Robot is Happy creating our robot overlords one day at a time

13Dec/095

Beacon Locating Robot – Powered by Arduino and IR Transceiver by Christopher Hazlett

After I built my first Arduino-based robot, I wanted to graduate to a little more advanced behavior, and I had it my mind to make a robot that would find a home base via an IR Beacon. Plus I saw that Pololu had the perfect parts for the job, the IR Beacon Transceiver pair. My wife was gracious enough to get me some IR distance sensors, a servo and the transceivers for my birthday in August. If she keeps supporting my hobbies like this, she'll have more robots than she can handle. As always, I'll start with the parts.

The Parts

I, of course, re-used parts from my last robot, but I'll include the links here as well. My robots are nothing if not a source of parts for the next robot.

I also used various crimped and un-crimped wires lying around that I use regularly, but that's a separate post.

The Robot

Beacon Locating Robot

Beacon Locating Robot

It's a pretty simple concept, place a home base somewhere and then have the robot find said home base from it's current location and make it's way there. When I first started thinking about how to execute this project, I thought it was going to be much more complicated to institute the seeking behavior I was looking for. The IR transceivers from Pololu.com were much better than I thought they'd be and had a lot of power. As you can see in the video below, the beacons are powerful enough to work around corners, so I never ended up putting a seeking algorithm in place. The beacon took care of that for me. All I had to do was make sure it avoided walls on its way to the home base. To accomplish that, I put the servo and Sharp distance sensor on the front and performed a sweep with the sensor and read the values from analog input 0. That's the bare bones of the robot.

The Home Base

Home-Base

For the home base, I took one of the transceivers and raised it to the height of the robot's head. This ended up being unnecessary. The robot would find the beacon if it was at any level. The home base didn't have to do anything, so I just powered it up and let it run.

The Code

There are a couple of gotchas when writing the code. Because the IR transceivers are always reading, I had to do a comparison of each reading to determine which of the directional sensors was the highest. You can't just read the input as an on or off. The second and harder portion of the code (and actually the most fun) was determining which direction to make the robot move. At first, I just let the robot move after determining which direction was currently being read from the beacon. In practice, this seems completely fine, but you'll see in the videos that the beacon itself changes directions quite frequently. This made the robot indecisive. To combat this problem, I figure out the Mode of the readings. Essentially, I took the last ten readings and counted what the most prevalent direction was. This smoothed out the robot's behavior and it behaved as expected.

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#include <Servo.h>
#include <AFMotor.h>
#define TOPSPEED 200
 
// SERVO SCANNING VARIABLES //
Servo myservo;  // create servo object to control a servo
int servoPosition = 0;    // variable to store the servo position
const int SERVO_PIN = 10;
int floorState = 0;
long frontReading = 0;
boolean scanIncrement = true;  //increase position?
byte servoIncrementValue = 6;
byte servoDecrementValue = 6;
 
// MOTOR VARIABLES //
AF_DCMotor rightMotor(4, MOTOR12_8KHZ);
AF_DCMotor leftMotor(3, MOTOR12_8KHZ); 
 
// TRANSCEIVER VARIABLES //
int notFoundSensitivity = 500;
int west = 0;
int south = 0;
int east = 0;
int north = 0;
int dir = 0;
boolean detected = false;
 
// TRANSCEIVER DIRECTION MODE VARIABLES //
const int NUM_READINGS = 10;
int directionReadings[NUM_READINGS];
int modeOfDirections = 1;
int index = 0;
 
void setup()
{
  Serial.begin(38400);
  myservo.attach(SERVO_PIN);  // attaches the servo on pin 9 to the servo object
  myservo.write(0);
  rightMotor.setSpeed(200);
  leftMotor.setSpeed(200);
  delay(1500);
} 
 
void loop()
{
  scan();
  move();
} 
 
void move()
{
    if(servoPosition >= 0 && servoPosition <= 84 && frontReading > 550){ //Object on the left
      turnLeft();
    }else if((servoPosition >= 85 && servoPosition <= 105) && frontReading > 600){ // Object in Front
      turnAround();
    }else if((servoPosition >= 106 && servoPosition <= 180) && frontReading > 550){ // Object on the Right
      turnRight();
    }else{
      moveTowardBeacon();
    }
}
 
void moveTowardBeacon()
{
  readTransceiverandSetDirection();
  if(modeOfDirections == 3 || modeOfDirections == 4){ //South or West
    turnRight();
  } else if(modeOfDirections == 2) { // East
    turnLeft();
  } else if(modeOfDirections == 1){ //North
    moveForward();
  }
}
 
void scan()
{
   scanIncrement ? servoPosition+=servoIncrementValue : servoPosition-=servoDecrementValue; //increment or decrement current position
   if (servoPosition >= 180){
     scanIncrement = false;
     servoPosition = 180;
   } else if (servoPosition &lt;= 1){
     scanIncrement = true;
     servoPosition = 1;
   }
   frontReading = measureFront();
   //Serial.print(servoPosition);
   //Serial.print("|");
   //Serial.print(frontReading);
   //Serial.print(";");
   myservo.write(servoPosition);
   delay(15);
}
 
