7 Segment Display with 74HC595 Shift Register and Raspberry Pi

This project shows how to use the Raspberry Pi to drive a 7 Segment Display with the help of a 74HC595 chip.

Parts used in this project:

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
some Python code

Here is a schematic made with fritzing of the project when it is ready. Here a link to download the 7-segment-display with 74HC595 and Raspberry Pi fritzing project.

the interresting thing here is the 74HC595 Chip. It takes some time to understand what it does. I think that the video from Kevin Darrah describes it fast and easy.

Here is the Python code: rpi_7_segment_74hc595

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#!/usr/bin/python
importRPi.GPIO as GPIO
importtime
#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=[]
forvalue inletter.values():
    letterrange.append(value)
forvalue inletter.values():
    ifvalue !="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
defsetup():
    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
defcleanup():
    #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)
defshift(input):
   ifinput==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
defwriteout():
   #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
defwritenumber(number):
    forx inrange(0,8):
        shift((number>>x)%2)
#writes a range of character to the display        
defwriterange(range):
    forx inrange:
        writenumber(x)
        writeout()
#additive and following substractive writeout of a range of characters
defwriteaddrange(range):
    character=0
    forx inrange:
        character+=x
        writenumber(character)
        writeout()
    forx inrange:
        character-=x
        writenumber(character)
        writeout()
#additive and following substractive writeout with reversed call of a range of characters
defwriteaddremrange(range):
    character=0
    forx inrange:
        character+=x
        writenumber(character)
        writeout()
    forx inrange:
        character-=x
        writenumber(character)
        writeout()
    forx inreversed(range):
        character+=x
        writenumber(character)
        writeout()
    forx inreversed(range):
        character-=x
        writenumber(character)
        writeout()
#additive and following reversed substractive writeout of characters        
defwriteaddbackrange(range):
    character=0
    forx inrange:
        character+=x
        writenumber(character)
        writeout()
    forx inreversed(range):
        character-=x
        writenumber(character)
        writeout()
#chained XORed and reversed XORed writeout of characters
defwritexorrange(range):
    #close the chain to have no interrupts while displaying
    character=range[0]&range[-1]
    forx inrange:
        character^=x
        writenumber(character)
        writeout()
    forx inrange:
        character^=x
        writenumber(character)
        writeout()
    forx inreversed(range):
        character^=x
        writenumber(character)
        writeout()
    forx inreversed(range):
        character^=x
        writenumber(character)
        writeout()
print("####Setup####")
setup()
#Tryout of most ranges and displayfunctions
try:    print("####Write Stuff####")
    whileTrue:
        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()

For more detail: 7 Segment Display with 74HC595 Shift Register and Raspberry Pi

7 Segment Display with 74HC595 Shift Register and Raspberry Pi

About The Author

Ibrar Ayyub

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