BangleApps/apps/gpstimeserver/README.md

GPS Time Server

A widget which automatically starts the GPS and turns Bangle.js into a Bluetooth time server, UUID 0x1805.

Other Espruino Bluetooth devices can then find it and use it to synchronise time.

Note: Because GPS is kept on, you'll need to keep your Bangle.js on charge for this to be useful.

Usage

Just install this widget, and from then on any app which loads widgets will display the icon in the top left, and Bangle.js will be broadcasting the current time to any device that connects.

Technical

This implements the Bluetooth Time Service listed here.

The Bluetooth docs are verbose and hard to read, so here's a rundown of how it works.

• The Bangle advertises service 0x1805
• You connect to it, and request service 0x1805 and characteristic 0x2A2B
• A 10 byte array is returned:

[
  year_lowbyte,
  year_highbyte,
  month,
  day_of_month,
  hours,
  minutes,
  seconds,
  day_of_week, // 1=monday...7=sunday
  subseconds, // 0..255
  update_reason // 0=unknown currently
]

//NRF.requestDevice({ filters: [{ services: ['1805'] }] }).then(print)

var gatt;
NRF.connect("c7:4b:2e:c6:f5:45 random").then(function(g) {
  gatt = g;
  return gatt.getPrimaryService("1805");
}).then(function(service) {
  return service.getCharacteristic("2A2B");
}).then(function(c) {
  return c.readValue();
}).then(function(d) {
  console.log("Got:", JSON.stringify(d.buffer));
  var year = d.getUint16(0,1);
  // ...
  gatt.disconnect();
}).catch(function(e) {
  console.log("Something's broken.",e);
});