Arduino UNO Q - DHT22 - LCD
Combine the DHT22 high-precision humidity and temperature sensor with a 16x2 I2C LCD on Arduino UNO Q. The DHT22 delivers better accuracy than the DHT11 — perfect for projects that require precise environment monitoring with a clear display.
In this tutorial, you will learn:
- What the DHT22 sensor is and how it compares to DHT11
- How to wire the DHT22 and 16x2 I2C LCD to the Arduino UNO Q MCU
- How to program the MCU (C/C++ Arduino code) to read DHT22 and display data on the LCD
- How to program both the Linux side (Python) and MCU side (C/C++) to read sensor data via Bridge
- How to receive Telegram alerts when temperature or humidity exceeds thresholds on Arduino UNO Q
- How to use OpenClaw on Arduino UNO Q with the DHT22 and LCD
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: Alternatively, you can assemble the LCD I2C display using LCD 1602 Display and PCF8574 I2C Adapter Module.
Overview of the DHT22 Sensor
Pinout
The DHT22 has four pins (when using the common 3-pin module):
- GND: Connect to GND
- VCC: Connect to 3.3V or 5V
- DATA: Connect to digital pin 2 on the Arduino UNO Q MCU
How It Works
The DHT22 uses a single-wire digital protocol to transmit humidity and temperature. It offers higher precision than the DHT11:
- Humidity: 0–100% RH (±2–5% accuracy)
- Temperature: -40–80°C (±0.5°C accuracy)
Allow at least 2–3 seconds between readings.
Overview of the LCD Display
The 16x2 I2C LCD connects via I2C and displays two rows of 16 characters. The top row shows temperature (°C and °F) and the bottom row shows humidity. Default I2C address: 0x27.
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
DHT22 to Arduino UNO Q MCU:
| DHT22 Pin | Arduino UNO Q MCU |
|---|---|
| GND | GND |
| VCC | 3.3V |
| DATA | D2 |
LCD I2C to Arduino UNO Q MCU:
| LCD Pin | Arduino UNO Q MCU |
|---|---|
| GND | GND |
| VCC | 5V |
| SDA | SDA |
| SCL | SCL |
How To Program For DHT22 + LCD
- Include the required libraries:
#include <DHT.h>
#include <LiquidCrystal_I2C.h>
- Initialize the DHT22 and LCD:
DHT dht22(DHT22_PIN, DHT22);
LiquidCrystal_I2C lcd(0x27, 16, 2);
- Read temperature and humidity (wait at least 3 seconds between reads):
float humidity = dht22.readHumidity();
float tempC = dht22.readTemperature();
float tempF = dht22.readTemperature(true);
- Always check for failed reads:
if (isnan(humidity) || isnan(tempC) || isnan(tempF)) {
// sensor read failed
}
- Display on LCD:
lcd.setCursor(0, 0);
lcd.print("T: ");
lcd.print(tempC, 1);
lcd.print((char)223);
lcd.print("C ");
lcd.setCursor(0, 1);
lcd.print("Humidity: ");
lcd.print(humidity, 1);
lcd.print("%");
Arduino UNO Q Code
The Arduino UNO Q has two processors working together:
- The STM32 MCU reads the DHT22 sensor and controls the LCD — all sensor and display logic runs on the MCU
- 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 MCU reads DHT22 every 3 seconds, displays temperature and humidity on the LCD, and prints to the Serial Monitor.
/*
* 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-dht22-lcd
*/
#include <DHT.h>
#include <DIYables_LCD_I2C.h>
#define DHT22_PIN 2
DHT dht22(DHT22_PIN, DHT22);
DIYables_LCD_I2C lcd(0x27, 16, 2);
void setup() {
Serial.begin(9600);
lcd.init();
lcd.backlight();
lcd.setCursor(0, 0);
lcd.print("DHT22 Sensor");
lcd.setCursor(0, 1);
lcd.print("Initializing...");
dht22.begin();
delay(2000); // allow sensor to stabilize
Serial.println("Arduino UNO Q DHT22 + LCD ready");
}
void loop() {
float humidity = dht22.readHumidity();
float tempC = dht22.readTemperature();
float tempF = dht22.readTemperature(true);
if (isnan(humidity) || isnan(tempC) || isnan(tempF)) {
Serial.println("Failed to read from DHT22 sensor!");
lcd.setCursor(0, 0);
lcd.print("Sensor Error! ");
delay(3000);
return;
}
lcd.setCursor(0, 0);
lcd.print("T: ");
lcd.print(tempC, 1);
lcd.print((char)223);
lcd.print("C ");
lcd.print(tempF, 1);
lcd.print((char)223);
lcd.print("F ");
lcd.setCursor(0, 1);
lcd.print("Humidity: ");
lcd.print(humidity, 1);
lcd.print("% ");
Serial.print("Humidity: ");
Serial.print(humidity, 1);
Serial.print("% Temp: ");
Serial.print(tempC, 2);
Serial.print("°C / ");
Serial.print(tempF, 2);
Serial.println("°F");
delay(3000);
}
Detailed Instructions
First time with Arduino UNO Q? Follow the Getting Started with Arduino UNO Q tutorial before proceeding.
