Background operation of BLE Library with Android 8 - Request for Example

[Acutetech]

I would like to ask Nordic to create an example of an Android background service that can detect a device advertising.

Android imposes background execution limits which affect scanning for devices. The issue for beacons is described here and a solution implemented in the Android Beacon Library. Of course, the issue affects all devices and not just beacons. I have asked about this in an earlier post and since then done a fairly ugly implementation.

To set the context: I am working on a digital health sensor with a BLE interface. The user operates the sensor which collects data and saves it. It then starts advertising and will transfer the data when the sensor and the smart phone are next in radio range. The phone then transfers the reading to the cloud. The user does not need to have his phone when he operates the medical device, and he does not need to fire up an app manually in order to send the data to the cloud.

I have an experimental Android app that combines Nordic's Android BLE Library and the Android Beacon Library. I have hacked the Android Beacon Library to listen for my custom 128-bit UUID. This works in Android background mode. When the app detects my BLE custom UUID it fires an event and then I switch over to Nordic's BLE Library to connect to my device and transfer data. (This is obviously out of scope for the Andorid Beacon Library).

Clearly my specific use case can can be generalised: it should be possible for any BLE sensor (not just beacons) to send data to a phone that the user sees as "off".

Most of the time this works very well. But (a) my hack of the Android Beacon Library is pretty ugly, and (b) sometimes my app does not hear my device advertising and I must reset the phone. This is probably because of (a). Also, (c) the Android Beacon Library contains much more code than my app requires.

I would much prefer to work with one library and not two. What chance is the that I can get Nordic to work with me on this? The spec is to create an example Android app that listens for a BLE device in background mode, connects to it, transfers data and disconnects. I would work with you on this.

[Aleksander Nowakowski]

Hi Acutetech,

We already have https://github.com/NordicSemiconductor/Android-Scanner-Compat-Library which may be used for scanning. Its intent was to emulate all the new features on older devices, including scanning with Pending Intent (a way to scan with background executions limits). On pre-Oreo device it starts a background service that scans and triggers the Pending Intent if a device was found. It of course is using a lot of battery, as requires running service, possibly filtering in CPU, etc, but should work for short scanning periods.

For long lasting beacon scanning I would, actually, recommend either min SDK set to Oreo and using Pending Intents only, or clear option for the user to disable this on older phones, as this really may kill the battery quickly, a specially before Lollipop.

[sarbogast]

This library looks amazing and exactly what I was looking for, but the documentation is a little light, especially when you don't have any prior experience with BLE on Android or PendingIntents. A sample project that integrates all of that and shows how all the pieces fit together would be very helpful.

[Aleksander Nowakowski]

The library API is identical to the official one, just the package names are different. Check the Android scanning API documentation. I agree that more documentation and samples would be better, but unfortunately we don't have time at the moment.

[Acutetech]

Aleksander and Sarbogast: I have had reasonable success with this library. I have built a reasonably simple Android app that can be tested with a PCA10040 development board, and have documented it. It supports automatic resumption of scanning after the Android device reboots. It is not perfect but I am happy to offer this to both of you: to Sarbogast as a starting point for your own work, and to Aleksander in the hope that Nordic might make constructive criticisms then rework it as their own "perfect" example.

If this is of use, please advise how best to send the app.

[Aleksander Nowakowski]

That sounds great! Ideally, if you could fork the Android-Scanner-Compat-Library on GitHub, add an "app" module with your example and create a Pull Request. If you don't want, You may also attach the app here in ZIP, so others can get it immediately. Or, just send it to [email protected] and we will "perfectify" it, but this may take some time.

I will do my best not to complain a lot ;)

[Acutetech]

The HTSScanner.zip file is an Android Studio project that uses the Nordic Android BLE Scanner Compat library to scan for
advertisements from a PCA10040 programmed as a Health Thermometer.

See app/readme.txt for some documentation. The app prints many messages to logcat.

For instructions on setting up the PCA10040 see the ble_app_hts folder.