7.5 Shift Register Binary Counter

Shift Register Binary Counter project demonstration

The goal of this project is to demonstrate how to expand digital outputs using a 74HC595 shift register.
With just three pins from the NULA MINI, we can control multiple LEDs — an essential concept when working with limited I/O pins.

This example creates a 4-bit binary counter, displaying values from 0 to 15 across four LEDs connected to the shift register.
It teaches how to send serial data to the register, latch it, and visualize binary counting in real time.

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In this documentation you will learn:

How a 74HC595 shift register works and connects to the NULA MINI
How to use the shiftOut() function to send serial data
How to control multiple LEDs using only three output pins
How to visualize binary numbers using LEDs

Hardware required

1× Soldered NULA MINI board
1× 74HC595 shift register
4× LEDs
4× 330 ohm resistors
Breadboard
Jumper wires
USB-C cable

All components required for Shift Register Binary Counter project

How it works

The 74HC595 is an 8-bit serial-in, parallel-out shift register.
It allows you to send 8 bits of data one at a time through a single data pin.
When all bits are loaded, you latch the output — updating all LEDs at once.

In this project, the NULA MINI sends 4-bit values (0–15) representing a binary counter.
Each LED corresponds to one bit of that number:

Decimal	Binary	LED pattern (Q3 Q2 Q1 Q0)
0	0000	All OFF
1	0001	Rightmost LED ON
7	0111	Three right LEDs ON
15	1111	All ON

Concept: sending binary data to LEDs through 74HC595 shift register

Wiring and connections

74HC595 Pin	Function	NULA MINI Pin	Description
DS (Pin 14)	Serial Data Input	IO2	Data sent from NULA MINI
SH_CP (Pin 11)	Clock	IO4	Shifts each bit into the register
ST_CP (Pin 12)	Latch	IO3	Updates LED outputs
Q0–Q3 (Pins 15,1,2,3)	Outputs	4 LEDs (via 220 Ω resistors)	Display binary value
MR (Pin 10)	Master Reset	5V	Keeps register active
OE (Pin 13)	Output Enable	GND	Enables outputs
VCC (Pin 16)	Power	5V	Power supply
GND (Pin 8)	Ground	GND	Common ground

Pinout for 74HC595 IC

Wiring diagram for 74HC595 shift register and 4 LEDs

Full code

Below is the full example code for this project:

int latchPin = 3;  // ST_CP pin (Latch)
int clockPin = 4; // SH_CP pin (Clock)
int dataPin = 2;  // DS pin (Data)

int counter = 0;   // 4-bit counter (0–15)

void setup() {
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}

void loop() {
  // Limit counter to 4 bits (0–15)
  byte value = counter & 0x0F;  

  digitalWrite(latchPin, LOW);    // Prepare shift register for data
  shiftOut(dataPin, clockPin, MSBFIRST, value);  // Send data bits
  digitalWrite(latchPin, HIGH);   // Latch outputs to LEDs

  counter++;  // Increment counter
  if (counter > 15){
    counter = 0;  // Wrap around to 0 after 15
  } 

  delay(500);  // Wait half a second
}

Full example

Full Shift Register Binary Counter demonstration video

Check out the full example code on the link below: