Arduino UNO Q - Motion Sensor - Relay
In this guide, you will learn how to use an HC-SR501 motion sensor to automatically activate a relay when motion is detected and deactivate it when motion stops, using Arduino UNO Q.
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 .
Additionally, some of these links are for products from our own brand, DIYables .
Overview of Motion Sensor and Relay
Learn about the motion sensor and relay 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-relay
*/
#define MOTION_SENSOR_PIN 7 // The Arduino UNO Q pin connected to the OUTPUT pin of the motion sensor
#define RELAY_PIN 9 // The Arduino UNO Q pin connected to the IN pin of the relay
int motion_state = LOW;
int motion_state_prev = LOW;
void setup() {
pinMode(MOTION_SENSOR_PIN, INPUT);
pinMode(RELAY_PIN, OUTPUT);
digitalWrite(RELAY_PIN, LOW); // relay off initially
}
void loop() {
motion_state_prev = motion_state;
motion_state = digitalRead(MOTION_SENSOR_PIN);
if (motion_state_prev == LOW && motion_state == HIGH) {
// Motion detected
digitalWrite(RELAY_PIN, HIGH); // turn relay on
} else if (motion_state_prev == HIGH && motion_state == LOW) {
// Motion stopped
digitalWrite(RELAY_PIN, LOW); // turn relay 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, relay IN → pin 9.
- 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_MotionRelay
- 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
No bricks added...
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 relay should activate when motion is detected and deactivate 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 relay are both connected to the MCU (STM32) — sensor on pin 7, relay on pin 9.
- The MPU cannot control them directly — it calls Bridge.call("check_motion") on the MCU, which reads the sensor and updates the relay accordingly.
- The MPU has Wi-Fi — because the MPU runs full Debian Linux with Wi-Fi, it can forward relay status to Telegram.
- Communication: Bridge.call() on the Linux side invokes Bridge.provide_safe() on the MCU side (since digitalWrite() is used to control the relay)
- ⚠️ 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 relay, and reports to Monitor.
MCU sketch — motion sensor controls relay 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-relay
*/
#include "Arduino_RouterBridge.h"
#define MOTION_SENSOR_PIN 7
#define RELAY_PIN 9
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(RELAY_PIN, HIGH);
Monitor.println("Motion detected! Relay ON");
} else if (motion_state_prev == HIGH && motion_state == LOW) {
digitalWrite(RELAY_PIN, LOW);
Monitor.println("Motion stopped! Relay OFF");
} else {
Monitor.println(motion_state == HIGH ? "Motion: ACTIVE | Relay: ON" : "Motion: none | Relay: OFF");
}
}
void setup() {
Bridge.begin();
Monitor.begin();
pinMode(MOTION_SENSOR_PIN, INPUT);
pinMode(RELAY_PIN, OUTPUT);
digitalWrite(RELAY_PIN, LOW);
Bridge.provide_safe("check_motion", check_motion);
Monitor.println("Motion Sensor Relay 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-relay
*/
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 relay 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 Relay Bridge ready
Motion detected! Relay ON
Motion stopped! Relay OFF
Motion detected! Relay ON
Motion stopped! Relay OFF
Telegram Integration
Monitor motion-activated relay state 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 relay:
/*
* 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-relay
*/
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 relay")
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 relay.
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 relay 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 | Relay: OFF
[2026-04-29 12:01:30] Telegram: /status
[2026-04-29 12:01:30] Motion detected! Relay 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 relay 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 appliance control: Turn a fan, heater, or light on when someone enters the room
- Security system: Activate a siren relay when motion is detected at night
- Smart door unlock: Trigger an electromagnetic lock relay when someone approaches
- Energy management: Automatically power down equipment when no motion is detected for an extended period
Challenge Yourself
- Easy: Add a buzzer to sound when the relay turns on
- Medium: Keep the relay on for 30 seconds after motion stops before turning it off
- Advanced: Send a Telegram notification automatically whenever the relay activates