Arduino UNO Q - Rain Sensor
A rain sensor can detect rain or snow and measure rainfall intensity. It provides both a digital output (rain/no rain) and an analog output (intensity level). On Arduino UNO Q, the MCU's 12-bit ADC gives higher resolution intensity readings. With Bridge and Telegram, you get instant rain alerts on your phone.
In this tutorial, you will learn:
- What a rain sensor is and how it works
- How to wire the rain sensor to the Arduino UNO Q MCU
- How to read both the digital (DO) and analog (AO) outputs
- How to use Bridge to expose rain state and events to the Linux side (Python)
- How to receive Telegram alerts when rain is detected on Arduino UNO Q
- How to use OpenClaw on Arduino UNO Q with the rain sensor
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 the Rain Sensor
The rain sensor has two parts: a sensing pad and an electronic module.
Sensing pad: Placed outdoors (on a roof or window ledge). Has alternating power and sensor copper lines — water bridges these lines when rain falls.
Electronic module: Converts the pad signal into readable outputs:
- VCC pin: 3.3V to 5V power supply
- GND pin: Ground
- DO pin: Digital output — HIGH = no rain, LOW = rain detected. Sensitivity set by onboard potentiometer.
- AO pin: Analog output — lower value = more rain, higher value = less rain. Potentiometer does NOT affect AO.
It also has two LEDs:
- PWR-LED: Power indicator
- DO-LED: Lights up when rain is detected (DO pin LOW)
How It Works
- DO pin: The potentiometer sets a threshold. If rain exceeds the threshold, DO goes LOW. Adjust the potentiometer to set sensitivity.
- AO pin: Continuously outputs an analog voltage proportional to the water on the pad. On Arduino UNO Q the MCU reads this as a 12-bit value (0–4095) — lower values mean more rain.
※ NOTE THAT:
Connect VCC to a digital output pin (not always-on 5V) and power the sensor only during readings. This reduces electrochemical corrosion and extends sensor lifetime.
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
| Rain Sensor Pin | Arduino UNO Q MCU |
|---|---|
| GND | GND |
| VCC | D3 (controlled power) |
| DO | D4 |
| AO | A0 |
How To Program For Rain Sensor
- Set up pins:
pinMode(POWER_PIN, OUTPUT);
pinMode(DO_PIN, INPUT);
- Power sensor, read both outputs, then power off:
digitalWrite(POWER_PIN, HIGH); // power on
delay(10); // stabilize
int do_state = digitalRead(DO_PIN); // HIGH = no rain, LOW = rain
int ao_value = analogRead(AO_PIN); // 0-4095, lower = more rain
digitalWrite(POWER_PIN, LOW); // power off
- Check rain from digital output:
if (do_state == LOW) {
Serial.println("Rain DETECTED");
} else {
Serial.println("No rain");
}
Arduino UNO Q Code
The Arduino UNO Q has two processors working together:
- The STM32 MCU reads both DO (digital) and AO (analog) outputs from the rain sensor every second
- 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.
※ NOTE THAT:
The Arduino UNO Q MCU uses a 12-bit ADC (0–4095). The AO intensity values will be in this range — adjust detection thresholds accordingly.
/*
* 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-rain-sensor
*/
// COPYRIGHT newbiely.com
// AUTHOR: newbiely
// This code is made available for public use without restriction.
// For complete instructions, tutorials, and further information, visit:
// https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-rain-sensor
// Rain sensor has two outputs:
// DO: digital — HIGH = no rain, LOW = rain detected
// AO: analog — lower value = more rain (12-bit ADC: 0-4095)
// POWER_PIN: power sensor only when reading to reduce corrosion
#define POWER_PIN 3 // The Arduino UNO Q MCU pin providing power to the rain sensor
#define DO_PIN 4 // The Arduino UNO Q MCU pin connected to DO of the rain sensor
#define AO_PIN A0 // The Arduino UNO Q MCU pin connected to AO of the rain sensor
void setup() {
Serial.begin(9600);
pinMode(POWER_PIN, OUTPUT);
pinMode(DO_PIN, INPUT);
digitalWrite(POWER_PIN, LOW); // start with sensor powered off
Serial.println("Arduino UNO Q Rain Sensor ready");
}
void loop() {
digitalWrite(POWER_PIN, HIGH); // power the sensor
delay(10); // allow sensor to stabilize
int do_state = digitalRead(DO_PIN); // HIGH = no rain, LOW = rain
int ao_value = analogRead(AO_PIN); // 0-4095: lower = more rain
digitalWrite(POWER_PIN, LOW); // power off sensor
// Digital output
if (do_state == LOW) {
Serial.print("Rain DETECTED | ");
} else {
Serial.print("No rain | ");
}
// Analog output
Serial.print("Intensity (AO): ");
Serial.println(ao_value);
delay(1000);
}
Detailed Instructions
First time with Arduino UNO Q? Follow the Getting Started with Arduino UNO Q tutorial before proceeding.
