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.. _1.1.5_py:

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|

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/python/

**Step 3:** Run the executable file.

.. raw:: html

   <run></run>

.. code-block::

    sudo python3 1.1.5_4-Digit.py

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

**Code**

.. note::

    You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to  source code path like ``raphael-kit/python``. After modifying the code, you can run it directly to see the effect.

.. raw:: html

    <run></run>

.. code-block:: python

    import RPi.GPIO as GPIO
    import time
    import threading

    SDI = 24
    RCLK = 23
    SRCLK = 18

    placePin = (10, 22, 27, 17)
    number = (0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90)

    counter = 0
    timer1 = 0

    def clearDisplay():
        for i in range(8):
            GPIO.output(SDI, 1)
            GPIO.output(SRCLK, GPIO.HIGH)
            GPIO.output(SRCLK, GPIO.LOW)
        GPIO.output(RCLK, GPIO.HIGH)
        GPIO.output(RCLK, GPIO.LOW)    

    def hc595_shift(data): 
        for i in range(8):
            GPIO.output(SDI, 0x80 & (data << i))
            GPIO.output(SRCLK, GPIO.HIGH)
            GPIO.output(SRCLK, GPIO.LOW)
        GPIO.output(RCLK, GPIO.HIGH)
        GPIO.output(RCLK, GPIO.LOW)

    def pickDigit(digit):
        for i in placePin:
            GPIO.output(i,GPIO.LOW)
        GPIO.output(placePin[digit], GPIO.HIGH)

    def timer():  
        global counter
        global timer1
        timer1 = threading.Timer(1.0, timer) 
        timer1.start()  
        counter += 1
        print("%d" % counter)

    def loop():
        global counter                    
        while True:
            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])

    def setup():
        GPIO.setmode(GPIO.BCM)
        GPIO.setup(SDI, GPIO.OUT)
        GPIO.setup(RCLK, GPIO.OUT)
        GPIO.setup(SRCLK, GPIO.OUT)
        for i in placePin:
            GPIO.setup(i, GPIO.OUT)
        global timer1
        timer1 = threading.Timer(1.0, timer)  
        timer1.start()       

    def destroy():   # When "Ctrl+C" is pressed, the function is executed.
        global timer1
        GPIO.cleanup()
        timer1.cancel()  # cancel the timer

    if __name__ == '__main__':  
        setup()
        try:
            loop()
        except KeyboardInterrupt:
            destroy()

**Code Explanation**

.. code-block:: python

    placePin = (10, 22, 27, 17)

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

.. code-block:: python

    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:: python

    def clearDisplay():
        for i in range(8):
            GPIO.output(SDI, 1)
            GPIO.output(SRCLK, GPIO.HIGH)
            GPIO.output(SRCLK, GPIO.LOW)
    GPIO.output(RCLK, GPIO.HIGH)
    GPIO.output(RCLK, GPIO.LOW) 

Write "1" for eight times in SDI., so that the eight LEDs on the 7-segment Dispaly will turn off so as to clear the displayed content.

.. code-block:: python

    def pickDigit(digit):
        for i in placePin:
            GPIO.output(i,GPIO.LOW)
        GPIO.output(placePin[digit], GPIO.HIGH)

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:: python

    def loop():
        global counter                    
        while True:
            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 function is used to set the number displayed on the 4-digit 7-segment Dispaly.

First, start the fourth segment display, write the single-digit number. Then start the third segment display, and type in the tens digit; after that, start the second and the first segment display respectively, and write the hundreds and thousands digits respectively. Because the refreshing speed is very fast, we see a complete four-digit display.

.. code-block:: python

    timer1 = threading.Timer(1.0, timer)  
    timer1.start()  

The module, threading is the common threading module in Python，and Timer is the subclass of it.
The prototype of code is:

.. code-block:: python

    class threading.Timer(interval, function, args=[], kwargs={})

After the interval, the function will be run. Here, the interval is 1.0，and the function is timer().
start () means the Timer will start at this point.

.. code-block:: python

    def timer():  
        global counter
        global timer1
        timer1 = threading.Timer(1.0, timer) 
        timer1.start()  
        counter += 1
        print("%d" % counter)

After Timer reaches 1.0s, the Timer function is called; add 1 to counter, and the Timer is used again to execute itself repeatedly every second.


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

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