An Arduino circuit that reads temperature and humidity from a DHT11 sensor every 2 seconds and displays live readings in the Serial Monitor.
The DHT11 has 3 pins (on the module version): VCC, Data, and GND. Connect it to the Arduino in 3 wires.
// Wiring (DHT11 module with 3 pins):
//
// DHT11 Module Arduino Uno
// ───────────── ───────────
// VCC ─────── 5V
// Data ─────── Digital Pin 2
// GND ─────── GND
//
// If using bare DHT11 (4 pins):
// Pin 1 (VCC) → 5V
// Pin 2 (Data) → Digital 2 + 10kΩ resistor to 5V (pull-up)
// Pin 3 → not connected
// Pin 4 (GND) → GNDOpen the Arduino IDE Library Manager and install the DHT sensor library.
// In Arduino IDE:
// 1. Go to Sketch → Include Library → Manage Libraries
// 2. Search for "DHT sensor library" by Adafruit
// 3. Click Install
// 4. Also install "Adafruit Unified Sensor" if prompted
// Or via Arduino CLI:
// arduino-cli lib install "DHT sensor library"
// arduino-cli lib install "Adafruit Unified Sensor"Read temperature and humidity every 2 seconds and print to Serial Monitor.
#include <DHT.h>
#define DHTPIN 2 // Digital pin connected to DHT11
#define DHTTYPE DHT11 // DHT11 or DHT22
DHT dht(DHTPIN, DHTTYPE);
void setup() {
Serial.begin(9600);
dht.begin();
Serial.println("Temperature & Humidity Monitor");
Serial.println("==============================");
}
void loop() {
delay(2000); // DHT11 needs at least 1 second between reads
float humidity = dht.readHumidity();
float tempC = dht.readTemperature(); // Celsius
float tempF = dht.readTemperature(true); // Fahrenheit
float heatIndex = dht.computeHeatIndex(tempC, humidity, false);
// Check for read errors
if (isnan(humidity) || isnan(tempC)) {
Serial.println("Failed to read from DHT sensor — check wiring!");
return;
}
Serial.print("Humidity: "); Serial.print(humidity); Serial.println(" %");
Serial.print("Temperature: "); Serial.print(tempC); Serial.print(" °C / ");
Serial.print(tempF); Serial.println(" °F");
Serial.print("Heat Index: "); Serial.print(heatIndex); Serial.println(" °C");
Serial.println("------------------------------");
}Temperature & Humidity Monitor ============================== Humidity: 62.00 % Temperature: 28.00 °C / 82.40 °F Heat Index: 30.21 °C ------------------------------ Humidity: 61.00 % Temperature: 28.00 °C / 82.40 °F Heat Index: 30.05 °C ------------------------------
Blink the built-in LED when temperature exceeds a threshold.
#include <DHT.h>
#define DHTPIN 2
#define DHTTYPE DHT11
#define ALERT_TEMP 35.0 // Alert if above this temperature (°C)
DHT dht(DHTPIN, DHTTYPE);
void setup() {
Serial.begin(9600);
pinMode(LED_BUILTIN, OUTPUT);
dht.begin();
}
void loop() {
delay(2000);
float humidity = dht.readHumidity();
float tempC = dht.readTemperature();
if (isnan(humidity) || isnan(tempC)) return;
Serial.print(tempC); Serial.print("°C "); Serial.print(humidity); Serial.println("%");
if (tempC > ALERT_TEMP) {
Serial.println("⚠️ HIGH TEMPERATURE ALERT!");
// Blink LED 3 times
for (int i = 0; i < 3; i++) {
digitalWrite(LED_BUILTIN, HIGH); delay(200);
digitalWrite(LED_BUILTIN, LOW); delay(200);
}
} else {
digitalWrite(LED_BUILTIN, LOW);
}
}Your Arduino is now a live environmental sensor. Connect it to an LCD display (I2C 16x2) to show readings without a computer. The same code works with DHT22 — just change DHTTYPE to DHT22 for higher precision readings.
Spotted a bug, broken code, or something that doesn't look right? Tell us what's off and we'll fix it.