SENSORS/ACTUATORS

INTERNET OF THING (IoT)

ESP32 UNO - 74HC595 4-Digit 7-Segment Display

Need a bright four-digit readout for your ESP32 Uno project? A 74HC595 4-digit 7-segment display gives you one with just three signal wires. Hook the shift register module to the ESP32 Uno form board, add the DIYables library in the Arduino IDE, and print counters, decimal values, short words, temperatures or a clock face.

By the end, you can:

Connect a 74HC595 shift register display to the ESP32 Uno with three GPIO pins.
Add the DIYables_4Digit7Segment_74HC595 library from the Arduino IDE Library Manager.
Print whole numbers and decimal numbers on the 7-segment LED display.
Show words, a degree sign and a temperature reading.
Make an HH.MM clock readout with a flashing middle dot.

ESP32 Uno 74HC595 4-digit 7-segment display

Components You Need

1	×	ESP32 Uno-form Board
1	×	USB Cable Type-A to Type-C (for USB-A PC)
1	×	USB Cable Type-C to Type-C (for USB-C PC)
1	×	74HC595 4-digit 7-segment Display
1	×	Jumper Wires

Or you can buy the following kits:

DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables .

Inside the 74HC595 4-Digit Display Module

After this part, you know what each of the five module pins does.

Item	Value
Digits	4, each with 7 segments and a decimal point
Total LEDs	32
Driver chip	74HC595 serial-in, parallel-out shift register
Signal pins used	3 (clock, latch, data)
Supply	3.3V or 5V
Refresh method	Multiplexing, done in software by the library

Only one digit glows at any instant. The library jumps from digit to digit many hundreds of times per second, so your eye sees a steady four-digit number. Your sketch sets the value with print(), and display.loop() keeps the scan running.

Pin Roles

Module Pin	Signal Name	Job
SCLK (SH_CP)	Shift clock	Each pulse pushes one data bit into the register
RCLK (ST_CP)	Latch clock	Moves the shifted bits to the outputs in one step
DIO (DS)	Serial data	Carries the bits, one per clock pulse
VCC	Supply	Accepts anything from 3.3V to 5V
GND	Ground	Shared ground with the board

ESP32 Uno Pinout

On the ESP32 Uno form board, every Uno header label has its own GPIO number, and the sketch needs that number. Look at the diagram to pair D5, D6 and D7 with their GPIOs before you wire.

How to Connect

After this part, the display module sits on three ESP32 Uno digital pins plus power.

The wiring diagram between ESP32 Uno 74HC595 4-digit 7-segment display

This image is created using Fritzing. Click to enlarge image

Display Pin	ESP32 Uno Pin
SCLK	D7 (GPIO14)
RCLK	D6 (GPIO27)
DIO	D5 (GPIO16)
VCC	5V
GND	GND

Good to know: D5, D6 and D7 are plain I/O pins on the ESP32 Uno. None of them is a boot strapping pin, so the board starts and uploads normally with the module plugged in.

※ NOTE THAT:

The three signal lines travel from the ESP32 Uno to the module, never back. So no 5V level ever lands on an ESP32 Uno pin, which matters because ESP32 Uno pins are NOT 5V tolerant. The board drives 3.3V logic. A 74HC595 on a 5V supply usually reads that fine, but if segments look scrambled, power the module from the 3V3 pin instead. It runs a bit dimmer there.

Add the Library in Arduino IDE

After this part, the IDE can compile every example on this page.

Plug in the board. Use a USB Type-C cable between the ESP32 Uno and your computer.
Pick the board. In the Arduino IDE, choose ESP32 Dev Module and the COM port of the board (CH340).
Go to the Library Manager. It is the Libraries button (book icon) in the sidebar.
Search. Enter "DIYables_4Digit7Segment_74HC595" and find the entry by DIYables.
Install. Press Install and choose version 2.0.0 or later.

Search for DIYables_4Digit7Segment_74HC595 created by DIYables.io and click the Install button.

