Arduino, Android e Bluetooth: costruire un’auto telecomandata

Dopo mesi di inattività ho ripreso in mano il mio primo progetto con Arduino e ho deciso di evolverlo in qualcosa di più interattivo, così ho creato un auto telecomanda via Bluetooth da uno smartphone Android.

Questo progetto quindi mi ha richiesto lo studio (in realtà meno approfondito di quando mi aspettassi) della piattaforma mobile di Google.

Per rendere tutto più semplice ho deciso di utilizzare il toolkit Amarino, che permette la comunicazione tra Android e Arduino via Bluetooth, mettendo a disposizione due librerie, una per parte.

L’applicazione Android che funge da telecomando ha due modalità di controllo: tramite pulsanti oppure tramite i sensori di accelerazione dello smartphone (in base all’inclinazione viene inviato un segnale).

Elenco componenti

Il materiale di base necessario per questo progetto è lo stesso del suo predecessore, con l’aggiunta di:

• un modulo Bluetooth HC-05
• uno smartphone Android (la mia app è stata testata su un LG Nexus 4 con Android 4.3)

Assemblaggio

Le indicazioni da seguire per il montaggio della macchinina sono quelle presenti nel mio precedente articolo.
L’unico passo aggiuntivo da compiere per realizzare questa evoluzione è il collegamento del modulo Bluetooth HC-05.
L’immagine seguente rappresenta lo schema elettrico del sistema:

E qui si vede dove sono andato a posizionare il modulo:

Codice sorgente

Per semplificare il progetto ho utilizzato la libreria MeetAndroid per la comunicazione.
Ad essa ho apportato una modifica per poterla combinare con la libreria SoftwareSerial in maniera tale da poter mappare il Bluetooth su una seconda porta seriale per tenere libera quella hardware (Pin 0 e 1) di Arduino (vedere sezione Download in fondo).

Di seguito il codice per Arduino:

#include <Servo.h>
#include <MeetAndroid.h>
#include <SoftwareSerial.h>


// On boards other than the Mega, use of the library disables analogWrite() (PWM)
// functionality on pins 9 and 10, whether or not there is a Servo on those pins.
Servo myservo;

const long baud = 38400;

// bluetooth
const int rxPin = 2;
const int txPin = 3;

const int servoPin  = 5;  // PWM

const int redPin    = 6;
const int yellowPin = 7;
const int greenPin  = 8;

const int motorPin1 = 9;  // H-bridge leg 1 (1A)
const int motorPin2 = 10; // H-bridge leg 2 (2A)
const int motorEnab = 11; // H-bridge enable pin (PWM)

const int signalPin = 12; // SRF05

int distance = 0;            // obstacle distance
const int numOfReadings = 3; // number of readings to take items in the array
int readings[numOfReadings]; // stores the distance readings in an array
int arrayIndex = 0;          // arrayIndex of the current item in the array
int total = 0;               // stores the cumlative total
int avgDistance = 0;         // stores the average value

// stop threshold
int thStop;


MeetAndroid meetAndroid(rxPin,txPin,baud);

String pDist;
String pVelo;
String pDire;
String pVers;

String strPrint;

void setup()
{
  Serial.begin(baud); // open serial port to receive data
  myservo.attach(servoPin); // attaches the servo pin to the servo object

  pinMode(redPin,  OUTPUT);
  pinMode(yellowPin, OUTPUT);
  pinMode(greenPin,  OUTPUT);
  pinMode(motorPin1, OUTPUT);
  pinMode(motorPin2, OUTPUT);
  pinMode(motorEnab, OUTPUT);

  // turn off motor
  digitalWrite(motorEnab, LOW);

  // steering in central position
  myservo.write(0);
  delay(100);
  straight();

  thStop = 10;

  // create array loop to iterate over every item in the array
  for (int thisReading = 0; thisReading < numOfReadings; thisReading++) {
    readings[thisReading] = 0;
  }

  // register callback function
  meetAndroid.registerFunction(moveCar, 'a');
}

void loop()
{
  distance = getDistance();

  total = total - readings[arrayIndex]; // subtract the last distance
  readings[arrayIndex] = distance;      // add distance reading to array
  total = total + readings[arrayIndex]; // add the reading to the total
  arrayIndex++;                         // go to the next item in the array

  // at the end of the array then start again
  if (arrayIndex >= numOfReadings)  {
    arrayIndex = 0;
  }

  // calculate the average distance
  avgDistance = total / numOfReadings;
  pDist = String(avgDistance);

  // you need to keep this in your loop() to receive events
  meetAndroid.receive();
}

