TTN-decode.js

function Decoder(bytes, port) {
    // Decode an uplink message from a buffer
    // (array) of bytes to an object of fields.
    var decoded = {};
    
    // Weight
    codedWeight = bytes[0] + bytes[1] * 256;
    decoded.weight = codedWeight *2;

    // temperature 
    codedTemp = bytes[2] + bytes[3] * 256;
    decoded.degreesC = sflt162f(codedTemp) * 100;
    
    // humidity 
    decoded.humidity = bytes[4];

    // pressure
    decoded.pressure = bytes[5] + 900;

    // Voltage
    decoded.voltage = bytes[6] *10;

    // Counter
    decoded.counter = bytes[8] + 256 * bytes[7];
    
    return decoded;
  }
  
  function sflt162f(rawSflt16)
      {
      // rawSflt16 is the 2-byte number decoded from wherever;
      // it's in range 0..0xFFFF
      // bit 15 is the sign bit
      // bits 14..11 are the exponent
      // bits 10..0 are the the mantissa. Unlike IEEE format, 
      // 	the msb is transmitted; this means that numbers
      //	might not be normalized, but makes coding for
      //	underflow easier.
      // As with IEEE format, negative zero is possible, so
      // we special-case that in hopes that JavaScript will
      // also cooperate.
      //
      // The result is a number in the open interval (-1.0, 1.0);
      // 
      
      // throw away high bits for repeatability.
      rawSflt16 &= 0xFFFF;
  
      // special case minus zero:
      if (rawSflt16 == 0x8000)
          return -0.0;
  
      // extract the sign.
      var sSign = ((rawSflt16 & 0x8000) != 0) ? -1 : 1;
      
      // extract the exponent
      var exp1 = (rawSflt16 >> 11) & 0xF;
  
      // extract the "mantissa" (the fractional part)
      var mant1 = (rawSflt16 & 0x7FF) / 2048.0;
  
      // convert back to a floating point number. We hope 
      // that Math.pow(2, k) is handled efficiently by
      // the JS interpreter! If this is time critical code,
      // you can replace by a suitable shift and divide.
      var f_unscaled = sSign * mant1 * Math.pow(2, exp1 - 15);
  
      return f_unscaled;
      }