5 circular shifts of the template so it can lock onto the rhythm regardless of which beat in the measure it begins tracking.
• Real-time BPM Estimation: Computes the estimated tempo in Beats Per Minute (BPM) based on the total duration of the matched measure:

  \text{BPM} = \frac{240,000}{\text{Measure Duration in ms}}

• Onboard LED Feedback: Flashes the Pico 2 onboard green LED (GP25) briefly on each detected beat.
• Consecutive Bar Tracking: Counts consecutive bars matched and triggers an achievement message when 16+ consecutive bars are locked in.
• Automatic Silence Reset: Resets the bar counter to zero if no beats are detected for more than 5 seconds.

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🔌 Hardware Wiring Guide

The INMP441 operates as an I2S slave. The Pico 2 acts as the I2S master, generating the bit clock (SCK) and word select clock (WS/LRCK) signals.

Important

The PIO clock generation code requires that the WS pin be connected to the GPIO pin immediately following the SCK pin (SCK pin + 1).

INMP441 Pin	Pin Marking	Function	Pico 2 GP Pin	Pico 2 Physical Pin	Connection Description
VDD	VDD	Power Input	3V3 (OUT)	Pin 36	3.3V Power Supply (1.8V - 3.6V max)
GND	GND	Ground	GND	Pin 3 (or any GND)	Power Ground (0V)
SCK	SCK	Serial Bit Clock	GP20	Pin 26	SPI/I2S Clock generated by Pico 2
WS	WS	Word Select (LRCK)	GP21	Pin 27	Frame sync signal (Left/Right channel clock)
SD	SD	Serial Data Out	GP22	Pin 29	Digital audio data line to Pico 2
L/R	L/R	Channel Select	GND	GND	Pull to GND for Left channel mono output

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🛠️ Build and Compiling Instructions

Prerequisites

Ensure you have the Raspberry Pi Pico SDK installed and the PICO_SDK_PATH environment variable set. For example:

export PICO_SDK_PATH=/home/bethany/code/pico-sdk

Compiling the Code

1. Navigate to the noise-detector directory:

   cd noise-detector
   

2. Create a build directory and run CMake (specifying pico2 as the target board):

   mkdir build
   cd build
   cmake -DPICO_BOARD=pico2 ..
   

3. Compile the project:

   make -j$(nproc)
   

This will produce the compiled firmware files in the build/ directory, including noise_detector.uf2.

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⚡ Flashing the Firmware

1. Unplug your Pico 2 from the computer.
2. Hold down the white BOOTSEL button on the board.
3. While holding the button, plug the Pico 2 back into your computer's USB port.
4. Release the BOOTSEL button. The Pico 2 will mount as a USB mass storage device named RP2350.
5. Drag and drop the noise_detector.uf2 file into the mounted directory.
6. The board will flash, reboot automatically, and start running the visualizer.

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🖥️ Monitoring the Output

You can monitor the output from a terminal over USB CDC Serial. On Linux, you can run:

minicom -b 115200 -o -D /dev/ttyACM0

Output Example

When you perform the syncopated rhythm (e.g. by tapping your fingers on the desk), the console will log the intervals and matches:

Beat transient! Interval: 704 ms

=======================================================
>>> [MATCH] Bar #24 Detected! (Est. Tempo: 90.4 BPM)
    Intervals: [704, 320, 352, 928, 352] ms
=======================================================

!!! [ACHIEVEMENT] Target met: 16+ consecutive bars locked! !!!

If you stop tapping or break the rhythm, the system resets:

[SILENCE] Rhythm broken. Resetting counter.