Arduino Nano 33 IoT - 74HC595 4-Digit 7-Segment Display
Discover how to drive a 4-digit 7-segment display with a 74HC595 shift register using the Arduino Nano 33 IoT. The Nano 33 IoT runs a SAMD21 Cortex-M0+ processor at 48 MHz, includes built-in Wi-Fi and Bluetooth Low Energy, and operates at 3.3V logic. Despite all that, it keeps the same compact Nano footprint.
Along the way, you will discover:
- How to connect the 74HC595 display module to the Nano 33 IoT.
- How to display integers, floats, and text.
- How to show temperature with a degree symbol.
- How to present time in HH.MM format with a blinking separator.
Hardware Preparation
Or you can buy the following kits:
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
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Introducing the 74HC595 4-Digit 7-Segment Display
This module puts four 7-segment digits behind a 74HC595 shift register so you only need 3 data pins. The shift register accepts serial data and converts it to parallel segment outputs. The library multiplexes through each digit rapidly, making all four appear lit at the same time.
| Function | Pin | Description |
|---|---|---|
| SCLK (SH_CP) | Serial Clock | Clocks data into the shift register |
| RCLK (ST_CP) | Register Clock | Latches data to the output pins |
| DIO (DS) | Data Input | Serial data line |
| VCC | Power | 3.3V or 5V |
| GND | Ground | Common ground |
Note: The Nano 33 IoT uses 3.3V logic. The 74HC595 module works fine at 3.3V.
Wiring Diagram
Connect the display module to the Nano 33 IoT:
- SCLK to D7
- RCLK to D6
- DIO to D5
- VCC to 3.3V
- GND to GND
This image is created using Fritzing. Click to enlarge image
Preparing the Library
- Connect the Arduino Nano 33 IoT to your computer using a Micro-B USB cable.
- In Arduino IDE, choose Arduino NANO 33 IoT as the board and select the correct port.
- Open the Libraries panel from the left sidebar.
- Search for "DIYables_4Digit7Segment_74HC595" and locate the one published by DIYables.
- Press Install to add it. Select version 2.0.0 or later.
No additional dependencies needed - everything is bundled in.
Core Sketch
The core structure that every DIYables_4Digit7Segment_74HC595 sketch builds on:
#include <DIYables_4Digit7Segment_74HC595.h>
#define SCLK_PIN 7
#define RCLK_PIN 6
#define DIO_PIN 5
DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN);
void setup() {
display.begin();
display.print(1234);
}
void loop() {
display.loop();
}
Initialize with begin(), set the value with print(), and keep display.loop() running. The multiplexing is handled internally. For waits, use display.delay() instead of delay().
Discover - Display Integers
Displays a series of integers and demonstrates zero-padding.
/*
* This Arduino Nano 33 IoT code was developed by newbiely.com
*
* This Arduino Nano 33 IoT code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-nano-iot/arduino-nano-33-iot-74hc595-4-digit-7-segment-display
*/
#include <DIYables_4Digit7Segment_74HC595.h>
// Pin configuration - change these to match your wiring
#define SCLK_PIN 7 // The Arduino Nano 33 IoT pin connected to the Serial clock pin of 7-segment display
#define RCLK_PIN 6 // The Arduino Nano 33 IoT pin connected to the Register clock / latch pin of 7-segment display
#define DIO_PIN 5 // The Arduino Nano 33 IoT pin connected to the Data (DS) pin of 7-segment display
DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN);
int numbers[] = {0, 42, 1234, -5, -123, 9999};
int numCount = 6;
int currentIndex = 0;
bool showZeroPad = false;
unsigned long lastChange = 0;
void setup() {
Serial.begin(9600);
display.begin();
Serial.println("4-Digit 7-Segment 74HC595 - Integer Example");
}
void loop() {
display.loop(); // Must be called frequently to refresh the display
if (millis() - lastChange >= 2000) {
lastChange = millis();
if (!showZeroPad) {
display.print(numbers[currentIndex]);
Serial.print("Displaying: ");
Serial.println(numbers[currentIndex]);
currentIndex++;
if (currentIndex >= numCount) {
currentIndex = 0;
showZeroPad = true;
}
} else {
display.print(42, true); // Shows "0042"
Serial.println("Displaying: 0042 (zero-padded)");
showZeroPad = false;
}
}
}
Give It a Try
- Wire the display to the Nano 33 IoT as shown above.
- Connect the Nano 33 IoT to your computer with a Micro-B USB cable.
- In Arduino IDE, select the board and port, paste the code, and press Upload.
- Open the Serial Monitor to see what happens.
