Milesight GS301: LoRaWAN Odor Detector (NH3 & H2S)

function decodeUplink(input) {
  var bytes = input.bytes;
  var data = {};

  for (var i = 0; i < bytes.length; ) {
    var channel = bytes[i++];
    var type = bytes[i++];

    if (channel === 0x01 && type === 0x75) {          // battery (%)
      data.battery = bytes[i]; i += 1;
    } else if (channel === 0x02 && type === 0x67) {   // temperature (degC)
      data.temperature = readInt16LE(bytes, i) / 10; i += 2;
    } else if (channel === 0x03 && type === 0x68) {   // humidity (%RH)
      data.humidity = bytes[i] / 2; i += 1;
    } else if (channel === 0x04 && type === 0x7d) {   // NH3 (ppm)
      var nh3 = readUInt16LE(bytes, i); i += 2;
      if (nh3 === 0xfffe || nh3 === 0xffff) {
        data.nh3_status = nh3 === 0xffff ? "device_error" : "polarizing";
      } else {
        data.nh3 = nh3 / 100;
      }
    } else if (channel === 0x05 && type === 0x7d) {   // H2S (ppm), firmware <= v1.1
      var h2s = readUInt16LE(bytes, i); i += 2;
      if (h2s === 0xfffe || h2s === 0xffff) {
        data.h2s_status = h2s === 0xffff ? "device_error" : "polarizing";
      } else {
        data.h2s = h2s / 100;
      }
    } else if (channel === 0x06 && type === 0x7d) {   // H2S (ppm), firmware >= v1.2
      var h2s12 = readUInt16LE(bytes, i); i += 2;
      if (h2s12 === 0xfffe || h2s12 === 0xffff) {
        data.h2s_status = h2s12 === 0xffff ? "device_error" : "polarizing";
      } else {
        data.h2s = h2s12 / 1000;
      }
    } else {
      break;
    }
  }
  return { data: data };
}

function readUInt16LE(b, i) {
  return (b[i + 1] << 8) | b[i];
}

function readInt16LE(b, i) {
  var v = readUInt16LE(b, i);
  return v > 0x7fff ? v - 0x10000 : v;
}