Activity 5: High-performance IR Navigation

The style of pre-programmed maneuvers from the last activity were fine for whiskers, but are unnecessarily slow when using the IR detectors.  With whiskers, the BOE Shield-Bot had to make contact and then back up to navigate around obstacles.  With infrared, your BOE Shield-Bot will detect most obstacles before it runs into them, and can just find a clear path around the obstacle.

Increase the Sampling Rate to Avoid Collisions

You can reduce all your maneuver durations to 20 ms, which means your sketch will check and recheck for objects almost 50 times per second.  (It’s actually a little slower, more like 40 times per second, because the code execution and IR detection all takes time too.)  As your BOE Shield-Bot navigates, it will execute a series of small turns to avoid an obstacle before it ever runs into it.  With that approach, it never turns further than it has to, and it can neatly find its way around obstacles and successfully navigate more complex courses.  After experimenting with this next sketch, you’ll likely agree that it’s a much better way for the BOE Shield-Bot to roam. 

Example Sketch – FastIrRoaming

• Enter, save, upload FastIrRoaming, then test it with the same obstacles you used from the previous activity.

/*
 * Robotics with the BOE Shield - FastIrRoaming
 * 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
  {
    maneuver(-200, -200, 20);                // Backward 20 milliseconds
  }
  else if(irLeft == 0)                       // If only left side detects
  {
    maneuver(200, -200, 20);                 // Right for 20 ms
  }
  else if(irRight == 0)                      // If only right side detects
  {
    maneuver(-200, 200, 20);                 // Left for 20 ms
  }
  else                                       // Otherwise, no IR detects
  {
    maneuver(200, 200, 20);                  // Forward 20 ms
  }
}

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 maneuver(int speedLeft, int speedRight, int msTime)
{
  // speedLeft, speedRight ranges: Backward  Linear  Stop  Linear   Forward
  //                               -200      -100......0......100       200
  servoLeft.writeMicroseconds(1500 + speedLeft);   // Set left servo speed
  servoRight.writeMicroseconds(1500 - speedRight); // Set right servo speed
  if(msTime==-1)                                   // if msTime = -1
  {                                  
    servoLeft.detach();                            // Stop servo signals
    servoRight.detach();   
  }
  delay(msTime);                                   // Delay for msTime
}

How FastIrRoaming Works

This sketch uses the maneuver function from the TestManeuverFunction sketch.  The maneuver function expects three parameters: speedLeft, speedRight, and msTime.  Recall that both speed parameters use 200 for full speed forward, ‑200 for full speed backward,  and values between -100 and +100 for linear speed control.  Also, remember msTime values are 20, so each maneuver executes for 20 ms before returning to the loop function.

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
  {
    maneuver(-200, -200, 20);                // Backward 20 milliseconds
  }
  else if(irLeft == 0)                       // If only left side detects
  {
    maneuver(200, -200, 20);                 // Right for 20 ms
  }
    else if(irRight == 0)                    // If only right side detects
  {
    maneuver(-200, 200, 20);                 // Left for 20 ms
  }
  else                                       // Otherwise, no IR detects
  {
    maneuver(200, 200, 20);                  // Backward 20 ms
  }
}

Your Turn

• Save FastIrRoaming as FastIrRoamingYourTurn. 
• Add code to make the LEDs indicate that the BOE Shield-Bot has detected an object.
• Try modifying the values that speedLeft and speedRight are set to so that the BOE Shield-Bot does everything at half speed.  (Remember that 200 and -200 are overkill, so try 50 for half speed forward and –50 for half speed backward).