Control ESP32 via Flutter BLE - flutter

Question

I am using this library (https://pub.dev/packages/flutter_blue/example) to control my ESP32 (Arduino). I have two buttons that work perfectly, one to turn off the led and one to turn on the led. My problem is that I want to receive data that the arduino sends (notify). I don’t know how to do it.
main.dart
// Copyright 2017, Paul DeMarco.
// All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:async';
import 'dart:convert' show utf8;
import 'package:flutter/material.dart';
import 'package:flutter_blue/flutter_blue.dart';
import 'package:minertti/widgets.dart';
void main() {
runApp(FlutterBlueApp());
}
class FlutterBlueApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
color: Colors.lightBlue,
home: StreamBuilder<BluetoothState>(
stream: FlutterBlue.instance.state,
initialData: BluetoothState.unknown,
builder: (c, snapshot) {
final state = snapshot.data;
if (state == BluetoothState.on) {
return FindDevicesScreen();
}
return BluetoothOffScreen(state: state);
}),
);
}
}
class BluetoothOffScreen extends StatelessWidget {
const BluetoothOffScreen({Key? key, this.state}) : super(key: key);
final BluetoothState? state;
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.lightBlue,
body: Center(
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
Icon(
Icons.bluetooth_disabled,
size: 200.0,
color: Colors.white54,
),
Text(
'Bluetooth Adapter is ${state != null ? state.toString().substring(15) : 'not available'}.',
style: Theme.of(context)
.primaryTextTheme
.subtitle1
?.copyWith(color: Colors.white),
),
],
),
),
);
}
}
class FindDevicesScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Find Devices'),
),
body: RefreshIndicator(
onRefresh: () =>
FlutterBlue.instance.startScan(timeout: Duration(seconds: 4)),
child: SingleChildScrollView(
child: Column(
children: <Widget>[
StreamBuilder<List<BluetoothDevice>>(
stream: Stream.periodic(Duration(seconds: 2))
.asyncMap((_) => FlutterBlue.instance.connectedDevices),
initialData: [],
builder: (c, snapshot) => Column(
children: snapshot.data!
.map((d) => ListTile(
title: Text(d.name),
subtitle: Text(d.id.toString()),
trailing: StreamBuilder<BluetoothDeviceState>(
stream: d.state,
initialData: BluetoothDeviceState.disconnected,
builder: (c, snapshot) {
if (snapshot.data ==
BluetoothDeviceState.connected) {
return RaisedButton(
child: Text('OPEN'),
onPressed: () => Navigator.of(context).push(
MaterialPageRoute(
builder: (context) =>
DeviceScreen(device: d))),
);
}
return Text(snapshot.data.toString());
},
),
))
.toList(),
),
),
StreamBuilder<List<ScanResult>>(
stream: FlutterBlue.instance.scanResults,
initialData: [],
builder: (c, snapshot) => Column(
children: snapshot.data!
