Payload Decoder

The payload decoder transforms raw device data (bytes) into structured JSON that the platform can store and visualize.

Codec Types

• NONE: Raw data passthrough — the platform expects valid JSON payloads
• CUSTOM: A JavaScript decoder script processes raw bytes into JSON

Writing a Custom Decoder

Three function signatures are supported. Choose the one that fits your needs.

function decodeUplink(input) {
  // input.bytes: Uint8Array of raw payload
  // input.fPort: LoRaWAN port number (if applicable)
  return {
    data: {
      temperature: (input.bytes[0] << 8 | input.bytes[1]) / 100,
      humidity: input.bytes[2]
    }
  };
}

function Decoder(bytes, port) {
  return {
    temperature: (bytes[0] << 8 | bytes[1]) / 100,
    humidity: bytes[2]
  };
}

function decode(bytes, port) {
  return {
    temperature: (bytes[0] << 8 | bytes[1]) / 100
  };
}

Built-in Templates

The platform provides starter templates you can use and modify:

1. Temperature & Humidity (TTN v3) — 3-byte sensor reading
2. Temperature & Humidity (Legacy) — Legacy decoder format
3. GPS Coordinates — 8-byte latitude/longitude
4. Multi-Sensor — Temperature + humidity + battery level
5. Bitwise Operations — Packed bitfield extraction
6. Simple Decode — Minimal example

Testing Decoders

Use the built-in Test Decoder feature on the profile page:

1. Write or paste your decoder function in the code editor
2. Enter a sample hex payload in the test input (e.g., 09D53C)
3. Click Test
4. Verify the decoded output matches your expected values

Hex Auto-Detection

If the MQTT payload is a pure hexadecimal ASCII string, the platform automatically converts it to bytes before passing it to the decoder.

Example: "48656C6C6F" → [0x48, 0x65, 0x6C, 0x6C, 0x6F]

Security Constraints

Decoder scripts run in an isolated V8 sandbox with strict limits: