Data TTN to Thingspeak problem with Payload Decoder from Array

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I have a question regarding decoding in TTN specifically for Thingspeak.
The code in Arduino IDE for a MKR1310 is the following:
String sensorString = String(airTemperatureReading);// + "-" + String(altitudeReading)+ "-" + String(pressureReading)+ "-" + String(sensorValueRain);
char payload[sensorString.length()+1];
sensorString.toCharArray(payload, sensorString.length() +1);
modem.write(payload, sizeof(payload));
Here I tested just one sensor data, to make it easier to understand whats going on with the payload function in general. But I didn´t really manage with that. In TTN the decoding is ok, so I get with the decoder -just for TTN usage- 24 from Hex 323400. However, now I have to switch the decoder to Thingspeak readable data but with the following Decoder I just get 50 in field1, but 24°C is the right temperature.
Decoder TTN:
function Decoder(bytes, port)
var tem = (bytes[0]<<0) | bytes[0];
return {
field1: tem
Test Byte Payload -> Complete uplink data
"f_port": 3,
"frm_payload": "MjQA",
"decoded_payload": {
"field1": 50
The complete Arduino Sketch is from here:
Thank you very much
Karsten Fenske
Karsten Fenske on 27 Jun 2022
The question is, how to decode the payload - > an array of strings (sensor data for example temperature) sent to TTN, into readable format for Thingspeak?

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Answers (1)

Christopher Stapels
Christopher Stapels on 27 Jun 2022
Around 4:01 in this video, I'm explaining my payload formatter. Or you can see the instructions in this example in the doc. The doc is a bit outdated for TTN, (version 2 instead of 3) but the payload formatting is still true. The video is up to date for version 3.


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