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.. _1.1.5_py_pi5:

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:: ../python_pi5/img/1.1.5_4_digit_list.png

.. raw:: html

   <br/>

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

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

.. image:: ../python_pi5/img/1.1.5_4_digit_schmatic.png


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

**Step 1**: Build the circuit.

.. image:: ../python_pi5/img/1.1.5_4-Digit_circuit.png

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

.. raw:: html

   <run></run>

.. code-block::

    cd ~/davinci-kit-for-raspberry-pi/python-pi5

**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.

.. warning::

    If there is an error prompt  ``RuntimeError: Cannot determine SOC peripheral base address``, please refer to :ref:`faq_soc` 

**Code**

.. note::

    You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to  source code path like ``davinci-kit-for-raspberry-pi/python-pi5``. After modifying the code, you can run it directly to see the effect.

.. raw:: html

    <run></run>

.. code-block:: python

   #!/usr/bin/env python3
   from gpiozero import OutputDevice
   import time
   import threading

   # Define GPIO pins for the 74HC595 shift register
   SDI = OutputDevice(24)   # Serial Data Input
   RCLK = OutputDevice(23)  # Register Clock
   SRCLK = OutputDevice(18) # Shift Register Clock

   # Define GPIO pins for digit selection on the 7-segment display
   placePin = [OutputDevice(pin) for pin in (10, 22, 27, 17)]

   # Define segment codes for numbers 0-9 for the 7-segment display
   number = (0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90)

   counter = 0  # Initialize counter for display
   timer1 = 0   # Initialize timer for counter increment

   def clearDisplay():
       """ Clear the 7-segment display. """
       for _ in range(8):
           SDI.on()
           SRCLK.on()
           SRCLK.off()
       RCLK.on()
       RCLK.off()

   def hc595_shift(data):
       """ Shift a byte of data to the 74HC595 shift register. """
       for i in range(8):
           SDI.value = 0x80 & (data << i)  # Set SDI high/low based on data bit
           SRCLK.on()  # Pulse the Shift Register Clock
           SRCLK.off()
       RCLK.on()  # Latch data on the output by pulsing Register Clock
       RCLK.off()

   def pickDigit(digit):
       """ Select a digit for display on the 7-segment display. """
       for pin in placePin:
           pin.off()  # Turn off all digit selection pins
       placePin[digit].on()  # Turn on the selected digit

   def timer():
       """ Timer function to increment the counter every second. """
       global counter, timer1
       timer1 = threading.Timer(1.0, timer)  # Reset timer for next increment
       timer1.start()
       counter += 1  # Increment counter
       print("%d" % counter)  # Print current counter value

   def setup():
       """ Setup initial state and start the timer. """
       global timer1
       timer1 = threading.Timer(1.0, timer)  # Initialize and start the timer
       timer1.start()

   def loop():
       """ Main loop to update the 7-segment display with counter value. """
       global counter
       while True:
           for i in range(4):  # Loop through each digit
               clearDisplay()  # Clear display before setting new digit
               pickDigit(i)    # Select digit for display

               # Choose the digit of counter to display
               digit = (counter // (10 ** i)) % 10

               hc595_shift(number[digit])  # Shift digit value to 74HC595
               time.sleep(0.001)  # Short delay for display stability

   def destroy():
       """ Cleanup GPIO resources and stop timer on exit. """
       global timer1
       timer1.cancel()  # Stop the timer
       for device in [SDI, RCLK, SRCLK] + placePin:
           device.close()  # Close GPIO devices

   try:
       setup()  # Initialize the setup
       while True:
           loop()  # Start the main loop
           
   except KeyboardInterrupt:
       # Handle script interruption (e.g., Ctrl+C)
       destroy()  # Cleanup resources on exit


**Code Explanation**

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

   .. code-block:: python

       # Define GPIO pins for digit selection on the 7-segment display
       placePin = [OutputDevice(pin) for pin in (10, 22, 27, 17)]

#. A segment code array from 0 to 9 in hexadecimal (common anode).

   .. code-block:: python

       # Define segment codes for numbers 0-9 for the 7-segment display
       number = (0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90)

#. Initializes a timer that triggers the `timer` function every second. This sets up the recurring counter increment.

   .. code-block:: python

       def setup():
           """ Setup initial state and start the timer. """
           global timer1
           timer1 = threading.Timer(1.0, timer)  # Initialize and start the timer
           timer1.start()

#. 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.

   .. code-block:: python

       def timer():
           """ Timer function to increment the counter every second. """
           global counter, timer1
           timer1 = threading.Timer(1.0, timer)  # Reset timer for next increment
           timer1.start()
           counter += 1  # Increment counter
           print("%d" % counter)  # Print current counter value

#. Shifts a byte of data into the 74HC595 shift register, controlling the display segments.

   .. code-block:: python

       def hc595_shift(data):
           """ Shift a byte of data to the 74HC595 shift register. """
           for i in range(8):
               SDI.value = 0x80 & (data << i)  # Set SDI high/low based on data bit
               SRCLK.on()  # Pulse the Shift Register Clock
               SRCLK.off()
           RCLK.on()  # Latch data on the output by pulsing Register Clock
           RCLK.off()

#. Continuously updates the display with the current counter value, showing each digit sequentially.

   .. code-block:: python

       def loop():
           """ Main loop to update the 7-segment display with counter value. """
           global counter
           while True:
               for i in range(4):  # Loop through each digit
                   clearDisplay()  # Clear display before setting new digit
                   pickDigit(i)    # Select digit for display
                   digit = (counter // (10 ** i)) % 10
                   hc595_shift(number[digit])  # Shift digit value to 74HC595
                   time.sleep(0.001)  # Short delay for display stability


#. Clears the 7-segment display by setting all segments off before displaying the next digit.

   .. code-block:: python

       def clearDisplay():
           """ Clear the 7-segment display. """
           for _ in range(8):
               SDI.on()
               SRCLK.on()
               SRCLK.off()
           RCLK.on()
           RCLK.off()


#. Selects which digit of the 7-segment display to activate. Each digit is controlled by a separate GPIO pin.

   .. code-block:: python

       def pickDigit(digit):
           """ Select a digit for display on the 7-segment display. """
           for pin in placePin:
               pin.off()  # Turn off all digit selection pins
           placePin[digit].on()  # Turn on the selected digit



#. Properly releases the GPIO resources and stops the timer when the program is interrupted.

   .. code-block:: python

       except KeyboardInterrupt:
           # Handle script interruption (e.g., Ctrl+C)
           destroy()  # Cleanup resources on exit