.map(
(r) => ScanResultTile(
result: r,
onTap: () => Navigator.of(context)
.push(MaterialPageRoute(builder: (context) {
r.device.connect();
return DeviceScreen(device: r.device);
})),
),
)
.toList(),
),
),
],
),
),
),
floatingActionButton: StreamBuilder<bool>(
stream: FlutterBlue.instance.isScanning,
initialData: false,
builder: (c, snapshot) {
if (snapshot.data!) {
return FloatingActionButton(
child: Icon(Icons.stop),
onPressed: () => FlutterBlue.instance.stopScan(),
backgroundColor: Colors.red,
);
} else {
return FloatingActionButton(
child: Icon(Icons.search),
onPressed: () => FlutterBlue.instance
.startScan(timeout: Duration(seconds: 4)));
}
},
),
);
}
}
class DeviceScreen extends StatelessWidget {
const DeviceScreen({Key? key, required this.device}) : super(key: key);
final BluetoothDevice device;
List<Widget> _buildServiceTiles(List<BluetoothService> services) {
return services
//just show the last service
.sublist(services.length - 1)
.map(
(s) => ServiceTile(
service: s,
characteristicTiles: s.characteristics
.map(
(c) => CharacteristicTile(
characteristic: c,
//turnOff: () => c.read(),
turnOff: () => c.write(utf8.encode("0")),
turnOn: () => c.write(utf8.encode("1")),
extraButton: () => c.write(utf8.encode("2")),
onNotificationPressed: () async {
await c.setNotifyValue(!c.isNotifying);
await c.read();
},
descriptorTiles: c.descriptors
.map(
(d) => DescriptorTile(
descriptor: d,
//turnOff: () => d.read(),
//turnOn: () => d.read(),
),
)
.toList(),
),
)
.toList(),
),
)
.toList();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(device.name),
actions: <Widget>[
StreamBuilder<BluetoothDeviceState>(
stream: device.state,
initialData: BluetoothDeviceState.connecting,
builder: (c, snapshot) {
VoidCallback? onPressed;
String text;
switch (snapshot.data) {
case BluetoothDeviceState.connected:
onPressed = () => device.disconnect();
text = 'DISCONNECT';
break;
case BluetoothDeviceState.disconnected:
onPressed = () => device.connect();
text = 'CONNECT';
break;
default:
onPressed = null;
text = snapshot.data.toString().substring(21).toUpperCase();
break;
}
return FlatButton(
onPressed: onPressed,
child: Text(
text,
style: Theme.of(context)
.primaryTextTheme
.button
?.copyWith(color: Colors.white),
));
},
)
],
),
body: SingleChildScrollView(
child: Column(
children: <Widget>[
StreamBuilder<BluetoothDeviceState>(
stream: device.state,
initialData: BluetoothDeviceState.connecting,
builder: (c, snapshot) => ListTile(
leading: (snapshot.data == BluetoothDeviceState.connected)
? Icon(Icons.bluetooth_connected)
: Icon(Icons.bluetooth_disabled),
title: Text(
'Device is ${snapshot.data.toString().split('.')[1]}.'),
subtitle: Text('${device.id}'),
trailing: StreamBuilder<bool>(
stream: device.isDiscoveringServices,
initialData: false,
builder: (c, snapshot) => IndexedStack(
index: snapshot.data! ? 1 : 0,
children: <Widget>[
IconButton(
icon: Icon(Icons.refresh),
onPressed: () => device.discoverServices(),
),
IconButton(
icon: SizedBox(
child: CircularProgressIndicator(
valueColor: AlwaysStoppedAnimation(Colors.grey),
),
width: 18.0,
height: 18.0,
),
onPressed: null,
)
],
),
),
),
),
StreamBuilder<int>(
stream: device.mtu,
initialData: 0,
builder: (c, snapshot) => ListTile(
title: Text('MTU Size'),
subtitle: Text('${snapshot.data} bytes'),
trailing: IconButton(
icon: Icon(Icons.edit),
onPressed: () => device.requestMtu(223),
),
),
),
StreamBuilder<List<BluetoothService>>(
stream: device.services,
initialData: [],
builder: (c, snapshot) {
return Column(
children: _buildServiceTiles(snapshot.data!),
);
},
),
],
),
),
);
}
}
device.dart
// Copyright 2017, Paul DeMarco.
