Arduino UNO Q - 74HC595 4-Digit 7-Segment Display
Want to display numbers on a compact 4-digit LED display using your Arduino UNO Q? This beginner-friendly tutorial shows you how to use a 74HC595 4-digit 7-segment display with Arduino UNO Q — step by step.
In this tutorial, you will learn:
- What a 74HC595 4-digit 7-segment display is and how it works
- How to wire the 74HC595 display to Arduino UNO Q
- How to program the MCU (C/C++ Arduino code) to show integers, floats, and count values
- How to program both the Linux side (Python) and MCU side (C/C++) to control the display remotely via Bridge
- How to send Telegram messages to Arduino UNO Q to update the 7-segment display
- How to use OpenClaw on Arduino UNO Q to control the 7-segment display
Hardware Preparation
Or you can buy the following kits:
| 1 | × | 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 .
Additionally, some of these links are for products from our own brand, DIYables .
Overview of the 74HC595 4-Digit 7-Segment Display
The 74HC595-based 4-digit 7-segment display combines four LED digit modules with a shift register, so you only need 3 MCU pins to control all four digits.
Key specs and features:
- Digits: 4 digits, each with 7 LED segments + decimal point
- Shift register: 74HC595 — data shifted in serially using 3 wires
- Interface: SPI-like (SCLK, RCLK, DIO) — simple and efficient
- Power: 3.3V or 5V compatible
- Library: DIYables_4Digit7Segment_74HC595 — supports integers, floats, text, temperature, and time display
- Multiplexing: The library handles digit multiplexing — call display.loop() frequently to keep the display refreshed
Pinout
| Pin | Function | Description |
|---|---|---|
| SCLK (SH_CP) | Serial Clock | Clock signal for shifting data |
| RCLK (ST_CP) | Register Clock | Latch to push data to outputs |
| DIO (DS) | Data Input | Serial data fed into the shift register |
| VCC | Power | 3.3V or 5V supply |
| GND | Ground | Common ground |
Wiring Diagram
Connect the 74HC595 4-digit 7-segment display to the Arduino UNO Q MCU as shown:
This image is created using Fritzing. Click to enlarge image
| 74HC595 Display Pin | Arduino UNO Q MCU Pin | Description |
|---|---|---|
| SCLK | D7 | Serial clock |
| RCLK | D6 | Register clock / latch |
| DIO | D5 | Data input |
| VCC | 5V | Power supply |
| GND | GND | Ground |
Arduino UNO Q Code
The Arduino UNO Q has two processors working together:
- The STM32 MCU drives the 74HC595 7-segment display directly via digital pins — it handles all multiplexing
- The Qualcomm MPU runs Debian Linux and handles Wi-Fi, Python, and cloud connectivity
- In this section, only the MCU is programmed — the Linux side stays idle. A later section shows how both processors work together via Bridge.
The sketch below counts from 0 to 9999 on the 7-segment display, incrementing every second.
Important: Always call display.loop() inside the Arduino loop() function. The library uses this to multiplex through all 4 digits. Never use delay() directly — use display.delay() instead.
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-74hc595-4-digit-7-segment-display
*/
#include <DIYables_4Digit7Segment_74HC595.h>
#define SCLK_PIN 7 // MCU pin connected to SCLK of 74HC595 7-segment display
#define RCLK_PIN 6 // MCU pin connected to RCLK of 74HC595 7-segment display
#define DIO_PIN 5 // MCU pin connected to DIO of 74HC595 7-segment display
DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN);
int count = 0;
unsigned long lastUpdate = 0;
void setup() {
display.begin();
display.print(0);
}
void loop() {
display.loop(); // Must be called frequently to refresh the display
if (millis() - lastUpdate >= 1000) {
lastUpdate = millis();
count++;
if (count > 9999)
count = 0;
display.print(count);
}
}
Detailed Instructions
First time with Arduino UNO Q? Follow the Getting Started with Arduino UNO Q tutorial to get your development environment ready before proceeding.
- Connect: Wire the 74HC595 display to the Arduino UNO Q as shown, then plug in the USB-C cable.
- Open Arduino App Lab: Launch Arduino App Lab and wait until it detects your Arduino UNO Q — this can take several minutes on first launch.
- Create a new App: Click the Create New App button.
- Give the App a name, for example: DIYables_7Seg74HC595
- Click Create to confirm.
