esense_flutter

eSense Flutter

This plugin supports the eSense earable computing platform on both Android and iOS.

Install (Flutter)

Add esense_flutter as a dependency in pubspec.yaml. For help on adding as a dependency, view the pubspec documenation.

Android

The package uses bluetooth to fetch data from the eSense earplugs. Therefore permission to access bluetooth must be enabled.

Add the following entry to your manifest.xml file, in the Android part of your application:

<uses-permission
    android:name="android.permission.BLUETOOTH"
    android:maxSdkVersion="30" />
<uses-permission
    android:name="android.permission.BLUETOOTH_ADMIN"
    android:maxSdkVersion="30" />
<uses-permission
    android:name="android.permission.BLUETOOTH_SCAN" 
    android:usesPermissionFlags="neverForLocation" /> 
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT"/>

Also make sure to obtain permissions in your app to use bluetooth. See the example app on how to e.g. use the permission_handler for this. Note that the plugin does not handle permissions - this has to be done on an app level.

Set the Android compile and minimum SDK versions to compileSdkVersion 28, and minSdkVersion 23 respectively, inside the android/app/build.gradle file.

iOS

Requires iOS 10 or later. Hence, in your Podfile in the ios folder of your app, make sure that the platform is set to 10.0.

platform :ios, '10.0'

Add this permission in the Info.plist file located in ios/Runner:

<key>NSBluetoothAlwaysUsageDescription</key>
<string>Uses bluetooth to connect to the eSense device</string>
<key>UIBackgroundModes</key>
  <array>
 <string>bluetooth-central</string>
 <string>bluetooth-peripheral</string>
  <string>audio</string>
  <string>external-accessory</string>
  <string>fetch</string>
</array>

Note that on iOS, connecting to the eSense device may take several seconds.

Usage

The eSense Flutter plugin has been designed to resemble the Android eSense API almost 1:1. Hence, you should be able to recognize the names of the different classes and class variables.
For example, the methods on the ESenseManager class is mapped 1:1. See the eSense Android documentation on how it all works.

However, one major design change has been done; this eSense Flutter plugin complies to the Dart/Flutter reactive programming architecture using Streams. Hence, you do not 'add listeners' to an eSense device (as you do in Java) -- rather, you obtain a Dart stream and listen to this stream (and exploit all the other very nice stream operations which are available in Dart). Below, we shall describe how to use the eSense streams. But first -- let's see how to set up and connect to an eSense device in the first place.

Note that playing and recording audio are performed via the Bluetooth Classic interface and are not supported by the eSense library described here.

Setting up and Connecting to an eSense Device

All operations on the eSense device happens via the ESenseManager. When creating the ESenseManager, specify the name of the device (typically on the form eSense-xxxx).

import 'package:esense_flutter/esense.dart';

...

// create an ESenseManager by specifying the name of the device
ESenseManager eSenseManager = ESenseManager('eSense-0332');

...

// first listen to connection events before trying to connect
eSenseManager.connectionEvents.listen((event) {
  print('CONNECTION event: $event');
}

...

// try to connect to the eSense device 
bool connecting = await eSenseManager.connect();

Everything with the eSense API happens asynchronously. Hence, the connect call merely initiates the connection process. In order to know the status of the connection process (successful or not), you should listen to connection events (ConnectionEvent). This is done via the connectionEvents stream. Note, that if you want to know if your connection to the device is successful, you should initiate listening before the connection is initiated, as shown above.

Listen to Sensor Events

You can access a stream of SensorEvent events via the ESenseManager.sensorEvents stream. Sampling rate can be set when not listening.

StreamSubscription subscription = eSenseManager.sensorEvents.listen((event) {
  print('SENSOR event: $event'
});

...

subscription.cancel();
eSenseManager.setSamplingRate(5);

... 

subscription = eSenseManager.sensorEvents.listen((event) {
  print('SENSOR event: $event');
});

Read eSense Device Events

Reading properties of the eSense device happens asynchronously. Hence, in order to obtain properties, you should do two things:

1. listen to the ESenseManager.eSenseEvents stream
2. invoke read operation on the ESenseManager

Invoking read operations will trigger ESenseEvent events of various kinds.

// set up a event listener
eSenseManager.eSenseEvents.listen((event) {
  print('ESENSE event: $event');
}

// now invoke read operations on the manager
eSenseManager.getDeviceName();

When the button on the eSense device is pressed, the eSenseEvents stream will send an ButtonEventChanged event.

Change the Configuration of the eSense Device

The ESenseManager exposes methods to change the configuration of the eSense device. With the plugin, you can change the device name using setDeviceName(), change the advertising and connection interval using setAdvertisementAndConnectiontInterval(), and change the IMU sensor configuration using setSensorConfig().

Note: At the time of writing, the setSensorConfig() method is not implemented.

Limitations in the eSense BTLE interface

Note that there is a limitation to the eSense BTLE interface which implie that you should not invoke methods on the ESenseManager in a fast pace after each other. For example, the following code will not work:

// set up a event listener
eSenseManager.eSenseEvents.listen((event) {
  print('ESENSE event: $event');
}

// now invoke read operations on the manager
// THIS WILL NOT WORK!
eSenseManager.getDeviceName();
eSenseManager.getAccelerometerOffset();
eSenseManager.getAdvertisementAndConnectionInterval();

In this case, the first operation (listening to the Esense Events) will succeed - the rest will fail. In the example app, this has been fixed by adding delays to method call, like;

// get the battery level every 10 secs
Timer.periodic(Duration(seconds: 10), (timer) async => await eSenseManager.getBatteryVoltage());

// wait 2, 3, 4, 5, ... secs before getting the name, offset, etc.
// it seems like the eSense BTLE interface does NOT like to get called
// several times in a row -- hence, delays are added in the following calls
Timer(Duration(seconds: 2), () async => await eSenseManager.getDeviceName());
Timer(Duration(seconds: 3), () async => await eSenseManager.getAccelerometerOffset());
Timer(Duration(seconds: 4), () async => await eSenseManager.getAdvertisementAndConnectionInterval());
Timer(Duration(seconds: 5), () async => await eSenseManager.getSensorConfig());

Authors

• Jakob E. Bardram Technical University of Denmark
• The iOS implementation uses the eSense iOS Library.