- Connect: Wire the DHT22 and LCD 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: Dht22Lcd
- Click Create to confirm.
- Paste the sketch: Copy the MCU code above and paste it into sketch/sketch.ino. 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 DHT sensor library created by Adafruit 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 LCD I2C 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.
- Watch temperature and humidity appear on the LCD and Serial Monitor every 3 seconds.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] Arduino UNO Q DHT22 + LCD ready
[2026-04-29 09:00:04] Humidity: 55.2% Temp: 26.30°C / 79.34°F
[2026-04-29 09:00:07] Humidity: 55.1% Temp: 26.35°C / 79.43°F
[2026-04-29 09:00:10] Humidity: 55.3% Temp: 26.40°C / 79.52°F
Bridge: Linux + MCU
This section shows how to program both processors of the Arduino UNO Q so the Linux side can read DHT22 data and control the LCD via Bridge:
- The DHT22 sensor and LCD are connected to the MCU — all reading and display logic runs on the MCU every 3 seconds
- The MPU cannot access the sensor or LCD directly — it calls Bridge functions to retrieve readings or clear the display
- The MPU has Wi-Fi — running full Debian Linux, it can log readings, publish to dashboards, or send Telegram alerts
- 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 reads DHT22 every 3s and updates LCD → MPU reads via Bridge → MPU sends alerts over Wi-Fi.
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-dht22-lcd
*/
#include <DHT.h>
#include <DIYables_LCD_I2C.h>#include "Arduino_RouterBridge.h"
#define DHT22_PIN 2
DHT dht22(DHT22_PIN, DHT22);
DIYables_LCD_I2C lcd(0x27, 16, 2);
float last_humidity = 0.0;
float last_temp_c = 0.0;
float last_temp_f = 0.0;
unsigned long last_read_ms = 0;
void lcd_show(float tempC, float tempF, float humidity) {
lcd.setCursor(0, 0);
lcd.print("T: ");
lcd.print(tempC, 1);
lcd.print((char)223);
lcd.print("C ");
lcd.print(tempF, 1);
lcd.print((char)223);
lcd.print("F ");
lcd.setCursor(0, 1);
lcd.print("Humidity: ");
lcd.print(humidity, 1);
lcd.print("% ");
}
String get_humidity(String arg) {
return String(last_humidity, 1);
}
String get_temp_c(String arg) {
return String(last_temp_c, 2);
}
String get_temp_f(String arg) {
return String(last_temp_f, 2);
}
String clear_lcd(String arg) {
lcd.clear();
Monitor.println("LCD cleared");
return "OK";
}
String get_status(String arg) {
return "Temp: " + String(last_temp_c, 2) + "°C / " + String(last_temp_f, 2) + "°F Humidity: " + String(last_humidity, 1) + "%";
}
void setup() {
Bridge.begin();
Monitor.begin();
lcd.init();
lcd.backlight();
lcd.setCursor(0, 0);
lcd.print("DHT22 Sensor");
lcd.setCursor(0, 1);
lcd.print("Initializing...");
dht22.begin();
delay(2000); // allow sensor to stabilize
float h = dht22.readHumidity();
float c = dht22.readTemperature();
float f = dht22.readTemperature(true);
if (!isnan(h) && !isnan(c) && !isnan(f)) {
last_humidity = h;
last_temp_c = c;
last_temp_f = f;
lcd_show(c, f, h);
}
Bridge.provide("get_humidity", get_humidity);
Bridge.provide("get_temp_c", get_temp_c);
Bridge.provide("get_temp_f", get_temp_f);
Bridge.provide_safe("clear_lcd", clear_lcd);
Bridge.provide("get_status", get_status);
Monitor.println("Arduino UNO Q DHT22 + LCD Bridge ready");
}
void loop() {
unsigned long now = millis();
if (now - last_read_ms >= 3000) {
last_read_ms = now;
float h = dht22.readHumidity();
float c = dht22.readTemperature();
float f = dht22.readTemperature(true);
if (isnan(h) || isnan(c) || isnan(f)) {
Monitor.println("Failed to read from DHT22 sensor!");
} else {
last_humidity = h;
last_temp_c = c;
last_temp_f = f;
lcd_show(c, f, h);
Monitor.println("Humidity: " + String(h, 1) + "% Temp: " + String(c, 2) + "°C / " + String(f, 2) + "°F");
}
}
}
Python Code (Bridge)
"""
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-dht22-lcd
"""
from arduino.app_utils import *
import time
def loop():
status = Bridge.call("get_status")
print(status)
time.sleep(3)
App.run(user_loop=loop)
Detailed Instructions
- Connect: Wire the DHT22 and LCD 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 Dht22LcdBridge, 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.
- Watch the LCD update every 3 seconds and readings appear in the Python console.
