How to print "1" value once and revert back to "0"

Projects Programming
1

What I am looking to do is when I hold my hand over a photocell sensor, it prints out a 0 once and goes back to printing constant 1's even though my hand blocking the sensor light.

With the code I have right now, it is printing constant 1's when the light is being shined into the sensor and 0's when I hold my hand over the sensor.

int threshold = 1023;
//PHOTOCELL ---------------
//light off= 1023

int pr0;
int np0= analogRead(0);

void setup() {
  Serial.begin(9600); 
}

void loop(){
//Serial.println(np0);
  
//a0
    if (np0 == threshold) {
      pr0 = 0;
    }else{
      pr0 = 1;
    }
Serial.println(pr0);
  
}

I tried to store and call previous values to reset to 1. But doesn't do exactly what I want.

int threshold = 1023;
//PHOTOCELL ---------------
//light off= 1023

int pr0;
int np0;
int static op0;


void setup() {
  Serial.begin(9600); 

}

void loop(){
//Serial.println(np0);
  
//a0
  np0= analogRead(0);
  op0=np0;
  
    if (np0 == threshold) {
      pr0 = 0;
    }else{
      pr0 = 1;
    }

    if(op0 == 0){
       pr0 = 1;
     }
Serial.println(pr0);
  
}

Tried while loops, breaks, switch cases and do while loops but no luck.

help please?

2

Hi and welcome to the forum!

You want to print a 0 when the photocell sensor becomes covered, not when it is covered.

google

arduino state change detection

and try a few hits. See if anything makes sense.

I can’t do better than the first article or two that just turned up for me. It’s a classic problem with easy solution once you see it in code.

HTH

a7

3

This statement should reside in loop(), not only executed once after Reset.

Odds are good that np0 never is exactly threshold. Compare lower or higher instead of equal.

4

Here is something to get you started:

#define SENSE_PIN 0

bool blocked;

void setup() {
	Serial.begin(9600);
	pinMode(SENSE_PIN, INPUT);
	
	// assume that the sensor is not initially blocked so that a 0 is printed right away
	blocked = false;
}

void loop() {


	// check to see if the light is blocked - fill in this condition yourself
	if (analogRead(SENSE_PIN) > [something]) {
	
		// make sure that the previous reading saw that the sensor was _not_
		// blocked, so that we only print 0 when it changes from nonblocked to blocked
		if (!blocked) {
			Serial.println("0");
			blocked = true;
		}
		
	}
	
	// if the sensor is not blocked, print out 1 always, and set the blocked state
	// to false in case the sensor is blocked
	else {
		Serial.println("1");
		blocked = false;
	}
	
}

You need to fill in the condition for a blocked state (i.e. analogRead(SENSE_PIN) > 1000) and then it should work.

5

thank you so much!

Is it possible to print the 0/1 outside of the if/else loop?
I want to have multiple instances of this (multiple sensors) print out a single array of the 0/1 for each of the sensors.
I tried to comment out the Serial.println and use a variable to link the outputs of each if/else statements from each pin.

#define PIN_ONE 0
#define PIN_TWO 1

int delays = 300;
int threshold = 800;

bool b1;
bool b2;

int out0;
int out1;

void setup() {
  Serial.begin(9600);
  pinMode(PIN_ONE, INPUT);
  pinMode(PIN_TWO, INPUT);
  
  b1 = false;
  b2 = false;
}

void loop() {

//a0
  if (analogRead(PIN_ONE) < threshold) {
    if (!b1) {
     //Serial.println("0");
     //out0 = 0;
      b1 = true;
    }
  }
  else {
    //Serial.println("1");
    //out0 = 1;
    b1 = false;
    delay(delays);
  }

if (b1 = true){
  out0 = 0;
}else {
  out0 = 1;
}
  Serial.print(out0);
  Serial.print("\t");
  Serial.println(out1);
}
6

Hi, I'm not entirely sure what you mean. If you want to use multiple sensors and have them do the same thing, then you can simply duplicate the if-else statement from earlier but check a different pin.

7

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