2.4 Microchip - 74HC595

Welcome to this exciting project! In this project, we will be using the 74HC595 chip to control a flowing display of 8 LEDs.

Imagine triggering this project and witnessing a mesmerizing flow of light, as if a sparkling rainbow is jumping between the 8 LEDs. Each LED will light up one by one and quickly fade away, while the next LED continues to shine, creating a gorgeous and dynamic effect.

By cleverly utilizing the 74HC595 chip, we can control the on and off states of multiple LEDs to achieve the flowing effect. This chip has multiple output pins that can be connected in series to control the sequence of LED illumination. Moreover, thanks to the chip’s expandability, we can easily add more LEDs to the flowing display, creating even more spectacular effects.

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
ESP32 Starter Kit	320+	ESP32 Starter Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
ESP32 WROOM 32E	BUY
ESP32 Camera Extension	-
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
74HC595	BUY

Available Pins

Here is a list of available pins on the ESP32 board for this project.

Available Pins

IO13, IO12, IO14, IO27, IO26, IO25, IO33, IO32, IO15, IO2, IO0, IO4, IO5, IO18, IO19, IO21, IO22, IO23

Schematic

• When MR (pin10) is high level and CE (pin13) is low level, data is input in the rising edge of SHcp and goes to the memory register through the rising edge of SHcp.

• If the two clocks are connected together, the shift register is always one pulse earlier than the memory register.

• There is a serial shift input pin (DS), a serial output pin (Q7’) and an asynchronous reset button (low level) in the memory register.

• The memory register outputs a Bus with a parallel 8-bit and in three states.

• When OE is enabled (low level), the data in memory register is output to the bus(Q0 ~ Q7).

Wiring

Code

Note

• Open the 2.4_microchip_74hc595.py file located in the esp32-starter-kit-main\micropython\codes path, or copy and paste the code into Thonny. Then, click “Run Current Script” or press F5 to execute it.

• Make sure to select the “MicroPython (ESP32).COMxx” interpreter in the bottom right corner.

import machine
import time

# Initialize the pins for the 74HC595 shift register
sdi = machine.Pin(25, machine.Pin.OUT)  # DS
rclk = machine.Pin(27, machine.Pin.OUT)  # STcp
srclk = machine.Pin(26, machine.Pin.OUT)  # SHcp

# Define the hc595_shift function to shift data into the 74HC595 shift register
def hc595_shift(dat):
    # Set the RCLK pin to low
    rclk.off()

    # Iterate through each bit (from 7 to 0)
    for bit in range(7, -1, -1):
        # Extract the current bit from the input data
        value = 1 & (dat >> bit)

        # Set the SRCLK pin to low
        srclk.off()

        # Set the value of the SDI pin
        sdi.value(value)

        # Clock the current bit into the shift register by setting the SRCLK pin to high
        srclk.on()

    # Latch the data into the storage register by setting the RCLK pin to high
    rclk.on()

num = 0

# Shift data into the 74HC595 to create a moving LED pattern
for i in range(16):
    if i < 8:
        num = (num << 1) + 1  # Shift left and set the least significant bit to 1
    elif i >= 8:
        num = (num & 0b01111111) << 1  # Mask the most significant bit and shift left
    hc595_shift(num)  # Shift the current value into the 74HC595
    print("{:0>8b}".format(num))  # Print the current value in binary format
    time.sleep_ms(200)  # Wait 200 milliseconds before shifting the next value

During script execution, you will see the LED light up one by one, and then turn off in the original order.

How it works?

This code is used to control an 8-bit shift register (74595), and output different binary values to the shift register, with each value displayed on an LED for a certain period of time.

1. The code imports the machine and time modules, where the machine module is used to control hardware I/O, and the time module is used for implementing time delays and other functions.

   import machine
   import time
   

2. Three output ports are initialized using the machine.Pin() function, corresponding to the data port (SDI), storage clock port (RCLK), and shift register clock port (SRCLK) of the shift register.

   # Initialize the pins for the 74HC595 shift register
   sdi = machine.Pin(25, machine.Pin.OUT)  # DS
   rclk = machine.Pin(27, machine.Pin.OUT)  # STcp
   srclk = machine.Pin(26, machine.Pin.OUT)  # SHcp
   

3. A function called hc595_shift() is defined to write an 8-bit data to the shift register.

   def hc595_shift(dat):
       # Set the RCLK pin to low
       rclk.off()
   
       # Iterate through each bit (from 7 to 0)
       for bit in range(7, -1, -1):
           # Extract the current bit from the input data
           value = 1 & (dat >> bit)
   
           # Set the SRCLK pin to low
           srclk.off()
   
           # Set the value of the SDI pin
           sdi.value(value)
   
           # Clock the current bit into the shift register by setting the SRCLK pin to high
           srclk.on()
   
       # Latch the data into the storage register by setting the RCLK pin to high
       rclk.on()
   

4. About the for loop.

   for i in range(16):
           if i < 8:
               num = (num << 1) + 1  # Shift left and set the least significant bit to 1
           elif i >= 8:
               num = (num & 0b01111111) << 1  # Mask the most significant bit and shift left
           hc595_shift(num)  # Shift the current value into the 74HC595
           print("{:0>8b}".format(num))  # Print the current value in binary format
           time.sleep_ms(200)  # Wait 200 milliseconds before shifting the next value
   

   • The variable i is used to control the output binary value. In the first 8 iterations, the value of num will be successively 00000001, 00000011, 00000111, …, 11111111, which is left-shifted by one bit and then added by 1.

   • In the 9th to 16th iterations, the highest bit of 1 is first changed to 0, and then left-shifted by one bit, resulting in the output values of 00000010, 00000100, 00001000, …, 10000000.

   • In each iteration, the value of num is passed to the hc595_shift() function to control the shift register to output the corresponding binary value.

   • At the same time as outputting the binary value, the print() function outputs the binary value as a string to the terminal.

   • After outputting the binary value, the program pauses for 200 milliseconds using the time.sleep_ms() function, so that the value on the LED remains displayed for a certain period of time.