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.

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

Name	ITEMS IN THIS KIT	LINK
Raphael Kit	337	Raphael Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
GPIO Extension Board	BUY
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
4-Digit 7-Segment Display	-
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

Experimental Procedures¶

Step 1: Build the circuit.

Step 2: Go to the folder of the code.

cd ~/raphael-kit/python/

Step 3: Run the executable file.

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.

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

placePin = (10, 22, 27, 17)

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

number = (0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90)

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

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.

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.

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.

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:

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.

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.