Skip to main content

24. Shift Registers and 7-Segment Display

The 74HC595 is an 8-bit serial-in, parallel-out shift register. This means it can take in a serial data input (one bit at a time) and then output the data in parallel (all 8 bits at once). This functionality is particularly useful for expanding the number of output pins available on a microcontroller. A 7-segment display is a simple electronic display device that can display digits from 0 to 9. It consists of seven LEDs (segments) arranged in a pattern that can form each digit. Each segment is labeled with a letter from 'a' to 'g'.

Materials​

ComponentImage
Breadboard
Jumper wires
Arduino Uno R4 Minima
Resistors (220 ohms for the LED, optional if using internal pull-up resistors for buttons)
7 Segment Display
74HC595 Shift Register

Instructions​

  1. Make the following connections using the breadboard and jumper wires.

74HC595 Shift Register Connections​

  • DS (Data Pin) to Arduino pin 2
  • SH_CP (Clock Pin) to Arduino pin 4
  • ST_CP (Latch Pin) to Arduino pin 3
  • VCC to 5V on Arduino
  • GND to GND on Arduino

7 Segment Display to Shift Register​

  • Q0 (Pin 15 on 74HC595): Connect to Segment A (Pin 10 on 7-segment display)
  • Q1 (Pin 1 on 74HC595): Connect to Segment B (Pin 7 on 7-segment display)
  • Q2 (Pin 2 on 74HC595): Connect to Segment C (Pin 4 on 7-segment display)
  • Q3 (Pin 3 on 74HC595): Connect to Segment D (Pin 2 on 7-segment display)
  • Q4 (Pin 4 on 74HC595): Connect to Segment E (Pin 1 on 7-segment display)
  • Q5 (Pin 5 on 74HC595): Connect to Segment F (Pin 9 on 7-segment display)
  • Q6 (Pin 6 on 74HC595): Connect to Segment G (Pin 5 on 7-segment display)
  • Q7 (Pin 7 on 74HC595): Connect to Decimal Point (Pin 6 on 7-segment display)(optional)
  1. Paste the following code into your main Arduino sketch:

Code​

byte seven_seg_digits[10] = { B11111100,  // = 0
                              B01100000,  // = 1
                              B11011010,  // = 2
                              B11110010,  // = 3
                              B01100110,  // = 4
                              B10110110,  // = 5
                              B10111110,  // = 6
                              B11100000,  // = 7
                              B11111110,  // = 8
                              B11100110   // = 9
                             };
 

int latchPin = 3;

int clockPin = 4;

int dataPin = 2;
 
void setup() {
  Serial.begin(9600);
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}
 

void sevenSegWrite(byte digit) {
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, LSBFIRST, seven_seg_digits[digit]);  
  digitalWrite(latchPin, HIGH);
}
 
void loop() {       
  
  for (byte digit = 10; digit > 0; --digit) {
    delay(1000);
    sevenSegWrite(digit - 1); 
    Serial.println(digit - 1);
  }
   
  // suspend 4 seconds
  delay(3000);
}

  1. Connect your Arduino to your laptop using a USB-C cable and upload the code to the arduino.

  2. Test! Check to see if the numbers bring printed onto the serial monitor are corresponding to the numbers on the hex display.

PrevNext
23. Photocell25. Shift Registers and 4 Digit Display