- You will see a set of folders and files generated inside your new App.
- Find the sketch/sketch.ino file — this is where you will paste the MCU sketch.
Paste the sketch: Copy the MCU code above and paste it into that sketch file. Keep other files as default.
- Install the library: Click the Add sketch library button (the open book icon with a + sign) in the left sidebar.
- Search for Arduino_RouterBridge created by Arduino and click the Install button.
Bricks
No bricks added...
Sketch Libraries
No sketch libra...
Files
python
sketch
.gitignore
README.md
app.yaml
sketch.ino
- Search for DIYables_4Digit7Segment_74HC595 created by DIYables.io and click the Install button.
Bricks
No bricks added...
Sketch Libraries
No sketch libra...
Files
python
sketch
.gitignore
README.md
app.yaml
sketch.ino
- Upload: Click the Run button in Arduino App Lab to compile and upload to the STM32.
Your 7-segment display will start counting from 0 to 9999, incrementing once per second!
- Pro Tip: If your display shows garbled characters, try passing false as the 4th constructor argument: DIYables_4Digit7Segment_74HC595 display(SCLK_PIN, RCLK_PIN, DIO_PIN, false) — this switches from common anode (default) to common cathode mode.
Bridge: Linux + MCU
This section shows how to program both processors of the Arduino UNO Q so the Linux side can control the 7-segment display remotely:
- The 74HC595 7-segment display is connected to the MCU (STM32) — the MCU drives all digit multiplexing
- The MPU cannot control the display directly — it must request the MCU to update values via Bridge.call()
- The MPU has Wi-Fi — running full Debian Linux, it can connect to the Internet and push display updates remotely
- Arduino_RouterBridge enables RPC communication between the two processors
- ⚠️ /dev/ttyHS1 (Linux) and Serial1 (MCU) are RESERVED by the router — never open them in user code
In short: MCU drives the 7-segment display → MPU sends values → MPU can update the display from anywhere over the Internet.
MCU Code (Bridge)
Note: In the Bridge sketch, display.loop() is called inside the Arduino loop() to keep the display refreshed — this is required for the multiplexed 7-segment display and does not interfere with Bridge communication.
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-74hc595-4-digit-7-segment-display
*/
#include "Arduino_RouterBridge.h"
#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);
String current_value = "";
void display_number(String text) {
int number = text.toInt();
current_value = text;
display.print(number);
Monitor.println("7SEG: " + text);
}
void display_float(String text) {
float value = text.toFloat();
current_value = text;
display.print(value, 1);
Monitor.println("7SEG float: " + text);
}
void clear_display() {
current_value = "";
display.print(0);
Monitor.println("7SEG cleared");
}
String get_status() {
if (current_value == "")
return "Display shows: 0";
return "Display shows: " + current_value;
}
void setup() {
Bridge.begin();
Monitor.begin(9600);
display.begin();
display.print(0);
Bridge.provide_safe("display_number", display_number);
Bridge.provide_safe("display_float", display_float);
Bridge.provide_safe("clear_display", clear_display);
Bridge.provide("get_status", get_status);
}
void loop() {
display.loop(); // Keep refreshing the 7-segment display
}
Python Code (Bridge)
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-74hc595-4-digit-7-segment-display
*/
from arduino.app_utils import *
import time
def loop():
result = Bridge.call("display_number", "1234")
print(result)
time.sleep(3)
result = Bridge.call("display_float", "26.5")
print(result)
time.sleep(3)
result = Bridge.call("display_number", "-42")
print(result)
time.sleep(3)
result = Bridge.call("clear_display")
print(result)
time.sleep(2)
result = Bridge.call("get_status")
print(result)
time.sleep(2)
App.run(user_loop=loop)
Detailed Instructions
- Connect: Wire the 74HC595 display to the Arduino UNO Q and plug in the USB-C cable.
- Open Arduino App Lab: Launch Arduino App Lab and wait for the board to be detected.
- Create a new App: Click Create New App, name it DIYables_7Seg74HC595Bridge, then click Create.
- Paste the MCU sketch: Copy the MCU Bridge code above and paste it into sketch/sketch.ino.
- Paste the Python code: Copy the Python Bridge code above and paste it into the Python file in the App.