- Connect: Wire the rain sensor to the Arduino UNO Q MCU as shown in the wiring diagram.
- 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: RainSensor
- Click Create to confirm.
- Paste the sketch: Copy the MCU code above and paste it into sketch/sketch.ino. Keep other files as default.
- No library required — uses only the built-in digitalRead() and analogRead().
- Upload: Click the Run button in Arduino App Lab.
- Place a few drops of water on the sensing pad and observe the output in the Serial Monitor.
- Adjust the potentiometer on the module if the DO LED does not respond correctly.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] Arduino UNO Q Rain Sensor ready
[2026-04-29 09:00:02] No rain | Intensity (AO): 4090
[2026-04-29 09:00:03] No rain | Intensity (AO): 4088
[2026-04-29 09:00:04] Rain DETECTED | Intensity (AO): 1243
[2026-04-29 09:00:05] Rain DETECTED | Intensity (AO): 876
[2026-04-29 09:00:06] Rain DETECTED | Intensity (AO): 512
[2026-04-29 09:00:07] No rain | Intensity (AO): 3950
Bridge: Linux + MCU
This section shows how to program both processors of the Arduino UNO Q so the Linux side can read rain state and receive rain start events via Bridge:
- The rain sensor is connected to the MCU — the MCU reads DO and AO every second and caches the values
- The MPU cannot read the sensor pins directly — it calls Bridge functions to get state, analog value, or events
- The MPU has Wi-Fi — running full Debian Linux, it can send Telegram alerts the moment rain is detected
- 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 detects rain via DO pin → sets event flag → MPU polls Bridge → MPU sends Telegram alert.
MCU 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-rain-sensor
*/
// COPYRIGHT newbiely.com
// AUTHOR: newbiely
// This code is made available for public use without restriction.
// For complete instructions, tutorials, and further information, visit:
// https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-rain-sensor
#include "Arduino_RouterBridge.h"
#define POWER_PIN 3 // The Arduino UNO Q MCU pin providing power to the rain sensor
#define DO_PIN 4 // The Arduino UNO Q MCU pin connected to DO of the rain sensor
#define AO_PIN A0 // The Arduino UNO Q MCU pin connected to AO of the rain sensor
// Cache
int cached_ao = 4095; // start at max (dry)
bool cached_rain = false; // from DO pin
bool rain_event = false;
bool prev_rain = false;
unsigned long last_read_ms = 0;
const unsigned long READ_INTERVAL = 1000;
String get_state(String arg) {
return cached_rain ? "rain" : "no_rain";
}
String get_value(String arg) {
return String(cached_ao);
}
String get_event(String arg) {
if (rain_event) {
rain_event = false;
return "rain_detected";
}
return "none";
}
void setup() {
Bridge.begin();
Monitor.begin();
pinMode(POWER_PIN, OUTPUT);
pinMode(DO_PIN, INPUT);
digitalWrite(POWER_PIN, LOW);
Bridge.provide("get_state", get_state);
Bridge.provide("get_value", get_value);
Bridge.provide("get_event", get_event);
Monitor.println("Arduino UNO Q Rain Sensor Bridge ready");
}
void loop() {
unsigned long now = millis();
if (now - last_read_ms >= READ_INTERVAL) {
last_read_ms = now;
digitalWrite(POWER_PIN, HIGH);
delay(10);
int do_state = digitalRead(DO_PIN);
cached_ao = analogRead(AO_PIN);
digitalWrite(POWER_PIN, LOW);
cached_rain = (do_state == LOW); // LOW = rain detected
if (cached_rain && !prev_rain) {
rain_event = true;
Monitor.print("Rain detected! AO value: ");
Monitor.println(cached_ao);
} else if (!cached_rain && prev_rain) {
Monitor.println("Rain stopped.");
}
prev_rain = cached_rain;
}
}
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-rain-sensor
*/
# COPYRIGHT newbiely.com
# AUTHOR: newbiely
# This code is made available for public use without restriction.
# For complete instructions, tutorials, and further information, visit:
# https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-rain-sensor
from arduino.app_utils import *
import time
def loop():
state = Bridge.call("get_state")
value = Bridge.call("get_value")
print(f"Rain state: {state} AO value: {value}")
time.sleep(1)
App.run(user_loop=loop)
Detailed Instructions
- Connect: Wire the rain sensor to the Arduino UNO Q as shown in the wiring diagram.
