4.1 74HC595
Meet the 74HC595 shift register - your GPIO pin multiplier! Instead of using 8 precious GPIO pins to control 8 LEDs, this clever chip lets you control 8 outputs using only 3 pins. It’s like having a digital assistant that takes your commands and distributes them to multiple devices.
The magic: Send an 8-bit number (like 11010011) to the chip, and it instantly sets 8 output pins to match that pattern. Need to control 16 LEDs? Chain two 74HC595s together! Need 24? Chain three! The possibilities are endless.
Perfect for LED displays, digital clocks, status indicators, or any project where you need lots of outputs but have limited GPIO pins.
Component List
Raspberry Pi Pico W x1
MicroUSB cable x1
830 Tie-Points Breadboard x1
LED x8
Resistor 220Ω x8
74HC595 x1
Jumper Wire Several
Component knowledge
74HC595
How the 74HC595 works:
Simple 3-Pin Control: - DATA pin: Send your 8-bit pattern one bit at a time - CLOCK pin: Each pulse shifts the data one position - LATCH pin: When pulsed, all 8 outputs update simultaneously
The Process: 1. Send 8 bits of data (one per clock pulse) 2. Pulse the latch pin 3. All 8 LEDs instantly show your pattern!
Connect
Code
Note
Open the
4.1_74hc595.pyfile under the path ofUltimate-Starter-Kit-for-Pico-W\Python\1.Projector copy this code into Thonny, then click “Run Current Script” or simply press F5 to run it.Don’t forget to click on the “MicroPython (Raspberry Pi Pico)” interpreter in the bottom right corner.
After running the code, watch the mesmerizing “flowing water” LED effect! The LEDs progressively light up from left to right, creating a smooth flowing pattern, then flow back in the opposite direction. This demonstrates how you can create complex animations with just simple binary patterns sent to the 74HC595.
The following is the program code:
"""
74HC595 Smooth Flowing LED Project
Creates a smooth flowing LED effect using a 74HC595 shift register.
LEDs progressively light up and then smoothly flow back, creating
a continuous mesmerizing water-like animation.
Hardware: 74HC595 shift register + 8 LEDs with current limiting resistors
"""
import machine
import time
# 74HC595 Pin Configuration Constants
DATA_PIN = 0 # DS (Serial Data Input) - pin 14 of 74HC595
LATCH_PIN = 1 # ST_CP (Storage Register Clock) - pin 12 of 74HC595
CLOCK_PIN = 2 # SH_CP (Shift Register Clock) - pin 11 of 74HC595
# Animation Timing Constants
FLOW_DELAY_MS = 150 # Delay between flow steps for smooth animation
class HC595FlowingLED:
"""74HC595 Smooth Flowing LED Controller"""
def __init__(self):
"""Initialize 74HC595 control pins"""
self.data_pin = machine.Pin(DATA_PIN, machine.Pin.OUT)
self.latch_pin = machine.Pin(LATCH_PIN, machine.Pin.OUT)
self.clock_pin = machine.Pin(CLOCK_PIN, machine.Pin.OUT)
# Smooth Flowing LED Patterns
self.flow_patterns = [
0b00000000, # All off (start)
0b00000001, # 1 LED
0b00000011, # 2 LEDs
0b00000111, # 3 LEDs
0b00001111, # 4 LEDs
0b00011111, # 5 LEDs
0b00111111, # 6 LEDs
0b01111111, # 7 LEDs
0b11111111, # All on (peak)
0b11111110, # Flow back: 7 LEDs
0b11111100, # 6 LEDs
0b11111000, # 5 LEDs
0b11110000, # 4 LEDs
0b11100000, # 3 LEDs
0b11000000, # 2 LEDs
0b10000000, # 1 LED
0b00000000 # All off (end cycle)
]
# Clear all LEDs initially
self.update_shift_register(0b00000000)
print("74HC595 Smooth Flowing LED initialized")
def update_shift_register(self, pattern):
"""
Update Shift Register
Sends data to 74HC595 and latches the output.
"""
self.latch_pin.low() # Prepare for data
self.shift_out_msb_first(pattern) # Send 8 bits
self.latch_pin.high() # Latch data to outputs
def shift_out_msb_first(self, data):
"""
Shift out data MSB first (Most Significant Bit first)
Equivalent to Arduino's shiftOut() function
"""
for bit in range(7, -1, -1): # Start from bit 7 down to bit 0
self.clock_pin.low()
time.sleep_ms(1)
# Extract the bit value
bit_value = (data >> bit) & 1
self.data_pin.value(bit_value)
time.sleep_ms(1)
self.clock_pin.high()
time.sleep_ms(1)
def run_smooth_flowing_animation(self):
"""
Run Smooth Flowing Animation
Creates a mesmerizing water-like flow effect that builds up
all LEDs then smoothly flows back to create continuous motion.
"""
for i, pattern in enumerate(self.flow_patterns):
self.update_shift_register(pattern)
print(f"Step {i:2d}: {pattern:08b}")
time.sleep_ms(FLOW_DELAY_MS)
def run_continuous_animation(self):
"""Run continuous smooth flowing animation"""
print("Starting smooth flowing LED animation...")
print("Press Ctrl+C to stop")
try:
while True:
self.run_smooth_flowing_animation()
except KeyboardInterrupt:
print("\nAnimation stopped")
self.update_shift_register(0b00000000) # Clear all LEDs
def test_all_leds(self):
"""Test all LEDs individually"""
print("Testing all LEDs individually...")
for i in range(8):
pattern = 1 << i # Light up LED i
self.update_shift_register(pattern)
print(f"LED {i}: {pattern:08b}")
time.sleep_ms(300)
# Turn off all LEDs
self.update_shift_register(0b00000000)
print("LED test complete")
def custom_pattern(self, pattern):
"""Display a custom pattern"""
self.update_shift_register(pattern)
print(f"Custom pattern: {pattern:08b}")
# Create and run the flowing LED controller
if __name__ == "__main__":
try:
led_controller = HC595FlowingLED()
# Optional: Test all LEDs first
# led_controller.test_all_leds()
# time.sleep_ms(1000)
# Run continuous smooth flowing animation
led_controller.run_continuous_animation()
except Exception as e:
print(f"Error: {e}")