🔢 Display Numbers Using 74HC595 and 7-Segment Displays

In this tutorial, you’ll learn how to use a 74HC595 shift register IC to control a 2-digit 7-segment display using an Arduino. This setup drastically reduces the number of required GPIO pins on the Arduino, making it ideal for microcontroller projects with limited pin availability.

The demonstration includes full wiring instructions, code walkthrough, and a working example. This article also explains the internal logic of the 74HC595 and how it helps multiplex multiple displays with only three control pins.

📦 You can download the complete source code and required library files (ShiftRegister74HC595.h and .cpp) as a ZIP package at the end of this article.

⏱️ Video Chapters

• 00:00 Introduction

• 03:10 Wiring Explained

• 03:48 Arduino Code Explained

• 18:20 Demonstration

🧠 How the 74HC595 Works

The 74HC595 is an 8-bit serial-in, parallel-out shift register with a storage register and 3-state outputs. It allows you to shift in serial data and output it in parallel, reducing the number of control pins needed.

It operates using 3 main lines:

• DS (Data) – Input serial data

• SHCP (Shift Clock) – Moves the bit inside shift register

• STCP (Storage Clock/Latch) – Sends the bits to output pins

Each clock pulse shifts a bit through the register. After 8 bits are in, the latch pin updates the outputs all at once. This makes it perfect for driving 7-segment displays (which typically require 8 lines per digit).

🔌 Wiring Overview

To connect the two-digit 7-segment display with the 74HC595:

• Connect DS, SHCP, and STCP of the 74HC595 to Arduino digital pins (defined in code).

• Each segment of the digit is connected via current-limiting resistors to the output of the shift register.

• The digit control (for selecting left or right digit) is handled by enabling transistor or direct pin toggle.

This lets us multiplex digits: display one digit at a time fast enough that both appear lit continuously to the human eye.

💻 Arduino Code Overview

This project uses a custom library ShiftRegister74HC595 that handles digit-to-segment logic. Below are key parts of the code:

1. Library and Pin Configuration

cppCopyEdit#include <ShiftRegister74HC595.h>

#define DATA_PIN  2
#define LATCH_PIN 3
#define CLOCK_PIN 4
ShiftRegister74HC595 sr(DATA_PIN, LATCH_PIN, CLOCK_PIN);

• Initializes the shift register with designated pins.

• Only 3 Arduino pins are used for the entire 2-digit display.

2. Digit Control

cppCopyEditint digit1 = 5; // right digit
int digit2 = 6; // left digit

void setup() {
  pinMode(digit1, OUTPUT);
  pinMode(digit2, OUTPUT);
}

• digit1 and digit2 are used to control which of the two digits is active.

• The loop alternates between the two to show complete 2-digit numbers.

3. Displaying Numbers

cppCopyEditvoid displayNumber(int value) {
  int rightDigit = value % 10;
  int leftDigit = value / 10;

  digitalWrite(digit2, LOW);
  sr.displayNumber(rightDigit);
  digitalWrite(digit1, HIGH);
  delay(5);
  digitalWrite(digit1, LOW);

  sr.displayNumber(leftDigit);
  digitalWrite(digit2, HIGH);
  delay(5);
  digitalWrite(digit2, LOW);
}

• The number is split into two digits.

• Each digit is turned on and updated briefly using the shift register.

• This function is called repeatedly in the loop() to refresh the display.

4. Main Loop

cppCopyEditint number = 0;

void loop() {
  displayNumber(number);
  number++;
  if (number > 99) number = 0;
  delay(1000);
}

• Continuously counts from 0 to 99, displaying the value on the 2-digit 7-segment display.

✅ Demonstration

At 18:20 in the video, you can see the full demo of the counter incrementing on the 2-digit display. The digits switch rapidly and appear stable to the human eye, thanks to fast multiplexing.

📥 Download Section

You can download the following files as a ZIP archive:

• Seven_segment_2_digits.ino (Arduino Sketch)

• ShiftRegister74HC595.h

• ShiftRegister74HC595.cpp

This project is ideal for learning multiplexing and shift register logic. It can easily be extended to more digits or used in combination with sensors and inputs to build interactive counters or timers.