youtube demo ----  https://www.youtube.com/watch?v=y8UL7Ijpvgc
//
// flutter program simple dcc ble
// uses:
//   ble         - hm19 module
//   pico        - rp2040 core a
//   booster     - cytron md13s
//   dcc station - github.com/pico-cs/firmware
//
// bluetooth module connections:
//   hm19 ground   - pico ground
//   hm19 vcc      - pico +5v
//   hm19 rxd      - pico gpio0
//   hm19 txd      - pico gpio1
//
// booster connections:
//   md13s ground  - pico ground
//   md13s pwm     - pico +5v
//   md13s dir     - pico gpio2
//
// use nrf connect to find ble mac address
// if having problem with ble on android, give app location permision
//
import 'package:flutter/material.dart';
import 'package:flutter/services.dart'; // needed for exit
import 'package:get/get.dart';
import 'package:flutter_reactive_ble/flutter_reactive_ble.dart';
import 'package:wheel_chooser/wheel_chooser.dart';
import 'dart:async';
import 'dart:convert'; // needed for utf8.encode

final buttonStyle = ButtonStyle(backgroundColor:
  MaterialStateProperty.all<Color?>(Colors.teal[100]));

void main() {WidgetsFlutterBinding.ensureInitialized(); // without this, error tx has not been initialized
  runApp(MaterialApp(home:Home()));}

class Home extends StatelessWidget{
final ble=FlutterReactiveBle();
late QualifiedCharacteristic tx;
dynamic trackPower=false.obs;
var status='connect to ble'.obs;
int currentSpeed = 0;

void send(val) async {
  List<int> data=utf8.encode(val);
  await ble.writeCharacteristicWithoutResponse(tx,value:data);}

void ble_connect() async{
  status.value='connecting...';
  late StreamSubscription<ConnectionStateUpdate> c;
  c=ble.connectToDevice(id:'A4:DA:32:55:06:1E').listen((s){
  if (s.connectionState == DeviceConnectionState.connected){
    status.value='connected';
    tx=QualifiedCharacteristic(serviceId:Uuid.parse('0000ffe0-0000-1000-8000-00805f9b34fb'),
    characteristicId:Uuid.parse('0000ffe1-0000-1000-8000-00805f9b34fb'),
    deviceId:'A4:DA:32:55:06:1E');}});}

@override Widget build(BuildContext c){
return Scaffold(appBar:AppBar(title:Text('simple dcc bluetooth')),
body:Column(children:[

SizedBox(height:30),
ElevatedButton(onPressed:(){ble_connect();}, child: Obx(() =>Text('${status}')),
style:buttonStyle),

SizedBox(height:30),  
Padding(padding:EdgeInsets.all(16.0),child: Obx(() => Row(children:[Text('track power on: '),
(Switch(value:trackPower.value, activeColor:Colors.green,
onChanged:(bool v){send('+mte t\r'); trackPower.value=v;}))]))),

Expanded(child:WheelChooser.integer(
onValueChanged: (s) => currentSpeed = s,
maxValue: 20, minValue: 1, initValue: 1,
horizontal: true, unSelectTextStyle: TextStyle(color: Colors.grey))),
  
ElevatedButton(child:Text('set speed'), onPressed:(){send('+ls 15 ' + currentSpeed.toString() + '\r');},
style:buttonStyle),
    
SizedBox(height:30),
ElevatedButton(child:Text('toggle direction'), onPressed:(){send('+ld 15 ~\r');},
style:buttonStyle),

SizedBox(height:40),
//on exit turn off track power
ElevatedButton(child:Text('Exit'), onPressed:(){
send('+mte f\r'); SystemNavigator.pop();})]));}}