JS uplink formatter for The Things Industries LoRaWAN for the Rejeee SL 300 CO2 sensor

rejee_SL_300_CO2_tti_uplink_decoder.js

// xref https://www.thethingsindustries.com/docs/integrations/payload-formatters/javascript/uplink/

// code for uplink formatter for The Things Industries LoRaWAN for the Rejeee SL 300 CO2 sensor.
// based on code in the Rejee documentation


// Convert a hex string to a byte array
// from https://stackoverflow.com/a/34356351/40387
function hexToBytes(hex) {
    for (var bytes = [], c = 0; c < hex.length; c += 2)
        bytes.push(parseInt(hex.substr(c, 2), 16));
    return bytes;
}

function decodeUplinkBytes(bytesArray)
{
   var obj = {};
    var warnings = [];
    var len = bytesArray ? bytesArray.length : 0;
    var offset = 0;
    var dtype;

    do {
        dtype = bytesArray[offset++]; /* dtype: Sensor Type */

        switch (dtype) {
            case 0x00: {
                obj.ver = bytesArray[offset] &  0xE0;
                obj.battery = bytesArray[offset] & 0x1F;
                offset = offset + 2;
                break;
            }
            case 0x04: {
                obj.temperature = (bytesArray[offset] << 8) + bytesArray[offset + 1];
                offset = offset + 2;
                break;
            }
            case 0x05: {
                obj.humidity = bytesArray[offset];
                offset = offset + 1; 
                break;
            }
            case 0x30: {
                /**
                 * dtype 30： Mixed gas sensor, like CO2, H2S
                 * volume：Gas concentration detection，Unit: 0.01
                 */
                var l = bytesArray[offset++];
                var gastype = bytesArray[offset++];
                 obj.gastype=gastype;
                obj.volume = ((bytesArray[offset] << 24) + (bytesArray[offset + 1] << 16) +
                    (bytesArray[offset + 2] << 8) + bytesArray[offset + 3]) / 100;
                offset =offset+ 4;
                if (obj.volume < 0) {
                    warnings.push("it's invalid");
                }
                break;
            }
        }
    } while (offset < len);

  
    return {
        data: obj,
        warnings: warnings
    };
}

function decodeUplink(input) {
   return decodeUplinkBytes(input.bytes);
}