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.

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

Experimental Procedures

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

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

Step 3: Run the executable file.

sudo python3 1.1.5_4-Digit_zero.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 davinci-kit-for-raspberry-pi/python-pi5. After modifying the code, you can run it directly to see the effect.

#!/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

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

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

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

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

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

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

4. 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.

   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
   

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

   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()
   

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

   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
   

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

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

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

   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
   

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

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