---
title: Decoder LoRaWAN – helmet tracker (TTN/Chirpstack)
description: "[decode-helmet-tracker-ttn_chirpstackv4.js](https://www.lansitec.com/wp-content/uploads/2026/08/decode-helmet-tracker-ttn_chirpstackv4.js.zip)[Download](https://www.lansitec.com/wp-content/uploads/2026/08/decode-helmet-tracker-ttn_chirpstackv4.js.zip) Below the full decoder code: ``` // Decode uplink function. // // Input is an object with the following fields: // - bytes = Byte array containing the uplink payload, e.g. [255, 230, 255, 0] // - fPort =…"
url: "https://www.lansitec.com/docs/decoders/decoder-lorawan-helmet-tracker-ttn-chirpstack/"
updated: "2026-08-26"
category: Decoders
---

# Decoder LoRaWAN – helmet tracker (TTN/Chirpstack)

[decode-helmet-tracker-ttn_chirpstackv4.js](https://www.lansitec.com/wp-content/uploads/2026/08/decode-helmet-tracker-ttn_chirpstackv4.js.zip)[Download](https://www.lansitec.com/wp-content/uploads/2026/08/decode-helmet-tracker-ttn_chirpstackv4.js.zip)

Below the full decoder code:

```
// Decode uplink function.
//
// Input is an object with the following fields:
// - bytes = Byte array containing the uplink payload, e.g. [255, 230, 255, 0]
// - fPort = Uplink fPort.
// - variables = Object containing the configured device variables.
//
// Output must be an object with the following fields:
// - data = Object representing the decoded payload.

// Helmet Tracker
function decodeUplink(input) {
  // bytes
  var bytes = input.bytes;
  // type
  var uplinkType = (bytes[0] >> 4) & 0x0f;
  switch (uplinkType) {
    case 0x01:
      return { data: decodeRegistration(bytes) };

    case 0x02:
      return { data: decodeHeartbeat(bytes) };

    case 0x03:
      return { data: decodeGNSSPosition(bytes) };

    case 0x05:
      return { data: decodeUUIDReport(bytes) };

    case 0x07:
      return { data: decodeBeacon(bytes) };

    case 0x08:
      return { data: decodeAlarm(bytes) };

    case 0x0c:
	    return { data: decodeBracelet(bytes) };

    default:
      return null;
  }
}

// type: 0x1 Registration
function decodeRegistration(bytes) {
  var data = {};
  data.type = "Registration";
  // adr
  data.adr = ((bytes[0] >> 3) & 0x1) == 0 ? "OFF" : "ON";
  // power
  data.power = ((bytes[2] >> 3) & 0x1f) + "dBm";
  // dr
  data.dr = (bytes[3] >> 4) & 0x0f;
  // gnssEnable
  data.gnssEnable = ((bytes[3] >> 3) & 0x01) == 0 ? "Disable" : "Enable";
  // positionReportMode
  var positionReportMode = (bytes[3] >> 1) & 0x03;
  if (positionReportMode == 0) {
    data.positionReportMode = "Period";
  } else if (positionReportMode == 0) {
    data.positionReportMode = "Autonomous";
  } else if (positionReportMode == 0) {
    data.positionReportMode = "On-Demand";
  }
  // bleEnable
  data.bleEnable = (bytes[3] & 0x01) == 0 ? "Disable" : "Enable";
  // blePositionReportInterval
  data.blePositionReportInterval =
    (((bytes[4] << 8) & 0xff00) | (bytes[5] & 0xff)) * 5 + "s";
  // gnssPositionReportInterval
  data.gnssPositionReportInterval =
    (((bytes[6] << 8) & 0xff00) | (bytes[7] & 0xff)) * 5 + "s";
  // heartbeatPeriod
  data.heartbeatPeriod = (bytes[8] & 0xff) * 30 + "s";
  // version
  data.version =
