heart_bpm

Widget to measure heart rate in beats per minute using the camera of smartphone.

Working principle

Covering the camera lens with the fingertip enables the camera to measure the subtle changes in skin tone. These are proportional to the changes in the blood flow through the arteries just below the skin of the fingertip. This is in-turn correlated to the heart beats. Hence, the variations in the skin tone can be approximated to the instances of heart beats. Measuring the time differences between the peaks provides Beats per Minute.

These values are not stable and hence, an exponential moving average filter is implemented. The smoothing factor α, can be controlled by the user from the calling widget.

Implementation

To access the camera, the module utilizes the camera package. Hence, the requirements to use this package have the same requirements.

Android

Minimum android SDK version: 21

Change the minimum Android sdk version to 21 (or higher) in your android/app/build.gradle file.

minSdkVersion 21

iOS

iOS 10.0 of higher is needed to use the camera plugin. If compiling for any version lower than 10.0 make sure to check the iOS version before using the camera plugin. For example, using the device_info plugin.

Add two rows to the file ios/Runner/Info.plist:

  • one with the key Privacy - Camera Usage Description and a usage description.
  • and one with the key Privacy - Microphone Usage Description and a usage description.

Or in text format add the key:

<key>NSCameraUsageDescription</key>
<string>Heart BPM plugin would like to use camera to measure your heart rate.</string>
<key>NSMicrophoneUsageDescription</key>
<string>Can I use the mic please?</string>

The microphone key is required though the feature is not being used and no audio is enabled in the implementation.

Getting Started

The module can be used simply by accessing it as a widget.

  1. Import the module:

    import 'package:heart_bpm/heart_bpm.dart';
    
  2. Access the widget as simply as:

     /// list to store raw values in
     List<SensorValue> data = [];
    
     /// variable to store measured BPM value
     int bpmValue;
    
     @override
     Widget build(BuildContext context) {
     return Scaffold(
         appBar: AppBar(
             title: Text('Heart BPM Demo'),
         ),
         body: Column(
         children: [
             isBPMEnabled ? HeartBPMDialog(
                     context: context,
                     onRawData: (value) {
                         setState(() {
                             // add raw data points to the list
                             // with a maximum length of 100
                             if (data.length == 100)
                                 data.removeAt(0);
                             data.add(value);
                         });
                     },
                     onBPM: (value) => setState(() {
                         bpmValue = value;
                     }),
                 )
               : SizedBox(),
           Center(
             child: ElevatedButton.icon(
                 icon: Icon(Icons.favorite_rounded),
                 label: Text(isBPMEnabled
                     ? "Stop measurement" : "Measure BPM"),
                 onPressed: () => setState(() =>
                     isBPMEnabled = !isBPMEnabled
                 ),
             ),
           ),
         ],
       ),
     );
    

Libraries

heart_bpm
heart_bpm