long measureFront()
{
  return analogRead(0);
}
 
void moveForward(){
  Serial.println("Move Forward");
  rightMotor.run(FORWARD);
  leftMotor.run(FORWARD);
}
 
void speedUp(){
  for (int i=0; i==TOPSPEED; i++) {
    rightMotor.setSpeed(i);
    leftMotor.setSpeed(i);
  }
}
 
void slowToStop(){
  for (int i=TOPSPEED; i==0; i--) {
    rightMotor.setSpeed(i);
    leftMotor.setSpeed(i);
  }
  rightMotor.run(RELEASE);
  leftMotor.run(RELEASE);
}
 
void turnLeft(){
  Serial.println("Turn Left");
  rightMotor.run(BACKWARD);
  leftMotor.run(FORWARD);
}
 
void turnRight(){
  Serial.println("Turn Right");
  rightMotor.run(FORWARD);
  leftMotor.run(BACKWARD);
}
 
void stop(){
  Serial.println("Stop");
  rightMotor.run(RELEASE);
  leftMotor.run(RELEASE);
  delay(500);
}
 
void turnAround(){
   stop();
   delay(500);
   moveBackward();
   delay(300);
   turnLeft();
   delay(300);
   stop();
   //runAway = true;
}
 
void moveBackward(){
  Serial.println("Move Backward");
  rightMotor.run(RELEASE);
  leftMotor.run(RELEASE);
  rightMotor.run(BACKWARD);
  leftMotor.run(BACKWARD);
}
 
//  BEACON LOGIC  //
void readTransceiverandSetDirection(){
  west = analogRead(2);
  south = analogRead(3);
  east = analogRead(4);
  north = analogRead(5);
  getDirection();
  setModeOfDirections();
}
 
boolean foundBeacon(){
  if(west < notFoundSensitivity and east < notFoundSensitivity and south < notFoundSensitivity and north < notFoundSensitivity){     return false;   }else{     return true;   } } void getDirection(){   int minValue = 1200;   if(minValue > west){
    minValue = west;
    dir = 4;
  }
 
  if(minValue > south){
    minValue = south;
    dir = 3;
  }
 
  if(minValue > east){
    minValue = east;
    dir = 2;
  }
 
  if(minValue > north){
    minValue = north;
    dir = 1;
  }
 
  addDirectionToReadings();
 
  //Serial.print("W:");
  //Serial.print(west);
  //Serial.print(" | S:");
  //Serial.print(south);
  //Serial.print(" | E:");
  //Serial.print(east);
  //Serial.print(" | N:");
  //Serial.println(north);
  //Serial.println("=================================");
  //if(dir == 1){
  //  Serial.println("North");
  //}else if(dir == 2){
  //  Serial.println("East");
  //}else if(dir == 3){
  //  Serial.println("South");
  //}else if(dir == 4){
  //  Serial.println("West");
  //}
}
 
void addDirectionToReadings(){
  directionReadings[index] = dir;
 
  index = (index + 1);
  if (index &gt;= NUM_READINGS)             // if we're at the end of the array...
    index = 0;
}
 
// =========================================
// In order to smooth out the directions readings from the
// IR transceiver, You have to take the mode (most prevalent number in a collection)
// of the directionReadings Array.  This allows the program to determine which
// direction is being read the most from the device.
// Otherwise, the readings make the robot squirrelly.
// ========================================
void setModeOfDirections(){
  int currentValue = directionReadings[0];
  int counter = 1;
  int maxCounter = 1;
  int modeValue = modeOfDirections;
  int directionCounts[4] = {0,0,0,0}; //{North(1), East(2), South(3), West(4)}
 
  for (int i = 1; i < NUM_READINGS; ++i){
    Serial.print(directionReadings[i]);
    Serial.print("|");
     ++directionCounts[directionReadings[i]-1];
  }
 
  //Determine mode of directions from count array
  Serial.println("");
  int modeCount[2] = {1,directionCounts[0]}; //This array holds the current maximum count and the direction it points to.
  for(int i = 0; i < 4; ++i){
    //Serial.print(directionCounts[i]);
    //Serial.print("|");
    if(modeCount[1] >= directionCounts[i]){
      modeCount[0] = i + 1; // set direction
      modeCount[1] = directionCounts[i]; //set count
    }
  }
 
  modeOfDirections = modeCount[0];
  Serial.println("");
  Serial.print("Direction Mode: ");
  Serial.println(modeOfDirections);
}

There you have it. Let me know if you have any questions about the code or construction.

- Chris

7Dec/090

Soh-cah-toa Processing Tutorial by Christopher Hazlett

As I beef up for my next project, a self-guided GPS mapping robot (I still have to write about my beacon seeking robot), I was reviewing the processing language to parse the GPS logged data.

Found this tutorial exceptionally helpful: http://processing.org/learning/trig/.

- Chris

   

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