Circuit Documentation

Summary

This circuit is designed to interface a DHT22 temperature and humidity sensor with an Arduino UNO microcontroller, displaying the readings on a 16x2 I2C LCD. The DHT22 sensor provides accurate temperature and humidity data, while the LCD allows for easy visualization of this information. A resistor is used in the circuit to ensure proper signal levels from the DHT22 sensor.

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Component List

DHT22

• Description: A digital temperature and humidity sensor.
• Pins:
  • GND: Ground connection
  • VCC: Power supply (3.3V to 6V)
  • DAT: Data output pin

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Arduino UNO

• Description: A microcontroller board based on the ATmega328P.
• Pins:
  • GND: Ground connection
  • 5V: Power supply output
  • D2: Digital pin used for reading data from the DHT22
  • SCL: Serial Clock Line for I2C communication
  • SDA: Serial Data Line for I2C communication

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16x2 I2C LCD

• Description: A 16x2 character LCD with I2C interface for easy connection to microcontrollers.
• Pins:
  • GND: Ground connection
  • VCC: Power supply
  • SCL: Serial Clock Line for I2C communication
  • SDA: Serial Data Line for I2C communication

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Resistor

• Description: A passive electrical component used to limit current flow.
• Pins:
  • pin1: Connected to the DHT22 data pin
  • pin2: Connected to the VCC of the DHT22

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Wiring Details

DHT22

• GND: Connected to GND of Arduino UNO
• VCC: Connected to 5V of Arduino UNO and pin2 of the Resistor
• DAT: Connected to D2 of Arduino UNO through pin1 of the Resistor

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Arduino UNO

• GND: Connected to GND of DHT22 and 16x2 I2C LCD
• 5V: Connected to VCC of DHT22 and 16x2 I2C LCD
• D2: Connected to DAT of DHT22
• SCL: Connected to SCL of 16x2 I2C LCD
• SDA: Connected to SDA of 16x2 I2C LCD

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16x2 I2C LCD

• GND: Connected to GND of Arduino UNO and DHT22
• VCC: Connected to 5V of Arduino UNO and DHT22
• SCL: Connected to SCL of Arduino UNO
• SDA: Connected to SDA of Arduino UNO

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Resistor

• pin1: Connected to DAT of DHT22
• pin2: Connected to VCC of DHT22 and 5V of Arduino UNO

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Documented Code

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <Adafruit_Sensor.h>
#include <DHT.h>
#include <DHT_U.h>

#define DHTPIN 2       // DHT22 data on Arduino D2
#define DHTTYPE DHT22  // DHT 22 (AM2302)

LiquidCrystal_I2C lcd(0x27, 16, 2);  // Change 0x27 to 0x3F if your module uses that address
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  // Initialize LCD
  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("DHT22 Demo");
  lcd.setCursor(0, 1);
  lcd.print("Init...");
  
  // Start DHT
  dht.begin();

  delay(1500);
  lcd.clear();
}

void loop() {
  // DHT22 max sample rate ~0.5 Hz; wait at least 2s between reads
  float h = dht.readHumidity();
  float t = dht.readTemperature(); // Celsius

  if (isnan(h) || isnan(t)) {
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Sensor error");
    lcd.setCursor(0, 1);
    lcd.print("Check wiring");
  } else {
    // Line 1: Temperature
    lcd.setCursor(0, 0);
    lcd.print("T:");
    printFixed(lcd, t, 1);  // one decimal
    lcd.print((char)223);   // degree symbol
    lcd.print("C   ");      // pad to clear remnants

    // Line 2: Humidity
    lcd.setCursor(0, 1);
    lcd.print("H:");
    printFixed(lcd, h, 1);
    lcd.print("%   ");
  }

  delay(2000);
}

// Helper to print fixed-point with trimming
void printFixed(LiquidCrystal_I2C &lcd, float val, uint8_t decimals) {
  char buf[12];
  dtostrf(val, 0, decimals, buf);
  lcd.print(buf);
}

This documentation provides a comprehensive overview of the circuit, detailing each component, its connections, and the code used to operate the system.