Arduino UNO Q - Button - LED
This tutorial shows how to use a button to control an LED with Arduino UNO Q. Two applications are covered:
Application 1 — LED follows button state:
- LED turns ON when the button is pressed
- LED turns OFF when the button is released
Application 2 — LED toggles on each press:
- Each button press flips the LED between ON and OFF
- Releasing the button does not change the LED state
- Includes debounce-free and debounced versions (using ezButton)
Hardware Preparation
Or you can buy the following kits:
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
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Additionally, some of these links are for products from our own brand, DIYables .
Buy Note: Use the LED Module for easier wiring. It includes an integrated resistor.
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
Application 1 — LED Follows Button State
MCU Code
The Arduino UNO Q has two processors: the STM32 MCU (handles real-time hardware control) and the Qualcomm MPU (runs Debian Linux). In this section, only the STM32 MCU is programmed — the Linux side stays idle. A later section will show how both processors work together.
When the button is pressed (LOW), the LED turns ON. When released (HIGH), the LED turns OFF:
/*
* 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-button-led
*/
#define BUTTON_PIN 7 // pin connected to the button
#define LED_PIN 3 // pin connected to the LED
void setup() {
pinMode(BUTTON_PIN, INPUT_PULLUP); // set pin to input pull-up mode
pinMode(LED_PIN, OUTPUT); // set pin to output mode
}
void loop() {
int buttonState = digitalRead(BUTTON_PIN); // read button state
if (buttonState == LOW) {
digitalWrite(LED_PIN, HIGH); // button pressed → LED on
} else {
digitalWrite(LED_PIN, LOW); // button released → LED off
}
}
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.
- Wire the components: Connect the button to pin 7 and the LED (with 220 Ω resistor) to pin 3 according to the wiring diagram.
- Connect: Plug the Arduino UNO Q into your computer with a USB-C cable.
- Open Arduino App Lab: Launch Arduino App Lab and wait until it detects your Arduino UNO Q.
- Create a new App: Click the Create New App button.
- Give the App a name, for example: DIYables_ButtonLED
- 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 the sketch file. Keep other files as default.
Upload: Click the Run button in Arduino App Lab to compile and upload to the STM32.
- Press and hold the button — the LED should turn ON. Release it — the LED should turn OFF.
Application 2 — LED Toggles on Each Button Press
MCU Code — Without Debounce
This version detects a HIGH→LOW transition and toggles the LED. Without debounce, rapid contact bouncing may cause multiple toggles per press:
/*
* 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-button-led
*/
#define BUTTON_PIN 7 // pin connected to the button
#define LED_PIN 3 // pin connected to the LED
int led_state = LOW;
int button_state;
int prev_button_state;
void setup() {
pinMode(BUTTON_PIN, INPUT_PULLUP); // set pin to input pull-up mode
pinMode(LED_PIN, OUTPUT); // set pin to output mode
button_state = digitalRead(BUTTON_PIN);
}
void loop() {
prev_button_state = button_state;
button_state = digitalRead(BUTTON_PIN); // read new state
if (prev_button_state == HIGH && button_state == LOW) {
// button just pressed — toggle LED
led_state = !led_state;
digitalWrite(LED_PIN, led_state);
}
}
Detailed Instructions
- Use the same wiring and App from Application 1.
- Replace the sketch with the code above and click Run.
- Press and release the button several times — the LED should toggle each time.
- You may notice erratic behavior (double-toggle) — this is caused by button bounce.
MCU Code — With Debounce (using ezButton)
The ezButton library handles debouncing automatically — each button press triggers exactly one isPressed() event:
/*
* 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-button-led
*/
#include <ezButton.h>
#define BUTTON_PIN 7 // pin connected to the button
#define LED_PIN 3 // pin connected to the LED
ezButton button(BUTTON_PIN); // create ezButton object attached to pin 7
int led_state = LOW;
void setup() {
pinMode(LED_PIN, OUTPUT);
button.setDebounceTime(50); // set debounce time to 50 milliseconds
}
void loop() {
button.loop(); // MUST call the loop() function first
if (button.isPressed()) {
// toggle LED state
led_state = !led_state;
digitalWrite(LED_PIN, led_state);
}
}
Detailed Instructions
- Use the same wiring and App from above.
- Replace the sketch with the debounced version and click Run.
- Install the library: Click the Add sketch library button (the open book icon with a + sign) in the left sidebar.
- Search for ezButton created by ArduinoGetStarted.com 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 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
- Press and release the button multiple times — the LED now toggles exactly once per press.
Linux + MCU Bridge Programming
The Arduino UNO Q has two processors that work together: the MPU (Qualcomm, runs Debian Linux) and the MCU (STM32, runs Zephyr OS with your Arduino sketch). They communicate using RPC via the Arduino_RouterBridge library — never via raw serial ports.
- The button and LED are connected to the MCU (STM32) — the button is wired to a digital input pin and the LED to a digital output pin on the STM32. The MCU handles the toggle logic and debounce using ezButton.
- The MPU cannot read the button or control the LED directly — it must request the LED state from the MCU via Bridge.call().
- The MPU has Wi-Fi — because the MPU runs full Debian Linux with Wi-Fi, it can report the LED state via Telegram on demand.
- Communication: Bridge.call() on the Linux side invokes Bridge.provide() functions on the MCU side
- ⚠️ Reserved: /dev/ttyHS1 (Linux) and Serial1 (MCU) are used by the Arduino Router — never open them directly
In short: MPU requests LED state → MCU reads current state → MCU reports ON or OFF → MPU logs or forwards it.
