Setup decoder for a device

Obtain the decoder source

Go to https://github.com/decentlab/decentlab-decoders and get the respective JavaScript decoder source.

Modify the source for Chirpstack

Chirpstack expects a function with the following signature:

function Decode(fPort, bytes, variables) {
  ...
}

So we modify the source such that the decoder's decode function is called from the above function. Also we remove the main function and its calls, which are for testing purposes.

For DL-DS18, the final source code would look like below:

/* https://www.decentlab.com/products/temperature-sensor-for-lorawan */

var decentlab_decoder = {
  PROTOCOL_VERSION: 2,
  SENSORS: [
    {length: 1,
     values: [{name: 'temperature',
               displayName: 'Temperature',
               convert: function (x) { return (x[0] - 32768) / 16; },
               unit: '°C'}]},
    {length: 1,
     values: [{name: 'battery_voltage',
               displayName: 'Battery voltage',
               convert: function (x) { return x[0] / 1000; },
               unit: 'V'}]}
  ],

  read_int: function (bytes, pos) {
    return (bytes[pos] << 8) + bytes[pos + 1];
  },

  decode: function (msg) {
    var bytes = msg;
    var i, j;
    if (typeof msg === 'string') {
      bytes = [];
      for (i = 0; i < msg.length; i += 2) {
        bytes.push(parseInt(msg.substring(i, i + 2), 16));
      }
    }

    var version = bytes[0];
    if (version != this.PROTOCOL_VERSION) {
      return {error: "protocol version " + version + " doesn't match v2"};
    }

    var deviceId = this.read_int(bytes, 1);
    var flags = this.read_int(bytes, 3);
    var result = {'protocol_version': version, 'device_id': deviceId};
    // decode payload
    var pos = 5;
    for (i = 0; i < this.SENSORS.length; i++, flags >>= 1) {
      if ((flags & 1) !== 1)
        continue;

      var sensor = this.SENSORS[i];
      var x = [];
      // convert data to 16-bit integer array
      for (j = 0; j < sensor.length; j++) {
        x.push(this.read_int(bytes, pos));
        pos += 2;
      }

      // decode sensor values
      for (j = 0; j < sensor.values.length; j++) {
        var value = sensor.values[j];
        if ('convert' in value) {
          result[value.name] = {displayName: value.displayName,
                                value: value.convert.bind(this)(x)};
          if ('unit' in value)
            result[value.name]['unit'] = value.unit;
        }
      }
    }
    return result;
  }
};

function Decode(fPort, bytes, variables) {
  return decentlab_decoder.decode(bytes);
}

Set the decoder

Place the modified code in the corresponding device profile codec and save.

A decoded output: