• Hey there!
    I'm using NRF.setAdvertising() to advertise temperature readings from Puck.js.
    The examples in docs sadly only mention byte arrays, integers and string fragments as supported data:

    // straight from official docs
    setInterval(function() {
        0x1809 : [Math.round(E.getTemperature())]
    }, 30000);

    What I'm trying to do is advertise the floating point temperature without rounding. Puck currently reports temperature with 0.25 accuracy, but I'm struggling with how to encode it in a way, that would make EspruinoHub understand it.

    The official BLE GATT spec for thermometer actually supports extra flags in the first byte and temp. reading (default is Celsius) as a Float32.

    The node on puck doesn't sadly provide Buffer so I tried encoding with TypedArrays like so:

    setInterval(function() {
        0x1809 : temperatureAsArray()
    }, 30000);
    function temperatureAsArray() {
      const a = new Float32Array(1);
      a[0] = E.getTemperature();
      const b = new Uint8Array(a.buffer);
      const c = new Uint8Array(5);
      c[0] = 0;    // the first byte set to 0 means a single celsius measurement without timestamp
     // I've also tried without this byte, didn't change anything
      c.set(b, 1);
      const result = [];
      for (let x = 0; x < c.length; x ++) {
        result[x] = c[x];
      return result;

    The resulting array is something like: [0, 0, 0, 236, 65] for temperature of around 21 deg, or [0, 0, 236, 65] if you don't include the "flags" byte and just have BE 32-bit float.

    However, when I receive it in EspruinoHUB, the debug shows me:

    d1:bf:fb:93:39:bf - Puck.js (RSSI -57)
      1809 => {"temp":0}

    It seems to struggle to decode those Float32 byte arrays.
    When I sent something like [236, 65] (without the GATT flags and trimmed to just 2 bytes) then it shows me:

    d1:bf:fb:93:39:bf - Puck.js (RSSI -57)
      1809 => {"temp":168.76}

    I have no idea how it got 168.75 from those bytes.

    Any idea what EspruinoHub/Noble/bleno expect as a format for floats?

    Have anyone succeeded in encoding floats for BLE Adv. ?


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