Function not returning expected results

Projects Programming
1

I've got a strange error and I'm hoping that I just overlooked something, but I can't for the life of me determine my issue. I've written a function to change the value that will be written to a servo, but for some reason the value isn't changing within the code. The following code my be incomplete syntax wise(I'm only including relative pieces), but it does compile and upload through the IDE.

The following code contains my setup and loop functions.

#include <Servo.h>

// ULTRASONIC PIN DEFINITIONS 

#define TrigPin 7
#define RightEcho 8
#define LeftEcho 10

//SERVO DEFINITION
Servo servo1;


#define led 9    //LED USED FOR INITIAL TESTING



long RightTime, LeftTime, RightDistance, LeftDistance;
float servotime; //DECLARE VARIABLE


void setup(){
  
// I/O DECLARATIONS
  pinMode(TrigPin, OUTPUT);
  pinMode(RightEcho, INPUT);
  pinMode(LeftEcho, INPUT);
  pinMode(led,OUTPUT);        //LED USED FOR INITIAL TESTING
  
  servo1.attach(6);          //ATTACH SERVO TO PIN 6
  int servotime = 1500; //init servo angle
  servo1.writeMicroseconds(servotime);  //INITIALIZE POSITION
  
  digitalWrite(TrigPin, LOW); //Initialize trigger as low 
  
  Serial.begin(9600);    //Serial Communication for troubleshooting
  
}

void loop(){
  
  LeftTime = readHCSR04(TrigPin, LeftEcho);
  RightTime = readHCSR04(TrigPin, RightEcho);
  
  
  RightDistance = (RightTime / 148);      //Distance in Inches, eqn from datasheet
  LeftDistance = (LeftTime / 148);        //Distance in Inches, eqn from datasheet
  
  calcTime(LeftTime, RightTime, servotime);
  servo1.writeMicroseconds(servotime);
}

This code contains the calcTime function

  float calcTime( float left, float right, int timetowrite){      //May need to change floats to ints
    // 5% Tolerance
    if (((.95 * left) > right) == 1){    //if left is more than right (w/ tol)
        timetowrite = timetowrite + ((left - right)/2);  // add half of the difference (half brings them equal)
    }
    if (((.95 * right) > left) == 1) {    //if right is more than left (with tol)
        timetowrite = timetowrite - ((right - left)/2);    //subtract half of the difference
    }
    return timetowrite;
  }

The problem I'm have is the timetowrite variable in the calcTime function is always return a 0. When I run the serial monitor, I have the two conditions being met(The .95*left > right and vice versa), so I'm fairly certain that the loop is being executed(although I'm going to do some further testing on that as soon as I'm done with this post).

I'm wondering if I have an issue with the types of variables I'm doing math with. I'm declaring a long in the setup and then utilizing a float in my calcTime function. I guess I don't know enough about programming concepts to know if that's allowed or not.

Any insight on this would be much appreciated as I'm at a loss as to why it's always returning a 0.

2

You are calculating an INT and returning it as a FLOAT. You probably intended to do that calculations with FLOATs.

3

Calctime() returns a value which you discard. You are using the last parameter as if it was changed by the function. It is not, in order for a function to change a variable in the calling program the calling program must pass a pointer to the variable and the function must be written to handle a pointer, not a value.

But you can use the returmed value like this:

 servotime = calcTime(LeftTime, RightTime, servotime);
  servo1.writeMicroseconds(servotime);
4

Your function returns a value that you totally ignore in your loop. Instead in your loop you use servotime, which is not affected by your calc function.

You are also passing the value of servotime to your calc function BUT, as far as I see, it doesn't hold anything worth sending.

Edit nilton61 got there before me.

5

int servotime;

...

calcTime(LeftTime, RightTime, &servotime);

...

float calcTime( float left, float right, int *timetowrite){
...
}

6

Your suggestions have fixed my problem.

Thank you guys.

7

Mastrofski:
Your suggestions have fixed my problem.

Thank you guys.

Which suggestion that you implement?

8

ieee488:
Which suggestion that you implement?

ieee488:
Which suggestion that you implement?

I ended up matching the variable types in my function to those that I declared earlier. I also did the servotime=calcTime( left, right, servotime); and those two changes ended up making my program work.