// All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:convert' show utf8;
import 'package:flutter/material.dart';
import 'package:flutter_blue/flutter_blue.dart';
class ScanResultTile extends StatelessWidget {
const ScanResultTile({Key? key, required this.result, this.onTap})
: super(key: key);
final ScanResult result;
final VoidCallback? onTap;
Widget _buildTitle(BuildContext context) {
if (result.device.name.length > 0) {
return Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
result.device.name,
overflow: TextOverflow.ellipsis,
),
Text(
result.device.id.toString(),
style: Theme.of(context).textTheme.caption,
)
],
);
} else {
return Text(result.device.id.toString());
}
}
Widget _buildAdvRow(BuildContext context, String title, String value) {
return Padding(
padding: EdgeInsets.symmetric(horizontal: 16.0, vertical: 4.0),
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(title, style: Theme.of(context).textTheme.caption),
SizedBox(
width: 12.0,
),
Expanded(
child: Text(
value,
style: Theme.of(context)
.textTheme
.caption
?.apply(color: Colors.black),
softWrap: true,
),
),
],
),
);
}
String getNiceHexArray(List<int> bytes) {
return '[${bytes.map((i) => i.toRadixString(16).padLeft(2, '0')).join(', ')}]'
.toUpperCase();
}
String getNiceManufacturerData(Map<int, List<int>> data) {
if (data.isEmpty) {
return 'N/A';
}
List<String> res = [];
data.forEach((id, bytes) {
res.add(
'${id.toRadixString(16).toUpperCase()}: ${getNiceHexArray(bytes)}');
});
return res.join(', ');
}
String getNiceServiceData(Map<String, List<int>> data) {
if (data.isEmpty) {
return 'N/A';
}
List<String> res = [];
data.forEach((id, bytes) {
res.add('${id.toUpperCase()}: ${getNiceHexArray(bytes)}');
});
return res.join(', ');
}
#override
Widget build(BuildContext context) {
return ExpansionTile(
title: _buildTitle(context),
leading: Text(result.rssi.toString()),
trailing: RaisedButton(
child: Text('CONNECT'),
color: Colors.black,
textColor: Colors.white,
onPressed: (result.advertisementData.connectable) ? onTap : null,
),
children: <Widget>[
_buildAdvRow(
context, 'Complete Local Name', result.advertisementData.localName),
_buildAdvRow(context, 'Tx Power Level',
'${result.advertisementData.txPowerLevel ?? 'N/A'}'),
_buildAdvRow(context, 'Manufacturer Data',
getNiceManufacturerData(result.advertisementData.manufacturerData)),
_buildAdvRow(
context,
'Service UUIDs',
(result.advertisementData.serviceUuids.isNotEmpty)
? result.advertisementData.serviceUuids.join(', ').toUpperCase()
: 'N/A'),
_buildAdvRow(context, 'Service Data',
getNiceServiceData(result.advertisementData.serviceData)),
],
);
}
}
class ServiceTile extends StatelessWidget {
final BluetoothService service;
final List<CharacteristicTile> characteristicTiles;
const ServiceTile(
{Key? key, required this.service, required this.characteristicTiles})
: super(key: key);
#override
Widget build(BuildContext context) {
if (characteristicTiles.length > 0) {
return ExpansionTile(
title: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text('Service'),
Text('0x${service.uuid.toString().toUpperCase().substring(4, 8)}',
style: Theme.of(context).textTheme.bodyText1?.copyWith(
color: Theme.of(context).textTheme.caption?.color))
],
),
children: characteristicTiles,
);
} else {
return ListTile(
title: Text('Service'),
subtitle:
Text('0x${service.uuid.toString().toUpperCase().substring(4, 8)}'),
);
}
}
}
class CharacteristicTile extends StatelessWidget {
final BluetoothCharacteristic characteristic;
final List<DescriptorTile> descriptorTiles;
final VoidCallback? turnOff;
final VoidCallback? extraButton;
final VoidCallback? turnOn;
