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Fun with Bluetooth @ Halfstack

Fun with Bluetooth @ Halfstack

Time for the browser to get physical. With WebBluetooth the browser can actually take control of all kinds of physical devices in the real world like lightbulbs, robots and even drones. This talk will teach you the basics that you need to get started and will show you some more advanced topics like building your own Bluetooth devices using just JavaScript.

Niels Leenheer

November 17, 2017
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  1. classic bluetooth the reason everybody 
 hates bluetooth bluetooth low

    energy vs. control drones and other cool shit
  2. i device information manufacturer model number serial number hardware revision

    firmware revision software revision ... multiple characteristics 
 per service
  3. not recommended any UUID outside of the range
 xxxxxxxx-0000-1000-8000-00805F9B34FB 16

    bit 128 bit light steering control flight c still, everybody does this
  4. i 0x180A 0x2A29 0x2A24 0x2A25 0x2A27 0x2A26 0x2A28 ... bad

    for readability, 
 good for saving bandwidth
  5. navigator.bluetooth.requestDevice({ filters: [ { namePrefix: 'PLAYBULB' } ], optionalServices: [

    0xff0f ] }) .then(device => device.gatt.connect()) .then(server => server.getPrimaryService(0xff0f)) .then(service => service.getCharacteristic(0xfffc)) .then(characteristic => { return characteristic.writeValue( new Uint8Array([ 0x00, r, g, b ]) ); }) 1 we tell the browser what 
 kind of device we want
  6. navigator.bluetooth.requestDevice({ filters: [ { namePrefix: 'PLAYBULB' } ], optionalServices: [

    0xff0f ] }) .then(device => device.gatt.connect()) .then(server => server.getPrimaryService(0xff0f)) .then(service => service.getCharacteristic(0xfffc)) .then(characteristic => { return characteristic.writeValue( new Uint8Array([ 0x00, r, g, b ]) ); }) 2 connect to the server
  7. navigator.bluetooth.requestDevice({ filters: [ { namePrefix: 'PLAYBULB' } ], optionalServices: [

    0xff0f ] }) .then(device => device.gatt.connect()) .then(server => server.getPrimaryService(0xff0f)) .then(service => service.getCharacteristic(0xfffc)) .then(characteristic => { return characteristic.writeValue( new Uint8Array([ 0x00, r, g, b ]) ); }) 3 get the service
  8. navigator.bluetooth.requestDevice({ filters: [ { namePrefix: 'PLAYBULB' } ], optionalServices: [

    0xff0f ] }) .then(device => device.gatt.connect()) .then(server => server.getPrimaryService(0xff0f)) .then(service => service.getCharacteristic(0xfffc)) .then(characteristic => { return characteristic.writeValue( new Uint8Array([ 0x00, r, g, b ]) ); }) 4 get the characteristic
  9. navigator.bluetooth.requestDevice({ ... }) .then(device => device.gatt.connect()) .then(server => server.getPrimaryService(0xff0f)) .then(service

    => service.getCharacteristic(0xfffc)) .then(c => { return c.writeValue( new Uint8Array([ 0x00, r, g, b ]) ); }) write some bytes
  10. navigator.bluetooth.requestDevice({ ... }) .then(device => device.gatt.connect()) .then(server => server.getPrimaryService(0xff0f)) .then(service

    => service.getCharacteristic(0xfffc)) .then(c => c.readValue()) .then(value => { let r = value.getUint8(1); let g = value.getUint8(2); let b = value.getUint8(3); }) read some bytes
  11. navigator.bluetooth.requestDevice({ ... }) .then(device => device.gatt.connect()) .then(server => server.getPrimaryService(0xff0f)) .then(service

    => service.getCharacteristic(0xfffc)) .then(c => { c.addEventListener('characteristicvaluechanged', e => { let r = e.target.value.getUint8(1); let g = e.target.value.getUint8(2); let b = e.target.value.getUint8(3); }); c.startNotifications(); }) add event listener don't forget to start listening
  12. writing a value: function(r, g, b) { return new Uint8Array([

    0x00, r, g, b ]); } reading a value: function(buffer) { return { 
 r: buffer.getUint8(1), 
 g: buffer.getUint8(2), 
 b: buffer.getUint8(3) 
 } } writing to and reading
 from the same characteristic
  13. writing a value: function(r, g, b) { return new Uint8Array([

    0x01, g, 0x01, 0x00, 0x01, 
 b, 0x01, r, 0x01, 0x00 
 ]); } reading the current 
 color is not possible
  14. writing a value: 
 function(r, g, b) { var buffer

    = new Uint8Array([ 
 0xaa, 0x0a, 0xfc, 0x3a, 0x86, 0x01, 0x0d, 
 0x06, 0x01, r, g, b, 0x00, 0x00, 
 (Math.random() * 1000) & 0xff, 0x55, 0x0d 
 ]); for (var i = 1; i < buffer.length - 2; i++) { buffer[15] += buffer[i]; } return buffer; } reading the current 
 color is not possible
  15. writing a value: 
 function(r, g, b, position) { let

    buffer = new Uint8Array([ 0x07, 0x02, position + 1, r, g, b ]); return buffer; }
  16. writing a value: 
 function(r, g, b, position) { let

    buffer = new Uint8Array([ 0x58, r, g, b, 0x01, position ]); ...
  17. writing a value: 
 function(r, g, b, position) { let

    buffer = new Uint8Array([ 0x58, r, g, b, 0x01, position ]); let payload = new Uint8Array(buffer.length + 4); payload[0] = payload.length - 2; payload[1] = payload.length - 2 >>> 8; payload.set(buffer, 2); let checksum = payload.reduce((a, b) => a + b, 0); payload[payload.length - 2] = checksum; payload[payload.length - 1] = checksum >>> 8; let extra = payload.filter(value => {

  18. message[m] = 0x03; message[m + 1] = 0x05; m +=

    2; } else if (payload[i] === 0x03) { message[m] = 0x03; message[m + 1] = 0x06; m += 2; } else { message[m] = payload[i]; m++; } } message[0] = 0x01; message[message.length - 1] = 0x02; return message; }