Code issue with PING Sensor and while loop Heeelp!

Brennn10 · February 13, 2011, 8:05pm

Hey guys,

I have a robot with a PING Sensor and a Motor Shield from adafruit. At the moment, I am trying to get my robot to move forward until an object is located within a certain distance, and then move backward and turn right once an object is located within a certain distance.

With the code I have right now, my robot just moves forward into the object, and doesn't recognize that an object is in the way. My PING sensor is functional and works with other test code, so I know that is not the problem.

Here is what I have so far:

#include <AFMotor.h>

 
AF_DCMotor motor1(1, MOTOR12_8KHZ);
AF_DCMotor motor2(2, MOTOR12_8KHZ);
AF_DCMotor motor3(3, MOTOR12_1KHZ);
AF_DCMotor motor4(4, MOTOR12_1KHZ);
const int pingPin = 19;


void setup() {
  Serial.begin(9600);           // set up Serial library at 9600 bps
  motor1.setSpeed(200);     // set the speed to 200/255
  motor2.setSpeed(200);
  motor3.setSpeed(200);
  motor4.setSpeed(200);
}

void forward()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(FORWARD);
  motor4.run(FORWARD);
}

void backward()
{
  motor1.run(BACKWARD);
  motor2.run(BACKWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);
}

void haltMotors()
{
  motor1.run(RELEASE);
  motor2.run(RELEASE);
  motor3.run(RELEASE);
  motor4.run(RELEASE);
  
}

void turnRight()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);

void loop() {
  long duration, inches;
  
  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);
  
  pinMode(pingPin, INPUT);
  duration = pulseIn(pingPin, HIGH);
  
  inches = microsecondstoInches(duration);
  
  while (inches > 5)  //while robot is 5 inches away from object
    {
     forward();
    }
  haltMotors();      //stop the motors before reversing direction
  while (inches < 10) //move robot back 10 inches before turning
   {
     backward();
    }
  turnRight();
}
long microsecondstoInches (long microseconds)
{
  return microseconds / 74 / 2;
}

system · February 13, 2011, 8:14pm

while (inches > 5)  //while robot is 5 inches away from object
{
  forward();
}

That's the problem. You will always stay in that while loop because "inches" never gets the chance to be changed. You need to look for the distance in that while loop to.

Ditto for the other while loop, you must check the new distance some times

JanD

Brennn10 · February 13, 2011, 8:21pm

Would I check the distance with an if-statement inside of the while loop?

system · February 13, 2011, 8:47pm

Would I check the distance with an if-statement inside of the while loop?

No, you just read it - the check is performed by the "while".

retrolefty · February 13, 2011, 8:47pm

Brennn10:
Would I check the distance with an if-statement inside of the while loop?

No, just update the distance reading while inside the while.

Lefty

Brennn10 · February 14, 2011, 12:04am

So, inches = microsecondstoInches(duration); should go inside of the while loop?

retrolefty · February 14, 2011, 12:09am

Brennn10:
So, inches = microsecondstoInches(duration); should go inside of the while loop?

To obtain a new updated distance value inside your while statement you need to do both:

duration = pulseIn(pingPin, HIGH);
inches = microsecondstoInches(duration);

Lefty

Brennn10 · February 14, 2011, 12:13am

Now the motors just seem to be randomly moving and twitching. Should all of the PING code go inside of the loop? Here is what I have at the moment.

#include <AFMotor.h>

 
AF_DCMotor motor1(1, MOTOR12_8KHZ);
AF_DCMotor motor2(2, MOTOR12_8KHZ);
AF_DCMotor motor3(3, MOTOR12_1KHZ);
AF_DCMotor motor4(4, MOTOR12_1KHZ);
const int pingPin = 19;


void setup() {
  Serial.begin(9600);           // set up Serial library at 9600 bps
  motor1.setSpeed(200);     // set the speed to 200/255
  motor2.setSpeed(200);
  motor3.setSpeed(200);
  motor4.setSpeed(200);
}

void forward()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(FORWARD);
  motor4.run(FORWARD);
}

void backward()
{
  motor1.run(BACKWARD);
  motor2.run(BACKWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);
}

void haltMotors()
{
  motor1.run(RELEASE);
  motor2.run(RELEASE);
  motor3.run(RELEASE);
  motor4.run(RELEASE);
  
}

void turnRight()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);

}
void loop() {
  const int pingPin = 19;
  long duration, inches;
  
  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);
  
  pinMode(pingPin, INPUT);
  duration = pulseIn(pingPin, HIGH);
  
  inches = microsecondstoInches(duration);
  
  while (inches > 5)  //while robot is 5 inches away from object
    {
      duration = pulseIn(pingPin, HIGH);
      inches = microsecondstoInches(duration);
      forward();
    }
  haltMotors();      //stop the motors before reversing direction
  while (inches < 10) //move robot back 10 inches before turning
   {
     duration = pulseIn(pingPin, HIGH);
     inches = microsecondstoInches(duration);
     backward();
    }
  turnRight();
}
long microsecondstoInches (long microseconds)
{
  return microseconds / 74 / 2;
}

system · February 14, 2011, 12:16am

Should all of the PING code go inside of the loop?

Make life easy on yourself. Write a function that does the pinging, and returns a distance. Call that function when you need to know a distance.

