blue
b5d1169392
Product name BikeAudio -> "Resound" (the device isn't bike-specific — works at
home, backyard, camping, parties, group rides). This is the A2DP advertise name
the phone connects to: sink.start("Resound"). All banners/comments + README
updated. (After reflashing the sink, the phone must forget "BikeAudio" and
connect to "Resound".)
Firmware vocabulary clarified (the old hub/sink/source was confusing —
"source" read backwards since those boards SEND audio):
hub_s3.cpp / env hub_s3 -> hud.cpp / env hud
board_sink.cpp -> sink.cpp (env sink)
board_source.cpp -> broadcaster.cpp (envs broadcaster_headset
0x11, broadcaster_speaker1 0x10,
broadcaster_guest 0x12)
hub_proto.h -> bus_proto.h
default_envs = sink + the three broadcasters. All envs build clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
104 lines
5.1 KiB
Markdown
104 lines
5.1 KiB
Markdown
# Resound — 3-board Bluetooth relay
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Relays iPhone audio to **two** Bluetooth speakers (JBL Charge 5 + Cardo "Tangerine EDGE")
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at the same time.
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## Why three boards?
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One ESP32 **cannot** do this alone:
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1. **Sink + source can't coexist.** To receive from the iPhone the ESP32 must be an
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A2DP *sink*; to play through a speaker it must be an A2DP *source*. The ESP32's
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classic-Bluetooth stack registers only one A2DP role at a time (the ESP32-A2DP
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library keeps a single global instance that each role overwrites). Running a sink
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and a source together orphans the sink — the iPhone can't even see it.
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2. **A source reaches only one speaker.** An A2DP source holds a single outgoing
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link, so one board can drive one speaker, not two.
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So the job is split: one board receives, one board per speaker sends, and they pass
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audio between them over a short digital **I2S** wire bus.
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```
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iPhone ))BT)) ┌──────────────┐ I2S bus (BCK/WS/DATA + GND)
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│ Board A │═══════════════╦═══════════════╗
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│ A2DP SINK │ ║ ║
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│ I2S MASTER │ ▼ ▼
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└──────────────┘ ┌────────────┐ ┌────────────┐
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│ Board B │ │ Board C │
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│ A2DP SOURCE│ │ A2DP SOURCE│
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│ I2S SLAVE │ │ I2S SLAVE │
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└─────┬──────┘ └─────┬──────┘
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))BT)) ))BT))
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JBL Charge 5 Tangerine EDGE (Cardo)
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```
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## Wiring
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Board A is the I2S **master** (it generates the clocks). Boards B and C are
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**slaves** that listen to A's bus in parallel. Tie the three signals from A to the
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matching input pins on **both** B and C, and tie **all grounds together**.
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| Signal | Board A (master, out) | Board B (slave, in) | Board C (slave, in) |
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|-------------|-----------------------|---------------------|---------------------|
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| Bit clock | **GPIO5** (BCK) | GPIO19 | GPIO19 |
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| Word select | **GPIO25** (WS/LRCK) | GPIO18 | GPIO18 |
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| Data | **GPIO23** (DATA out) | GPIO22 (in) | GPIO22 (in) |
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| Ground | **GND** | GND | GND |
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- A·GPIO5 → B·GPIO19 **and** C·GPIO19
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- A·GPIO25 → B·GPIO18 **and** C·GPIO18
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- A·GPIO23 → B·GPIO22 **and** C·GPIO22
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- A·GND → B·GND **and** C·GND (mandatory — shared clock reference)
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Each board can be powered from its own USB/5V; only the grounds must be common.
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### Sync (touch pads on each source board)
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JBL and Cardo have independent Bluetooth buffering, so one lags the other. Each
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source board has an **adjustable delay** (0–200 ms) you trim live, by ear, with two
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capacitive-touch pads — raise the delay on whichever speaker is *early* until they
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line up. The value is saved to flash (survives power-cycles).
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| Touch pad | Pin | Action |
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|-----------|-------|--------------------------------|
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| **+** | GPIO4 | tap = +5 ms, hold = ramp up |
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| **−** | GPIO27 | tap = −5 ms, hold = ramp down |
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Attach a short wire or a bit of foil to GPIO4 and GPIO27 on each source board and
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touch the end. (There is intentionally **no Wi-Fi/phone UI**: Wi-Fi + Bluetooth +
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the audio buffer don't fit in RAM on the classic ESP32 — it starves the Bluetooth
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stack — so the control is local touch.)
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## Build & flash
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```
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pio run # builds all three
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pio run -e sink # Board A
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pio run -e source_jbl # Board B (target "JBL Charge 5")
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pio run -e source_cardo # Board C (target "Tangerine EDGE")
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```
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Flash each board with the matching environment's artifacts
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(`.pio/build/<env>/{bootloader,partitions,firmware}.bin`).
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**Power-on order:** bring up **Board A first** so the I2S bus is clocking before
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B and C start reading it.
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## First-time pairing
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1. Put the **JBL** and **Cardo** in pairing mode.
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2. Power Board B and Board C — each connects to its speaker by name
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(auto-reconnects on later power-ups).
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3. Power Board A; on the iPhone, connect to **"Resound"**.
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4. Play audio — both speakers should output together.
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## Known limitations
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- **The two speakers are not sample-synchronized.** JBL and Cardo each have their
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own Bluetooth buffering, so one lags the other. The per-board touch delay (above)
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lets you trim a fixed offset to line them up by ear; it is not continuous
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sample-lock, so slow drift over long sessions is possible. Fine for music/intercom;
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not suitable for tight stereo L/R separation.
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- Audio is fixed at the SBC standard **44.1 kHz / 16-bit / stereo**.
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- If Board A reboots, the slave boards' audio pauses until A is clocking again.
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