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wellue-o2ring-protocol

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Reverse-engineered Bluetooth Low Energy protocol documentation for the Wellue O2Ring pulse oximeter

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# Wellue O2Ring Bluetooth Low Energy Protocol

Reverse-engineered BLE protocol documentation for the **Wellue O2Ring** pulse oximeter.

## Overview

The O2Ring communicates via Bluetooth Low Energy (BLE) using a custom GATT service. This document describes the protocol for:
- Retrieving device information
- Reading real-time sensor data
- Downloading stored measurement files

## BLE Service & Characteristics

| Type | UUID |
|------|------|
| **Service** | `14839ac4-7d7e-415c-9a42-167340cf2339` |
| **Notify** (read responses) | `0734594a-a8e7-4b1a-a6b1-cd5243059a57` |
| **Write** (send commands) | `8b00ace7-eb0b-49b0-bbe9-9aee0a26e1a3` |

## Packet Structure

All packets follow this structure:

```
┌──────┬─────┬──────────┬───────┬────────┬──────────┬─────┐
│ 0xAA │ CMD │ CMD^0xFF │ BLOCK │ LENGTH │ DATA ... │ CRC │
└──────┴─────┴──────────┴───────┴────────┴──────────┴─────┘
  1B     1B      1B        2B       2B      var       1B
```

| Field | Size | Description |
|-------|------|-------------|
| Header | 1 byte | Always `0xAA` |
| CMD | 1 byte | Command code |
| CMD XOR | 1 byte | `CMD ^ 0xFF` (validation) |
| Block | 2 bytes | Block number (little-endian), used for file reads |
| Length | 2 bytes | Data length (little-endian) |
| Data | variable | Command-specific payload |
| CRC | 1 byte | CRC-8 checksum |

### CRC-8 Algorithm

```python
def crc8(data):
    crc = 0
    for b in data:
        chk = crc ^ b
        crc = 0
        if chk & 0x01: crc = 0x07
        if chk & 0x02: crc ^= 0x0e
        if chk & 0x04: crc ^= 0x1c
        if chk & 0x08: crc ^= 0x38
        if chk & 0x10: crc ^= 0x70
        if chk & 0x20: crc ^= 0xe0
        if chk & 0x40: crc ^= 0xc7
        if chk & 0x80: crc ^= 0x89
    return crc
```

## Commands

| Code | Name | Description |
|------|------|-------------|
| `0x14` (20) | INFO | Get device info (JSON response) |
| `0x17` (23) | READ_SENSORS | Real-time SpO2/pulse reading |
| `0x03` (3) | FILE_OPEN | Open a stored file for reading |
| `0x04` (4) | FILE_READ | Read next block from open file |
| `0x05` (5) | FILE_CLOSE | Close the open file |

### INFO Command (0x14)

Request device information including battery status and file list.

**Request:** Empty data payload

**Response:** JSON string with device info:
```json
{
  "CurBAT": "75%",
  "FileList": "20260116233312.vld,20260115221045.vld",
  "Model": "O2Ring",
  "SN": "XXXX"
}
```

### FILE_OPEN Command (0x03)

Open a stored measurement file for download.

**Request:** Filename as ASCII string, **must be null-terminated** (`\x00`)

**Response:**
- Byte 1: Status (0 = success)
- Bytes 7-10: File size (32-bit little-endian)

**Important:** The null terminator is required, otherwise the device returns error code 9.

### FILE_READ Command (0x04)

Read a block of data from the currently open file.

**Request:** Block number in the BLOCK field (starts at 0)

**Response:** File data in the DATA field

Continue incrementing the block number until you've read `file_size` bytes.

### FILE_CLOSE Command (0x05)

Close the currently open file.

**Request:** Empty data payload

**Response:** Status confirmation

## VLD File Format (Version 3)

The O2Ring stores measurements in `.vld` files with the following binary format:

### Header (26 bytes)

| Offset | Size | Type | Description |
|--------|------|------|-------------|
| 0 | 2 | uint16_le | Version (3 for VLD3) |
| 2 | 2 | uint16_le | Year |
| 4 | 1 | uint8 | Month |
| 5 | 1 | uint8 | Day |
| 6 | 1 | uint8 | Hour |
| 7 | 1 | uint8 | Minute |
| 8 | 1 | uint8 | Second |
| 9-17 | 9 | - | Reserved/flags |
| 18 | 2 | uint16_le | Duration in seconds |
| 20-25 | 6 | - | Reserved |

### Measurement Records (starting at offset 40)

Each record is **5 bytes**:

| Offset | Size | Type | Description |
|--------|------|------|-------------|
| 0 | 1 | uint8 | SpO2 percentage (70-100 valid, 0xFF = no finger) |
| 1 | 1 | uint8 | Heart rate BPM (40-200 valid, 0xFF = no finger) |
| 2 | 1 | bool | Invalid flag |
| 3 | 1 | uint8 | Motion indicator |
| 4 | 1 | uint8 | Vibration alert status |

### Calculating Timestamps

The time interval between records can be calculated as:
```
interval = duration_seconds / record_count
```

Typically ~4 seconds per record for overnight recordings.

## Device States

The O2Ring must be in **Standby Mode** to accept BLE connections for data sync.

### Entering Standby Mode

**After a recording session:**
```
Remove ring from finger → Saves data → Countdown 10→0 → "END" → Standby
```

**From powered-off state:**
```
Insert finger briefly and remove → Shows time/battery → Standby
```

**Note:** The device automatically powers off after ~2 minutes without a BLE connection.

## Implementation Notes

### BLE Write Chunking

BLE characteristic writes are limited to 20 bytes. Split larger packets:
```python
for i in range(0, len(packet), 20):
    await client.write_gatt_char(WRITE_UUID, packet[i:i+20], response=False)
    await asyncio.sleep(0.02)  # Small delay between chunks
```

### Response Assembly

Responses may arrive in multiple notifications. Accumulate data until you have:
- At least 7 bytes (header complete)
- Total length matches: `7 + data_length + 1` (header + data + CRC)

## References

- [MackeyStingray/o2r](https://github.com/MackeyStingray/o2r) - Original protocol research
- [ecostech/viatom-ble](https://github.com/ecostech/viatom-ble) - Viatom/Wellue BLE implementations

## License

This documentation is provided for educational and interoperability purposes.

## Contributing

Contributions welcome! If you discover additional commands or file format details, please submit a PR.

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