    (bytes[9] & 0xff).toString(16).toUpperCase() +
    "." +
    (bytes[10] & 0xff).toString(16).toUpperCase();
  // cfmmsg
  data.cfmmsg = "1 Confirmed every " + (bytes[11] & 0xff) + " Heartbeat";
  // hbCount
  data.hbCount = "Disconnect Judgement " + (bytes[12] & 0xff);
  // fallDetectFeatureThreshold
  data.fallDetectFeatureThreshold = (bytes[13] & 0xff) * 0.5 + " meters";

  return data;
}

// type: 0x2 Heartbeat
function decodeHeartbeat(bytes) {
  var data = {};
  // type
  data.type = "Heartbeat";
  // battery
  data.battery = bytes[1] + "%";
  // rssi
  data.rssi = bytes[2] * -1 + "dBm";
  // snr
  data.snr = (((bytes[3] << 8) & 0xff00) | (bytes[4] & 0xff)) / 100 + "dB";
  // bleReceivingNumber
  data.bleReceivingNumber = bytes[5];
  // gnssSearchingNumber
  data.gnssSearchingNumber = bytes[6];
  // chargeTime
  data.chargeTime = bytes[7] * 30 + "s";
  // wearTime
  data.wearTime = bytes[8] * 30 + "s";
  // moveState
  data.moveState = (bytes[9] >> 4) & 0x0f;
  // temperature
  data.temperature = 0;

  return data;
}

// type: 0x3 GNSSPosition
function decodeGNSSPosition(bytes) {
  var data = {};
  // type
  data.type = "GNSSPosition";
  // gnssState
  data.gnssState = ((bytes[0] >> 3) & 0x01) == 0 ? "Success" : "Fail";
  // wearState
  data.wearState = (bytes[0] & 0x01) == 0 ? "Do not wear" : "Wear";
  // pressure
  let pressure =
    (bytes[1] << 24) | (bytes[2] << 16) | (bytes[3] << 8) | bytes[4];
  data.pressure = pressure / 10 + "pa";
  // longitude
  let longitude =
    (bytes[5] << 24) | (bytes[6] << 16) | (bytes[7] << 8) | bytes[8];
  data.longitude = hex2float(longitude);
  // latitude
  let latitude =
    (bytes[9] << 24) | (bytes[10] << 16) | (bytes[11] << 8) | bytes[12];
  data.latitude = hex2float(latitude);
  // time
  let time =
    (bytes[13] << 24) | (bytes[14] << 16) | (bytes[15] << 8) | bytes[16];
  data.time = timestampToTime((time + 8 * 60 * 60) * 1000);
    // altitude
  let altitude =
    (bytes[17] << 24) | (bytes[18] << 16) | (bytes[19] << 8) | bytes[20];
  data.altitude = hex2float(altitude) + "m";

  return data;
}

// type: 0x5 UUIDReport
function decodeUUIDReport(bytes) {
  var data = {};
  // type
  data.type = "UUIDReport";
  // number
  data.number = Math.floor((bytes.length - 1) / 17);
  var beaconUUIDList = [];
  for (let i = 0; i < data.number; i++) {
    var beaconTypeId = bytes[1 + 17 * i] & 0x03;
    if (beaconTypeId == 0x00) {
      beaconTypeId = "PositionBeaconUUID";
    } else if (beaconTypeId == 0x01) {
      beaconTypeId = "AssetBeaconUUID";
    } else if (beaconTypeId == 0x02) {
      beaconTypeId = "SpecialBeaconUUID";
    } else if (beaconTypeId == 0x03) {
      beaconTypeId = "SearchBeaconUUID";
    }

    var beaconUUID = "";
    for (let j = 0; j < 16; j++) {
      beaconUUID += (bytes[2 + 17 * i + j] & 0xff)
        .toString(16)
        .toUpperCase()
        .padStart(2, "0");
    }
    beaconUUIDList.push({ beaconTypeId, beaconUUID });
  }
  data.beaconUUIDList = beaconUUIDList;

  return data;
}

// type: 0x7 Beacon
function decodeBeacon(bytes) {
  var data = {};
  data.type = "Beacon";
  // wearState
