DIY Adjustable Countdown Timer with Arduino Mega 2560

About this project

Countdown timer is probably the most natural project for the 4-digit 7-segment display. While exploring what is available online I found several projects, but did not find the one that I had in mind, namely, a standalone adjustable countdown timer that you can conveniently adjust with the buttons (and not by uploading a modified code). So I decided to make one.

I spent some time to write a code that will make it easy to use and adjust the timer, so that it can be used in practice.

The included code also can be used in other projects with 4-digit 7-segment display. In particular, it has the function that displays a given number (0-9999) for a given time interval. Maybe this functionality is in some of the libraries, but a quick search did not reveal it. Since programming this display is a bit tricky (as you can show only one digit at a time), such a function is really handy.

Code

• 4-digit 7-segment display countdown timer

4-digit 7-segment display countdown timerC/C++

#include <math.h>

int digit_pin[] = {6, 9, 10, 11}; // PWM Display digit pins from left to right

int speakerPin = 15;

#define DIGIT_ON  LOW
#define DIGIT_OFF  HIGH

int segA = 2; 
int segB = 3; 
int segC = 4; 
int segD = 5; 
int segE = A0; //pin 6 is used bij display 1 for its pwm function
int segF = 7; 
int segG = 8; 
//int segPD = ; 


int button1=13;
int button2=12;
int button3=16;
int button4=17;

int countdown_time = 60;

struct struct_digits {
    int digit[4];
  };


void setup() {                
  pinMode(segA, OUTPUT);
  pinMode(segB, OUTPUT);
  pinMode(segC, OUTPUT);
  pinMode(segD, OUTPUT);
  pinMode(segE, OUTPUT);
  pinMode(segF, OUTPUT);
  pinMode(segG, OUTPUT);

  for (int i=0; i<4; i++) {
    pinMode(digit_pin[i], OUTPUT);
  }

  pinMode(speakerPin, OUTPUT);

  pinMode(button1,INPUT_PULLUP);
  pinMode(button2,INPUT_PULLUP);
  pinMode(button3,INPUT_PULLUP);
  pinMode(button4,INPUT_PULLUP);
}


void playTone(int tone, int duration) {
  for (long k = 0; k < duration * 1000L; k += tone * 2) {  
    digitalWrite(speakerPin, HIGH);
    delayMicroseconds(tone);
    digitalWrite(speakerPin, LOW);
    delayMicroseconds(tone);
  }
}


void lightNumber(int numberToDisplay) {

#define SEGMENT_ON  HIGH
#define SEGMENT_OFF LOW

  switch (numberToDisplay){

  case 0:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_OFF);
    break;

  case 1:
    digitalWrite(segA, SEGMENT_OFF);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_OFF);
    break;

  case 2:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_OFF);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 3:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 4:
    digitalWrite(segA, SEGMENT_OFF);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 5:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_OFF);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 6:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_OFF);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 7:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_OFF);
    break;

  case 8:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_ON);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 9:
    digitalWrite(segA, SEGMENT_ON);
    digitalWrite(segB, SEGMENT_ON);
    digitalWrite(segC, SEGMENT_ON);
    digitalWrite(segD, SEGMENT_ON);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_ON);
    digitalWrite(segG, SEGMENT_ON);
    break;

  case 10:
    digitalWrite(segA, SEGMENT_OFF);
    digitalWrite(segB, SEGMENT_OFF);
    digitalWrite(segC, SEGMENT_OFF);
    digitalWrite(segD, SEGMENT_OFF);
    digitalWrite(segE, SEGMENT_OFF);
    digitalWrite(segF, SEGMENT_OFF);
    digitalWrite(segG, SEGMENT_OFF);
    break;  
  }
 
}



void SwitchDigit(int digit) {
  for (int i=0; i<4; i++) {
    if (i == digit) {
      digitalWrite(digit_pin[i], DIGIT_ON);
    } else {
      digitalWrite(digit_pin[i], DIGIT_OFF);
    }
  }
}


struct struct_digits IntToDigits(int n){
  struct struct_digits dig;
  int zeros=0;
  int d;
  for (int i=0; i<4; i++) {
    d=n/pow(10,3-i);
    zeros += d;
    n = n - d*pow(10,3-i);
    if (zeros!=0 || i==3) {
      dig.digit[i]=d;
    } else {
      dig.digit[i]=10;
    }
  }
  return dig;
}

void PrintNumber(int n, int time) {
  struct struct_digits dig;

  dig = IntToDigits(n);
  
  for (int i=0; i<= time/20; i++) {
    if (digitalRead(button2)==LOW) {
      return;
    }
    for (int j=0; j<4; j++) {
      SwitchDigit(j);
      lightNumber(dig.digit[j]);
      delay(5);
    }
  }
}


bool Countdown(int n, int del){
  for (int q=n; q>0; q--){
    PrintNumber(q,del);
    if (digitalRead(button2)==LOW) {
      return false;
    }
  }
  PrintNumber(0,0);
  playTone(1519,1000);
  return true;
}



void reset() {
  int m, zeros, d, pressed3 = 0, pressed4 = 0;
  m=countdown_time;
  struct struct_digits dig;

  dig = IntToDigits(countdown_time);
  
  while (digitalRead(button1)==HIGH) {
    for (int j=0; j<4; j++) {
      SwitchDigit(j);
      lightNumber(dig.digit[j]);
      delay(5);
    }
    if (digitalRead(button3)==LOW) { 
      if (pressed3 == 0 || pressed3 > 30) {
        if (countdown_time > 0) {
          countdown_time -= 1 ;
        }
        dig = IntToDigits(countdown_time);
      } 
      pressed3 += 1;
    }
    else if (digitalRead(button4)==LOW) { 
      if (pressed4 == 0 || pressed4 > 30) {
        if (countdown_time <9999) {
          countdown_time += 1 ;
        }
        dig = IntToDigits(countdown_time);
      } 
      pressed4 += 1;
    }
    if (digitalRead(button3)==HIGH) {
      pressed3=0;
    }
    if (digitalRead(button4)==HIGH) {
      pressed4=0;
    }
  }
}

void loop(){
  reset();
  while (!Countdown(countdown_time,962)) {
    reset();
  }
  while (digitalRead(button2)==1){};
}

Schematics