/**
 * Calculate the distance of nearby obstacle
 * @return unsigned long
 */
long getDistance()
{
  unsigned long pulseTime;
  unsigned long distance;

  pinMode(signalPin, OUTPUT);
  digitalWrite(signalPin, LOW);      // set signal pin low
  delayMicroseconds(2);              // for 2 microseconds
  digitalWrite(signalPin, HIGH);     // send a trigger pulse
  delayMicroseconds(10);             // 10 microseconds long
  digitalWrite(signalPin, LOW);      // signal pin low waiting for echo pulse

  pinMode(signalPin, INPUT);
  pulseTime = pulseIn(signalPin, HIGH); // read echo pulse length in microseconds
  distance = pulseTime/58;              // distance in centimeters

  return distance;
}

/**
 * Turn on motor and move forward
 * @param int speed  Percentage 0-100%
 */
void forward(int speed)
{
  // obstacle too close
  if(avgDistance<=thStop)
  {
    speed = 0;
    digitalWrite(greenPin,LOW);
    digitalWrite(redPin,HIGH);
  }
  else
  {
    digitalWrite(greenPin,HIGH);
    digitalWrite(redPin,LOW);
  }

  int vel = map(speed, 0, 100, 0, 255);

  pDire = "Forward";
  pVelo = String(vel);

  if(speed==0)
  {
    pDire = "Stop";
  }

  digitalWrite(motorPin1, LOW);
  digitalWrite(motorPin2, HIGH);

  analogWrite(motorEnab, vel);
}

/**
 * Turn on motor and move backward
 * @param int speed  Percentage 0-100%
 */
void backward(int speed)
{
  int vel = map(speed, 0, 100, 100, 255);

  pDire = "Backward";
  pVelo = String(vel);

  digitalWrite(motorPin1, HIGH);
  digitalWrite(motorPin2, LOW);

  analogWrite(motorEnab, vel);
}

/**
 * Move the steering wheel
 * @param int direction  0=right, 1=left
 */
void steer(int direction)
{
  if(direction == 0)
  {
    // right
    myservo.write(180);
    pVers = "Right";
  }
  else if(direction == 1)
  {
    // left
    myservo.write(0);
    pVers = "Left";
  }
  else
  {
    pVers = "ERROR";
  }
}


/**
 * Move the steering in middle position
 */
void straight()
{
  if(myservo.read()==180)
  {
    // from right to middle
    myservo.write(50);
    pVers = "Straight";
  }
  else if(myservo.read()==0)
  {
    // from left to middle
    myservo.write(110);
    pVers = "Straight";
  }
}

/**
 * Read commands from remote control and make car moves
 */
void moveCar(byte flag, byte numOfValues)
{
  int length = meetAndroid.stringLength();
  char inputString[length];

  meetAndroid.getString(inputString);

  strPrint = String("Len=") + length + " - str=" + inputString;
  Serial.println(strPrint);

  int *lastCmd = split(inputString, ',');

  switch(*lastCmd)
  {
    case 0: // "stop"
      forward(0);
      break;

    case 1: // "forward"
      forward(100);
      break;

    case 2: // "backward"
      backward(100);
      break;
  }

  switch(*(lastCmd+1))
  {
    case 0: // "straight"
      straight();
      break;

    case 1: //"right"
      steer(0);
      break;

    case 2: // "left"
      steer(1);
      break;
  }

  // log on serial port
  strPrint = pDist+","+pVelo+","+pDire+","+pVers+","+(*lastCmd)+","+(*(lastCmd+1))+",#"+inputString+"#";
  Serial.println(strPrint);
}

/**
 * Split command string in parts
 * @param String string  The input string
 * @param char   delim   The boundary string
 */
int * split(String command, char delim)
{
  static int data[2];
  int numArgs = 0;
  int idx;
  String tmp;

  do
  {
    idx = command.indexOf(delim);
    if(idx != -1)
    {
	  tmp = command.substring(0, idx);
	  data[numArgs++] = tmp.toInt();
      command = command.substring(idx+1, command.length());
    }
    else if(command.length() > 0)
    {
      // last iteration
	  data[numArgs++] = command.toInt();
    }
  } while(idx>=0);

  Serial.println(String("uno=")+data[0]+" / due="+data[1]+" / tre="+data[2]);

  return data;
}

Per quanto riguarda il codice per Android riporto solo la porzione più significativa, il progetto completo è nella sezione Download.