final VoidCallback? onNotificationPressed;
const CharacteristicTile(
{Key? key,
required this.characteristic,
required this.descriptorTiles,
this.turnOff,
this.extraButton,
this.turnOn,
this.onNotificationPressed})
: super(key: key);
#override
Widget build(BuildContext context) {
return StreamBuilder<List<int>>(
stream: characteristic.value,
initialData: characteristic.lastValue,
builder: (c, snapshot) {
final value = snapshot.data;
return ExpansionTile(
title: ListTile(
title: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text('Characteristic'),
Text(
'0x${characteristic.uuid.toString().toUpperCase().substring(4, 8)}',
style: Theme.of(context).textTheme.bodyText1?.copyWith(
color: Theme.of(context).textTheme.caption?.color))
],
),
subtitle: Text(value.toString()),
contentPadding: EdgeInsets.all(0.0),
),
trailing: Row(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
IconButton(
icon: Icon(
Icons.lightbulb_outline,
color: Theme.of(context).iconTheme.color?.withOpacity(0.5),
),
onPressed: turnOff,
),
IconButton(
icon: Icon(Icons.lightbulb,
color: Theme.of(context).iconTheme.color?.withOpacity(0.5)),
onPressed: turnOn,
),
//iconButton for add
IconButton(
icon: Icon(
Icons.add_circle,
color: Theme.of(context).iconTheme.color?.withOpacity(0.5),
),
onPressed: extraButton,
),
IconButton(
icon: Icon(
characteristic.isNotifying
? Icons.sync_disabled
: Icons.sync,
color: Theme.of(context).iconTheme.color?.withOpacity(0.5)),
onPressed: onNotificationPressed,
)
],
),
children: descriptorTiles,
);
},
);
}
}
class DescriptorTile extends StatelessWidget {
final BluetoothDescriptor descriptor;
final VoidCallback? turnOff;
final VoidCallback? turnOn;
final VoidCallback? extraButton;
const DescriptorTile(
{Key? key,
required this.descriptor,
this.turnOff,
this.extraButton,
this.turnOn})
: super(key: key);
#override
Widget build(BuildContext context) {
return ListTile(
title: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text('Descriptor'),
Text('0x${descriptor.uuid.toString().toUpperCase().substring(4, 8)}',
style: Theme.of(context)
.textTheme
.bodyText1
?.copyWith(color: Theme.of(context).textTheme.caption?.color))
],
),
subtitle: StreamBuilder<List<int>>(
stream: descriptor.value,
initialData: descriptor.lastValue,
builder: (c, snapshot) => Text(snapshot.data.toString()),
),
trailing: Row(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
IconButton(
icon: Icon(
Icons.lightbulb_outline,
color: Theme.of(context).iconTheme.color?.withOpacity(0.5),
),
onPressed: turnOff,
),
IconButton(
icon: Icon(
Icons.lightbulb,
color: Theme.of(context).iconTheme.color?.withOpacity(0.5),
),
onPressed: turnOn,
),
IconButton(
icon: Icon(
Icons.add_circle,
color: Theme.of(context).iconTheme.color?.withOpacity(0.5),
),
onPressed: extraButton,
)
],
),
);
}
}
class AdapterStateTile extends StatelessWidget {
const AdapterStateTile({Key? key, required this.state}) : super(key: key);
final BluetoothState state;
#override
Widget build(BuildContext context) {
return Container(
color: Colors.redAccent,
child: ListTile(
title: Text(
'Bluetooth adapter is ${state.toString().substring(15)}',
style: Theme.of(context).primaryTextTheme.subtitle1,
),
trailing: Icon(
Icons.error,
color: Theme.of(context).primaryTextTheme.subtitle1?.color,
),
),
);
}
}
ESP32 Code:
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>
BLECharacteristic *pCharacteristic;
bool deviceConnected = false;
float txValue = 0;
const int readPin = 32; // Use GPIO number. See ESP32 board pinouts
const int LED = 2; // Could be different depending on the dev board. I used the DOIT ESP32 dev board.
