Arduino code for digital counter device with 4-digit 7-segment display

counter.c

#define SEG_C 4
#define SEG_E 21
#define SEG_D 20
#define SEG_B 0
#define SEG_G 3
#define SEG_A 2
#define SEG_F 1
 
#define DISP_4 19
#define DISP_3 18
#define DISP_2 17
#define DISP_1 16
 
#define NONE 10

#define RESET 9
#define PAUSE 10
#define INCREASE 8
#define DECREASE 14


byte digitSegments[11] = {
  //1gfedcba
  0b01000000, //0
  0b01111001, //1 
  0b00100100, //2
  0b00110000, //3
  0b00011001, //4
  0b00010010, //5
  0b00000010, //6
  0b01111000, //7
  0b00000000, //8
  0b00010000, //9
  0b01111111 //NONE
};

byte segmentPin[7] = {
  SEG_A, SEG_B, SEG_C, SEG_D, SEG_E, SEG_F, SEG_G
};

byte displayPin[4] = {
  DISP_4, DISP_3, DISP_2, DISP_1  
};

volatile int counter = 0;
volatile bool counterVisible = true;
volatile bool pause = false;

int resetLastState = HIGH;
int pauseLastState = HIGH;
int increaseLastState = HIGH;
int decreaseLastState = HIGH;

void setup() {
  for (int i = 0; i < 7; i++) {
    pinMode(segmentPin[i], OUTPUT);
  }
  for (int i = 0; i < 4; i++) {
    pinMode(displayPin[i], OUTPUT);
  }
  pinMode(RESET, INPUT_PULLUP);
  pinMode(PAUSE, INPUT_PULLUP);
  pinMode(INCREASE, INPUT_PULLUP);
  pinMode(DECREASE, INPUT_PULLUP);
  delay(500);
}

#define DIGIT_INTERVAL 2000
#define PAUSE_INTERVAL 200000

void loop() {
  showCounter();
  
  int resetState = digitalRead(RESET);
  if (resetState == HIGH && resetLastState == LOW) {
    reset();
  }
  resetLastState = resetState;
  
  int pauseState = digitalRead(PAUSE);
  if (pauseState == HIGH && pauseLastState == LOW) {
    togglePause();
  }
  pauseLastState = pauseState;
  
  int increaseState = digitalRead(INCREASE);
  if (increaseState == HIGH && increaseLastState == LOW) {
    increase();
  }
  increaseLastState = increaseState;
  
  int decreaseState = digitalRead(DECREASE);
  if (decreaseState == HIGH && decreaseLastState == LOW) {
    decrease();
  }
  decreaseLastState = decreaseState;
}

void reset() {
  counter=0; 
  pause=false;
  counterVisible=true;
}

void togglePause() {
  pause = !pause;
  if (!pause) counterVisible = true;
}

void increase() {
  if (pause) {
    return;
  }
  counter++;
  if (counter > 9999) {
    counter=0;
  }
}

void decrease() {
  if (pause) {
    return;
  }
  if (counter != 0) {
    counter--;
  }
}

void showCounter() {
  static int digitPosition = 1;
  static int tens = 1;
  static unsigned long previousTime;
  static unsigned long previousPauseTime;
  unsigned long currentTime = micros();
  if (pause && (currentTime - previousPauseTime >= PAUSE_INTERVAL)) {
    previousPauseTime = currentTime;
    counterVisible = !counterVisible;
    if (!counterVisible) {
      showDigit(NONE);
    }
  }
  if (counterVisible && (currentTime - previousTime >= DIGIT_INTERVAL)) {
     previousTime = currentTime;
     showDigit(NONE);
     digitPosition ++;
     tens = tens * 10;
     if (digitPosition > 4) {
      digitPosition = 1;
      tens = 1;
     }
     setDigitPosition(digitPosition);

     if (counter >= tens || (tens == 1 && counter == 0)) {
      showDigit((counter / tens) % 10);
     }
  }
}

void setDigitPosition(int digitPosition) {
  digitalWrite(DISP_1, digitPosition != 1);
  digitalWrite(DISP_2, digitPosition != 2);
  digitalWrite(DISP_3, digitPosition != 3);
  digitalWrite(DISP_4, digitPosition != 4);
}

void showDigit( int digit) {
  byte segments = digitSegments[digit < 10? digit: NONE];
  for (int i = 0; i < 7; i++) {
    digitalWrite(segmentPin[i], (segments >> i) & 1);
  }
}