The display runs through 0, 42, 1234, -5, -123, 9999, then 0042 (zero-padded).
API Essentials
| Method | Role | Usage Example |
|---|---|---|
| print(int) | Display an integer | display.print(1234) |
| print(int, true) | Integer with leading zeros | display.print(42, true) |
| loop() | Keep display refreshed | display.loop() |
Discover - Display Floats
Shows floats with auto and fixed decimal places.
/*
* This Arduino Nano 33 IoT code was developed by newbiely.com
*
* This Arduino Nano 33 IoT code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-nano-iot/arduino-nano-33-iot-74hc595-4-digit-7-segment-display
*/
#include <DIYables_4Digit7Segment_74HC595.h>
// Pin configuration - change these to match your wiring
#define SCLK_PIN 7 // The Arduino Nano 33 IoT pin connected to the Serial clock pin of 7-segment display
#define RCLK_PIN 6 // The Arduino Nano 33 IoT pin connected to the Register clock / latch pin of 7-segment display
#define DIO_PIN 5 // The Arduino Nano 33 IoT pin connected to the Data (DS) pin of 7-segment display
DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN);
void setup() {
Serial.begin(9600);
display.begin();
Serial.println("4-Digit 7-Segment 74HC595 - Float Example");
}
void loop() {
// Auto decimal placement
display.print(1.5); // Shows " 1.5"
Serial.println("Auto decimal: 1.5");
display.delay(2000);
display.print(12.34); // Shows "12.34"
Serial.println("Auto decimal: 12.34");
display.delay(2000);
display.print(3.141); // Shows "3.141"
Serial.println("Auto decimal: 3.141");
display.delay(2000);
display.print(-1.2); // Shows "-1.20"
Serial.println("Auto decimal: -1.20");
display.delay(2000);
display.print(0.5); // Shows " 0.5"
Serial.println("Auto decimal: 0.5");
display.delay(2000);
// Fixed decimal places
display.print(23.5, 1); // 1 decimal place: shows "23.5"
Serial.println("1 decimal place: 23.5");
display.delay(2000);
display.print(1.5, 2); // 2 decimal places: shows "1.50"
Serial.println("2 decimal places: 1.50");
display.delay(2000);
// Zero-padded
display.print(1.5, 2, true); // Shows "01.50"
Serial.println("2 decimal places, zero-padded: 01.50");
display.delay(2000);
}
Give It a Try
- Upload the sketch and open the Serial Monitor.
Cycles through auto-decimal floats, then 1 and 2 fixed decimal places, and zero-padded output.
Discover - Text and Temperature
Displays text strings, degree symbols, and temperature readings.
/*
* This Arduino Nano 33 IoT code was developed by newbiely.com
*
* This Arduino Nano 33 IoT code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-nano-iot/arduino-nano-33-iot-74hc595-4-digit-7-segment-display
*/
#include <DIYables_4Digit7Segment_74HC595.h>
// Pin configuration - change these to match your wiring
#define SCLK_PIN 7 // The Arduino Nano 33 IoT pin connected to the Serial clock pin of 7-segment display
#define RCLK_PIN 6 // The Arduino Nano 33 IoT pin connected to the Register clock / latch pin of 7-segment display
#define DIO_PIN 5 // The Arduino Nano 33 IoT pin connected to the Data (DS) pin of 7-segment display
DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN);
const char* texts[] = {"HELP", "Hi", "COOL", "done"};
int textCount = 4;
int currentIndex = 0;
int phase = 0;
unsigned long lastChange = 0;
void setup() {
Serial.begin(9600);
display.begin();
Serial.println("4-Digit 7-Segment 74HC595 - Text and Degree Example");
}
void loop() {
display.loop(); // Must be called frequently to refresh the display
if (millis() - lastChange >= 2000) {
lastChange = millis();
if (phase == 0) {
// Display text strings
display.print(texts[currentIndex]);
Serial.print("Text: ");
Serial.println(texts[currentIndex]);
currentIndex++;
if (currentIndex >= textCount) {
currentIndex = 0;
phase = 1;
}
} else if (phase == 1) {
// Display temperature 25 degrees C
display.printTemperature(25, 'C');
Serial.println("Temperature: 25 C");
phase = 2;
} else if (phase == 2) {
// Display temperature 72 degrees F
display.printTemperature(72, 'F');
Serial.println("Temperature: 72 F");
phase = 3;
} else if (phase == 3) {
// Display degree symbol using string with DEGREE_CHAR constant
char degStr[5];
degStr[0] = '2';
degStr[1] = '5';
degStr[2] = DEGREE_CHAR;
degStr[3] = 'C';
degStr[4] = '\0';
display.print(degStr);
Serial.println("String with degree: 25 deg C");
phase = 4;
} else {
// Display string with dots
display.print("1.2.3.4");
Serial.println("Dots: 1.2.3.4");
phase = 0;
}
}
}
Give It a Try
- Upload the sketch and open the Serial Monitor.
