forked from FOSS/BangleApps
139 lines
3.9 KiB
Markdown
139 lines
3.9 KiB
Markdown
# GPS Service
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A configurable, low power GPS widget that runs in the background.
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## Goals
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To develop a low power GPS widget that runs in the background and to
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facilitate an OS grid reference display in a watch face.
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* An app that turns on the GPS and constantly displays the screen
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will use around 75mA, the battery will last between 3-4 hours.
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* Using the GPS in a Widget in Super-E Power Saving Mode (PSM) with
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the screen off most of the time, will consume around 35mA and you
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might get 10hrs before a recharge.
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* Using the GPS in Power Saving Mode On/Off (PSMOO) with suitable
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settings can reduce the average consumption to around 15mA. A
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simple test using a 120s update period, 6s search period was still
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running with 45% battery 20 hours after it started.
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## Settings
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The Settings App enables you set the following options for the GPS
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Service. Go to Settings, select App/Widgets and then 'GPS Service'.
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- GPS - On/Off. When this value is changed the GPS Service will be
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powered on or off and the GPS Widget will be displayed.
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- Power Mode:
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- SuperE - the factory default setup for the GPS. The recommended
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power saving mode.
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- PSMOO - On/Off power saving mode. Configured by interval and
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search time. Choose this mode if you are happy to get a GPS
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position update less often (say every 1 or 2 minutes). The longer
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the interval the more time the GPS will spend sleeping in low
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power mode (7mA) between obtaining fixes (35mA). For walking in
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open country an update once every 60 seconds is adequate to put
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you within a 6 digit grid refernce sqaure.
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- update - the time between two position fix attempts.
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- search - the time between two acquisition attempts if the receiver
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is unable to get a position fix.
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## Screenshots
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### GPS Watch face
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* The Age value is the number of seconds since the last position fix was received.
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### Grid Reference Watch face
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* The time shown is the timestamp of the last position fix.
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* The age value is shown at the bottom of the screen.
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## Interface for Apps
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The code below demonstrates how you can setup and start the gpsservice from your own App.
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```js
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function test_gps_on() {
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var settings = WIDGETS.gpsservice.gps_get_settings();
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// change the settings to what you require
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settings.gpsservice = true;
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settings.update = 65;
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settings.search = 5;
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settings.power_mode = "PSMOO";
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WIDGETS.gpsservice.gps_set_settings(settings);
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WIDGETS.gpsservice.reload(); // will power on
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}
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```
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In your app can retrieve the last fix as and when required.
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```js
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var fix = {
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fix: 0,
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alt: 0,
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lat: 0,
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lon: 0,
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speed: 0,
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time: 0,
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satellites: 0
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};
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// only attempt to get gps fix if gpsservice is loaded
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if (WIDGETS.gpsservice !== undefined) {
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fix = WIDGETS.gpsservice.gps_get_fix();
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gps_on = WIDGETS.gpsservice.gps_get_status();
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}
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if (fix.fix) {
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var time = formatTime(fix.time);
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var age = timeSince(time);
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```
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When done you can turn the gpsservice off using the code below.
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```js
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function test_gps_off() {
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var settings = WIDGETS.gpsservice.gps_get_settings();
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settings.gpsservice = false;
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settings.power_mode = "SuperE";
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WIDGETS.gpsservice.gps_set_settings(settings);
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WIDGETS.gpsservice.reload(); // will power off
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}
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```
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## To Do List
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* add a logging option with options for interval between log points
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* add graphics and icons to the watch faces to make them look nicer
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## References
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* [UBLOX M8 Receiver Data Sheet](https://www.u-blox.com/sites/default/files/products/documents/u-blox8-M8_ReceiverDescrProtSpec_%28UBX-13003221%29.pdf)
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* [UBLOX Power Management App Note](https://www.u-blox.com/sites/default/files/products/documents/PowerManagement_AppNote_%28UBX-13005162%29.pdf)
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* Some useful code on Github and be found [here](https://portal.u-blox.com/s/question/0D52p0000925T00CAE/ublox-max-m8q-getting-stuck-when-sleeping-with-extint-pin-control)
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and [here](https://github.com/thasti/utrak/blob/master/gps.c)
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