This device receives FFT frequency analysis data via I2C from the Speech Recognition AudioCapture master device and displays it as a real-time frequency spectrum on a 3.5" TFT display.

• Raspberry Pi Pico 2 (RP2350)
• 3.5" TFT Display with ST7796SU1 controller (320x480 resolution)
• 2 push buttons for address selection
• Connections as specified in the pin configuration below

• Firmware target board: PICO_BOARD=pico2
• MCU platform: RP2350 (rp2350-arm-s)
• Generated output files in build/ (including .uf2, .elf, .bin, .hex) are built for Pico 2 / RP2350.

Use these direct wire connections between the two Pico boards:

Optional/Recommended:

• Add 4.7kΩ pull-up resistors from SDA to 3.3V and SCL to 3.3V if your bus does not already have pull-ups.
• Keep wiring short (preferably <30 cm) for stable 400 kHz operation.
• Use 3.3V logic only (RP2350 and RP2040 are 3.3V compatible on I/O).

• I2C address range: 0x60 - 0x67
• Press GPIO 14 button to increment address
• Receives 41-byte packets from audio beamforming master:
  • 1 byte header (0xAA)
  • 40 frequency bins × 1 byte each (8-bit values)
• I2C slave mode on I2C0 @ 400 kHz
• Raspberry Pi Pico SDK installed
• CMake and build tools configured

cd I2C_TestDevice
mkdir -p build
cd build
cmake ..
ninja

Or use VS Code task: Ctrl+Shift+B → "Compile I2C_TestDevice"

1. Hold BOOTSEL button on Pico
2. Connect USB cable
3. Copy I2C_TestDevice.uf2 from build folder to RPI-RP2 drive

Or use picotool:

picotool load build/I2C_TestDevice.uf2 -fx

1. Build and flash I2C_TestDevice firmware to the slave Pico.
2. Build and flash Speech_Recognition_AudioCapture firmware to the master Pico.
3. Wire I2C exactly as shown in I2C Link to Speech_Recognition_AudioCapture (Master).
4. Confirm both boards share GND.
5. Power both boards.
6. Set test device address with buttons:

• Start with 0x60 to view the -60° beam.

7. Verify display updates when master is running and transmitting.

1. Power on the device
2. Display shows "I2C FFT Display" during initialization
3. Default address is 0x60 (beam -60° from master)
4. Press buttons to change address and select different beam angles:
   • 0x60 = -60° beam
   • 0x61 = -30° beam
   • 0x62 = 0° beam (center)
   • 0x63 = +30° beam
   • 0x64 = +60° beam
5. Connect I2C from audio capture master (Master GPIO8→Slave GPIO20, Master GPIO9→Slave GPIO21, and GND↔GND)
6. Observe frequency bars update in real-time

• I2C0 slave (GPIO 20/21) receives a 41-byte packet: header 0xAA + 40 bins (8-bit).
• Buttons on GPIO 14/15 change the active I2C address (0x60–0x67).
• The TFT renders a 40-bin spectrogram with column dividers.
• Serial output prints the received bin values for validation.

Derived from $f_s=16000$, $N=256$, start bin 8 (500 Hz), with 40 output bins formed by summing pairs of FFT bins across the 500–5500 Hz range. Approximate bin centers are:

$$f_{bin}(n) = 500 + 125n;\text{Hz},\quad n=0\ldots39$$

┌─────────────────────────────────────────────────┐ │ I2C: 0x60 (yellow, size 2) │ │ │ │ Frequency Spectrum (white, size 2) │ │ │ │ │││││││││││││││││││││││││││││││││││││││││ │ │ │││││││││││││││││││││││││││││││││││││││││ │ │ (40-bin spectrogram with column dividers) │ │ │ │ 500-5500 Hz (40 bins) (gray, size 1) │ └─────────────────────────────────────────────────┘

• Verify power supply is adequate (TFT can draw significant current)
• Check CS, DC, and RST pins are correctly connected

• Verify cross-device wiring: Master GPIO8→Slave GPIO20 and Master GPIO9→Slave GPIO21
• Verify both devices share a common GND
• Ensure pull-up resistors on I2C bus (usually 4.7kΩ)
• Check master device is transmitting to correct address
• Use USB serial monitor to see debug output (115200 baud)

• Check buttons are connected between GPIO 14/15 and GND
• Verify pull-ups are enabled (done in software)
• Wait 200ms between button presses (debounce delay)

• Ensure buttons are properly debounced
• Check serial output for address change confirmation
• Verify address is within range 0x60-0x67

Connect USB cable and open serial monitor at 115200 baud to see:

• Startup messages
• Current I2C address
• Received packet information
• Frequency bin values
• Address change confirmations

• Custom driver implementation in st7796_driver.c
• SPI communication @ 32 MHz
• 16-bit color (RGB565)
• Hardware-accelerated rectangle fills
• Simple 5x7 bitmap font for text

• Display update throttled to once every 2 seconds to reduce SPI load
• Non-blocking visualization updates

• Pico Breadboard Kit Plus Version (as referenced in design)
• Any RP2040 board with sufficient GPIO pins
• Standard 3.5" ST7796-based TFT displays

See LICENSE file in parent directory.

• Raspberry Pi Pico SDK
• ST7796 Datasheet
• Main Audio Capture Project: ../Speech_Recognition_AudioCapture/