TTN decoder for AM100/AM102 sensors

am102_decoder.js

function Decoder(bytes, port) {
  // Decode an uplink message from a buffer
  // (array) of bytes to an object of fields.
  var decoded = {};

  // for Ursalink AM100/AM102 Payload Structure
  // From: https://resource.ursalink.com/document/am100_series_payload_structure.pdf
  for (i = 0; i < bytes.length;) {
    // BATTERY (%)
    if (bytes[i] == 0x01 && bytes[i+1] == 0x75) {
        decoded.battery = bytes[i+2];
        i += 3;
        continue;
    }
    // TEMPERATURE (degC)
    else if (bytes[i] == 0x03 && bytes[i+1] == 0x67) {
      // If there's already a reading, ignore
      if (typeof decoded.temperature == 'undefined') {
        decoded.temperature = readUInt16LE(bytes.slice(i+2, i+3)) / 10;
      }
      i += 4;
      continue;
    }
    // HUMIDITY (% abs)
    else if (bytes[i] == 0x04 && bytes[i+1] == 0x68) {
      // If there's already a reading, ignore
      if (typeof decoded.humidity == 'undefined') {
        decoded.humidity = bytes[i+2]/2 ;
      }
      i += 3;
      continue;
    }
    // Light levels (lux)
    else if (bytes[i] == 0x06 && bytes[i+1] == 0x65) {
      // If there's already a reading, ignore
      if (typeof decoded.illumination == 'undefined') {
        decoded.illumination = readUInt16LE(bytes.slice(i+2, i+3)) ;
        decoded.visible_infrared = readUInt16LE(bytes.slice(i+4, i+5)) ;
        decoded.infrared = readUInt16LE(bytes.slice(i+6, i+7)) ;
      }
      i += 8;
      continue;
    }
    // PIR Activity (number of events)
    else if (bytes[i] == 0x05 && bytes[i+1] == 0x6a) {
      // If there's already a reading, ignore
      if (typeof decoded.activity == 'undefined') {
        //decoded.activity = readUInt16LE(bytes.slice(i+2, i+3)) ;
        decoded.activity = (bytes[i+3] << 8) + bytes[i+2];
      }
      i += 4;
      continue;
    }
    // CO2 concentration (ppm)
    else if (bytes[i] == 0x07 && bytes[i+1] == 0x7d) {
      // If there's already a reading, ignore
      if (typeof decoded.co2 == 'undefined') {
        //decoded.co2 = readUInt16LE(bytes.slice(i+2, i+3)) ;
        decoded.co2 = (bytes[i+3] << 8) + bytes[i+2];
        //decoded.co2_hex = toHexString(bytes.slice(i+2, i+3)) ;
      }
      i += 4;
      continue;
    }
    // TVOC concentration (ppb)
    else if (bytes[i] == 0x08 && bytes[i+1] == 0x7d) {
      // If there's already a reading, ignore
      if (typeof decoded.tvoc == 'undefined') {
        decoded.tvoc = (bytes[i+3] << 8) + bytes[i+2];
      }
      i += 4;
      continue;
    }
    // Barometric Pressure (kPa)
    else if (bytes[i] == 0x09 && bytes[i+1] == 0x73) {
      // If there's already a reading, ignore
      if (typeof decoded.pressure == 'undefined') {
        decoded.pressure = ((bytes[i+3] << 8) + bytes[i+2]) / 10;
      }
      i += 4;
      continue;
    }
    else {
      // nothing matched
      i++;
    }
  }
  
  return decoded;
}

/* isEmpty
*/ 
function isEmpty(obj) {
  return Object.getOwnPropertyNames(obj).length === 0;
}

/* toHexString
*/
function toHexString(byteArray) {
  var s = '0x';
  byteArray.forEach(function(byte) {
    s += ('0' + (byte & 0xFF).toString(16)).slice(-2);
  });
  return s;
}

/* ******************************************
 * bytes to number
 ********************************************/
function readUInt8LE(bytes) {
    return (bytes & 0xFF);
}

function readInt8LE(bytes) {
    var ref = readUInt8LE(bytes);
    return (ref > 0x7F) ? ref - 0x100 : ref;
}

function readUInt16LE(bytes) {
    var value = (bytes[1] << 8) + bytes[0];
    return (value & 0xFFFF);
}

function readInt16LE(bytes) {
    var ref = readUInt16LE(bytes);
    return (ref > 0x7FFF) ? ref - 0x10000 : ref;
}

function readUInt32LE(bytes) {
    var value = (bytes[3] << 24) + (bytes[2] << 16) + (bytes[1] << 8) + bytes[0];
    return (value & 0xFFFFFFFF);
}

function readInt32LE(bytes) {
    var ref = readUInt32LE(bytes);
    return (ref > 0x7FFFFFFF) ? ref - 0x100000000 : ref;
}

function readFloatLE(bytes) {
    // JavaScript bitwise operators yield a 32 bits integer, not a float.
    // Assume LSB (least significant byte first).
    var bits = bytes[3] << 24 | bytes[2] << 16 | bytes[1] << 8 | bytes[0];
    var sign = (bits >>> 31 === 0) ? 1.0 : -1.0;
    var e = bits >>> 23 & 0xff;
    var m = (e === 0) ? (bits & 0x7fffff) << 1 : (bits & 0x7fffff) | 0x800000;
    var f = sign * m * Math.pow(2, e - 150);
    return f;
}