Activity 4: Object Detection and Avoidance

An interesting thing about these IR detectors is that their outputs are just like the whiskers.  When no object is detected, the output is high; when an object is detected, the output is low.  In this activity,  the example sketch RoamingWithWhiskers is modified so that it works with the IR detectors; all it takes is few simple modifications.  Here are the steps:

1. Save the sketch RoamingWithWhiskers as RoamingWithIr
2. Add the irDetect function.

int irDetect(int irLedPin, int irReceiverPin, long frequency)
{
  tone(irLedPin, frequency, 8);              
  delay(1);                                  
  int ir = digitalRead(irReceiverPin);       
  delay(1);                                  
  return ir;                                 
}

3. Replace these digitalRead calls:

  byte wLeft = digitalRead(5);                 
  byte wRight = digitalRead(7);  

…with these calls to irDetect:

  int irLeft = irDetect(9, 10, 38000);       
  int irRight = irDetect(2, 3, 38000);

4. Replace all instances of wLeft with irLeft and wRight with irRight.
5. Update the /*…*/ and // comments.                             

Example Sketch – RoamingWithIr

• Open RoamingWithWhiskers.
• Save it as RoamingWithIr.
• Modify it so that it matches the sketch below.
• Save it; then, upload it into the Arduino.
• Disconnect the BOE Shield-Bot from its programming cable.
• Reconnect the battery pack and move the 3-position switch to position 2.
• Place your BOE Shield-Bot somewhere where it can roam and avoid obstacles.
• Verify that it behaves like RoamingWithWhiskers (aside from the fact that there’s no contact required).

/*
 * Robotics with the BOE Shield - RoamingWithIr
 * Adaptation of RoamingWithWhiskers with IR object detection instead of
 * contact switches.
 */

#include <Servo.h>                           // Include servo library
 
Servo servoLeft;                             // Declare left and right servos
Servo servoRight;
 
void setup()                                 // Built-in initialization block
{
  pinMode(10, INPUT);  pinMode(9, OUTPUT);   // Left IR LED & Receiver
  pinMode(3, INPUT);  pinMode(2, OUTPUT);    // Right IR LED & Receiver

  tone(4, 3000, 1000);                       // Play tone for 1 second
  delay(1000);                               // Delay to finish tone

  servoLeft.attach(13);                      // Attach left signal to pin 13
  servoRight.attach(12);                     // Attach right signal to pin 12
}  
 
void loop()                                  // Main loop auto-repeats
{
  int irLeft = irDetect(9, 10, 38000);       // Check for object on left
  int irRight = irDetect(2, 3, 38000);       // Check for object on right

  if((irLeft == 0) && (irRight == 0))        // If both sides detect
  {
    backward(1000);                          // Back up 1 second
    turnLeft(800);                           // Turn left about 120 degrees
  }
  else if(irLeft == 0)                       // If only left side detects
  {
    backward(1000);                          // Back up 1 second
    turnRight(400);                          // Turn right about 60 degrees
  }
  else if(irRight == 0)                      // If only right side detects
  {
    backward(1000);                          // Back up 1 second
    turnLeft(400);                           // Turn left about 60 degrees
  }
  else                                       // Otherwise, no IR detected
  {
    forward(20);                             // Forward 1/50 of a second
  }
}

int irDetect(int irLedPin, int irReceiverPin, long frequency)
{
  tone(irLedPin, frequency, 8);              // IRLED 38 kHz for at least 1 ms
  delay(1);                                  // Wait 1 ms
  int ir = digitalRead(irReceiverPin);       // IR receiver -> ir variable
  delay(1);                                  // Down time before recheck
  return ir;                                 // Return 1 no detect, 0 detect
}  

void forward(int time)                       // Forward function
{
  servoLeft.writeMicroseconds(1700);         // Left wheel counterclockwise
  servoRight.writeMicroseconds(1300);        // Right wheel clockwise
  delay(time);                               // Maneuver for time ms
}

void turnLeft(int time)                      // Left turn function
{
  servoLeft.writeMicroseconds(1300);         // Left wheel clockwise
  servoRight.writeMicroseconds(1300);        // Right wheel clockwise
  delay(time);                               // Maneuver for time ms
}

void turnRight(int time)                     // Right turn function
{
  servoLeft.writeMicroseconds(1700);         // Left wheel counterclockwise
  servoRight.writeMicroseconds(1700);        // Right wheel counterclockwise
  delay(time);                               // Maneuver for time ms
}

void backward(int time)                      // Backward function
{
  servoLeft.writeMicroseconds(1300);         // Left wheel clockwise
  servoRight.writeMicroseconds(1700);        // Right wheel counterclockwise
  delay(time);                               // Maneuver for time ms
}