Newbiely | Arduino IDE 2.3.8

──

☐

Library Manager

DIYables_4Digit7Segment_74HC595

All

DIYables_4Digit7Segment_74HC595 by DIYables.io

Supports integers, floats, text, degree symbol, temperature, time display, zero-padding, individual dot control. Common anode and common cathode. Works with all Arduino-compatible boards. More info

2.0.0

INSTALL

Newbiely.ino

···

1 void setup() {

Output

Serial Monitor

Ln 1, Col 1

ESP32 Dev Module on COM15

The package pulls in nothing else. It is built only on core Arduino calls.

Basic Sketch Skeleton

After this part, you can read any of the examples below at a glance.

#include <DIYables_4Digit7Segment_74HC595.h> #define SCLK_PIN 14 // D7 (GPIO14) #define RCLK_PIN 27 // D6 (GPIO27) #define DIO_PIN 16 // D5 (GPIO16) DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN); void setup() { display.begin(); display.print(1234); } void loop() { display.loop(); }

Code Part	What It Does
#define SCLK_PIN / RCLK_PIN / DIO_PIN	Sets the GPIO numbers of D7, D6 and D5
display(...)	Creates the display object with those three pins
display.begin()	Sets the pins as outputs, runs once
display.print(1234)	Stores the value to show
display.loop()	Lights the next digit, so it must run all the time

The number stays on screen until your sketch prints a new one. When you need a pause, call display.delay(ms) in place of delay(), so the digit scan never stops.

Show Whole Numbers

After this part, the display counts through a list of positive and negative values.

/* * This ESP32 Uno code was developed by newbiely.com * * This ESP32 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-uno/esp32-uno-74hc595-4-digit-7-segment-display */ #include <DIYables_4Digit7Segment_74HC595.h> // Pin setup - edit these GPIO numbers if you wire it differently #define SCLK_PIN 14 // D7 (GPIO14) goes to the shift clock (SH_CP) pin of the display #define RCLK_PIN 27 // D6 (GPIO27) goes to the latch / storage clock (ST_CP) pin of the display #define DIO_PIN 16 // D5 (GPIO16) goes to the serial data (DS) pin of the 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(); // keep this call fast and frequent so all 4 digits stay lit 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); // leading zeros give "0042" Serial.println("Displaying: 0042 (zero-padded)"); showZeroPad = false; } } }

A millis() timer swaps the value every 2 seconds without blocking. The list is 0, 42, 1234, -5, -123 and 9999, then the sketch shows 42 as 0042 with leading zeros and starts over.

Upload and Test

First time with this board? Set it up with ESP32 Uno - Getting Started before you continue.
Build the circuit by following the wiring table above.
Plug in the USB Type-C cable between the ESP32 Uno and your computer.
Select the board in Arduino IDE: pick ESP32 Dev Module and the COM port of the board (CH340).
Paste the sketch into a new Arduino IDE window.
Click Upload and wait for "Done uploading".
Open the Serial Monitor at 9600 baud and compare its lines with the digits.
Pro tip: the values -5 and -123 use the far-left digit for the minus sign, so the largest negative number that fits is -999.

Newbiely | Arduino IDE 2.3.8

──

☐

Newbiely.ino

···

8 Serial.println("Hello World!");

Output

Serial Monitor

Message (Enter to send message to 'ESP32 Dev Module' on 'COM15')

New Line

9600 baud

Displaying: -123 Displaying: 9999 Displaying: 0042 (zero-padded) Displaying: 0 Displaying: 42

Ln 11, Col 1

ESP32 Dev Module on COM15

Method Cheat Sheet

Method	Result	Example
print(int)	Shows a whole number from -999 to 9999	display.print(1234)
print(int, true)	Fills empty digits with zeros	display.print(42, true)
loop()	Runs one step of the digit scan	display.loop()
begin()	Prepares the three pins	display.begin()

Show Decimal Numbers

After this part, you see how the decimal point is placed for you or by your own choice.

