Data Decoding

This tutorial guides you through the process of configuring payload codecs in ChirpStack v4 so that your LoRaWAN data can be properly decoded and viewed.

tip

If you need further assistance or a visual demonstration of the process described in this guide, consult the Video Guide.

LoRaWAN data is transmitted in a compressed format and needs to be decoded.

Go to Device Profiles → Codec.
Select Payload Codec and paste your decoding code.

For STICKER, choose JavaScript functions as the payload codec, then click Submit.

ChirStack v4 - Gateways

Viewing Decoded Data

Navigate to Applications → Events.
Select Up to view uplink messages.
You will now see decoded data.

Example of Codec (STICKER)

/**
* Decode uplink function
* 
* @param {object} input
* @param {number[]} input.bytes Byte array containing the uplink payload, e.g. [255, 230, 255, 0]
* @param {number} input.fPort Uplink fPort.
* @param {Record<string, string>} input.variables Object containing the configured device variables.
* 
* @returns {{data: object}} Object representing the decoded payload.
*/
function decodeUplink(input) {

function toSignedInt16(value) {
  return value > 0x7fff ? value - 0x10000 : value;
}

var data = {};
var bytes = input.bytes;
var header = (bytes[0] << 8) | bytes[1];
var index = 2;

if (header & (1 << 15)) {
  data.boot = true;
} else {
  data.boot = false;
}

if (header & (1 << 14)) {
  var orientation = header & 0xf;
  data.orientation = orientation === 0x0f ? null : orientation;
} else {
  data.orientation = null;
}

if (header & (1 << 13)) {
  var voltage = bytes[index++];
  data.voltage = voltage === 0xff ? null : voltage / 50;
} else {
  data.voltage = null;
}

if (header & (1 << 12)) {
  var temperature = (bytes[index++] << 8) | bytes[index++];
  data.temperature = temperature === 0x7fff ? null : toSignedInt16(temperature) / 100;
} else {
  data.temperature = null;
}

if (header & (1 << 11)) {
  var humidity = bytes[index++];
  data.humidity = humidity === 0xff ? null : humidity / 2;
} else {
  data.humidity = null;
}

if (header & (1 << 10)) {
  var illuminance = (bytes[index++] << 8) | bytes[index++];
  data.illuminance = illuminance === 0xffff ? null : illuminance * 2;
} else {
  data.illuminance = null;
}

if (header & (1 << 9)) {
  var ext_temperature_1 = (bytes[index++] << 8) | bytes[index++];
  data.ext_temperature_1 = ext_temperature_1 === 0x7fff ? null : toSignedInt16(ext_temperature_1) / 100;
} else {
  data.ext_temperature_1 = null;
}

if (header & (1 << 8)) {
  var ext_temperature_2 = (bytes[index++] << 8) | bytes[index++];
  data.ext_temperature_2 = ext_temperature_2 === 0x7fff ? null : toSignedInt16(ext_temperature_2) / 100;
} else {
  data.ext_temperature_2 = null;
}

if (header & (1 << 7)) {
  var motion_count = (bytes[index++] << 24) | (bytes[index++] << 16) | (bytes[index++] << 8) |
    bytes[index++];
  data.motion_count = motion_count === 0xffffffff ? null : motion_count;
} else {
  data.motion_count = null;
}

if (header & (1 << 6)) {
  var altitude = (bytes[index++] << 8) | bytes[index++];
  data.altitude = altitude === 0x7fff ? null : toSignedInt16(altitude) / 10;
}
else {
  data.altitude = null;
}

if (header & (1 << 5)) {
  var pressure = (bytes[index++] << 24) | (bytes[index++] << 16) | (bytes[index++] << 8) |
    bytes[index++];
  data.pressure = pressure === 0xffffffff ? null : pressure;
} else {
  data.pressure = null;
}

return {
  data: data,
  warnings: [],
  errors: []
};
}
/**
* Encode downlink function.
* 
* @param {object} input
* @param {object} input.data Object representing the payload that must be encoded.
* @param {Record<string, string>} input.variables Object containing the configured device variables.
* 
* @returns {{bytes: number[]}} Byte array containing the downlink payload.
*/
function encodeDownlink(input) {
return {
  // bytes: [225, 230, 255, 0]
};
}

Viewing Decoded Data​

Example of Codec (STICKER)​

Viewing Decoded Data

Example of Codec (STICKER)