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onju-v2/m5_echo
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justLV e4d7bc7ca5 End-of-speech protocol, LED tweaks, call-end guard 
- Handle zero-length Opus frame (0x00 0x00) as end-of-speech marker:
  exits opusDecodeTask cleanly, clears isPlaying, re-enables mic
- Zero I2S DMA buffer on opusDecodeTask exit (prevents stale DMA)
- Reject 0xAA audio commands when callActive is false (prevents
  bridge from restarting playback after user double-tapped to end)
- Don't reset mic_timeout after playback if call was ended
- LED: white flash for tap/interrupt, red-orange for call end
- Pipeline: append end-of-speech marker to Opus TCP payload
- ARCHITECTURE.md: document end-of-speech marker protocol
2026-04-07 16:41:59 -07:00
..
audio_compression.h Add M5Stack ATOM Echo PTT firmware and onjuino PTT mode flag 2026-04-03 15:36:42 -07:00
credentials.h.template Add M5Stack ATOM Echo PTT firmware and onjuino PTT mode flag 2026-04-03 15:36:42 -07:00
flash.sh Add LED toggle, TCP_NODELAY, volume controls, --no-monitor flag 2026-04-03 17:06:44 -07:00
m5_echo.ino End-of-speech protocol, LED tweaks, call-end guard 2026-04-07 16:41:59 -07:00
README.md Add M5Stack ATOM Echo PTT firmware and onjuino PTT mode flag 2026-04-03 15:36:42 -07:00
terminal.py Add M5Stack ATOM Echo PTT firmware and onjuino PTT mode flag 2026-04-03 15:36:42 -07:00
test_audio.py Add M5Stack ATOM Echo PTT firmware and onjuino PTT mode flag 2026-04-03 15:36:42 -07:00

README.md

M5 Echo - Push-to-Talk Voice Client

Firmware for the M5Stack ATOM Echo that connects to the esp32-bridge server using the same protocol as onjuino, but with push-to-talk (PTT) instead of voice-activity detection (VAD).

How it differs from onjuino

onjuino m5_echo
Board ESP32-S3 (custom PCB) ESP32-PICO-D4 (M5Stack ATOM Echo)
Mic Standard I2S (separate ADC) PDM (SPM1423, on-chip)
Speaker MAX98357A, 6 NeoPixel LEDs NS4168, 1 SK6812 LED
Interaction Capacitive touch: tap to start call, double-tap to end Physical button: hold to talk, release to listen
Mic control VAD-driven timeout (server extends via 0xDD) Push-to-talk only - mic active while button held
Call lifecycle Manual start/end via touch Auto-starts on boot, persistent until bridge disconnects
PSRAM Yes (2MB, large playback buffer) No (smaller buffers, more DMA buffers to compensate)
Opus Full encoder + decoder Decoder only (mic sends mu-law)
I2S Single config for simultaneous TX+RX Switches between PDM RX (mic) and I2S TX (speaker)

PTT behavior

  • Boot: Connects to WiFi, announces on multicast with PTT flag. Bridge auto-starts a call and opens a persistent TCP connection.
  • Idle: Bridge streams Opus audio over the persistent TCP connection. Device decodes and plays through the speaker.
  • Button press: Immediately stops speaker playback (I2S switches to PDM mic mode). Opus task keeps reading the TCP stream but discards frames. Mic audio is captured, mu-law encoded, and sent via UDP.
  • Button release: I2S switches back to speaker mode. Opus task resumes decoding and playing. The TCP connection stays alive throughout - no reconnection needed between turns.
  • Call end: Bridge closes the TCP connection. Device returns to idle, waiting for a new connection.

Hardware pin mapping (ATOM Echo)

Function GPIO Notes
I2S BCK 19 Shared speaker bit clock
I2S WS/PDM CLK 33 Speaker word select / mic PDM clock
I2S DOUT 22 Speaker data (NS4168)
I2S DIN / PDM DATA 23 Mic data (SPM1423)
Button 39 Active low, input only (no internal pullup)
LED 27 SK6812 RGB (1 LED, GRB order)

I2S quirks on ESP32-PICO-D4

The original ESP32's I2S driver with ALL_RIGHT channel format treats the DMA buffer as stereo-interleaved, unlike the ESP32-S3 which supports true mono. This means:

  • Speaker: sample_rate is set to SAMPLE_RATE / 2 (8000) so the effective mono playback rate is 16kHz
  • Mic: sample_rate is set to SAMPLE_RATE * 2 (32000) and samples are de-interleaved (every other sample) to get 16kHz mono
  • PDM mic channel: ALL_RIGHT is the only channel format that produces non-zero data from the SPM1423 on this board

Protocol compatibility

Uses the same TCP/UDP protocol as onjuino:

  • UDP 3000: Mic audio (mu-law encoded, 512 samples/packet)
  • TCP 3001: Server commands (0xAA audio, 0xBB LED set, 0xCC LED blink, 0xDD mic timeout)
  • Multicast: Device announces as "m5-echo m5echo PTT" on the configured multicast group

The PTT token in the multicast announcement tells the bridge to auto-start a call on discovery and keep the TCP connection open persistently (no silence-based disconnection).

Serial commands

Key Action
P Play local 440Hz test tone (bypasses network, tests I2S)
T Raw mic test (prints sample values)
M Force mic on for 10s (no button needed)
m Force mic off
A Re-send multicast announcement
c Enter config mode (ssid/pass/server/volume)
r Reboot

Config mode is also accessible during WiFi connection (if the stored SSID is wrong).

Building and flashing

./flash.sh              # auto-detect port, compile and flash
./flash.sh compile      # compile only
./flash.sh --regen      # regenerate WiFi credentials from keychain
./flash.sh --force      # force recompile

Requires arduino-cli with the esp32:esp32 core and Adafruit NeoPixel library installed. The Opus decoder uses the esp32_opus library (same as onjuino).

Testing

python3 terminal.py     # serial monitor with command input