- Upload: Click the Run button in Arduino App Lab.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] 7SEG: 1234
[2026-04-29 09:00:04] 7SEG float: 26.5
[2026-04-29 09:00:07] 7SEG: -42
[2026-04-29 09:00:09] 7SEG cleared
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] OK
[2026-04-29 09:00:04] OK
[2026-04-29 09:00:07] OK
[2026-04-29 09:00:09] OK
[2026-04-29 09:00:11] Display shows: 0
Telegram
Control the 74HC595 7-segment display from anywhere using Telegram. Send a number from your phone and the display updates instantly.
MCU sketch: Keep the same MCU sketch from the previous Bridge section.
Python Code (Telegram)
/*
* This Arduino UNO Q code was developed by newbiely.com
*
* This Arduino UNO Q code is made available for public use without any restriction
*
* For comprehensive instructions and wiring diagrams, please visit:
* https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-74hc595-4-digit-7-segment-display
*/
from arduino.app_utils import *
import requests
import time
TELEGRAM_TOKEN = "YOUR_TELEGRAM_BOT_TOKEN"
CHAT_ID = "YOUR_CHAT_ID"
last_update_id = 0
def get_updates():
global last_update_id
url = f"https://api.telegram.org/bot{TELEGRAM_TOKEN}/getUpdates"
params = {"offset": last_update_id + 1, "timeout": 5}
try:
response = requests.get(url, params=params, timeout=10)
data = response.json()
if data["ok"]:
return data["result"]
except Exception:
pass
return []
def send_message(text):
url = f"https://api.telegram.org/bot{TELEGRAM_TOKEN}/sendMessage"
requests.post(url, data={"chat_id": CHAT_ID, "text": text})
def loop():
global last_update_id
updates = get_updates()
for update in updates:
last_update_id = update["update_id"]
message = update.get("message", {})
text = message.get("text", "")
if text.startswith("/number "):
number = text[8:].strip()
result = Bridge.call("display_number", number)
send_message(result)
elif text.startswith("/float "):
value = text[7:].strip()
result = Bridge.call("display_float", value)
send_message(result)
elif text == "/clear":
result = Bridge.call("clear_display")
send_message(result)
elif text == "/status":
result = Bridge.call("get_status")
send_message(result)
elif text == "/start":
send_message("Commands:\n/number <value> - Show integer on display\n/float <value> - Show float on display\n/clear - Clear the display\n/status - Get current display value")
App.run(user_loop=loop)
Detailed Instructions
- Replace YOUR_TELEGRAM_BOT_TOKEN with your actual bot token from BotFather.
- Replace YOUR_CHAT_ID with your Telegram chat ID.
- Paste this Python code into your App's Python file (keep the same MCU sketch).
- Click the Run button. Open Telegram and send commands to your bot.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:15:00] Waiting for Telegram messages...
[2026-04-29 09:15:08] Received: /number 2025
[2026-04-29 09:15:22] Received: /float 23.4
[2026-04-29 09:15:40] Received: /status
Telegram
12:45
Welcome to Telegram!
ArduinoBot
10:19
Chatting with Arduino...
BotFather
Yesterday
Your bot has been created.
ArduinoBot
bot
OpenClaw
...OPENCLAW
OpenClaw support for Arduino UNO Q 74HC595 4-Digit 7-Segment Display is coming soon.
...OPENCLAW
Project Ideas
You can build many useful projects using a 74HC595 7-segment display with Arduino UNO Q:
- Remote Counter: Send a count value to the display via Telegram — useful for production counters or event tallies
- Live Temperature Display: Fetch temperature from a sensor on the MCU and show it on the 7-segment via Bridge
- Countdown Timer: Python sends a start value via Bridge, and the MCU counts down to zero on the display
- Internet Clock: Python fetches the current time via NTP and sends it to the MCU to display in HH.MM format
- Score Display: Use Telegram to update a live score on the 7-segment display for games or contests
Challenge Yourself
Ready to go further with the 74HC595 7-segment display on Arduino UNO Q? Try these challenges:
- Easy: Modify the MCU sketch to display 88.88 on startup, using the float display method with a decimal point.
- Medium: Use the Bridge to implement a /count <start> <end> Telegram command that makes the display count from <start> to <end> at 1-second intervals.
- Advanced: Build a Telegram-controlled stopwatch: /start begins counting up in seconds on the display, /stop freezes it, and /reset clears it back to zero.