/* * This ESP32 Uno code was developed by newbiely.com * * This ESP32 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-uno/esp32-uno-74hc595-4-digit-7-segment-display */ #include <DIYables_4Digit7Segment_74HC595.h> // Pin setup - edit these GPIO numbers if you wire it differently #define SCLK_PIN 14 // D7 (GPIO14) goes to the shift clock (SH_CP) pin of the display #define RCLK_PIN 27 // D6 (GPIO27) goes to the latch / storage clock (ST_CP) pin of the display #define DIO_PIN 16 // D5 (GPIO16) goes to the serial data (DS) pin of the 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() { // the library picks the decimal point position by itself display.print(1.5); // appears as " 1.5" Serial.println("Auto decimal: 1.5"); display.delay(2000); display.print(12.34); // appears as "12.34" Serial.println("Auto decimal: 12.34"); display.delay(2000); display.print(3.141); // appears as "3.141" Serial.println("Auto decimal: 3.141"); display.delay(2000); display.print(-1.2); // appears as "-1.20" Serial.println("Auto decimal: -1.20"); display.delay(2000); display.print(0.5); // appears as " 0.5" Serial.println("Auto decimal: 0.5"); display.delay(2000); // you choose how many digits follow the point display.print(23.5, 1); // one digit after the point -> "23.5" Serial.println("1 decimal place: 23.5"); display.delay(2000); display.print(1.5, 2); // two digits after the point -> "1.50" Serial.println("2 decimal places: 1.50"); display.delay(2000); // fill the empty left digits with zeros display.print(1.5, 2, true); // appears as "01.50" Serial.println("2 decimal places, zero-padded: 01.50"); display.delay(2000); }

Upload and Test

Paste the sketch into the Arduino IDE.
Press Upload and wait for the IDE to finish.
Open the Serial Monitor to see the name of each format.

Call	Display Shows
display.print(3.141)	3.141 (point placed automatically)
display.print(-1.2)	-1.20
display.print(23.5, 1)	23.5 (one fixed decimal)
display.print(1.5, 2)	1.50 (two fixed decimals)
display.print(1.5, 2, true)	01.50 (zero-padded)

This sketch uses display.delay(2000) between values, so the digits keep scanning during each 2-second wait.

Show Words and Temperature

After this part, the module prints short words and degree readings.

/* * This ESP32 Uno code was developed by newbiely.com * * This ESP32 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-uno/esp32-uno-74hc595-4-digit-7-segment-display */ #include <DIYables_4Digit7Segment_74HC595.h> // Pin setup - edit these GPIO numbers if you wire it differently #define SCLK_PIN 14 // D7 (GPIO14) goes to the shift clock (SH_CP) pin of the display #define RCLK_PIN 27 // D6 (GPIO27) goes to the latch / storage clock (ST_CP) pin of the display #define DIO_PIN 16 // D5 (GPIO16) goes to the serial data (DS) pin of the 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(); // keep this call fast and frequent so all 4 digits stay lit if (millis() - lastChange >= 2000) { lastChange = millis(); if (phase == 0) { // step through the short words one by one display.print(texts[currentIndex]); Serial.print("Text: "); Serial.println(texts[currentIndex]); currentIndex++; if (currentIndex >= textCount) { currentIndex = 0; phase = 1; } } else if (phase == 1) { // 25 with a degree sign and the letter C display.printTemperature(25, 'C'); Serial.println("Temperature: 25 C"); phase = 2; } else if (phase == 2) { // 72 with a degree sign and the letter F display.printTemperature(72, 'F'); Serial.println("Temperature: 72 F"); phase = 3; } else if (phase == 3) { // build the text by hand and put DEGREE_CHAR in the third slot 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 { // a dot after every digit display.print("1.2.3.4"); Serial.println("Dots: 1.2.3.4"); phase = 0; } } }

Upload and Test

Send the sketch to the board with the Upload button.
Check the Serial Monitor - each line names the item now on the digits.

