Need to make an action just once when condition is reached

Question

I'm making a device for the visually disabled that makes a sound when the water in a bowl reach certain levels.

I've already made the sensors for three levels of water and if statements to make the sound, but I need the sound to be played just once for every level change and it loops over and over. How can I make it to sound just one time?

Here is my code:

#include <PCM.h>
const unsigned char sample[] PROGMEM = { //Here goes the sample
};
int low = 0;
int mid = 0;
int high = 0;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:
  low = analogRead(A0);
  mid = analogRead(A1);
  high = analogRead(A2);
  Serial.print("nivel agua: ");

  if (high > 50){
    Serial.print("Alto");
    startPlayback(sample, sizeof(sample));
  }
  else if (mid >50){
    Serial.print("Medio");
    startPlayback(sample, sizeof(sample));
  }
  else if (low > 50){
    Serial.print("Bajo");
    startPlayback(sample, sizeof(sample));
  }
  delay(100);

Answer 1

A possible solution to your problem can be the following:

#include <PCM.h>
const unsigned char sample[] PROGMEM = { //Here goes the sample
};
int low = 0;
int mid = 0;
int high = 0;
bool first = true;
bool second = true;
bool third = true;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:
  low = analogRead(A0);
  mid = analogRead(A1);
  high = analogRead(A2);
  Serial.print("nivel agua: ");

  if (high > 50 && first){
    Serial.print("Alto");
    startPlayback(sample, sizeof(sample));
    first = false;
  }
  else if (mid >50 && second){
    Serial.print("Medio");
    startPlayback(sample, sizeof(sample));
    second = false;
  }
  else if (low > 50 && third){
    Serial.print("Bajo");
    startPlayback(sample, sizeof(sample));
    third = false;
  }
  delay(100);

In this way the sound for each level will be played only once. I hope this is what you were looking for.

Answer 2

As an addition to the answer of Mattia.

I suspect you have something like:

void loop() {
  // put your main code here, to run repeatedly:
  low = analogRead(A0);
  mid = analogRead(A1);
  high = analogRead(A2);
  Serial.print("nivel agua: ");

  if (resetVariables){
     first = true;
     second = true;
     third = true;
     resetVariables = false;
  }

  if (high > 50 && first){
    Serial.print("Alto");
    startPlayback(sample, sizeof(sample));
    first = false;
  }
  else if (mid >50 && second){
    Serial.print("Medio");
    startPlayback(sample, sizeof(sample));
    second = false;
  }
  else if (low > 50 && third){
    Serial.print("Bajo");
    startPlayback(sample, sizeof(sample));
    third = false;
  }

  if(buttonPressed){
    resetVariables = true;
  }
  delay(100);
}

A better practice would be to use another function

void resetFlags() {
  first = true;
  second = true;
  third = true;
}

And the main code would be:

void loop() {
  // put your main code here, to run repeatedly:
  low = analogRead(A0);
  mid = analogRead(A1);
  high = analogRead(A2);
  Serial.print("nivel agua: ");

  if (high > 50 && first){
    Serial.print("Alto");
    startPlayback(sample, sizeof(sample));
    first = false;
  }
  else if (mid >50 && second){
    Serial.print("Medio");
    startPlayback(sample, sizeof(sample));
    second = false;
  }
  else if (low > 50 && third){
    Serial.print("Bajo");
    startPlayback(sample, sizeof(sample));
    third = false;
  }

  if(buttonPressed){
    resetFlags();
  }
  delay(100);
}

Would this be faster?

• It would at least make your loop code more readable, instead of juggling flags around.
• resetFlags(); would act immediately and independent from the flag checking etc.
• It saves checking unnecessary if's (which equals a very little speed increase).
• It saves 1 boolean (byte maximal in memory) which equals a very little memory/speed increase.

But why mind speed if you have a 100msec delay? You could make it only output the water level when it changes. Then you can run the water checking extremely fast! (It wouldn't spam your console, plus, writing to console takes considerable amount of time, compared to checking if's.)