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7.5. Shift Register

Under construction
Short example demonstration video

In this project we will use 74HC595 shift register to implement a 4 bit binary counter, displaying values from 0 to 15 using four LEDs with only 3 pins.

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At the end of this example you will learn:

  • How 74HC595 shift register works
  • Bit manipulation (bit shifting)
  • How to implement a counter and display it with LEDs
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Parts required:

  • Soldered NULA Mini Board
  • Breadboard
  • 1 × 74HC595 shift register
  • 4 x LEDs
  • 4 x 330Ω resistors
  • Jumper wires
Under construction
Required components

Putting the components together​

Under construction
Components connected together

Code Example​

from machine import Pin
import time

# Bit value to send to the shift register
DATA = Pin(18, Pin.OUT)   
# Clock pin, tells the shift register to read the data bit
CLOCK = Pin(19, Pin.OUT)  
# Latch pin, when pulsed, updates the output pins of the shift register
LATCH = Pin(20, Pin.OUT) 

# Send one byte to the shift register
def shift_byte(value):
    # Shift out 8 bits, LSB first
    for i in range(8):
        DATA.value((value >> i) & 1)
        CLOCK.value(1)
        CLOCK.value(0)

# Pulse the latch line
def latch():
    LATCH.value(1)
    LATCH.value(0)

# Show a 4-bit nibble on the shift register outputs
def show_nibble(n):
    shift_byte(n & 0x0F)
    latch()

# Main loop that counts from 0 to 15 and displays with LEDs
count = 0
while True:
    show_nibble(count)
    time.sleep(0.3)
    # Increment the counter and wrap it from 15 back to 0
    count = (count + 1) & 0x0F