Extract the received value from downlink messages

[arjanvanb (Arjan)]

@adjaramillo

If I encode in binary will be something like this:

{
    "confirmed": true,
    "fPort": 10,
    "data": "01001110010101000100000101110111"
}

That’s not encoding in binary, that’s a text string that only holds ones and zeroes, but it’s still very much text. Even 32 characters of text! (And next, there’s some more encoding happening that we don’t know of, as we don’t know what library or API you’re using.)

Maybe Working with Bytes is a good start.

I don’t know what library you’re using in Node-RED, but when using plain MQTT you’d need something like:

@arjanvanb

msg.payload = {
  dev_id: devId,
  port: 1,
  confirmed: false,
  schedule: 'replace',
  payload_raw: Buffer.from(bytes).toString('base64')
};

And bytes should then be two bytes for your number 500, maybe using writeUInt16BE:

// Allocate 2 bytes, to hold a single 16 bits unsigned integer; you
// may need more to send multiple values, or to use larger values.
const bytes = Buffer.allocUnsafe(2);
// 16 bits integer, 0..65,535
bytes.writeUInt16BE(500, 0);

Alternatively: start with scheduling downlinks using TTN Console. The number 500 would be the 2 bytes 0x01F4 when written in hexadecimal:

All of the above should decode fine using descartes’:

@descartes

And then if you assign the result to an integer, you are ready to go with something like this:

int TxPeriod = ( LMIC.frame[LMIC.dataBeg] << 8 ) + LMIC.frame[LMIC.dataBeg+1];