Mini Weather Station

What You'll Build

This is your own weather station for a bedroom, greenhouse or classroom. A DHT11 sensor measures the temperature and the humidity of the air, and a small LCD screen displays both values, refreshing every couple of seconds. It is the first project where your Arduino talks back with words instead of blinking lights.

What You Need

• ✓Arduino Uno
• ✓DHT11 sensor module (3-pin)
• ✓16×2 I2C LCD
• ✓Breadboard
• ✓Jumper wires

How It Works

The DHT11 contains a tiny thermometer and a humidity-sensitive material. It packages both readings into a digital message the Arduino reads through one data wire. The LCD uses I2C, a two-wire system that lets many devices share the same pair of wires — that is why it only needs SDA and SCL instead of a dozen connections.

Before You Wire It

Wiring

Step-by-Step Instructions

1. 1

   Install the libraries

   In the Arduino IDE open Library Manager and install 'DHT sensor library' by Adafruit (it will also ask for 'Adafruit Unified Sensor' — accept) and 'LiquidCrystal I2C' by Frank de Brabander. Libraries are code other makers wrote so you do not have to.

2. 2

   Wire the sensor

   Three wires only: 5V, GND and DATA to pin 2. The little blue module has the pull-up resistor on the board already, so you do not add one. If readings come back as nan, check the wires and wait two seconds between reads.

3. 3

   Find your screen's I²C address

   Most backpacks are 0x27, but plenty are 0x3F. Run the Arduino IDE's 'i2c_scanner' example once and use whatever address it prints in LiquidCrystal_I2C lcd(0x27, 16, 2). If the screen stays blank or shows only white blocks, that address (or the contrast pot) is usually the reason.

4. 4

   Connect the screen

   Only four wires: power, ground, SDA, SCL. If nothing appears, turn the little blue potentiometer on the back to adjust contrast.

5. 5

   Print to the screen

   Upload the sketch. The first line shows temperature, the second shows humidity.

6. 6

   Log the weather

   Note the reading every hour for a day and see how your room changes between morning and night.

Arduino Code

#include <DHT.h>
#include <LiquidCrystal_I2C.h>

DHT dht(2, DHT11);
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  dht.begin();
  lcd.init();
  lcd.backlight();
}

void loop() {
  float temp = dht.readTemperature();
  float hum  = dht.readHumidity();

  if (isnan(temp) || isnan(hum)) {
    lcd.setCursor(0, 0);
    lcd.print("Sensor error   ");
    return;
  }

  lcd.setCursor(0, 0);
  lcd.print("Temp: ");
  lcd.print(temp);
  lcd.print((char)223);
  lcd.print("C ");

  lcd.setCursor(0, 1);
  lcd.print("Humidity: ");
  lcd.print(hum);
  lcd.print("%");

  delay(2000);
}

Understanding the Code

Challenges & Upgrades

Troubleshooting

Helpful Resources