//std::string rxValue; // Could also make this a global var to access it in loop()
// See the following for generating UUIDs:
// https://www.uuidgenerator.net/
#define SERVICE_UUID "6E400001-B5A3-F393-E0A9-E50E24DCCA9E" // UART service UUID
#define CHARACTERISTIC_UUID_RX "6E400002-B5A3-F393-E0A9-E50E24DCCA9E"
#define CHARACTERISTIC_UUID_TX "6E400003-B5A3-F393-E0A9-E50E24DCCA9E"
class MyServerCallbacks: public BLEServerCallbacks {
void onConnect(BLEServer* pServer) {
deviceConnected = true;
};
void onDisconnect(BLEServer* pServer) {
deviceConnected = false;
}
};
class MyCallbacks: public BLECharacteristicCallbacks {
void onWrite(BLECharacteristic *pCharacteristic) {
std::string rxValue = pCharacteristic->getValue();
if (rxValue.length() > 0) {
Serial.println("*********");
Serial.print("Received Value: ");
for (int i = 0; i < rxValue.length(); i++) {
Serial.print(rxValue[i]);
}
Serial.println();
// Do stuff based on the command received from the app
if (rxValue.find("1") != -1) {
Serial.println("Turning ON!");
digitalWrite(LED, HIGH);
}
else if (rxValue.find("0") != -1) {
Serial.println("Turning OFF!");
digitalWrite(LED, LOW);
}
Serial.println();
Serial.println("*********");
}
}
};
void setup() {
Serial.begin(115200);
pinMode(LED, OUTPUT);
// Create the BLE Device
BLEDevice::init("ESP32"); // Give it a name
// Create the BLE Server
BLEServer *pServer = BLEDevice::createServer();
pServer->setCallbacks(new MyServerCallbacks());
// Create the BLE Service
BLEService *pService = pServer->createService(SERVICE_UUID);
// Create a BLE Characteristic
pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID_TX,
BLECharacteristic::PROPERTY_NOTIFY
);
pCharacteristic->addDescriptor(new BLE2902());
BLECharacteristic *pCharacteristic = pService->createCharacteristic(
CHARACTERISTIC_UUID_RX,
BLECharacteristic::PROPERTY_WRITE
);
pCharacteristic->setCallbacks(new MyCallbacks());
// Start the service
pService->start();
// Start advertising
pServer->getAdvertising()->start();
Serial.println("Waiting a client connection to notify...");
}
void loop() {
if (deviceConnected) {
// Fabricate some arbitrary junk for now...
txValue = analogRead(readPin) / 3.456; // This could be an actual sensor reading!
// Let's convert the value to a char array:
char txString[8]; // make sure this is big enuffz
dtostrf(txValue, 1, 2, txString); // float_val, min_width, digits_after_decimal, char_buffer
// pCharacteristic->setValue(&txValue, 1); // To send the integer value
// pCharacteristic->setValue("Hello!"); // Sending a test message
pCharacteristic->setValue(txString);
pCharacteristic->notify(); // Send the value to the app!
Serial.print("*** Sent Value: ");
Serial.print(txString);
Serial.println(" ***");
// You can add the rxValue checks down here instead
// if you set "rxValue" as a global var at the top!
// Note you will have to delete "std::string" declaration
// of "rxValue" in the callback function.
// if (rxValue.find("A") != -1) {
// Serial.println("Turning ON!");
// digitalWrite(LED, HIGH);
// }
// else if (rxValue.find("B") != -1) {
// Serial.println("Turning OFF!");
// digitalWrite(LED, LOW);
// }
}
delay(1000);
}
The app correctly receives the information, but in a strange code that I don't understand. How do I convert it to letters and numbers?
In device.dart you can see that there is a part that says: "subtitle: Text(value.toString())"
That is the one that sends the data, but I don't understand it.
...
builder: (c, snapshot) {
final value = snapshot.data;
return ExpansionTile(
title: ListTile(
title: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text('Characteristic'),
Text(
'0x${characteristic.uuid.toString().toUpperCase().substring(4, 8)}',
style: Theme.of(context).textTheme.bodyText1?.copyWith(
color: Theme.of(context).textTheme.caption?.color))
],
),
subtitle: Text(value.toString()),
...
Arduino sends: 98.96 and I receive this data from value.toString(): [57, 56, 46, 57, 54]

Answer 1

Try using String.fromCharCodes to convert the received data ([57, 56, 46, 57, 54]) to 98.96.

Answer 2

Refer to this utf8 char table: https://cloud.netlifyusercontent.com/assets/344dbf88-fdf9-42bb-adb4-46f01eedd629/02572bcf-76c4-420a-90ac-65a0c8c71eae/iso-8859-5-php-orange.png
You are receiving Uint8List. Decode that data into string then parse it in double.
Try this:
String decodedData = utf8.decode(receivedData);
where receivedData -> Uint8List
Now in decodedData you will get the required string that you can parse into other data types.