Brennn10 · February 14, 2011, 12:22am

Ok, so I created a function called, getDistance(). Here is what I have, but it is still not moving correctly. I hate to ask for answers, but I am unsure where I am going wrong.

#include <AFMotor.h>

 
AF_DCMotor motor1(1, MOTOR12_8KHZ);
AF_DCMotor motor2(2, MOTOR12_8KHZ);
AF_DCMotor motor3(3, MOTOR12_1KHZ);
AF_DCMotor motor4(4, MOTOR12_1KHZ);
const int pingPin = 19;


void setup() {
  Serial.begin(9600);           // set up Serial library at 9600 bps
  motor1.setSpeed(200);     // set the speed to 200/255
  motor2.setSpeed(200);
  motor3.setSpeed(200);
  motor4.setSpeed(200);
}

void forward()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(FORWARD);
  motor4.run(FORWARD);
}

void backward()
{
  motor1.run(BACKWARD);
  motor2.run(BACKWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);
}

void haltMotors()
{
  motor1.run(RELEASE);
  motor2.run(RELEASE);
  motor3.run(RELEASE);
  motor4.run(RELEASE);
  
}

void turnRight()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);

}
void loop() {
  long duration, inches;
  duration = pulseIn(pingPin, HIGH);
  
  inches = microsecondstoInches(duration);
  
  while (inches > 5)  //while robot is 5 inches away from object
    {
      getDistance();
      forward();
    }
  haltMotors();      //stop the motors before reversing direction
  while (inches < 10) //move robot back 10 inches before turning
   {
     getDistance();
     backward();
    }
  turnRight();
}
long microsecondstoInches (long microseconds)
{
  return microseconds / 74 / 2;
}
float getDistance()
{
  long duration, inches;
  
  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);
  
  pinMode(pingPin, INPUT);
  duration = pulseIn(pingPin, HIGH);
  
  inches = microsecondstoInches(duration);
}

system · February 14, 2011, 12:27am

  while (inches > 5)  //while robot is 5 inches away from object
    {
      getDistance();

Perhaps if you actually returned a value in getDistance, and stored the value returned by getDistance in inches...

Brennn10 · February 14, 2011, 12:29am

Should the getDistance function hold the parameter 'inches'? How do I fix this problem?

system · February 14, 2011, 12:35am

The getDistance function is defined to return a float. There needs to, then, be a return statement, with the value to return. Since, presumably, the value to return is the distance in inches, and inches is a local variable, of type long, it is strange that getDistance()'s return type is not long.

Brennn10 · February 14, 2011, 1:14am

Alright, so I changed float getDistance(), to long getDistance(). I also added a return statement, to return the duration and the inches. But it is still having problems.

#include <AFMotor.h>

 
AF_DCMotor motor1(1, MOTOR12_8KHZ);
AF_DCMotor motor2(2, MOTOR12_8KHZ);
AF_DCMotor motor3(3, MOTOR12_1KHZ);
AF_DCMotor motor4(4, MOTOR12_1KHZ);
const int pingPin = 19;


void setup() {
  Serial.begin(9600);           // set up Serial library at 9600 bps
  motor1.setSpeed(200);     // set the speed to 200/255
  motor2.setSpeed(200);
  motor3.setSpeed(200);
  motor4.setSpeed(200);
}

void forward()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(FORWARD);
  motor4.run(FORWARD);
}

void backward()
{
  motor1.run(BACKWARD);
  motor2.run(BACKWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);
}

void haltMotors()
{
  motor1.run(RELEASE);
  motor2.run(RELEASE);
  motor3.run(RELEASE);
  motor4.run(RELEASE);
  
}

void turnRight()
{
  motor1.run(FORWARD);
  motor2.run(FORWARD);
  motor3.run(BACKWARD);
  motor4.run(BACKWARD);

}
void loop() {
  long duration, inches;
  duration = pulseIn(pingPin, HIGH);
  
  inches = microsecondstoInches(duration);
  
  while (inches > 5)  //while robot is 5 inches away from object
    {
      getDistance();
      forward();
    }
  haltMotors();      //stop the motors before reversing direction
  while (inches < 10) //move robot back 10 inches before turning
   {
     getDistance();
     backward();
    }
  turnRight();
}
long microsecondstoInches (long microseconds)
{
  return microseconds / 74 / 2;
}
float getDistance()
{
  long duration, inches;
  
  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);
  
  pinMode(pingPin, INPUT);
  duration = pulseIn(pingPin, HIGH);
  
  inches = microsecondstoInches(duration);
}

I get an error that says inches was not declared in the scope, and the first while loop was highlighted.

system · February 14, 2011, 6:29am

Change "getDistance();" inside the while loops to "inches = getDistance();" and add "return inches;" at the end of the getDistance() function. Also, I would change all places where you define "inches" as long so that it defines "inches" as float.

JanD

Topic		Replies	Views
While loop not holding variable value Programming	8	309	October 23, 2023
Problem with my PING code? Programming	10	2232	May 5, 2021
Problem in my code Programming	4	58	July 3, 2025
New ping bug with HCS04 sensor in main code Sensors	2	194	February 18, 2024
HC-SR04 wont continue working after one loop General Guidance	59	1421	August 23, 2023

Code issue with PING Sensor and while loop Heeelp!

Related topics