Lesson 14 · Program Your Car To Avoid Obstacles

Suggested Time: 60-75 minutes

Lesson Plan

Overview

In this section we’ll combine everything to program our car to move and avoid objects

Stopping Your Robot At A Wall

Note: This uses pins 4 and 5 for trigger and echo connections, respectively.

Stop Before We Crash

Let’s program that car to stop before we hit a wall! Let’s use what we have learned about the ultrasonic sensor to program our robot to do this. We’ll need to use if/else.

int motb_pin1 = 3;
int motb_pin2 = 11;

int mota_pin1 = 9;
int mota_pin2 = 10;

int button_pin = 2;

int trig_pin = 4;
int echo_pin = 5;

void setup() {
  //-Control Motor B
  pinMode(motb_pin1,OUTPUT);
  pinMode(motb_pin2,OUTPUT);
  
  //-Control Motor A
  pinMode(mota_pin1,OUTPUT);
  pinMode(mota_pin2,OUTPUT);
  
  //- button
  pinMode(button_pin,INPUT_PULLUP);
  
  //-ultrasonic pin
  pinMode(trig_pin,OUTPUT);
  pinMode(echo_pin,INPUT);
  
  Serial.begin(9600);
  
}

//-sends sound out and receives sound
//-returns the distance in centimeters
int ultrasonic() {
  long time;
  float distance;
 
  //-trigger a sound 
  // send out trigger signal
  digitalWrite(trig_pin, LOW);
  delayMicroseconds(2);
  digitalWrite(trig_pin, HIGH);
  delayMicroseconds(20);
  digitalWrite(trig_pin, LOW);
  
  //- a sound has gone out!!
  //- wait for a sound to come back
  
  time = pulseIn(echo_pin, HIGH);
  
  //- calculate the distance in centimeters
  distance = 0.01715 * time;
  return distance;
}

//- turn 90 degrees
void turnRight() {
  //- motor b is stopped
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,0);
  
  //- motor a moves forward
  analogWrite(mota_pin1,255);
  analogWrite(mota_pin2,0);
  
  delay(600);
  
  //- stop motor a
  analogWrite(mota_pin1,0);
  analogWrite(mota_pin2,0);
}

void turnLeft() {
  //- motor a is stopped
  analogWrite(mota_pin1,0);
  analogWrite(mota_pin2,0);
  
  //- motor b moves forward
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,255);
  
  delay(800);
  
  //- stop motor b
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,0);
}

void stop() {
  //- motor a
  analogWrite(mota_pin1,255);
  analogWrite(mota_pin2,255);
  
  //- motor b
  analogWrite(motb_pin1,255);
  analogWrite(motb_pin2,255);
}


void moveToWall(int speeda, int speedb) {
  //- move forward!
  //- motor a
  analogWrite(mota_pin1,speeda);
  analogWrite(mota_pin2,0);
  
  //- motor b
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,speedb);
  
  //-stop when you hit a wall!!
  
  int distance = ultrasonic();
  
  while (distance > 5) {
    //-do nothing except check distance
    distance = ultrasonic();
  }
  //-stop!!!
  stop();
}


void moveForward(int speeda, int speedb, int inches) {
  
  int myDelay;
  
  //- motor a
  analogWrite(mota_pin1,speeda);
  analogWrite(mota_pin2,0);
  
  //- motor b
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,speedb);
  
  //- move forward the distance in inches
  myDelay = inches*125;
  delay(myDelay);
  
  //- stop
  stop();
  
}

void moveBackward(int speeda, int speedb) {
  
  //- motor a
  analogWrite(mota_pin1,0);
  analogWrite(mota_pin2,speeda);
  
  //- motor b
  analogWrite(motb_pin1,speedb);
  analogWrite(motb_pin2,0);
}

void loop() {
  
  Serial.println(ultrasonic());
  delay(100);
  if (digitalRead(button_pin)==LOW) {
      moveToWall(120,120);
  }
  else {
    stop();
  }
}

Turn Before We Crash

Let’s program our car to not only stop before we hit a wall, but also turn to avoid it!

Let’s program the robot to turn right if it sees an object less than 20 cm away, else move forward. See the code below.

int motb_pin1 = 3;
int motb_pin2 = 11;

int mota_pin1 = 9;
int mota_pin2 = 10;

int button_pin = 2;

int trig_pin = 4;
int echo_pin = 5;

void setup() {

  //-Control Motor B
  pinMode(motb_pin1,OUTPUT);
  pinMode(motb_pin2,OUTPUT);

  //-Control Motor A
  pinMode(mota_pin1,OUTPUT);
  pinMode(mota_pin2,OUTPUT);

  //- button
  pinMode(button_pin,INPUT_PULLUP);

  //-ultrasonic pin
  pinMode(trig_pin,OUTPUT);
  pinMode(echo_pin,INPUT);

  Serial.begin(9600);

}

//-sends sound out and receives sound
//-returns the distance in centimeters
int ultrasonic() {

  long time;
  float distance;

  //-trigger a sound 
  // send out trigger signal
  digitalWrite(trig_pin, LOW);
  delayMicroseconds(2);
  digitalWrite(trig_pin, HIGH);
  delayMicroseconds(20);
  digitalWrite(trig_pin, LOW);

  //- a sound has gone out!!
  //- wait for a sound to come back

  time = pulseIn(echo_pin, HIGH);

  //- calculate the distance in centimeters
  distance = 0.01715 * time;

  return distance;

}

//- turn 90 degrees
void turnRight() {

  //- motor b is stopped
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,0);

  //- motor a moves forward
  analogWrite(mota_pin1,255);
  analogWrite(mota_pin2,0);

  delay(600);

  //- stop motor a
  analogWrite(mota_pin1,0);
  analogWrite(mota_pin2,0);  
}

void turnLeft() {

  //- motor a is stopped
  analogWrite(mota_pin1,0);
  analogWrite(mota_pin2,0);

  //- motor b moves forward
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,255);

  delay(800);

  //- stop motor b
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,0);
}

void stop() {
  //- motor a
  analogWrite(mota_pin1,255);
  analogWrite(mota_pin2,255);

  //- motor b
  analogWrite(motb_pin1,255);
  analogWrite(motb_pin2,255);
}


void moveToWall(int speeda, int speedb) {

  //- move forward!
  //- motor a
  analogWrite(mota_pin1,speeda);
  analogWrite(mota_pin2,0);

  //- motor b
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,speedb);

  //-stop when you hit a wall!!

  int distance = ultrasonic();

  while (distance > 5) {
    //-do nothing except check distance
    distance = ultrasonic();
  }
  //-stop!!!
  stop();

}


void moveForward(int speeda, int speedb, int inches) {

  int myDelay;

  //- motor a
  analogWrite(mota_pin1,speeda);
  analogWrite(mota_pin2,0);

  //- motor b
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,speedb);

  //- move forward the distance in inches
  myDelay = inches*125;
  delay(myDelay);

  //- stop
  stop();

}

void moveBackward(int speeda, int speedb) {

  //- motor a
  analogWrite(mota_pin1,0);
  analogWrite(mota_pin2,speeda);

  //- motor b
  analogWrite(motb_pin1,speedb);
  analogWrite(motb_pin2,0);
}



void loop() {

  Serial.println(ultrasonic());

  delay(100);

  if (digitalRead(button_pin)==LOW) {
      moveToWall(120,120);
      turnRight();
  }
  else {
    moveForward();
  }
}

Extra Challenges

  • When you stop at the wall, back up and then turn around
  • Once you see a wall, stop, back up and turn around.. and then keep going looking for walls. Once you see another wall, repeat!

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