Newbiely | Arduino IDE 2.3.8

──

☐

Newbiely.ino

···

8 Serial.println("Hello World!");

Output

Serial Monitor

Message (Enter to send message to 'ESP32 Dev Module' on 'COM15')

New Line

9600 baud

Text: COOL Text: done Temperature: 25 C Temperature: 72 F String with degree: 25 deg C

Ln 11, Col 1

ESP32 Dev Module on COM15

The order is "HELP", "Hi", "COOL", "done", then printTemperature(25, 'C') and printTemperature(72, 'F'). Next comes a hand-built string that places DEGREE_CHAR in slot three, and last "1.2.3.4" with a dot after each digit.

Good to know: seven segments cannot draw every letter well. Letters such as M, W and X look odd, so pick words like "HOLD", "Lo" or "End".

Show a Clock

After this part, the display reads 12.30 with a flashing middle dot.

Upload and Test

Flash this clock sketch onto your board.
Read the Serial Monitor - two start-up lines confirm the sketch runs.

Every 500 ms the sketch calls printTime(hours, minutes, colonOn) and flips colonOn, so the dot after the hour digits turns on and off once per second. To make a real clock, fill hours and minutes from internet time (NTP), which the ESP32 Uno can fetch over its own WiFi.

Flash the Display On and Off

After this part, three different values flash in turn.

/* * This ESP32 Uno code was developed by newbiely.com * * This ESP32 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-uno/esp32-uno-74hc595-4-digit-7-segment-display */ #include <DIYables_4Digit7Segment_74HC595.h> // Pin setup - edit these GPIO numbers if you wire it differently #define SCLK_PIN 14 // D7 (GPIO14) goes to the shift clock (SH_CP) pin of the display #define RCLK_PIN 27 // D6 (GPIO27) goes to the latch / storage clock (ST_CP) pin of the display #define DIO_PIN 16 // D5 (GPIO16) goes to the serial data (DS) pin of the display DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN); // phase 0 blinks a whole number, 1 a decimal number, 2 a word 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(); // keep this call fast and frequent so all 4 digits stay lit unsigned long now = millis(); // short rest before the next value starts blinking 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; } } } } }

Upload and Test

Load the blink sketch onto your board.
Watch the Serial Monitor - it names the value that flashes now.

The module flashes 1234 five times, rests for 1 second, flashes 12.34, rests again, then flashes "HELP" and loops. The 300 in the code is the on/off step in milliseconds.

Method Cheat Sheet

Method	Result	Example
off()	Blanks all digits	display.off()
on()	Brings the digits back	display.on()
delay(ms)	Waits while the scan keeps going	display.delay(2000)
yield()	Runs one scan step inside a long loop	display.yield()

ESP32 Uno vs UNO R4 for This Project

This table lists what changes when you move this display project from the UNO R4 to the ESP32 Uno.

Item	Arduino UNO R4	ESP32 Uno
Logic voltage	5V	3.3V
SCLK pin in code	7 (D7)	14 (D7)
RCLK pin in code	6 (D6)	27 (D6)
DIO pin in code	5 (D5)	16 (D5)
Library	DIYables_4Digit7Segment_74HC595	Same library, no change
Arduino IDE board	Arduino UNO R4 WiFi or Minima	ESP32 Dev Module
WiFi and Bluetooth	WiFi only on the R4 WiFi	WiFi plus Bluetooth Classic and BLE

The wires go to the same header holes, so the UNO R4 wiring works as-is. Only the three pin numbers in the sketch change. If the 5V-powered module shows wrong segments, run it from 3.3V.

Library Compatibility

The library is built on pinMode, digitalWrite and millis only. Those calls exist in the esp32 by Espressif Systems core, so the ESP32 Uno runs every example without changes beyond the pin numbers.

Go Wireless: Send a Number from Your Phone

With this idea, the four digits show whatever you type on your phone.

The ESP32 Uno has WiFi and Bluetooth on board. Open a chat page on your phone, type a value like "1234" or "Hi", and pass the received text to display.print(). You can also send each shown value back to a web monitor page to log it.

