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.. _ar_4_digit:

2.7 4-Digital 7-Segment Display
================================

Overview
---------

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
-------------------

.. image:: img/list_2.7.png

* :ref:`cpn_mega2560`
* :ref:`cpn_breadboard`
* :ref:`cpn_wires`
* :ref:`cpn_resistor`
* :ref:`cpn_4_digit`

Fritzing Circuit
----------------


.. image:: img/image438.png

Schematic Diagram
-----------------

.. image:: img/image439.png


Code
----



.. note::

    * You can open the file ``2.7_4digitalSegment.ino`` under the path of ``sunfounder_vincent_kit_for_arduino\code\2.7_4digitalSegment`` directly.
    
.. raw:: html

    <iframe src=https://create.arduino.cc/editor/sunfounder01/1a717c75-35df-4674-be90-a5d290f7065d/preview?embed style="height:510px;width:100%;margin:10px 0" frameborder=0></iframe>

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.

#. Variable and Constant Definitions:

    .. code-block:: arduino

        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.

#. 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.

    .. code-block:: arduino

        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, HIGH, HIGH, HIGH, LOW}, // 8
            {HIGH, HIGH, HIGH, HIGH, LOW, HIGH, HIGH, LOW}   // 9
        }; 

#. Setup Function:

    .. code-block:: arduino

        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.

#. Main Loop:

    .. code-block:: arduino

        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.

#. ``displayNumber()`` Function:

    .. code-block:: arduino

        // 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.

#. ``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.

    .. code-block:: arduino

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


#. ``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.

    .. code-block:: arduino

        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
            }
        }


#. ``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.

    .. code-block:: arduino

        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
------------------

.. image:: img/image104.jpeg