setup_decoder_LoRa-TTN-MQTT-Server-Connection.md

Setup decoder

1. Incoming Data

The Seeed or LoRa devices sends sensor data.
The LoRa device sends the data to The Things Network (TTN)

2. TTN sends data via MQTT

Server.js includes code that connects to TTN via MQTT (not the secure one yet).
When a message arrives, the server decodes the message.

3. Decoding

The recieved message looks something like the below JSON data.
The frm_payload is the message sent, in base64 format.

Received JSON data: {
  end_device_ids: {
    device_id: 'YourDeviceId',
    application_ids: { application_id: 'YourApplicationId' },
    dev_eui: 'YourDevEUI',
    join_eui: 'YourJoinEUI'
  },
  correlation_ids: [
    ...
    ...
  ],
  received_at: '2024-03-07T21:22:52.872345578Z',
  uplink_message: {
    f_port: 1,
    frm_payload: 'AQID',
    rx_metadata: [ [Object] ],
    settings: { data_rate: [Object], frequency: '868000000' }
  },
  simulated: true
}

The decoding steps done in this project are:

const data = JSON.parse(message.toString());            // Convert to JSON object to be able to extract the payload
const payload = data.uplink_message.frm_payload;        // Get the raw payload that is in base64
const bytes = Buffer.from(payload, 'base64');           // Convert it to bytes