Write Characteristic to Web Bluetooth.

[espruino-discuss]

Posted at 2019-07-24 by sammachin

I have a pixl that currently advertises a custom service and characteristic which a puck can then discover connect to and write to.
I would like to replicate this with webbluetooth so that the puck can control a browser app instead of the pixl, is that possible? obviously doing something on the page instead of turning on the LED
Below is the code on my pixl.

NRF.setServices({
  "60970001-dddd-49b8-acea-2b7f5d2660dd": {
    "60970002-dddd-49b8-acea-2b7f5d2660dd": {
      value : [0],
      maxLen : 1,
      writable : true,
      onWrite : function(evt) {
        digitalWrite(LED, evt.data[0]);
        digitalWrite(D13, evt.data[0]);
        
      }
    }
  }
}, { uart : true });


// On disconnect
NRF.on('disconnect', function() {
  digitalWrite(LED,0);
  digitalWrite(D13,0)
});
// Change name 
NRF.setAdvertising({}, {name:"BLEPTT"});6

[gfwilliams]

Posted at 2019-07-29 by @gfwilliams

I think I answered this at JSOxford, but if anyone else is interested:

Web Bluetooth doesn't let you create services on the device with the Web Browser.

However to 'push' data from Espruino to a device with a Web Bluetooth browser, you just need to use notifications: http://www.espruino.com/About+Bluetooth+LE#services-and-characteristics

So on Espruino you do:

NRF.setServices({
  0xBCDE : {
    0xABCD : {
      value : "Hello",
      maxLen : 5, 
      notify : true
}}});
function pushData(d) {
 NRF.updateServices({
  0xBCDE : {
    0xABCD : {
      value : d,
      notify : true
 }}});
}

And then on Web Bluetooth you get the characteristic as normal and then call startNotifications on it, which causes a characteristicvaluechanged event on it whenever you update the characteristic on Espruino.

I don't think there's any info on the Espruino site about that yet, but there is a workshop I did which has the relevant code: https://github.com/gfwilliams/workshop-thingy52/blob/master/step5.md