Javascript decoder

The Spirit LoRaWAN Radon Detector sends data compressed in a hex string format. To interpret this data, you need to use a JSON decoder in your LoRaWAN network server. Below is the JSON decoder that you can use to decode the payload sent by the Spirit device.

function hexToBytes(hex) {
  const bytes = [];
  for (let c = 0; c < hex.length; c += 2) {
    bytes.push(parseInt(hex.substr(c, 2), 16));
  }
  return bytes;
}

function byteToBinary(byte) {
  return byte.toString(2).padStart(8, "0");
}

function bytesToBinary(bytes) {
  return bytes.map(byteToBinary).join("");
}

function decodeStandalone(hex) {
  const bytes = hexToBytes(hex);

  // ---- Helper extractors ----
  function getSerieId() {
    return ((bytes[3] & 0x03) << 2) | ((bytes[2] & 0xf0) >> 4);
  }

  function getPacketNumber() {
    return ((bytes[2] & 0x0f) << 16) | (bytes[1] << 8) | bytes[0];
  }

  function getRadonLevel() {
    return ((bytes[5] & 0x0f) << 10) | (bytes[4] << 6) | ((bytes[3] & 0xfc) >> 2);
  }

  function getUncertainty() {
    return ((bytes[7] & 0x0f) << 12) | (bytes[6] << 4) | ((bytes[5] & 0xf0) >> 4);
  }

  function getTemp() {
    let val = bytes[8];
    return val / 2.0 - 40.0;
  }

  function getHumidity() {
    return bytes[9] / 2.0;
  }

  function getPressure() {
    return bytes[10] + 900;
  }

  function getVoltage() {
    return bytes[11] * 10 + 2500;
  }

  function getStatusBits() {
    return byteToBinary(bytes[12]);
  }

  function parseStatus(statusBits) {
    return {
      aggregatedTampering: parseInt(statusBits.substring(0, 3), 2),
      tampering: statusBits[5] === "1",
      errorExists: statusBits[4] === "1",
      charging: statusBits[3] === "1",
      onBattery: statusBits[7] === "1",
      radonSensorOff: statusBits[6] === "0", // invert like Java
    };
  }

  // ---- Build output object ----
  const statusBits = getStatusBits();
  const status = parseStatus(statusBits);

  return {
    dataFromDevice: {
      measureSerieId: getSerieId(),
      packetNumber: getPacketNumber(),
      radonLevel: getRadonLevel(),
      radonLevelUncertainty: getUncertainty(),

      temperature: getTemp(),
      relativeHumidity: getHumidity(),
      pressure: getPressure(),
      voltage: getVoltage(),

      onBattery: status.onBattery,
      radonSensorOn: !status.radonSensorOff,
      tampering: status.tampering,
      batteryCharging: status.charging,
      errorExists: status.errorExists,
      aggregatedTampering: status.aggregatedTampering,
    },
  };
}



// Example usage:
const hexInput = "EDDB211400300000813D699E22"; // replace with your real hex payload
const result = decodeStandalone(hexInput);
console.log(JSON.stringify(result, null, 2));