gometer

GPIO audio visualizer for Squeezelite. Reads the player's visualization shared-memory buffer and drives:

• a 7-LED bar-meter on Raspberry Pi GPIO when audio is playing
• a 32×16 WS2812 RGB matrix with a phosphor-trail waveform visualizer when audio is playing, and outdoor temperature when paused

A small embedded HTTP control surface exposes power on/off and live calibration sliders (brightness, gamma, per-channel color balance).

Hardware

• Raspberry Pi (4 recommended). Both PWM channels free.
• 5 V regulated PSU sized to the matrix: ~4 A typical, 10 A worst-case for default brightness on 512 pixels. See Power budget.
• WS2812 serpentine matrix, default 4×2 panels of 8×8 (32×16 = 512 pixels), driven as two horizontal halves on PWM0 (GPIO 12) and PWM1 (GPIO 13).
• 7 indicator LEDs on GPIO 4, 17, 22, 23, 24, 25, 27 with current limiting.
• 74AHCT125 (or similar) level shifter on the WS2812 data lines.
• Squeezelite running on the same Pi with visualization SHM enabled.
• I²S DAC HAT for audio output.

/boot/config.txt (or /boot/firmware/config.txt) needs:

dtparam=audio=off
dtoverlay=<your-dac-overlay>

dtparam=audio=off frees PWM0/PWM1 for the matrix. The DAC sits on I²S (GPIO 18-21), which doesn't collide.

Power budget

WS2812B pixels draw up to ~60 mA at 5 V at full white. Power scales roughly linearly with brightness × duty:

I  ≈  N × 0.060 A × (brightness/255) × duty

For N = 512, default brightness = 80:

Scenario	Brightness	Duty	Pixel current
Typical visualization	80	0.40	~3.9 A
All-white burst	80	1.00	~9.6 A
All-white at full brightness	255	1.00	~30.7 A

A 5 V / 15 A supply comfortably covers default brightness. Inject 5 V at the start of each panel row, fuse the rails, keep grounds common.

Matrix wiring

Eight 8×8 panels arranged 4×2, chained as a column-major serpentine, two halves driven independently:

Half	Pixels	GPIO	PWM channel
Top 8 rows	0-255	12	PWM0
Bottom 8 rows	256-511	13	PWM1

xyToIndex in internal/led/ws2812.go is the source of truth for the mapping.

Build & run

make build      # builds ./gometer for linux/arm64
sudo ./gometer  # root required for PWM-based WS2812 access

Configuration via --flag, env (GOMETER_*), or YAML at ~/.config/gometer/gometer.yaml. See internal/config/config.go for the full list (FFT window, EMA constants, beat boost, etc.).

By default the daemon:

• Watches /dev/shm/squeezelite* for the visualization buffer
• Drives the bar-meter on the configured GPIOs
• Drives the matrix on GPIO 12/13
• Serves the control UI on :9001

HTTP control

Open http://<pi>:9001/ for the htmx-driven UI: power on/off, plus live sliders for brightness, gamma, and per-channel color balance. The sliders write directly to the running visualizer.

For scripting:

curl -X POST -d 'action=toggle' http://localhost:9001/control
curl -X POST -d 'brightness=120' http://localhost:9001/tune
curl -X POST -d 'color_r=1.0&color_g=0.78&color_b=0.78' http://localhost:9001/tune
curl http://localhost:9001/status

/control actions: toggle, turn_on, turn_off, set_mode (with mode=auto/off). /tune accepts any subset of brightness (0-255), gamma, color_r, color_g, color_b.

Optional weather overlay

Point weather.url at an Ecowitt-style JSON endpoint (with tempf/humidity/solarradiation fields). When audio is silent for 10 s+, the matrix cycles through outdoor temperature, humidity, and solar readings. Empty (the default) disables.

# ~/.config/gometer/gometer.yaml
weather:
  url: "https://my-weather-host.example/latest"

Configuration notes

• http.enabled (default true); http.listen defaults to :9001.
• pins and thresholds slices must be the same length.
• color_balance is [R, G, B] (default [1.0, 0.85, 0.85]) compensating for the WS2812B's narrow-spectrum red die. Live-adjustable via the UI's sliders.
• led_order is msb (default) or lsb.

Credits

• WS281x PWM driver vendored from Jon-Bright/ledctl (MIT). See ledctl/LICENSE.md.
• Squeezelite SHM layout: ralph-irving/squeezelite.
• htmx 2.x (htmx.org), BSD 2-clause, vendored.

License

MIT. See LICENSE.