Decoding Catena 4450 sensor1 packets for The Things Network

TTN-decode-0x14.js

// Updated 2017-04-20 23:08 EDT tmm@mcci.com -- fix typos in comments
// Add this in your application's "payload formats" section of 
// https://console.thethingsnetwork.org
function Decoder(bytes, port) {
  // Decode an uplink message from a buffer
  // (array) of bytes to an object of fields.
  var decoded = {};

  if (port === 1) {
    cmd = bytes[0];
    if (cmd == 0x14) {
        // decode Catena 4450 M101 "sensor1" data

        // test vectors:
        //  14 01 18 00 ==> vBat = 1.5
        //  14 01 F8 00 ==> vBat = -0.5
        //  14 05 F8 00 42 ==> boot: 66, vBat: -0.5
        //  14 0D F8 00 42 17 80 59 35 80 ==> adds one temp of 23.5, rh = 50, p = 913.48

        // i is used as the index into the message. Start with the flag byte.
        var i = 1;
        // fetch the bitmap.
        var flags = bytes[i++];

        if (flags & 0x1) {
            // set vRaw to a uint16, and increment pointer
            var vRaw = (bytes[i] << 8) + bytes[i + 1];
            i += 2;
            // interpret uint16 as an int16 instead.
            if (vRaw & 0x8000)
                vRaw += -0x10000;
            // scale and save in decoded.
            decoded.vBat = vRaw / 4096.0;
        }

        if (flags & 0x2) {
            var vRaw = (bytes[i] << 8) + bytes[i + 1];
            i += 2;
            if (vRaw & 0x8000)
                vRaw += -0x10000;
            decoded.vBus = vRaw / 4096.0;
        }

        if (flags & 0x4) {
            var iBoot = bytes[i];
            i += 1;
            decoded.boot = iBoot;
        }

        if (flags & 0x8) {
            // we have temp, pressure, RH
            var tRaw = (bytes[i] << 8) + bytes[i + 1];
            if (tRaw & 0x8000)
                tRaw = -0x10000 + tRaw;
            i += 2;
            var pRaw = (bytes[i] << 8) + bytes[i + 1];
            i += 2;
            var hRaw = bytes[i++];

            decoded.tempC = tRaw / 256;
            decoded.error = "none"
            decoded.p = pRaw * 4 / 100.0;
            decoded.rh = hRaw / 256 * 100;
        }

        if (flags & 0x10) {
            // we have lux
            var luxRaw = (bytes[i] << 8) + bytes[i + 1];
            i += 2;
            decoded.lux = luxRaw;
        }
    }
  }
  return decoded;
}