App Lab Console Output
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:01] Arduino UNO Q DHT22 + LCD Bridge ready
[2026-04-29 09:00:04] Humidity: 55.2% Temp: 26.30°C / 79.34°F
[2026-04-29 09:00:07] Humidity: 55.1% Temp: 26.35°C / 79.43°F
[2026-04-29 09:00:10] Humidity: 55.3% Temp: 26.40°C / 79.52°F
sketch.ino
1#include "Arduino_RouterBridge.h"
Serial Monitor
Python
[2026-04-29 09:00:04] Temp: 26.30°C / 79.34°F Humidity: 55.2%
[2026-04-29 09:00:07] Temp: 26.35°C / 79.43°F Humidity: 55.1%
[2026-04-29 09:00:10] Temp: 26.40°C / 79.52°F Humidity: 55.3%
Telegram
Monitor DHT22 readings remotely and receive automatic Telegram alerts when temperature or humidity rises above thresholds.
MCU sketch: Keep the same MCU sketch from the previous Bridge section.
Python Code (Telegram)
"""
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-dht22-lcd
"""
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
TEMP_THRESHOLD_C = 35.0
HUMIDITY_THRESHOLD = 80.0
temp_alert_sent = False
humidity_alert_sent = False
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():
global temp_alert_sent, humidity_alert_sent
# Auto-alerts
temp_c_str = Bridge.call("get_temp_c")
humidity_str = Bridge.call("get_humidity")
try:
temp_c = float(temp_c_str)
humidity = float(humidity_str)
if temp_c > TEMP_THRESHOLD_C and not temp_alert_sent:
temp_alert_sent = True
temp_f = Bridge.call("get_temp_f")
msg = f"⚠️ High temperature alert: {temp_c_str}°C / {temp_f}°F"
print(msg)
send_message(CHAT_ID, msg)
elif temp_c <= TEMP_THRESHOLD_C:
temp_alert_sent = False
if humidity > HUMIDITY_THRESHOLD and not humidity_alert_sent:
humidity_alert_sent = True
msg = f"⚠️ High humidity alert: {humidity_str}%"
print(msg)
send_message(CHAT_ID, msg)
elif humidity <= HUMIDITY_THRESHOLD:
humidity_alert_sent = False
except ValueError:
pass
# Handle 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 DHT22 + LCD Bot\n"
"/temp - Temperature (°C and °F)\n"
"/humidity - Humidity reading\n"
"/clear - Clear LCD display\n"
"/status - Full sensor status")
elif text == "/temp":
temp_c = Bridge.call("get_temp_c")
temp_f = Bridge.call("get_temp_f")
send_message(chat_id, f"Temperature: {temp_c}°C = {temp_f}°F")
elif text == "/humidity":
result = Bridge.call("get_humidity")
send_message(chat_id, f"Humidity: {result}%")
elif text == "/clear":
result = Bridge.call("clear_lcd")
send_message(chat_id, f"LCD cleared: {result}")
elif text == "/status":
result = Bridge.call("get_status")
send_message(chat_id, result)
else:
send_message(chat_id, "Unknown command. Send /start for help.")
time.sleep(3)
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. Send /temp or /humidity from Telegram, or warm the sensor to trigger the high-temperature alert.
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 09:10:18] ⚠️ High temperature alert: 36.20°C / 97.16°F
[2026-04-29 09:10:35] Received: /humidity
Telegram
12:45
Welcome to Telegram!
ArduinoBot
10:19
Chatting with Arduino...
BotFather
Yesterday
Your bot has been created.
ArduinoBot
bot
OpenClaw
You can adapt the OpenClaw to this tutorial by refering the instruction on Arduino Uno Q - OpenClaw Tutorial
Project Ideas
You can build many useful projects with the DHT22 and LCD on Arduino UNO Q:
- Precision Room Thermometer-Hygrometer: The DHT22's ±0.5°C accuracy paired with the LCD's clear readout creates a reliable standalone instrument for room climate monitoring
- Food Storage Monitor: Keep tabs on humidity and temperature in a pantry or wine cellar — Telegram alerts notify when conditions drift outside safe ranges
- Plant Growing Station: Display temperature and humidity on the LCD to ensure ideal growing conditions — trigger a humidifier or fan via Bridge when readings drift
- Classroom Weather Station: Mount the DHT22 and LCD in a classroom — students can observe real-time readings and use the Bridge Python side to log and graph climate data over the school day
- Server Room Watchdog: Use the DHT22's extended temperature range (up to 80°C) to monitor rack temperatures — the LCD shows live status and Telegram sends immediate alerts before equipment damage occurs
Challenge Yourself
Ready to go further with the DHT22 and LCD on Arduino UNO Q? Try these challenges:
- Easy: Add scrolling text to the LCD — when temperature exceeds 35°C, scroll a warning message across the bottom row using lcd.scrollDisplayLeft().
- Medium: Implement a Telegram /setthreshold command that accepts a temperature value as argument and updates the alert threshold dynamically in the Python side (e.g., /setthreshold 30).
- Advanced: Build a dual-mode display — alternate the LCD between Celsius/Fahrenheit display and a dew point display every 5 seconds, with the dew point computed in Python via Bridge and sent back to the MCU via a set_dew_point(String) Bridge function.