How to read my three-button inputs?

Question

I am creating a three-person reaction time game but I would like to be able to read all three buttons' proximity to the start time - currently only the winner is displayed on the serial read.

Here is my code:

int ledPin = 12;         
int buttonPin1 = 7;     
int buttonPin2 = 6; 
int buttonPin3 = 5;    

void setup() {
  Serial.begin(9600);          
  Serial.println("Setup start"); 
  pinMode(ledPin, OUTPUT);     
  pinMode(buttonPin1, INPUT_PULLUP); 
  pinMode(buttonPin2, INPUT_PULLUP); 
  pinMode(buttonPin3, INPUT_PULLUP);  
  randomSeed(analogRead(A0)); 
  Serial.println("Setup complete"); 
}

void loop() {
  Serial.println("Game start"); 
  digitalWrite(ledPin, HIGH);  
  delay(2000);                 
  delay(random(1000, 3000));  
  digitalWrite(ledPin, LOW);  
  Serial.println("LED off, waiting for button press"); 

  unsigned long start_time = millis(); 
  int winner = 0;
 
  while (winner == 0) { 
    winner = check_buttons();
  }

  unsigned long end_time = millis();  
  unsigned long total_time = end_time - start_time;  

  Serial.print("Player ");
  Serial.print(winner);
  Serial.println(" wins!");
  Serial.print("It took ");
  Serial.print(total_time);
  Serial.println(" ms to press the button.");

  delay(5000);  
}

int check_buttons() {
  int player1 = digitalRead(buttonPin1);
  int player2 = digitalRead(buttonPin2);
  int player3 = digitalRead(buttonPin3);

  if (player1 == LOW) {
    return 1;  
  } else if  (player2 == LOW) {
    return 2; 
  } else if (player3 == LOW) {
    return 3;  
  } else {
    return 0;  
  } 
}

you cannot display data that does not exist ... you have to determine the timestamp when each button has been pressed, and you have to wait until all the buttons have been pressed before displaying the result — jsotola
– jsotola, Commented Jun 21, 2024 at 17:59
“i would like to be able to read all three buttons proximity to zero”: What does that mean? — Edgar Bonet
– Edgar Bonet, Commented Jun 21, 2024 at 19:11
What if all three players don't press their buttons? On a quiz show people often give up if someone else has pressed the button first. — Nick Gammon
– Nick Gammon ♦, Commented Jun 23, 2024 at 7:03

Greenonline · Accepted Answer · 2024-06-22 17:55:54Z

You will need an end_time variable for each of the players, either as a distinct variable for each player, or use an array. Define as a global:

unsigned long end_time_player1;
unsigned long end_time_player2;
unsigned long end_time_player3;

or

unsigned long end_time_player[3];

Then in check_buttons() you will need to record the respective end_time, like so

  if (player1 == LOW) {
    end_time_player[0] = millis();
    //end_time_player1 = millis();
    return 1;  
  } else if  (player2 == LOW) {
    end_time_player[1] = millis();
    //end_time_player2 = millis();
    return 2; 
  }else if (player3 == LOW) {
    end_time_player[2] = millis();
    //end_time_player3 = millis();
    return 3;  
  } else {
    return 0;  
  }

Obviously, if using an array, then the index of the array is one less than the player number.

An array is probably more elegant and expandable, so for four players:

const int kNumPlayers=4
unsigned long end_time_player[kNumPlayers];

If using arrays (for both the times and the buttons (as well as the players)), you could also turn the series of if statements into a for loop using kNumPlayers:

int buttonPin[kNumPlayers] = {7, 6, 5};

...

int check_buttons() {
  int player[kNumPlayers];

  for (n=0; n < kNumPLayers; n++) {
     player[0] = digitalRead(buttonPin[n]);
     if (player[0] == LOW) {
        end_time_player[n] = millis();
        return n+1;  
     } else {
        return 0;  
     }  
  } 
}

or, more simply, just dispense with the player local variable altogether

int buttonPin[kNumPlayers] = {7, 6, 5};

...

int check_buttons() {
  for (n=0; n < kNumPlayers; n++) {
     if (digitalRead(buttonPin[n]) == LOW) {
        end_time_player[n] = millis();
        return n+1; 
     } else {
        return 0;  
     }  
  } 
}

Then you will need to change the code in loop() to display the time for each user. I'll let you work that bit out yourself.

Yes, but what if the third player doesn't press the button? Or the second? — Nick Gammon
– Nick Gammon ♦, Commented Jun 23, 2024 at 7:02
Then the display in loop() won''t show a value for that player, or display "n/a". The while loop would no longer have to wait for just one winner, but rather wait for a time out (of say, one second, maybe two). If a player hasn't hit a button within that time frame, then it can be safely assumed that they have died of boredom..! :-) Yes, I must admit that there are some necessary logic changes required in loop() that I had overlooked... although, in fairness, I did leave that for the OP to figure out, as the question seemed to focus on the reading and not the displaying. — Greenonline
– Greenonline, Commented Jun 23, 2024 at 10:37

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