public class MainActivity extends Activity implements OnClickListener, SensorEventListener {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		imgConnected    = (View) findViewById(R.id.connected);
		imgDisconnected = (View) findViewById(R.id.disconnected);
		txtDevice   = (TextView) findViewById(R.id.txtDevice);
		mStatusView = (TextView) findViewById(R.id.status_view);
		tv1 = (TextView) findViewById(R.id.tv1);
		tv2 = (TextView) findViewById(R.id.tv2);
		tv3 = (TextView) findViewById(R.id.tv3);

		mWindowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
		mDisplay = mWindowManager.getDefaultDisplay();

		mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
		mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

		btnForward  = (Button) findViewById(R.id.btnForward);
		btnBackward = (Button) findViewById(R.id.btnBackward);
		btnRight    = (Button) findViewById(R.id.btnRight);
		btnLeft     = (Button) findViewById(R.id.btnLeft);
		btnAccelerometer = (ToggleButton) findViewById(R.id.btnAccelerometer);

		btnAccelerometer.setOnClickListener(this);

		writeLog("onCreate");
		setStatus(DISCONNECTED);
	}

	@Override
	protected void onStart() {
		super.onStart();

		motor = 0;
		direction = 0;

		lastChange = System.currentTimeMillis();

		registerReceiver(arduinoReceiver, new IntentFilter(AmarinoIntent.ACTION_CONNECTED));
		registerReceiver(arduinoReceiver, new IntentFilter(AmarinoIntent.ACTION_DISCONNECTED));
		registerReceiver(arduinoReceiver, new IntentFilter(AmarinoIntent.ACTION_CONNECTION_FAILED));
		registerReceiver(arduinoReceiver, new IntentFilter(AmarinoIntent.ACTION_PAIRING_REQUESTED));
		registerReceiver(arduinoReceiver, new IntentFilter(AmarinoIntent.ACTION_RECEIVED));

		if(device_address!=null)
		{
			Amarino.connect(this, device_address);
		}
	}

	@Override
	protected void onStop() {
		super.onStop();

		Amarino.disconnect(this, device_address);

		unregisterReceiver(arduinoReceiver);
	}

	/**
	 * Read the toggle button and set the command mode (buttons or sensors)
	 */
	private void setMode()
	{
		motor = 0;
		direction = 0;

		if(btnAccelerometer.isChecked())
        {
        	// turn on sensors
        	mSensorManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_NORMAL);

        	stopTimer();

    		if (D) Log.d(TAG, "setMode() - SENSOR ON");
        }
        else
        {
        	// turn off sensors
        	mSensorManager.unregisterListener(this);

        	startTimer();

    		if (D) Log.d(TAG, "setMode() - SENSOR OFF");
        }

		motor = 0;
		direction = 0;
	}

	/**
	 * Timer: every 100 milliseconds check buttons state and send commands
	 */
	public void startTimer(){
		t = new Timer();
		task = new TimerTask() {

			@Override
			public void run() {
				runOnUiThread(new Runnable() {

					@Override
					public void run() {

						// check buttons state
						motor = 0;
						direction = 0;

						if(btnForward.isPressed())
						{
							motor = 1;
						}
						else if(btnBackward.isPressed())
						{
							motor = 2;
						}

						if(btnRight.isPressed())
						{
							direction = 1;
						}
						else if(btnLeft.isPressed())
						{
							direction = 2;
						}

						updateState();
					}
				});
			}
		};

		t.scheduleAtFixedRate(task, 0, 100);
	}

	/**
	 * Stop the timer
	 */
	public void stopTimer(){

		t.cancel();
    	t.purge();
	}

	@Override
	public final void onSensorChanged(SensorEvent event)
	{
	    // Many sensors return 3 values, one for each axis.
	    float x = event.values[0];
	    float y = event.values[1];
	    float z = event.values[2];

	    // check phone orientation and adjust sensor values
	    switch (mDisplay.getRotation())
	    {
		    case Surface.ROTATION_0:
		        x = event.values[0];
		        y = event.values[1];
		        break;
		    case Surface.ROTATION_90:
		        x = -event.values[1];
		        y = event.values[0];
		        break;
		    case Surface.ROTATION_180:
		        x = -event.values[0];
		        y = -event.values[1];
		        break;
		    case Surface.ROTATION_270:
		        x = event.values[1];
		        y = -event.values[0];
		        break;
	    }

	    if(x>=-1 && x<=1)
	    {
	    	// straight
	    	direction = 0;
	    }
	    else if(x<-1)
	    {
	    	// right
	    	direction = 1;
	    }
	    else if(x>1)
	    {
	    	// left
	    	direction = 2;
	    }

	    if(y>=-1 && y<=1)
	    {
	    	// stop
	    	motor = 0;
	    }
	    else if(y<-1)
	    {
	    	// forward
	    	motor = 1;
	    }
	    else if(y>1)
	    {
	    	// backward
	    	motor = 2;
	    }

	    updateState();