- 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 RainSensorBridge, 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.
- 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
- Upload: Click the Run button in Arduino App Lab.
- Add water to the sensor pad — observe rain state change in both consoles.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] Arduino UNO Q Rain Sensor Bridge ready
[2026-04-29 09:00:05] Rain detected! AO value: 987
[2026-04-29 09:00:08] Rain stopped.
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:02] Rain state: no_rain AO value: 4090
[2026-04-29 09:00:05] Rain state: rain AO value: 987
[2026-04-29 09:00:08] Rain state: no_rain AO value: 4080
Telegram
Receive instant Telegram alerts when rain is detected on the Arduino UNO Q rain sensor.
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-rain-sensor
*/
# COPYRIGHT newbiely.com
# AUTHOR: newbiely
# This code is made available for public use without restriction.
# For complete instructions, tutorials, and further information, visit:
# https://newbiely.com/tutorials/arduino-uno-q/arduino-uno-q-rain-sensor
from arduino.app_utils import *
import requests
import time
TELEGRAM_BOT_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_BOT_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 as e:
print(f"Error getting updates: {e}")
return []
def send_message(chat_id, text):
url = f"https://api.telegram.org/bot{TELEGRAM_BOT_TOKEN}/sendMessage"
payload = {"chat_id": chat_id, "text": text}
try:
requests.post(url, data=payload, timeout=10)
except Exception as e:
print(f"Error sending message: {e}")
def loop():
# Auto-alert when rain starts
event = Bridge.call("get_event")
if event == "rain_detected":
value = Bridge.call("get_value")
print(f"Rain detected! AO value: {value}")
send_message(CHAT_ID, f"🌧️ Rain detected! Intensity (AO): {value}")
# Telegram commands
updates = get_updates()
for update in updates:
last_update_id = update["update_id"]
if "message" not in update:
continue
message = update["message"]
chat_id = message["chat"]["id"]
text = message.get("text", "").strip()
print(f"Received: {text}")
if text == "/start":
send_message(chat_id,
"Arduino UNO Q Rain Sensor Bot\n"
"/state - Rain detected or not (digital)\n"
"/value - Read analog intensity (0-4095)\n"
"Automatic alert when rain starts")
elif text == "/state":
result = Bridge.call("get_state")
send_message(chat_id, f"Rain state: {result}")
elif text == "/value":
result = Bridge.call("get_value")
send_message(chat_id, f"AO intensity value: {result}")
else:
send_message(chat_id, "Unknown command. Send /start for help.")
time.sleep(0.5)
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. Add drops of water to the sensor — receive the Telegram alert instantly.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:10:00] Waiting for Telegram messages...
[2026-04-29 09:10:05] Rain detected! AO value: 875
[2026-04-29 09:10:12] Received: /state
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 Rain Sensor is coming soon.
...OPENCLAW
Project Ideas
You can build many useful projects with the rain sensor and Arduino UNO Q:
- Rain Alert System: Mount the sensing pad on a rooftop — when rain starts, the MPU sends a Telegram alert with the AO intensity value, so you can take action (close windows, bring in laundry) from anywhere
- Automatic Awning Controller: Use the rain sensor with a motor/relay — when rain is detected, the MCU automatically closes an awning or blind via Bridge, and sends a Telegram notification
- Rainfall Logger: Log every rain detection event with timestamp and AO intensity to a CSV file on Linux — generate a daily rainfall summary and send it to Telegram at midnight
- Smart Irrigation Inhibitor: Combine with the pump tutorial — if rain is detected, Python skips the scheduled irrigation cycle to conserve water, and sends a Telegram message explaining why
- Rooftop Garden Monitor: Track rain intensity over time using AO values — Python calculates average rainfall every 15 minutes and sends a periodic Telegram summary
Challenge Yourself
Ready to go further with the rain sensor on Arduino UNO Q? Try these challenges:
- Easy: Classify AO intensity in Python: if int(value) > 3000 → "dry", > 1500 → "light rain", > 500 → "moderate rain", else "heavy rain" — include this label in every Telegram alert.
- Medium: Implement a rain duration tracker: record the start time when rain is detected and the end time when it stops — send a Telegram message when rain stops reporting how long it lasted.
- Advanced: Build a 24-hour rainfall chart: log AO values every minute to a list in Python — implement a /chart Telegram command that sends a text-based bar chart of rainfall intensity per hour over the last 24 hours.