Problems with IR distance sensor

Im making an object avoiding robot and I was going to use an IR distance sensor, but when I got it, it gave extremely fluctuating results that it would not even perform at all. to convert the non linear readings to linear i used the formula range = (6787/(logicvalue-3))-4 even with this conversion, my IR sensor would set off my motor reactions at completely random instances. Basically I have no control whatsoever over the IR sensor and I am looking for a solution. Would an ultrasonic sensor do this as well? I will attach my code and would appreciate any advice!! thank you. Im using an arduino uno with motor shield.

int sensorPin = A0;
int sensorValue = A0;

void setup(){
  Serial.begin(9600);
  pinMode(13,OUTPUT); //direction of ch. B
  pinMode(12,OUTPUT); //direction of ch. A
  pinMode(11,OUTPUT); //PWM ch. B
  pinMode(3,OUTPUT); //PWM ch. A
  pinMode(8,OUTPUT); //Brake B
  pinMode(9,OUTPUT); //Brake A
}

void loop(){
  
  int range = A0;
  
  digitalWrite(8,LOW); //Brake B disengage
  digitalWrite(9,LOW); //Brake A disengage
  digitalWrite(12,0); //A forward
  analogWrite(3,250); //A full speed/PWM
  digitalWrite(13,255); //B forward
  analogWrite(11,250); //B full speed/PWM
  
  range = readDistance();
  if (range < 16) {
    
    
    
    
    digitalWrite(12,LOW); // may just want to engage brakes
    digitalWrite(13,LOW);
    delay(500);
    //stop motors
    
    digitalWrite(12,255); //A reverse
    analogWrite(3, 123); //A half speed
    digitalWrite(13,0); //B reverse
    analogWrite(11, 123); //B half speed
    delay(1500);
    //reverse motors
    
    digitalWrite(12,LOW);
    digitalWrite(13,LOW);
    delay(200);
    //stops motors
    
    digitalWrite(12,0); //A forward
    analogWrite(3,250); //A speed
    digitalWrite(13,0); //B reverse
    analogWrite(11,250); //B speed
    delay(2000);
    //zero degree turn
  }
}
int readDistance(){
  sensorValue=analogRead(sensorPin);
  if (sensorValue > 3){
    int range = (6787 / (sensorValue-3)) - 4;
    return(range);
  }
}

Could you be more specific than "an IR distance sensor"? Model number might be helpful.

Don't you need to set the pinmode for your analog pin?

There is already a conversion formula(s) in the PING example. It gives both inches and centimeters.

int readDistance(){
  sensorValue=analogRead(sensorPin);
  if (sensorValue > 3){
    int range = (6787 / (sensorValue-3)) - 4;
    return(range);
  }
}

And the other return value?

Don't you need to set the pinmode for your analog pin?

Not if you're using it to read analogue values with [u]analog[/u]Read

I’m confused then, whats this bit about in the arduino reference.

The analogRead command will not work correctly if a pin has been previously set to an output, so if this is the case, set it back to an input before using analogRead.

http://www.arduino.cc/en/Reference/AnalogPins

int sensorPin = A0; // Good int sensorValue = A0; // Not good set to ZERO, not A0 int range = A0; // Not good set to ZERO, not A0

Where did you get that quote?

The analogRead command will not work correctly if a pin has been previously set to an output, so if this is the case, set it back to an input before using analogRead

AnalogREAD is looking for an INPUT, but can't, if it is set as an OUTPUT.

Where did you get that quote?

The link right under it.

The analogRead command will not work correctly if a pin has been previously set to an output

I don't understand your confusion - where has the sensor pin been set as an output?

@OP, I'd address that missing "else" I pointed out.

where has the sensor pin been set as an output?

Fair enough, I guess I wasn't sure if there was a default and if that default was input. I'm also not sure about how setting pinmode in one sketch effects subsequent steps, i.e. do pinModes carry over if you don't set them again.

@OP, do yourself a favour before your code grows much more:

const byte sensorPin = A0;

const byte dirA   = 12;
const byte pwmA   = 3;
const byte brakeA =  9;

const byte dirB   = 13;
const byte pwmB   = 11;
const byte brakeB =  8;

as a bare minimum. (you may want to substitute "left" and "right" for "A" and "B" or vice-versa)

Also digitalWrite(dirB,255); - it will work, but it's probably not a good habit to acquire until you really know what you're doing.

laadams85: Don't you need to set the pinmode for your analog pin?

No. The analogRead() function takes care of that.