	    // display values using TextView
	    tv1.setText("X axis\t\t"+x);
	    tv2.setText("Y axis\t\t"+y);
	    tv3.setText("Z axis\t\t" +z);
	}

	/**
     * Send commands to Arduino
     */
	private void updateState()
	{
		if(System.currentTimeMillis()-lastChange > DELAY) {

			String msg = motor+","+direction;
			Amarino.sendDataToArduino(this, device_address, 'a', msg);

			writeLog(motor+", "+direction);
			lastChange = System.currentTimeMillis();
		}
	}

	@Override
    public boolean onOptionsItemSelected(MenuItem item)
	{
		if (D) Log.d(TAG, "onOptionsItemSelected()");

        Intent serverIntent = null;
        switch (item.getItemId())
        {
	        case R.id.connect_scan:
	            // Launch the DeviceListActivity to see devices and do scan
	            serverIntent = new Intent(this, DeviceListActivity.class);
	            startActivityForResult(serverIntent, 0);
	            return true;
        }
        return false;
    }

	public void onActivityResult(int requestCode, int resultCode, Intent data)
	{
		if(resultCode == Activity.RESULT_OK)
		{
            connectDevice(data);
        }

		if (D) Log.d(TAG, "onActivityResult()");
    }

    private void connectDevice(Intent data)
    {
    	device_name = data.getExtras().getString(DeviceListActivity.EXTRA_DEVICE_NAME);
    	device_address = data.getExtras().getString(DeviceListActivity.EXTRA_DEVICE_ADDRESS);
    	Amarino.connect(this, device_address);

        if (D) Log.d(TAG, "connectDevice() - "+device_name+" - "+device_address);
    }

    /**
     * Show on the screen connection state, name and address of paired device
     * @param status
     */
	public void setStatus(int status)
	{
		if (D) Log.d(TAG, "setStatus() - BEGIN - "+status);

		switch(status)
		{
			case CONNECTED:
				txtDevice.setText(device_name+" ("+device_address+")");
				imgConnected.setBackgroundColor(getResources().getColor(R.color.connected_on));
				imgDisconnected.setBackgroundColor(getResources().getColor(R.color.disconnected_off));
				break;

			case DISCONNECTED:
				txtDevice.setText(R.string.nodevice);
				imgConnected.setBackgroundColor(getResources().getColor(R.color.connected_off));
				imgDisconnected.setBackgroundColor(getResources().getColor(R.color.disconnected_on));
				break;
		}

		if (D) Log.d(TAG, "setStatus() - END");
	}

	class ArduinoReceiver extends BroadcastReceiver {

		@Override
		public void onReceive(Context context, Intent intent) {
			final String action = intent.getAction();

			if (D) Log.d(TAG, "onReceive() - BEGIN");

			// this is how to retrieve the address of the sender
			//final String address = intent.getStringExtra(AmarinoIntent.EXTRA_DEVICE_ADDRESS);

			if (AmarinoIntent.ACTION_CONNECTED.equals(action)){
				// connection has been established
				setStatus(CONNECTED);
			}
			else if (AmarinoIntent.ACTION_DISCONNECTED.equals(action)){
				// disconnected from a device
				setStatus(DISCONNECTED);
			}
			else if (AmarinoIntent.ACTION_CONNECTION_FAILED.equals(action)){
				// connection attempt was not successful
				//setStatus(DISCONNECTED);
			}
			else if (AmarinoIntent.ACTION_PAIRING_REQUESTED.equals(action)){
				// a notification message to pair the device has popped up
				//setStatus(DISCONNECTED);
			}
			else if (AmarinoIntent.ACTION_RECEIVED.equals(intent.getAction())){

				// the device address from which the data was sent,
				// we don't need it here but to demonstrate how you retrieve it
				//final String address = intent.getStringExtra(AmarinoIntent.EXTRA_DEVICE_ADDRESS);

				// the type of data which is added to the intent
				final int dataType = intent.getIntExtra(AmarinoIntent.EXTRA_DATA_TYPE, -1);

				switch (dataType){

					case AmarinoIntent.STRING_EXTRA:
					//String data = intent.getStringExtra(AmarinoIntent.EXTRA_DATA);
					// do something useful with the received data
					break;
				}
			}

			if (D) Log.d(TAG, "onReceive() - END");
		}
	}
}

Download

• Schema circuito
• Codice sorgente Arduino
• Codice sorgente Android
• App Android installabile (APK)
• MeetAndroid+SoftwareSerial

Datasheets

• HC-05 User Instructional Manual
• HC-05 AT Command Set

Reference

• http://www.amarino-toolkit.net
• http://developer.android.com/training/index.html
• http://forum.arduino.cc/index.php?topic=104903.0