  data.wearState = (bytes[0] & 0x01) == 0 ? "Not wearing" : "Wearing";
  // pressure
  let pressure =
    (bytes[1] << 24) | (bytes[2] << 16) | (bytes[3] << 8) | bytes[4];
  data.pressure = pressure / 10 + "pa";
  // numner
  data.number = bytes[5] & 0x0f;
  for (let i = 0; i < data.number; i++) {
    var index = 7 + 5 * i;
    var major = ((bytes[index] << 8) | bytes[index + 1])
      .toString(16)
      .toUpperCase()
      .padStart(4, "0");
    var minor = ((bytes[index + 2] << 8) | bytes[index + 3])
      .toString(16)
      .toUpperCase()
      .padStart(4, "0");
    var rssi = bytes[index + 4] - 256 + "dBm";

    data["beacon" + (i + 1)] = major + minor;
    data["rssi" + (i + 1)] = rssi;
  }

  return data;
}

// type: 0x8 Alarm
function decodeAlarm(bytes) {
  var data = {};
  data.type = "Alarm";
  var alarmValue = bytes[1] & 0xff;
  if (alarmValue == 1) {
    data.alarm = "SOS";
  } else if (alarmValue == 2) {
    data.alarm = "Fall";
  } else if (alarmValue == 3) {
    data.alarm = "Special area";
  } else if (alarmValue == 4) {
    data.alarm = "Search";
  }
  return data;
}

// type: 0x0c Bracelet
function decodeBracelet(bytes) {
  var data = {};
  data.type = "Bracelet";
  var number =  bytes[1];
  data.number = number;
  var braceletList = [];
  for (let i = 0; i < number; i++) {
	  var bracelet = {};
      var mac = ""
	  for (let j = 0; j < 6; j++) {
		mac += bytes[j + 2 + i * 21]
		  .toString(16)
		  .toUpperCase()
		  .padStart(2, "0");
	  }
	  bracelet.mac = mac;
	  bracelet.batteryLevel = bytes[8 + i * 21]; // 电量等级
	  bracelet.heartrate = bytes[9 + i * 21]; // 心率
	  bracelet.systolicPressure = bytes[10 + i * 21]; // 收缩压
	  bracelet.diastolicPressure = bytes[11 + i * 21]; // 舒张压
	  bracelet.wristTemperature = (((bytes[12 + i * 21] << 8) & 0xff00) | (bytes[13 + i * 21] & 0xff)) / 10 + "℃"; // 腕温
	  bracelet.bodyTemperature = (((bytes[14 + i * 21] << 8) & 0xff00) | (bytes[15 + i * 21] & 0xff)) / 10 + "℃"; // 体温
	  bracelet.stepNumber = ((bytes[16 + i * 21] << 16) & 0xff0000) | ((bytes[17 + i * 21] << 8) & 0xff00) | (bytes[18 + i * 21] & 0xff); // 步数
	  bracelet.wearStatus = ((bytes[19 + i * 21]) & 0x01) == 0 ? "Not wearing" : "Wearing";
	  bracelet.bluetoothBroadcastInterval = (bytes[20 + i * 21] & 0xff) + "s";
	  bracelet.samplingInterval = (bytes[21 + i * 21]& 0x7f) + "s";
	  bracelet.rssi = (bytes[22 + i * 21] - 256) + "dBm";
	  braceletList.push(bracelet);
  }
  data.braceletList = braceletList;
  return data;
}

function hex2float(num) {
  var sign = num & 0x80000000 ? -1 : 1;
  var exponent = ((num >> 23) & 0xff) - 127;
  var mantissa = 1 + (num & 0x7fffff) / 0x7fffff;
  return sign * mantissa * Math.pow(2, exponent);
}

function timestampToTime(timestamp) {
  const date = new Date(timestamp);
  const year = date.getFullYear();
  const month = (date.getMonth() + 1).toString().padStart(2, "0");
  const day = date.getDate().toString().padStart(2, "0");
  const hour = date.getHours().toString().padStart(2, "0");
  const minute = date.getMinutes().toString().padStart(2, "0");
  const second = date.getSeconds().toString().padStart(2, "0");
  return `${year}-${month}-${day} ${hour}:${minute}:${second}`;
}
```