Is it possible to set more than one service ?

[espruino-discuss]

Posted at 2016-12-19 by @MaBecker

Was thinking of having more than one service set with NRF.setService.

NRF.setServices({
  0x1809 : { // Health Thermometer
    0x2A6E: {  // Temperature
      readable: true,
      value : [E.getTemperature().toFixed(2)]
  }},
  0x180F : { // Battery Service
    0x2A19: {  // Battery Level
      readable: true,
      value : [Puck.getBatteryPercentage()]
}}});

eBeacon or Bluefruit only display the service 0x1809

Any hints ?

[gfwilliams]

Posted at 2016-12-19 by @gfwilliams

NRF.setServices({
  0x1809 : { // Health Thermometer
    0x2A6E: {  // Temperature
      readable: true,
      value : [1]
  }},
  0x180F : { // Battery Service
    0x2A19: {  // Battery Level
      readable: true,
      value : [1]
}}});

The above works for me - I think it's because you were trying to send a string inside an array as the temperature.

It should really have errored though - I'm not sure why it didn't

[espruino-discuss]

Posted at 2016-12-19 by @MaBecker

only see 0x1809, no 0x180F , which application did you use to check this ?

Can I use a second puck to check this ?

• connect
• query services
• disconnect

[espruino-discuss]

Posted at 2016-12-19 by @MaBecker

Found it all in the documents ....

>NRF.findDevices(function(devices) {
:  console.log(devices);
:}, 1000);
=undefined
/*
[
  BluetoothDevice {
    "id": "f4:38:88:d0:bc:5c random",
    "rssi": -55,
    "services": [  ],
    "data": new ArrayBuffer([2, 1, 5, 13, 9, 80, 117, 99, 107, 46, 106, 115, 32, 98, 99, 53, 99]),
    "name": "Puck.js bc5c"
   }
 ]
*/

looks like the eBeacon and BlueFruit have problems with reading ...

[gfwilliams]

Posted at 2016-12-19 by @gfwilliams

I use the nRF connect app - it's been pretty reliable for me.

NRF.findDevices won't query the services you set with setServices - it's only the publically advertised services (not the ones you get when you connect). What you want is http://www.espruino.com/Reference#l_BluetoothRemoteGATTServer_getPrimaryServices

[espruino-discuss]

Posted at 2016-12-19 by @MaBecker

During testing with iPhone and iPad I realized that switching BLE off and on again also helped.

YES nRF connect works for me too, will stick to that tool !

---

Attachments:

• FullSizeRender.jpg

[gfwilliams]

Posted at 2016-12-19 by @gfwilliams

I imagine some other apps will just cache the BLE services and don't cope well with them changing.

[espruino-discuss]

Posted at 2016-12-20 by ChristianW

Actually I believe that iOS is doing the caching here.
So turning BLE off/on (or rebooting the whole device if things get worse) is the only thing you can do.
I have done a BLE app a few years ago and it's astounding what's happening under the hood in iOS.
I assume most if it is done to preserve battery...

[espruino-discuss]

Posted at 2016-12-21 by Fabio978

Nice idea! It's working for me but i get wrong temperature value (143.85°C instead of 18°C from the console).
Any suggestion?

[espruino-discuss]

Posted at 2016-12-21 by dklinkman

@fabio978 I get something similar. I believe it's because toFixed() returns a string and the temperature value is supposed to be 16 bit floating point number. The characters in the string that end up being read as a sint16 and converted to floating point for display just happen to represent 143.85. I tried just rounding the temperature down to an integer but that doesn't work at all. The battery works fine because it's being read as a byte, with a valid range of 0 to 100.

[espruino-discuss]

Posted at 2016-12-22 by Fabio978

I think the problem is that temperature must be specified in 11073-20601 16-bit FLOAT-Type format, but i couldn't find how to do that.

[espruino-discuss]

Posted at 2016-12-30 by dklinkman

I was able to figure this out eventually. Can't believe how much google searching and code searching. Bluetooth specs are specific but not much help to the uninformed.

Bottom line is that the value sent to the characteristic needs to be a signed 16 bit integer supplied as a mantissa with an 'implied' decimal exponent of -2. All along I was trying to fit a float16 or a half-precision float or a 4 bit exponent float variant into a sint16 and it just doesn't work. Duh.

This works:

function tempTo2a6e(temp) {
  var f = parseFloat(temp.toFixed(2)) * 100;
  if (tempTo2a6e.buf === undefined) tempTo2a6e.buf = new Uint8Array(2);
  tempTo2a6e.buf[0] = f & 0xff;
  tempTo2a6e.buf[1] = f >> 8 & 0xff;
  return tempTo2a6e.buf;
}
NRF.setServices({
  0x1809 : {
    0x2a6e : {
      readable : true, value : tempTo2a6e(E.getTemperature())
    }
  }
});

Be sure to disconnect from the puck and then connect using nRF Connect or whatever and look for the Health Thermometer service. The temperature now reads correctly as 18.75'C. If reading the value using another puck you just need to divide by 100 (or multiply by 10^-2).

Of course this simple example doesn't update the temperature value over time. NRF.updateServices in some sort of a timed loop would do that.

Writing a string to the characteristic does work (doesn't fail) and if you read back the data and interpet it as a string that will work too. But the spec for the characteristic is sint16. Tools like nRF Connect expect to see an sint16 vs an array of chacters which is why it appeared to display an incorrect value.

[espruino-discuss]

Posted at 2017-01-02 by Fabio978

Great find @dklinkman! I will try this tonight!

[espruino-discuss]

Posted at 2017-01-02 by Fabio978

@dklinkman your code works very well! Thank you!

[espruino-discuss]

Posted at 2017-01-06 by @MaBecker

@gfwilliams

are you planing functions to convert to the the different value formats for Characteristics ?

[gfwilliams]

Posted at 2017-01-06 by @gfwilliams

Afraid not - you can do a lot of value conversion using ArrayBuffers though.

a = new Uint8Array(2);
b = new Int16Array(a.buffer);
b[0] = 12345;
console.log(a);