Troubleshooting

Problem	Possible Cause	Solution
No COM port shows in the Arduino IDE	CH340 driver missing or charge-only USB cable	Install the CH340 driver and use a USB cable that carries data
Upload stops at "Failed to connect" or "Waiting for download"	Board did not enter download mode	Hold the BOOT button while the upload starts, then let go
All digits stay dark	VCC or GND loose, or display.loop() is never called	Check the power wires and make sure loop() calls display.loop() every pass
Only one digit lights or digits look frozen	A blocking delay() stops the digit scan	Swap delay() for display.delay() or a millis() timer
Segments show nonsense patterns	Pin numbers in the sketch do not match the wires	Use 14 for SCLK, 27 for RCLK and 16 for DIO, or check the D7, D6 and D5 wires
Every segment is inverted	Module is common cathode, the default is common anode	Add false as the fourth constructor argument
Segments flicker randomly on a 5V supply	3.3V logic is borderline for the module	Move the VCC wire to 3V3
"DIYables_4Digit7Segment_74HC595.h No such file"	Library not installed	Install version 2.0.0 or later from the Library Manager

FAQ

How many digits and LEDs does this 74HC595 module drive?

It has four digits. Each digit has seven segments plus a decimal point, so 32 LEDs in total. A single 74HC595 chip and software multiplexing control all of them through three wires.

What is the biggest and smallest number the display can show?

Whole numbers go from -999 up to 9999. The minus sign takes one digit, so negative values have only three digits left. Decimals depend on how many digits sit before the point, for example 12.34 or 3.141.

Should I power the module from 5V or 3.3V on the ESP32 Uno?

Both supplies work. 5V gives brighter segments. 3.3V matches the ESP32 Uno logic level exactly and is the safe choice if segments look random. The signal wires are the same either way.

Do I need a level shifter between the ESP32 Uno and the display?

No. Data only flows from the ESP32 Uno into the module, so no 5V signal enters the board. A level shifter would only be needed if a 5V output had to drive an ESP32 Uno input.

How do I use a common cathode module with this library?

Add false as a fourth argument when you create the object, for example DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN, false);. The library treats the module as common anode by default.

Can I run two 74HC595 displays from one ESP32 Uno?

Yes. Create a second display object on three other free output pins, such as D2 (GPIO26), D3 (GPIO25) and D4 (GPIO17). Call loop() on both objects in your main loop.

Why does the code use 14, 27 and 16 and not 7, 6 and 5?

ESP32 Uno code uses GPIO numbers, not Uno header labels. D7 is GPIO14, D6 is GPIO27 and D5 is GPIO16. If you write 7, 6 and 5, the sketch drives the wrong pins and the display stays dark.

Can I wire the display to A2 to A5 on the ESP32 Uno?

No. A2 to A5 (GPIO35, 34, 36 and 39) are input only, and this module needs three output pins. Keep the wires on the digital header, like D5, D6 and D7 in this guide.

Does the board need a driver before Arduino IDE can see it?

The ESP32 Uno talks to your computer through a CH340 USB chip. Windows and macOS often need the CH340 driver once. After that, the board appears as a COM port.

What if my project needs more pins than the Uno headers give?

The ESP32 Uno has a few extra holes near the power header: GPIO32 and GPIO33 (I/O, PWM, analog on ADC1, so they also work while WiFi is on) and GPIO15 (I/O, PWM, analog on ADC2). To reach them, solder on a short header strip, then put the plain GPIO number in your sketch. For this display, GPIO32 and GPIO33 are good spare outputs, for example for a buzzer next to a timer readout. Two warnings: GPIO15 and GPIO0 (the IO0 pin at the unused Uno NC position) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code, so use GPIO32 and GPIO33 first. Never use the six holes under the digital header (SD0 to SD3, CMD and CLK, which are GPIO6 to GPIO11). They are wired to the flash chip, and using them crashes the board.

Can the ESP32 Uno show internet time on this display?

Yes. Connect the ESP32 Uno to WiFi, read the time from an NTP server, and pass the hours and minutes to printTime(). That turns the clock example into a real clock without an RTC module.

Learn More

ESP32 UNO - TM1637 4-Digit 7-Segment Display

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