Pico Spectrogram Receiver

This project turns a Raspberry Pi Pico into an I²C slave device that receives spectrogram framebuffer data, displays it on an ST7789 display as a heatmap, and blinks the onboard LED to signal status or errors. Offloading spectrogram reception and initial rendering to the Pico frees up memory on an ESP32-S3 for higher-level analysis tasks.

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Next Steps

The next goal is to enable audio playback from a microSD card through an I²S speaker, while receiving an array of prediction results from the ESP32-S3 over I²C. This setup will allow the system to play predefined sound samples and collect corresponding model predictions, making it easier to test and evaluate the model’s accuracy, recall, F1 score, and overall performance in a controlled and repeatable way.

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Pinout

Signal	Pico Pin	ST7789 Pin
SPI SCK	GP10	SCK
SPI MOSI	GP11	MOSI
SPI CS	GP12	CS
SPI DC	GP13	DC
SPI RST	GP14	RST
SPI BL (Backlight)	GP15	BL
I²C SDA	GP4	SDA
I²C SCL	GP5	SCL
Onboard LED	GP25	—

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Dependencies

• pico-sdk
• pico_i2c_slave (added as submodule or via CMake FetchContent)

Custom libraries in this repo:

• display/st7789 — low‑level SPI driver for ST7789 displays
• heatmap/heatmap — palette setup + heatmap rendering routines

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Code Overview

1. main.c

   • Initializes stdio, onboard LED, display, and I²C slave
   • Sets up a 128×32 framebuffer + 256-color palette
   • Calls display_heatmap_centered() when a full frame arrives
   • Blinks LED codes for status (errors, ack, frame received)

2. i2c_handler()

   • Runs in interrupt context via pico_i2c_slave
   • Reads either 5-byte commands or bulk framebuffer data
   • Validates checksum or enters “frame receive” mode
   • Signals main loop via blink_code and receiving_framebuffer

3. heatmap module

   • init_palette() builds an RGB→RGB565 lookup table
   • display_heatmap_centered() scales the 128×32 buffer horizontally and vertically into the 240×320 display window

4. st7789 module

   • SPI initialization, reset, and command/data helpers
   • Full-screen fill, pixel‑stream write, window set, color inversion

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Purpose & Future Work

The Pico’s primary purpose here is to act as a dedicated I²C slave that safely receives spectrogram data and renders it, because the ESP32-S3’s limited RAM makes it difficult to simultaneously handle I²C streams, display, and higher‑level DSP/ML analysis. By offloading raw frame buffering and heatmap generation to the Pico, you

• Guarantee smooth data transfer and rendering
• Free the ESP32-S3 for advanced spectrogram processing (e.g., peak detection, ML inference)
• Simplify iterative testing of spectrogram display parameters

Future enhancements might include double buffering, DMA‑accelerated SPI writes, and on‑Pico preprocessing (e.g., log scaling, filtering) before visualization.