Shows "HELP", "Hi", "COOL", "done", then temperatures and inline dots.
Discover - Time Display
Clock-style HH.MM with a blinking separator dot.
/*
* This Arduino Nano 33 IoT code was developed by newbiely.com
*
* This Arduino Nano 33 IoT code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-nano-iot/arduino-nano-33-iot-74hc595-4-digit-7-segment-display
*/
#include <DIYables_4Digit7Segment_74HC595.h>
// Pin configuration - change these to match your wiring
#define SCLK_PIN 7 // The Arduino Nano 33 IoT pin connected to the Serial clock pin of 7-segment display
#define RCLK_PIN 6 // The Arduino Nano 33 IoT pin connected to the Register clock / latch pin of 7-segment display
#define DIO_PIN 5 // The Arduino Nano 33 IoT pin connected to the Data (DS) pin of 7-segment display
DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN);
int hours = 12;
int minutes = 30;
bool colonOn = true;
unsigned long lastToggle = 0;
void setup() {
Serial.begin(9600);
display.begin();
Serial.println("4-Digit 7-Segment 74HC595 - Time Example");
Serial.println("Displaying 12:30 with blinking dot separator");
}
void loop() {
display.loop(); // Must be called frequently to refresh the display
if (millis() - lastToggle >= 500) {
lastToggle = millis();
display.printTime(hours, minutes, colonOn);
colonOn = !colonOn; // Toggle dot separator every 500ms for blinking effect
}
}
Give It a Try
- Upload the sketch and open the Serial Monitor.
Displays 12.30 with the dot blinking every half second.
Discover - Blink
Blinks integers, floats, and text.
/*
* This Arduino Nano 33 IoT code was developed by newbiely.com
*
* This Arduino Nano 33 IoT code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-nano-iot/arduino-nano-33-iot-74hc595-4-digit-7-segment-display
*/
#include <DIYables_4Digit7Segment_74HC595.h>
// Pin configuration - change these to match your wiring
#define SCLK_PIN 7 // The Arduino Nano 33 IoT pin connected to the Serial clock pin of 7-segment display
#define RCLK_PIN 6 // The Arduino Nano 33 IoT pin connected to the Register clock / latch pin of 7-segment display
#define DIO_PIN 5 // The Arduino Nano 33 IoT pin connected to the Data (DS) pin of 7-segment display
DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN);
// States: 0 = blink int, 1 = blink float, 2 = blink text
int phase = 0;
int blinkCount = 0;
bool isOn = true;
unsigned long lastAction = 0;
unsigned long pauseUntil = 0;
void setup() {
Serial.begin(9600);
display.begin();
Serial.println("4-Digit 7-Segment 74HC595 - Blink Example");
display.print(1234);
Serial.println("Blinking: 1234");
}
void loop() {
display.loop(); // Must be called frequently to refresh the display
unsigned long now = millis();
// Pause between phases
if (now < pauseUntil) return;
if (now - lastAction >= 300) {
lastAction = now;
if (isOn) {
display.off();
isOn = false;
} else {
display.on();
isOn = true;
blinkCount++;
if (blinkCount >= 5) {
blinkCount = 0;
pauseUntil = now + 1000;
phase++;
if (phase > 2) phase = 0;
switch (phase) {
case 0:
display.print(1234);
Serial.println("Blinking: 1234");
break;
case 1:
display.print(12.34);
Serial.println("Blinking: 12.34");
break;
case 2:
display.print("HELP");
Serial.println("Blinking: HELP");
break;
}
}
}
}
}
Give It a Try
- Upload the sketch and open the Serial Monitor.
Blinks 1234, then 12.34, then "HELP" - five blinks each.
Troubleshoot
- Display stays blank -- Check VCC and GND wiring. Verify SCLK, RCLK, DIO match your code. Confirm begin() and display.loop() are in place.
- Wrong characters -- Default is common anode. For common cathode, use DIYables_4Digit7Segment_74HC595 display(7, 6, 5, false).
- Flickering -- Replace any delay() calls with display.delay().
- Board not recognized -- Make sure you have the Arduino SAMD Boards core installed via the Boards Manager.
Platform Support
Built on Arduino standard APIs - runs on every Arduino-compatible platform (architectures=*).