2.7 4-Digital 7-Segment Display


In this lesson, you will learn about the 4-Digital 7-Segment Display. It consists of four 7-segment displays working together so as to display 4 digit numbers.

Components Required


Fritzing Circuit


Schematic Diagram




  • You can open the file 2.7_4digitalSegment.ino under the path of sunfounder_vincent_kit_for_arduino\code\2.7_4digitalSegment directly.

Code Analysis

In essence, this code uses the principle of multiplexing to display a 4-digit number on a 7-segment display. By rapidly switching between digits and displaying one digit at a time, it gives the illusion of all digits being displayed concurrently. The stopwatch functionality is achieved by using the built-in millis() function to track time and increment the displayed number every second.

  1. Variable and Constant Definitions:

    int segmentPins[] = {2, 3, 4, 5, 6, 7, 8, 9};
    int digitPins[] = {13, 12, 11, 10};
    long n = 0; // Variable to store the current stopwatch number
    int del = 5; // Delay time (in milliseconds) to keep each digit illuminated
    unsigned long previousMillis = 0; // Store the last time the stopwatch incremented
    const long interval = 1000; // One-second interval (in milliseconds)
    • segmentPins and digitPins arrays define the pins that are connected to the segments and the digits of the 7-segment display, respectively.

    • n is a long variable that keeps track of the current stopwatch number, starting from 0 and incrementing.

    • del is a delay time to maintain the display of the current digit before transitioning to the next one.

    • previousMillis and interval are related to timing to decide when to increment the stopwatch.

  2. 7-Segment Patterns for Numbers:

    The 2D array numbers defines how each of the numbers 0-9 is represented on a common-cathode 7-segment display. Each sub-array has 8 values (either HIGH or LOW), corresponding to the 7 segments and a decimal point. This pattern helps in driving the appropriate segments for each number.

    byte numbers[10][8] = {
        {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW, LOW},  // 0
        {LOW, HIGH, HIGH, LOW, LOW, LOW, LOW, LOW},      // 1
        {HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH, LOW},   // 2
        {HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH, LOW},   // 3
        {LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH, LOW},    // 4
        {HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH, LOW},   // 5
        {HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH, LOW},  // 6
        {HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW, LOW},     // 7
        {HIGH, HIGH, HIGH, HIGH, LOW, HIGH, HIGH, LOW}   // 9
  3. Setup Function:

    void setup() {
        // Configure all segment and digit pins as OUTPUT
        for (int i = 0; i < 8; i++) {
            pinMode(segmentPins[i], OUTPUT);
        for (int i = 0; i < 4; i++) {
            pinMode(digitPins[i], OUTPUT);
            digitalWrite(digitPins[i], HIGH); // Initially turn off all digits (for common-cathode displays, HIGH is OFF)
    • All segment and digit pins are set to OUTPUT mode since they will drive the segments and digits of the display.

    • Initially, all the digits are turned off, denoted by writing HIGH for a common-cathode display.

  4. Main Loop:

    void loop() {
        // Check if a second has passed since the last increment
        if (millis() - previousMillis >= interval) {
            previousMillis += interval; // Update the last increment time
            n = (n + 1) % 10000; // Increment the stopwatch number and wrap around at 9999
        displayNumber(n); // Display the current stopwatch number on the 7-segment display
    • This section checks if the interval (which is set to 1000ms or 1 second) has passed since the last increment of the stopwatch. If so, it increments the number.

    • The number is then displayed on the 7-segment using the displayNumber() function.

  5. displayNumber() Function:

    // Function to display a 4-digit number on the 7-segment display
    void displayNumber(long num) {
        for (int digit = 0; digit < 4; digit++) {
            clearLEDs(); // Turn off all segments and digits
            pickDigit(digit); // Activate the current digit
            int value = (num / (int)pow(10, 3 - digit)) % 10; // Extract the specific digit from the number
            pickNumber(value); // Illuminate the segments to display the digit
            delay(del); // Keep the digit illuminated for a short time
    • This function breaks down the 4-digit number into individual digits and displays each digit one at a time in rapid succession. This creates the illusion of all digits being displayed simultaneously due to persistence of vision.

    • For each digit, the function first clears all LEDs, selects the appropriate digit using pickDigit(), and then displays the number on that digit using pickNumber().

    • The delay (del) ensures each digit is visible for a short time before transitioning to the next.

  6. pickDigit() Function:

    This function is responsible for selecting (or turning on) one of the four digits on the 7-segment display. This is achieved by setting the corresponding digit pin to LOW.

    void pickDigit(int x) {
        digitalWrite(digitPins[x], LOW); // Turn ON the selected digit (for common-cathode displays, LOW is ON)
  7. pickNumber() Function:

    Given a single number (0-9), this function drives the 7-segment display’s segments to show that number. It uses the previously defined numbers array to know which segments to turn on/off.

    void pickNumber(int x) {
        for (int i = 0; i < 8; i++) {
            digitalWrite(segmentPins[i], numbers[x][i]); // Set each segment according to the pattern for the given number
  8. clearLEDs() Function:

    As the name suggests, this function turns off all segments and digits. It’s used to ensure that only one digit is active at a time during the multiplexing process in the displayNumber() function.

    void clearLEDs() {
        for (int i = 0; i < 8; i++) {
            digitalWrite(segmentPins[i], LOW); // Turn off all segments
        for (int i = 0; i < 4; i++) {
            digitalWrite(digitPins[i], HIGH); // Turn off all digits

Phenomenon Picture