Dear Community,
I have a GPS Device from Global sat (LT-20) and would need some help to decode it to use the device in Chirpstack. I only have the uplink payload decoder code from TTN and little knowledge in JavaScript. Can someone please help me.
function hexToBits(hex) {
var out = "";
for (var c of hex) {
switch (c) {
case '0': out += "0000"; break;
case '1': out += "0001"; break;
case '2': out += "0010"; break;
case '3': out += "0011"; break;
case '4': out += "0100"; break;
case '5': out += "0101"; break;
case '6': out += "0110"; break;
case '7': out += "0111"; break;
case '8': out += "1000"; break;
case '9': out += "1001"; break;
case 'a': out += "1010"; break;
case 'b': out += "1011"; break;
case 'c': out += "1100"; break;
case 'd': out += "1101"; break;
case 'e': out += "1110"; break;
case 'f': out += "1111"; break;
default: return "";
}
}
return out;
}
//Convert Bits to Signed INT
function bitsToSigned(bits) {
var value = parseInt(bits, 2);
var limit = 1 << (bits.length - 1);
if (value >= limit) {
// Value is negative; calculate two's complement.
value = value - limit - limit;
}
return value;
}
function bitsToUnsigned(bits) {
return parseInt(bits, 2);
}
function toLittleEndianSigned(hex) {
// Creating little endian hex DCBA
var hexArray = [];
while (hex.length >= 2) {
hexArray.push(hex.substring(0, 2));
hex = hex.substring(2, hex.length);
}
// seems to already be reversed so not needed
//hexArray.reverse();
hex = hexArray.join('');
// Hex to Bits
var hex2bits = hexToBits(hex);
// To signed int
var signedInt = bitsToSigned(hex2bits);
return signedInt;
}
// Add leading zero if toString(16) removed it
function toPaddedHexString(number) {
hex = number.toString(16).toLowerCase();
if (hex.length % 2 !== 0) {
hex = '0' + hex;
}
return hex;
}
function decodeUplink(input) {
var data = {};
//protocol version
//data.protocolVersion = (input.bytes[0] << 8);
//command id
//data.commandID = (input.bytes[1] << 8);
//longitude
longitudeInteger = (input.bytes[2]) + (input.bytes[3] << 8) + (input.bytes[4] << 16);
data.longitude = ((toLittleEndianSigned(toPaddedHexString(longitudeInteger))) * 215) / 10 * 0.000001;
//latitude
latitudeInteger = (input.bytes[5]) + (input.bytes[6] << 8) + (input.bytes[7] << 16);
data.latitude = ((toLittleEndianSigned(toPaddedHexString(latitudeInteger))) * 108) / 10 * 0.000001;
//gps fix status and report type
//data.reportType = (input.bytes[8] << 8);
var gps = Math.round((bitsToUnsigned(hexToBits(toPaddedHexString(input.bytes[8] << 8))) / 256) / 32);
if (gps === 0) {
data.gps = "No fix";
} else if (gps == 1) {
data.gps = "2D fix";
} else if (gps == 2) {
data.gps = "3D fix";
}
var reportType = Math.round((bitsToUnsigned(hexToBits(toPaddedHexString(input.bytes[8] << 8))) / 256) % 32);
if (reportType === 2) {
data.reportType = "Periodic mode report";
} else if (reportType === 4) {
data.reportType = "Motion mode static report";
} else if (reportType === 5) {
data.reportType = "Motion mode moving report";
} else if (reportType === 6) {
data.reportType = "Motion mode static to moving report";
} else if (reportType === 7) {
data.reportType = "Motion mode moving to static report";
} else if (reportType === 15) {
data.reportType = "Low battery alarm report";
}
//battery capacity
data.batterypercent = bitsToUnsigned(hexToBits(toPaddedHexString(input.bytes[9] << 8))) / 256;
//preserved
//data.preserved = (input.bytes[10] << 8);
var warnings = [];
/* if (data.battery < 30) {
warnings.push("low battery");
} */
return {
data: data,
warnings: warnings
};
}
