Auto Car Project

Hardware

• Raspberry Pi
• L298N Dual H Bridge DC Motor Drive
• Ultrasonic Module HC-SR04 Distance Sensor
• 4 yellow motors

Software

• C++ language
  • link
• Blynk
  • version:0.4.10
  • working dir:blynk0.4.10/libraries/Blynk/linux/main.cpp

Code

• Setup distance sensor related GPIO
  • Use GPIO 2 as OUTPUT
  • Use GPIO 3 as INPUT
• Setup L298N Dual H Bridge DC Motor Drive related GPIO
  • Use GPIO 17, 18, 23 and 24 as OUTPUT
• Add call back function for
  • timer event
  • distance sensor

void setup()
{
  printf("Setup - uptime: %i\n", uptime);
  printf("Setup - milis time: %i\n", millis());

  // echoPin and trigPoin for the distance sensor
  unsigned int echoPin = 3;
  unsigned int trigPin = 2;
  
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(17, OUTPUT);
  pinMode(18, OUTPUT);
  pinMode(23, OUTPUT);
  pinMode(24, OUTPUT);
 
  // Call back function for timer event and distance sensor
  timer.setInterval(1000L, myTimerEvent);
  timer.setInterval(1000L, distanceSensor);
}

• main loop

void loop()
{
  Blynk.run();
  timer.run();
  autoRun();
}

• Timer event
  • Print the running time each 1 second to V10

void myTimerEvent()
{
    if (millis() % 10000 == 0)
    {
        printf("My Timer Event 2 - %i (ms)\n", millis());
    }

    Blynk.virtualWrite(V10, millis()/1000);
}

• Distance Sensor
  • Use sonar to detect the distance to an object like bats do
  • the transmitter (trig pin) send a signal high frequency sound
  • when the signal finds the object, it is reflected
  • the transmitter (echo pin) receives it
  • the time between the transmission and reception allows us to know the distance to an object

int getDistance()
{
  unsigned int echoPin = 3;
  unsigned int trigPin = 2;

  digitalWrite (trigPin, LOW);

  delayMicroseconds(2);
  digitalWrite (trigPin, HIGH);

  delayMicroseconds(10);
  digitalWrite (trigPin, LOW);

  long duration = pulseIn(echoPin, HIGH, 1000000);
  int distance = (duration/2) / 29.1;

  return distance;

}

• Auto run logic
  • if the distance between 20-50 cm, turn left
  • then move forward until the distance is less than 20

void autoRun()
{
    if (m_isAuto) {
        if (m_distance > 50) {
	    // forward
	    Execute(Action::forward);
	}
	else if (m_distance < 20){
	    // backward
	    Execute(Action::backward);
	}
	else {
	    // if the distance is 20 to 50 then turn left
	    Execute(Action::left);
	}
    }
}

• movement logic
  • when GPIO 17 is enable, the left motor move forward
  • when GPIO 18 is enable, the left motor move backward
  • when GPIO 23 is enable, the right motor move forward
  • when GPIO 24 is enable, the right motor move backward

void Execute(bool leftForward, bool leftBackward, bool rightForward, bool rightBackward)
{
    //analogWrite(21, 255); //Sets speed variable via PWM 
    digitalWrite(17, leftForward);
    digitalWrite(18, leftBackward);
    digitalWrite(23, rightForward);
    digitalWrite(24, rightBackward);
}

void Execute(Action action)
{
    if ( action != m_lastAction )
    {
        switch(action) 
        {
            case Action::left:
                printf("left\n");
                Execute(true, false, true, false); 
                break;
            
            case Action::right: 
                printf("right\n");
                Execute(false, true, false, true); 
                break;
            
            case Action::forward: 
                printf("forward\n");
                Execute(false, true, true, false); 
                break;
            
            case Action::backward: 
                printf("backward\n");
                Execute(true, false, false, true); 
                break;
            
            case Action::stop: 
                printf("stop\n");
                Execute(false, false, false, false); 
                break;

            default: 
                printf("default");
        }

        m_lastAction = action;
    }
}

GPIO Connection

Raspberry Pi GPIO Setup to L298N Dual H Bridge DC Motor Drive setup

• PIN 2 (5V PWR) connect to Motor Power supply
• PIN 39 (GND) connect to GND
• PIN 11 (GPIO 17) connect to IN4
• PIN 12 (GPIO 18) connect to IN3
• PIN 16 (GPIO 23) connect to IN2
• PIN 18 (GPIO 24) connect to IN1

L298N Dual H Bridge DC Motor Drive setup

• OUT1 connect to motor GND
• OUT2 connect to motor PWD
• OUT3 connect to motor GND
• OUT4 connect to motor PWD

Raspberry Pi GPIO Setup to Ultrasonic Module HC-SR04 Distance Sensor

• PIN 3 (GPIO 2) connect to Trig
• PIN 4 (5V PWR) connect to VCC (PWD)
• PIN 5 (GPIO 3) connect to Echo
• PIN 6 (GND) connect to GND