Break beam timer

Using Arduino Programming Questions
1

Hello,

I finally hooked up a break beam timer system where a toy car rolls by a start and finish line and a time is given. It is all going well and I am just printing on the serial monitor right now.

Unfortunately, it is printing multiple values (if the car is moving slowly and staying in the second beam). How can I end the code so that it only prints 1 value. Attached is the code.

// Define pin numbers
const int irDetectorPin1 = A0;   // Analog pin connected to the IR Detector (Receiver)
const int irDetectorPin2 = A1;

unsigned long timeFirst1; //first beam lane 1 speed trap beam
unsigned long timeSecond1; //finish line lane 1

float TotalT = 0;


void setup() {
  Serial.begin(9600);   // Initialize serial communication
}

void loop() {
  int sensorValue1 = analogRead(irDetectorPin1);  // Read the analog value from the IR Detector pin


  
  // Map the analog value to a detection status


delay (1);
///////
if(sensorValue1 < 100) 
{
timeFirst1 = millis(); //First sensor trigged start time
}


  int sensorValue2 = analogRead(irDetectorPin2);  // Read the analog value from the IR Detector pin 2

// wait/check for the Finish Line sensors to be triggered
if(sensorValue2 < 100 && timeFirst1 > 0)
{
timeSecond1 = millis();
TotalT = timeSecond1 - timeFirst1;


Serial.print (TotalT);
}


}

Thank you

2

I made some changes to your code.
See if it works as you need.

If it works, try to understand my modifications.

// Define pin numbers
const int irDetectorPin1 = A0;   // Analog pin connected to the IR Detector (Receiver)
const int irDetectorPin2 = A1;
unsigned long timeFirst1; //first beam lane 1 speed trap beam
unsigned long timeSecond1; //finish line lane 1
float TotalT = 0;
int sensorValue1;
int sensorValue2;
bool flagSensor1 = false;
bool flagSensor2 = false;
//------------------------------------------------------------------
void setup() {
  Serial.begin(9600);   // Initialize serial communication
}
//------------------------------------------------------------------
void loop() {
  sensorValue1 = analogRead(irDetectorPin1);  // Read the analog value from the IR Detector pin
  // Map the analog value to a detection status
  delay (1);
  ///////
  if (flagSensor1 == false) {
    if (sensorValue1 < 100) {
      timeFirst1 = millis(); //First sensor trigged start time
      flagSensor1 = true;
    }
  }
  sensorValue2 = analogRead(irDetectorPin2);  // Read the analog value from the IR Detector pin 2
  // wait/check for the Finish Line sensors to be triggered

  if (flagSensor2 == false) {
    if (sensorValue2 < 100 && timeFirst1 > 0) {
      timeSecond1 = millis();
      TotalT = timeSecond1 - timeFirst1;
      Serial.print (TotalT);
      flagSensor2 = true;
    }
  }
}
3

@ruilviana I tossed your sketch into the wokwi.

Nothing resets the flag sensor bools.

I haven't time to try to fix, nor even be sure, but it functions correctly, or should I say prints a good result time, just once per board reset.

a7

1 Like
4

OK, at the bottom of the loop


  if (flagSensor1 && flagSensor2) {
    Serial.println("\nGo Again!");

    flagSensor1 = false;
    flagSensor2 = false;

    timeFirst1 = 0;
  }
}

Just in time - she who must not be kept waiting is seconds out.

a7

5

Ok that works great to produce just 1 value. However, the board sensor doesn't ever reset so i cannot repeat it without power the board down and then back on.

How could I display the value for lets say 2 seconds and then reset the board to read another again?

Thank you

6

If it works, try to understand my modifications.

I got a few minutes to agree! Reading code is the best. @ruilviana's code was easy to read and understand.

Here's an alternate based on the same structure and logic: see a beam get broken, note the time, see the other beam, print the elapsed time, rinse and repeat.

I hope as easy to read and glean some things from which:

const int irDetectorPin1 = A0;   // Analog pins connected to the IR Detector (Receiver)
const int irDetectorPin2 = A1;

unsigned long timeFirst1;   //first beam lane 1 speed trap beam
unsigned long timeSecond1;  //finish line lane 1

void setup() {
  Serial.begin(115200);   // Initialize serial communication
}

void loop() {
  static bool inTiming;
  bool sensorValue1 = analogRead(irDetectorPin1) < 100;  // true = broken beam
  bool sensorValue2 = analogRead(irDetectorPin2) < 100;

  unsigned long now = millis();

// see if it is time to start
  if (sensorValue1) {
    if (!inTiming) {
      timeFirst1 = millis(); // start time
      inTiming = true;
    }
  }

// check for the Finish Line sensors to be triggered
  if (inTiming) {
    if (sensorValue2) {
      timeSecond1 = millis();
      float TotalT = timeSecond1 - timeFirst1; // elapsed time
      Serial.print (TotalT);

      inTiming = false;
      Serial.println("\nGo Again!");
    }
  }
}

a7
7

added this to the bottom and it seems to be working. Thank you very much.

On another note, I was only able to do this with analog. Is there a way I can do the exact same thing but trigger the timer with any sort of break of the beam (aka high or low)?

Thank you

8

Yes. Both sketches read an analog port, and develop variously a logic value based on comparison to a threshold.

Since digitalRead() provides a logic value directly, it can be used in place of those expressions.

a7