Arduino UNO Q - Motion Sensor - LED
In this guide, you will learn how to use an HC-SR501 motion sensor to automatically turn an LED on when motion is detected and off when motion stops, using Arduino UNO Q.
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 .
Buy Note: Use the LED Module for easier wiring. It includes an integrated resistor.
Overview of Motion Sensor and LED
Learn about the motion sensor and LED in the tutorials below:
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
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.
/*
* 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-motion-sensor-led
*/
#define MOTION_SENSOR_PIN 7 // The Arduino UNO Q pin connected to the OUTPUT pin of the motion sensor
#define LED_PIN 3 // The Arduino UNO Q pin connected to the LED
int motion_state = LOW;
int motion_state_prev = LOW;
void setup() {
pinMode(MOTION_SENSOR_PIN, INPUT);
pinMode(LED_PIN, OUTPUT);
}
void loop() {
motion_state_prev = motion_state;
motion_state = digitalRead(MOTION_SENSOR_PIN);
if (motion_state_prev == LOW && motion_state == HIGH) {
// Motion detected
digitalWrite(LED_PIN, HIGH); // turn LED on
} else if (motion_state_prev == HIGH && motion_state == LOW) {
// Motion stopped
digitalWrite(LED_PIN, LOW); // turn 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 sensor OUTPUT → pin 7, LED (with 220Ω resistor) → pin 3.
- 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_MotionLED
- 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.
- 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
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Sketch Libraries
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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.
- Test: Walk in front of the sensor — the LED should turn on when motion is detected and off when motion stops.
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 motion sensor and LED are both connected to the MCU (STM32) — sensor on pin 7, LED on pin 3.
- The MPU cannot control them directly — it calls Bridge.call("check_motion") on the MCU, which reads the sensor and updates the LED accordingly.
- The MPU has Wi-Fi — because the MPU runs full Debian Linux with Wi-Fi, it can forward motion events to Telegram.
- Communication: Bridge.call() on the Linux side invokes Bridge.provide_safe() on the MCU side (since digitalWrite() is used to control the LED)
- ⚠️ Reserved: /dev/ttyHS1 (Linux) and Serial1 (MCU) are used by the Arduino Router — never open them directly
In short: MPU polls sensor → MCU reads pin, updates LED, and reports to Monitor.
MCU sketch — motion sensor controls LED with 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-motion-sensor-led
*/
#include "Arduino_RouterBridge.h"
#define MOTION_SENSOR_PIN 7
#define LED_PIN 3
int motion_state = LOW;
int motion_state_prev = LOW;
void check_motion() {
motion_state_prev = motion_state;
motion_state = digitalRead(MOTION_SENSOR_PIN);
if (motion_state_prev == LOW && motion_state == HIGH) {
digitalWrite(LED_PIN, HIGH);
Monitor.println("Motion detected! LED ON");
} else if (motion_state_prev == HIGH && motion_state == LOW) {
digitalWrite(LED_PIN, LOW);
Monitor.println("Motion stopped! LED OFF");
} else {
Monitor.println(motion_state == HIGH ? "Motion: ACTIVE | LED: ON" : "Motion: none | LED: OFF");
}
}
void setup() {
Bridge.begin();
Monitor.begin();
pinMode(MOTION_SENSOR_PIN, INPUT);
pinMode(LED_PIN, OUTPUT);
Bridge.provide_safe("check_motion", check_motion);
Monitor.println("Motion Sensor LED Bridge ready");
}
void loop() {}
Python script (Arduino App Lab) — poll motion state every 0.5 seconds:
/*
* 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-motion-sensor-led
*/
from arduino.app_utils import *
import time
def loop():
Bridge.call("check_motion")
time.sleep(0.5)
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 into sketch/sketch.ino, install the Arduino_RouterBridge library, 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 — Python polls motion every 0.5 seconds; MCU updates the LED and Monitor.
- Check the console: Open the Console tab → MCU Monitor subtab and walk in front of the sensor.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
Motion Sensor LED Bridge ready
Motion detected! LED ON
Motion stopped! LED OFF
Motion detected! LED ON
Motion stopped! LED OFF
Telegram Integration
Control and monitor the motion-activated LED remotely 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 motion-activated LED:
/*
* 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-motion-sensor-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 == "/status":
status = Bridge.call("check_motion")
send_message(chat_id, status if status else "No motion state change since last check.")
else:
send_message(chat_id, "Commands:\n/status — check motion state and update LED")
time.sleep(0.5)
App.run(user_loop=loop)
- Note: Replace YOUR_BOT_TOKEN with the token obtained from @BotFather on Telegram.
- Send /status to manually check the motion sensor and update the LED.
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: Send /status — the bot replies with the motion state and LED state.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 12:00:01] Telegram: /status
[2026-04-29 12:00:01] Motion: none | LED: OFF
[2026-04-29 12:01:30] Telegram: /status
[2026-04-29 12:01:30] Motion detected! LED ON
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 motion sensor with LED is coming soon.
- Coming Soon: OpenClaw support for this project on Arduino UNO Q will be covered in a future update.
Application/Project Ideas
- Automatic room light: Turn room lights on when someone enters and off when they leave
- Staircase lighting: Light up stairs when someone approaches
- Night-mode light: Only activate the LED when it's dark AND motion is detected (combine with LDR)
- Security indicator: Flash the LED rapidly when motion is detected at night
Challenge Yourself
- Easy: Add a second LED that blinks while motion is ongoing
- Medium: Keep the LED on for 10 seconds after motion stops before turning it off
- Advanced: Send a Telegram notification automatically whenever motion is detected (no /status needed)