MCU sketch — button-LED toggle with Bridge and Monitor output:
/*
* 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-button-led
*/
#include "Arduino_RouterBridge.h"
#include <ezButton.h>
#define BUTTON_PIN 7
#define LED_PIN 3
ezButton button(BUTTON_PIN);
int led_state = LOW;
void get_led_state() {
Monitor.println(led_state == HIGH ? "LED: ON" : "LED: OFF");
}
void setup() {
pinMode(LED_PIN, OUTPUT);
button.setDebounceTime(50);
Bridge.begin();
Monitor.begin();
Bridge.provide("get_led_state", get_led_state);
Monitor.println("Button-LED Bridge ready");
}
void loop() {
button.loop();
if (button.isPressed()) {
led_state = !led_state;
digitalWrite(LED_PIN, led_state);
Monitor.println(led_state == HIGH ? "Button pressed → LED ON" : "Button pressed → LED OFF");
}
}
Python script (Arduino App Lab) — poll LED state from Linux:
"""
This Arduino UNO Q script was developed by newbiely.com
This Arduino UNO Q script 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-button-led
"""
from arduino.app_utils import *
import time
def loop():
while True:
state = Bridge.call("get_led_state")
print(f"LED state: {state}")
time.sleep(3)
App.run(user_loop=loop)
- Note: Make sure Bridge.begin() is called in the MCU sketch and the sketch is uploaded before running the Python script on the Linux side.
- ⚠️ Warning: Never directly open /dev/ttyHS1 (on Linux) or use Serial1 (on MCU) in your code — these are reserved by the Arduino Router and accessing them will break the Bridge.
Detailed Instructions
- Upload the MCU sketch: Open Arduino App Lab, create a new App, paste the Bridge MCU sketch above into sketch/sketch.ino, install the ezButton and Arduino_RouterBridge libraries, and click Run.
- Add the Python script: Paste the Python code above into the Python tab of the same App.
- Run the App: Click Run — the Python side polls the LED state every 3 seconds.
- Press the button multiple times to toggle the LED.
- Check the console: Open the Console tab → MCU Monitor subtab to see toggle events logged in real time.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
Button-LED Bridge ready
Button pressed → LED ON
Button pressed → LED OFF
Button pressed → LED ON
Telegram Integration
Check the current LED state remotely from anywhere via Telegram.
If you do not have a Telegram bot yet, see How to Create a Telegram Bot to get your bot token before continuing.
MCU sketch: Keep the same MCU sketch from the previous Bridge section — no changes needed. Make sure it is already uploaded and running on the STM32 before proceeding.
Python script (Arduino App Lab) — Telegram bot for LED state:
"""
This Arduino UNO Q script was developed by newbiely.com
This Arduino UNO Q script 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-button-led
"""
from arduino.app_utils import *
import requests
import time
BOT_TOKEN = "YOUR_BOT_TOKEN"
API_URL = f"https://api.telegram.org/bot{BOT_TOKEN}"
last_update_id = 0
def send_message(chat_id, text):
requests.post(f"{API_URL}/sendMessage", json={"chat_id": chat_id, "text": text})
def get_updates():
global last_update_id
resp = requests.get(f"{API_URL}/getUpdates", params={"offset": last_update_id + 1, "timeout": 5})
return resp.json().get("result", [])
def loop():
global last_update_id
updates = get_updates()
for update in updates:
last_update_id = update["update_id"]
msg = update.get("message", {})
chat_id = msg.get("chat", {}).get("id")
text = msg.get("text", "").strip()
if text == "/state":
state = Bridge.call("get_led_state")
send_message(chat_id, f"LED is currently: {state}")
else:
send_message(chat_id, "Commands:\n/state — check current LED state (ON or OFF)")
time.sleep(1)
App.run(user_loop=loop)
- Note: Replace YOUR_BOT_TOKEN with the token obtained from @BotFather on Telegram.
- Send /state to check whether the LED is currently ON or OFF.
Detailed Instructions
- Upload the MCU sketch: Use the Bridge MCU sketch from the previous section (upload it first if not already done).
- Paste the Telegram script: Copy the Python code above into the Python tab of your App in Arduino App Lab.
- Set your token: Replace YOUR_BOT_TOKEN in the script with your actual bot token.
- Run the App: Click Run — the bot starts listening for Telegram messages.
- Test it: Press the button to toggle the LED, then send /state — confirm the state matches.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 12:00:01] Telegram: /state
[2026-04-29 12:00:01] LED is currently: ON
[2026-04-29 12:03:20] Telegram: /state
[2026-04-29 12:03:20] LED is currently: OFF
Telegram
12:45
Welcome to Telegram!
ArduinoBot
10:19
Chatting with Arduino...
BotFather
Yesterday
Your bot has been created.
ArduinoBot
bot
OpenClaw Integration
OpenClaw integration for Arduino UNO Q button-LED control is coming soon.
- Coming Soon: OpenClaw support for button-LED interaction on Arduino UNO Q will be covered in a future update.
Application/Project Ideas
- Telegram LED monitor: Press a physical button to toggle a lamp and check its state remotely via Telegram
- Physical alarm toggle: Use a button to arm/disarm an alarm and confirm state from anywhere
- Presentation controller: Toggle a display or notification light with a button while checking state remotely
- Night mode switch: Press a button to toggle night mode on devices; monitor via Telegram
- Access confirmation: Press a button to confirm entry; check LED/gate state via Telegram
Challenge Yourself
- Easy: Add a second LED that turns OFF when the first LED turns ON (alternating LEDs)
- Medium: Extend the Bridge sketch to count total button presses and expose the count as get_press_count()
- Advanced: Build a Telegram bot that automatically sends a notification each time the LED state changes — use a monitoring loop in Python that polls state and compares to previous value