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.. _1.1.5_c:

1.1.5 4-Digit 7-Segment Display
====================================

Introduction
-----------------

Next, follow me to try to control the 4-digit 7-segment display.

Required Components
------------------------------

In this project, we need the following components. 

.. image:: ../img/list_4_digit.png

It's definitely convenient to buy a whole kit, here's the link: 

.. list-table::
    :widths: 20 20 20
    :header-rows: 1

    *   - Name	
        - ITEMS IN THIS KIT
        - LINK
    *   - Raphael Kit
        - 337
        - |link_Raphael_kit|

You can also buy them separately from the links below.

.. list-table::
    :widths: 30 20
    :header-rows: 1

    *   - COMPONENT INTRODUCTION
        - PURCHASE LINK

    *   - :ref:`cpn_gpio_extension_board`
        - |link_gpio_board_buy|
    *   - :ref:`cpn_breadboard`
        - |link_breadboard_buy|
    *   - :ref:`cpn_wires`
        - |link_wires_buy|
    *   - :ref:`cpn_resistor`
        - |link_resistor_buy|
    *   - :ref:`cpn_4_digit`
        - \-
    *   - :ref:`cpn_74hc595`
        - |link_74hc595_buy|

.. note::
    In this projiect, for the 4-Digit 7-Segment Display we should use BS model,if you use AS model it may not light up.

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

============ ======== ======== ===
T-Board Name physical wiringPi BCM
GPIO17       Pin 11   0        17
GPIO27       Pin 13   2        27
GPIO22       Pin 15   3        22
SPIMOSI      Pin 19   12       10
GPIO18       Pin 12   1        18
GPIO23       Pin 16   4        23
GPIO24       Pin 18   5        24
============ ======== ======== ===

.. image:: ../img/schmatic_4_digit.png


Experimental Procedures
-----------------------------------

**Step 1**: Build the circuit.

.. image:: ../img/image80.png

**Step 2**: Go to the folder of the code.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/raphael-kit/c/1.1.5/

**Step 3**: Compile the code.

.. raw:: html

   <run></run>

.. code-block::

    gcc 1.1.5_4-Digit.c -lwiringPi

**Step 4**: Run the executable file.

.. raw:: html

   <run></run>

.. code-block::

    sudo ./a.out

After the code runs, the program takes a count, increasing by 1 per second, and the 4-digit 7-segment display displays the count.


.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`install_wiringpi`.

**Code**

.. code-block:: c

    #include <wiringPi.h>
    #include <stdio.h>
    #include <wiringShift.h>
    #include <signal.h>
    #include <unistd.h>

    #define SDI 5
    #define RCLK 4
    #define SRCLK 1

    const int placePin[] = {12, 3, 2, 0};
    unsigned char number[] = {0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90};

    int counter = 0;

    void pickDigit(int digit)
    {
        for (int i = 0; i < 4; i++)
        {
            digitalWrite(placePin[i], 0);
        }
        digitalWrite(placePin[digit], 1);
    }

    void hc595_shift(int8_t data)
    {
        int i;
        for (i = 0; i < 8; i++)
        {
            digitalWrite(SDI, 0x80 & (data << i));
            digitalWrite(SRCLK, 1);
            delayMicroseconds(1);
            digitalWrite(SRCLK, 0);
        }
        digitalWrite(RCLK, 1);
        delayMicroseconds(1);
        digitalWrite(RCLK, 0);
    }

    void clearDisplay()
    {
        int i;
        for (i = 0; i < 8; i++)
        {
            digitalWrite(SDI, 1);
            digitalWrite(SRCLK, 1);
            delayMicroseconds(1);
            digitalWrite(SRCLK, 0);
        }
        digitalWrite(RCLK, 1);
        delayMicroseconds(1);
        digitalWrite(RCLK, 0);
    }

    void loop()
    {
        while(1){
        clearDisplay();
        pickDigit(0);
        hc595_shift(number[counter % 10]);

        clearDisplay();
        pickDigit(1);
        hc595_shift(number[counter % 100 / 10]);

        clearDisplay();
        pickDigit(2);
        hc595_shift(number[counter % 1000 / 100]);
    
        clearDisplay();
        pickDigit(3);
        hc595_shift(number[counter % 10000 / 1000]);
        }
    }

    void timer(int timer1)
    { 
        if (timer1 == SIGALRM)
        { 
            counter++;
            alarm(1); 
            printf("%d\n", counter);
        }
    }

    void main(void)
    {
        if (wiringPiSetup() == -1)
        { 
            printf("setup wiringPi failed !");
            return;
        }
        pinMode(SDI, OUTPUT); 
        pinMode(RCLK, OUTPUT);
        pinMode(SRCLK, OUTPUT);
        
        for (int i = 0; i < 4; i++)
        {
            pinMode(placePin[i], OUTPUT);
            digitalWrite(placePin[i], HIGH);
        }
        signal(SIGALRM, timer); 
        alarm(1);               
        loop(); 
    }



**Code Explanation**

.. code-block:: c

    const int placePin[] = {12, 3, 2, 0};

These four pins control the common anode pins of the four-digit 7-segment display.

.. code-block:: c

    unsigned char number[] = {0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90};

A segment code array from 0 to 9 in Hexadecimal (Common anode).

.. code-block:: c

    void pickDigit(int digit)
    {
        for (int i = 0; i < 4; i++)
        {
            digitalWrite(placePin[i], 0);
        }
        digitalWrite(placePin[digit], 1);
    }

Select the place of the value. there is only one place that should be enable each time. The enabled place will be written high.

.. code-block:: c

    void loop()
    {
        while(1){
        clearDisplay();
        pickDigit(0);
        hc595_shift(number[counter % 10]);

        clearDisplay();
        pickDigit(1);
        hc595_shift(number[counter % 100 / 10]);

        clearDisplay();
        pickDigit(2);
        hc595_shift(number[counter % 1000 / 100]);
    
        clearDisplay();
        pickDigit(3);
        hc595_shift(number[counter % 10000 / 1000]);
        }
    }

The functionis used to set the number displayed on the 4-digit 7-segment display.

* ``clearDisplay()``：write in 11111111 to turn off these eight LEDs on 7-segment display so as to clear the displayed content.
* ``pickDigit(0)``：pick the fourth 7-segment display.
* ``hc595_shift(number[counter%10])``：the number in the single digit of counter will display on the forth segment.

.. code-block:: c

    signal(SIGALRM, timer); 

This is a system-provided function, the prototype of code is:

.. code-block:: c

    sig_t signal(int signum,sig_t handler);

After executing the ``signal()`` , once the process receives the corresponding signum (in this case SIGALRM), it immediately pauses the existing task and processes the set function (in this case ``timer(sig)`` ).

.. code-block:: c

    alarm(1);

This is also a system-provided function. The code prototype is:

.. code-block:: c

    unsigned int alarm (unsigned int seconds);

It generates a SIGALRM signal after a certain number of seconds.

.. code-block:: c

    void timer(int timer1)
    { 
        if (timer1 == SIGALRM)
        { 
            counter++;
            alarm(1); 
            printf("%d\n", counter);
        }
    }

We use the functions above to implement the timer function.
After the ``alarm()`` generates the SIGALRM signal, the timer function is called. Add 1 to counter, and the function, ``alarm(1)`` will be repeatedly called after 1 second.

Phenomenon Picture
-----------------------

.. image:: ../img/image81.jpeg