mirror of https://github.com/espruino/BangleApps
60 lines
1.6 KiB
Markdown
60 lines
1.6 KiB
Markdown
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# GPS Time Server
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A widget which automatically starts the GPS and turns Bangle.js into a Bluetooth time server, UUID 0x1805.
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Other Espruino Bluetooth devices can then find it and use it to synchronise time.
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**Note:** Because GPS is kept on, you'll need to keep your Bangle.js on charge for this to be useful.
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## Usage
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Just install this widget, and from then on any app which loads widgets will
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display the icon  in the top left, and Bangle.js will be
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broadcasting the current time to any device that connects.
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## Technical
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This implements the [Bluetooth Time Service](https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=292957) listed [here](https://www.bluetooth.com/specifications/gatt/).
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The Bluetooth docs are verbose and hard to read, so here's a rundown of how it works.
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* The Bangle advertises service `0x1805`
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* You connect to it, and request service `0x1805` and characteristic `0x2A2B`
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* A 10 byte array is returned:
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```
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[
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year_lowbyte,
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year_highbyte,
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month,
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day_of_month,
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hours,
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minutes,
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seconds,
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day_of_week, // 1=monday...7=sunday
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subseconds, // 0..255
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update_reason // 0=unknown currently
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]
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```
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```
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//NRF.requestDevice({ filters: [{ services: ['1805'] }] }).then(print)
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var gatt;
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NRF.connect("c7:4b:2e:c6:f5:45 random").then(function(g) {
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gatt = g;
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return gatt.getPrimaryService("1805");
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}).then(function(service) {
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return service.getCharacteristic("2A2B");
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}).then(function(c) {
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return c.readValue();
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}).then(function(d) {
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console.log("Got:", JSON.stringify(d.buffer));
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var year = d.getUint16(0,1);
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// ...
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gatt.disconnect();
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}).catch(function(e) {
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console.log("Something's broken.",e);
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});
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```
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