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[on:]

I am trying to create an optical encoder with an ir sensor. to do this i am using the Sharp IR sensor that will reflect off of a white board that has black segments painted onto it. The sensor is to take the time at the beginning of each black segment and calculate the time it took to go between each of those black segments. I have put together a code that seems to me would work but obviously is not and i cant figure out what is wrong. If anybody has any ideas please let me know. Attached is a diagram of the setup to visualize what i mean. The sensor will be connected to an analog pin and that is why the pinmode has been commented out because someone told me i need to initialize the pin but since it is analog and pinmode is a digital function i dont believe i need it.

The issue that i am having is that the serial monitor continuously prints values when it is in a white segment and none when it is in a black segment. also it prints both positive and negative values and there should be no reason to be printing a negative value.

Code:

//User Changeable Variables
int desiredRevs = 3;
int WheelResolution = 3;

//DO NOT CHANGE ANYTHING BEYOND THIS POINT
int SensorPin = A0;
int time1 = 0;
int time2 = 0;
int time3 = 0;
int Flag0 = 0;
int Flag1 = 0;
int Flag2 = 0;
int Flag3 = 0;
int desiredPulses = WheelResolution * desiredRevs;
int val = 0;
int couple = 0; //1 = beginning of first black, 2 = beginning of white
int status1 = 0;
int deltaT = 0;
int pulses = 0;



void setup()
{
  //pinMode(SensorPin, INPUT);
  Serial.begin(9600);

}

void loop()
{
  if (pulses <= desiredPulses)
  {
    val = analogRead(SensorPin);
    if (val >= 50)
    {
      Flag1 = 1;
      status1 = 1;//black
    }
    else
    {
      Flag1 = 0;
      status1 = 0;//white
    }
    if ( Flag1 == 1 && couple == 0 && status1 ==1)
    {
      couple  = 1;
      time1 = micros() ;
      Serial.print(time1);
    }
    else if ( Flag1 == 0 && couple == 1 && status1 == 0)
    {
      couple = 2;
      time2 = micros();
      Serial.print(time2);

    }
    else if ( Flag1 == 1 && couple == 2 && status1 == 1)
    {
      time3 = micros();
      Serial.print(time3);
      //deltaT = time3 - time1;
      Serial.println(deltaT);
      couple = 1;
      time1 = time3;
      
    }
    
  }
  else
  Serial.println("Done");
  
}

[Reply #1 on:]

Flag1 and status1 always get set to the same thing, why have them both?

You should be looking to time between the rising edge and falling edge of the sensor. You can do this with a pulse in function, or failing that do it properly by noting the millis time on each transition and subtracting the two.
I can't follow what your code is trying to do but it looks way overly complex.

[Reply #2 on:]

I don't like you having   if () {} else if () {} else if () { }   

what if none of those apply ?    If you are having trouble figuring out what your system is doing,  add another "else"
at the end,  and print a message,  so you know which scenarios are not being dealt with.

I'm not clear on why you have three notable outcomes there.    You have something happen when you
go from white to black,    and from black to white .   What is the third one for ?    Can you be sure
your device only rotates in one direction ?

[Reply #3 on:]

Sorry i failed to comment this code. First off the sensor is going to be attached to a stationary bike that has a solid wheel so i can not use separate transmitter and receiver, that is why i have chosen the ir sensor i have. But what is going in is that the program will continually read values from the ir sensor, depending on what value is read > or < than 50, it "knows" what color segment it is in. I need the time it takes for the sensor to hit the beginning of one black segement to the beginning of another, not just from black to white and white to black, thus the reason for the second elseif{} condition.

So as the sensor reads values it determines whether it is in black or white and depending on which it determines it is in, it sets Flag1, couple, and status1 to the appropriate values. the reason there is status and flag is just an extra condition, there is no difference. So for the first time that it hits a black space the program will set Flag1 = 1 and status1 = 1 and couple is already 0. the program continues to run and in notices that the next if{} statement is true so it takes time1 and sets couple = 1. now as it continues reading values in the black segment nothing will happen because it meets none of the if{} or elseif{} statements since flag will equal 1, status1 =1, but couple = 1 and not 0. michinyon was wondering about not meeting any of these conditions and i thought if none of the conditions were met it would just begin the sequence again and go through reading values and trying to meet conditions until it did.

the next time it would meet a condition is when it hits the beginning of the "first" white segment where it will set Flag1 = 0, status1 = 0 and since couple is now 1 and not 0 it meets the first elseif{} condition. here it takes time2, for no apparent reason but to take a time. but than it sets couple = 2. again it should not do anything else while reading values in the white segement because flag1 = 0, status1 = 0 and couple now equals 2. so it should just keep reading values til it hits the next black segement.

once it hits the next black space it recognizes that flag1 = 1, status1 = 1, and couple is now 2. Thus it takes time3 and calculates the time it took to get from time1 to time3 (deltaT = time3 - time1). because time3 is a larger number than time1 it should never print a negative number which is one issue i am having. Anyways, it continues the program and sets couple back to one and sets time1 equal to time3. this is so that it restarts the program immediately and doesn't happen to skip this black segment and restart the readings until the "third" black segment.

i hope that clears some stuff up, let me know if there is something else you might be confused on.

[Reply #4 on:]

You are making it way too complicated. You need to detect edges, that means when the detector was showing one colour that is diffrent from the last time you measured it. So compair the current reading with the lasts one. At the end of the loop store the current reading in the lasts reading variable. That is all you need to do.

[Reply #5 on:]

You also cannot get away with just a single threshold - there will be noise in the signal
so you must add some hysteresis to the edge detecting.  Perhaps have two thresholds of
40 and 60.