7 Segment Display with 74HC595

How to use the Raspberry Pi to drive a 7 Segment Display with the help of a 74HC595 chip.

Parts you will need:

• Breadboard
• Wiring cables (Male-Male, Female-Male)
• 7 Segement display (it actually has 8 segments because of the dot)
• 74HC595 Chip
• Raspberry Pi Revision 2
• Python code

The video from Kevin Darrah describes very good how shift registers work based on 74HC595 processor.

#!/usr/bin/python

import RPi.GPIO as GPIO
import time

#Data Pins needed on the RPi
DATAIN=17 #DS
LATCH=27  #STCP
CLOCK=22  #SHCP
CLEAR=25  #MR Low
OE=11     #Output Enable Low

#inter character sleep
icsleep=0.06 

#defining all the single LEDs
led1=0x80 #10000000
led2=0x40 #01000000
led3=0x20 #00100000
led4=0x10 #00010000
led5=0x08 #00001000
led6=0x04 #00000100
led7=0x02 #00000010
led8=0x01 #00000001

#definition of all writeable letters and numbers
letter={"0":0xFC,
        "1":0x30,
        "2":0xDA,
        "3":0x7A,
        "4":0x36,
        "5":0x6E,
        "6":0xEE,
        "7":0x38,
        "8":0xFE,
        "9":0x3E,
        "a":0xBE,
        "b":0xE6,
        "c":0xCC,
        "d":0xF2,
        "e":0xCE,
        "f":0x8E,
        "g":0x7E,
        "h":0xB6,
        "i":0x30,
        "j":0xF0,
        "l":0xC4,
        "n":0xBC,
        "o":0xFC,
        "p":0x9E,
        "s":0x6E,
        "t":0x38,
        "u":0xF4,
        "x":0xB4,
        "y":0x76,
        "z":0xDE
}

#loading function sequence
load1=0x06 #00000110
load2=0x22 #00100010
load3=0x60 #01100000
load4=0xC0 #11000000
load5=0x82 #10000010
load6=0x12 #00010010
load7=0x18 #00011000
load8=0x0C #00001100

#up-down loading function sequence
ud1=led8
ud2=led2
ud3=led1+led3
ud4=led7
ud5=led6+led4
ud6=led5

#left-right loading function sequence
lr1=led1+led6
lr2=led2+led5+led7
lr3=led3+led4
lr4=led8

#rotational loading function sequence
rot1=led2+led5
rot2=led1+led6+led3+led4+led7

#putting all segments of the sequences in a list
letterrange=[]
hexrange=[]
for value in letter.values():
    letterrange.append(value)
for value in letter.values():
    if value != "g":
        hexrange.append(value)
loadrange=[load1,load2,load3,load4,load5,load6,load7,load8]
udrange=[ud1,ud2,ud3,ud4,ud5,ud6]
ledrange=[led1,led2,led3,led4,led5,led6,led7,led8]
lrrange=[lr1,lr2,lr3,lr4]
rotrange=[rot1,rot2]
spinrange=[led1,led2,led3,led4,led5,led6]

#GPIO definition
def setup():
    GPIO.setmode(GPIO.BCM)
    GPIO.cleanup()
    GPIO.setup(DATAIN,GPIO.OUT)
    GPIO.setup(CLOCK,GPIO.OUT)
    GPIO.setup(LATCH,GPIO.OUT)
    GPIO.setup(CLEAR,GPIO.OUT)
    GPIO.setup(OE,GPIO.OUT)

    GPIO.output(LATCH,False) #Latch is used to output the saved data
    GPIO.output(CLEAR,True)  #Clear must always be true. False clears registers
    GPIO.output(OE,False)    #Output Enable speaks for itself. Must be False to display
    GPIO.output(CLOCK,False) #Used to shift the value of DATAIN to the register
    GPIO.output(DATAIN,False)#Databit to be shifted into the register 

    #Clean up GPIO, set display to no character
def cleanup():
    #Set all leds to off
    writenumber(0)
    #writeout stored in character
    writeout()
    #writeout "nothing"
    writeout()
    time.sleep(0.7)
    GPIO.cleanup()

#shifts in a bit (but does not write it yet)
def shift(input):
   if input == 1:
       input=True
   else:
       input=False

   GPIO.output(DATAIN,input)
   GPIO.output(CLOCK,GPIO.HIGH)
   GPIO.output(CLOCK,GPIO.LOW)
   GPIO.output(DATAIN,GPIO.LOW)

#writes the stored data from register out to pins
def writeout():
   #Display LEDs
   GPIO.output(LATCH,GPIO.HIGH)
   #needed to read characters. otherwise the characters would be display to fast after each other
   time.sleep(icsleep)
   GPIO.output(LATCH,GPIO.LOW)

#writes a character to the register
def writenumber(number):
    for x in range(0,8):
        shift((number>>x)%2)

#writes a range of character to the display        
def writerange(range):
    for x in range:
        writenumber(x)
        writeout()

#additive and following substractive writeout of a range of characters
def writeaddrange(range):
    character=0
    for x in range:
        character+=x
        writenumber(character)
        writeout()
    for x in range:
        character-=x
        writenumber(character)
        writeout()

#additive and following substractive writeout with reversed call of a range of characters
def writeaddremrange(range):
    character=0
    for x in range:
        character+=x
        writenumber(character)
        writeout()
    for x in range:
        character-=x
        writenumber(character)
        writeout()
    for x in reversed(range):
        character+=x
        writenumber(character)
        writeout()
    for x in reversed(range):
        character-=x
        writenumber(character)
        writeout()

#additive and following reversed substractive writeout of characters        
def writeaddbackrange(range):
    character=0
    for x in range:
        character+=x
        writenumber(character)
        writeout()
    for x in reversed(range):
        character-=x
        writenumber(character)
        writeout()

#chained XORed and reversed XORed writeout of characters
def writexorrange(range):
    #close the chain to have no interrupts while displaying
    character=range[0]&range[-1]
    for x in range:
        character^=x
        writenumber(character)
        writeout()
    for x in range:
        character^=x
        writenumber(character)
        writeout()
    for x in reversed(range):
        character^=x
        writenumber(character)
        writeout()
    for x in reversed(range):
        character^=x
        writenumber(character)
        writeout()

print("####Setup####")
setup()

#Tryout of most ranges and displayfunctions
try:
    print("####Write Stuff####")
    while True:
        writerange(letterrange)
        writerange(hexrange)
        writerange(loadrange)
        writeaddremrange(udrange)
        writexorrange(loadrange)
        writexorrange(udrange)
        writexorrange(ledrange)
        writexorrange(lrrange)
        writexorrange(rotrange)
        writexorrange(spinrange)
        writeaddrange(ledrange) 
        writeaddbackrange(ledrange)
#Wait for KeyboardInterrupt or SystemExit (called by kill or others)
except (KeyboardInterrupt, SystemExit):
    print("Exit...")

finally:
    cleanup()

What is a raspberry pi and what is is used for?

A raspberry pi is a credit card-sized computer that can be used for a variety of purposes. It can be used as a regular computer, for gaming, or for educational purposes. It is also often used as a media center, playing videos and music from a connected storage device. The raspberry pi is relatively inexpensive and easy to use, making it a popular choice for many different types of projects.

What is a Segment Display on raspberry pi?

A segment display is a type of display that is commonly used to show information like time, temperature, or other data. They are often used in devices like clocks and thermometers. Segment displays usually have seven or more segments that can be illuminated to form different characters or symbols. The raspberry pi can be used to control a segment display in order to show information like the time, temperature, or other data.