SparkFun SAMD21 Pro RF Hookup Guide

Contributors: Elias The Sparkiest
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Decode Your Data

You may have noticed in the Application Data window that your payload is shown in raw bytes. In order to see "Hello, World!" encoded in ASCII, the way you sent it, you'll need to decode the payload. The Things Network includes tools for doing this right in the console! Navigate to the Application Overview page for your application and click on the Payload Formats tab. This menu allows you to write functions which will be applied to all incoming packets for this application.

Screenshot of the Payload Formats page, showing a field labeled "decoder" where code can be typed. Some example code is in the field by default. It doesn't appear to return anything.

So let's write our own decoder. We need to take the raw byte data and return a string that contains all of the characters corresponding to each byte. Take a look at this solution and then we'll walk through it:

function Decoder(bytes, port) {

return {
    ASCII: String.fromCharCode.apply(null, bytes)


Decoder is a Javascript function that The Things Network has already set up for us. It takes two arguments called bytes, an array containing our payload, and port, the LoRaWAN™ "FPort" of the packet. FPort identifies the end application or service that the packet is intended for. Port 0 is reserved for MAC messages. We don't need to know anything about the port number for our example.

We can return any value that we want from the Decoder function and it will appear alongside our payload in the Application Data window. In the example above, I've created a new property called "ASCII" which is equal to String.fromCharCode.apply(null, bytes). To break this down a little more, we're returning a new String object called "ASCII," and we're using the Javascript apply() method to call fromCharCode() with the argument bytes and stuff the result into our new String. The fromCharCode() method simply steps through each byte in the array bytes (which, remember, contains our payload) and returns the ASCII character represented by that character code.

After copying the above code into your decoder function, scroll down and click the save payload functions button. Now return to the Application Data window and you should see that all packets received after the decoder function was changed now have a new property:

Another screenshot of the Application Data page, this time showing several packets received. The latest packet at the top of the list has a new field beside payload labeled "ASCII" with the value "Hello, world!"

Our packet has been decoded! Neat!