Circuit Documentation

Summary

This circuit is designed to measure temperature and humidity using a DHT11 sensor and display the readings on a 16x2 I2C LCD. The circuit is controlled by an Arduino UNO, which reads data from the DHT11 sensor and updates the LCD display accordingly. A resistor is used to ensure proper operation of the DHT11 sensor.

Component List

DHT11 Humidity and Temperature Sensor

• Description: Measures temperature and humidity.
• Pins: VDD, DATA, NULL, GND

Resistor

• Description: Provides resistance to ensure proper operation of the DHT11 sensor.
• Properties:
  • Resistance: 200 Ohms
• Pins: pin1, pin2

Arduino UNO

• Description: Microcontroller used to control the circuit.
• Pins: UNUSED, IOREF, Reset, 3.3V, 5V, GND, Vin, A0, A1, A2, A3, A4, A5, SCL, SDA, AREF, D13, D12, D11, D10, D9, D8, D7, D6, D5, D4, D3, D2, D1, D0

16x2 I2C LCD

• Description: Displays temperature and humidity readings.
• Pins: GND, VCC, SDA, SCL

Wiring Details

DHT11 Humidity and Temperature Sensor

• VDD: Connected to 5V via a 200 Ohm resistor.
• DATA: Connected to Arduino UNO pin D9 via a 200 Ohm resistor.
• GND: Connected to GND.

Resistor

• pin1: Connected to 5V.
• pin2: Connected to DHT11 DATA pin and Arduino UNO pin D9.

Arduino UNO

• 5V: Connected to DHT11 VDD pin via a 200 Ohm resistor.
• GND: Connected to DHT11 GND pin and 16x2 I2C LCD GND pin.
• SCL: Connected to 16x2 I2C LCD SCL pin.
• SDA: Connected to 16x2 I2C LCD SDA pin.
• D9: Connected to DHT11 DATA pin via a 200 Ohm resistor.

16x2 I2C LCD

• GND: Connected to GND.
• VCC: Connected to 5V via a 200 Ohm resistor.
• SCL: Connected to Arduino UNO SCL pin.
• SDA: Connected to Arduino UNO SDA pin.

Code Documentation

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

// Initialize the LCD with the I2C address (usually 0x27 or 0x3F)
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Define the DHT sensor pin and type
#define DHTPIN 9
#define DHTTYPE DHT11

// Initialize the DHT sensor
DHT dht(DHTPIN, DHTTYPE);

unsigned long startTime;
float previousTemperature = NAN;

void setup() {
  // Initialize the LCD
  lcd.begin(16, 2);
  lcd.backlight();
  
  // Print a message to the LCD
  lcd.print("Initializing...");

  delay(500);
  
  // Initialize the start time
  startTime = millis();

  // Initialize the DHT sensor
  dht.begin();

  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);

  digitalWrite(6, LOW);
  digitalWrite(7, HIGH);
}

void loop() {
  // Calculate the elapsed time in milliseconds
  unsigned long elapsedTime = millis() - startTime;
  
  // Convert elapsed time to seconds with one decimal place
  float elapsedTimeSec = elapsedTime / 1000.0;
  
  // Read temperature as Celsius
  float temperature = dht.readTemperature();
  
  // Check if any reads failed and exit early (to try again).
  if (isnan(temperature)) {
    lcd.setCursor(0, 0);
    lcd.print("Error reading");
    return;
  }
  
  // Only update the display if the temperature has changed
  if (temperature != previousTemperature) {
    // Clear the first row
    lcd.setCursor(0, 0);
    lcd.print("                "); // Clear the first row by printing spaces
    
    // Set the cursor to the first row, first column
    lcd.setCursor(0, 0);
    lcd.print("Temp: ");
    
    // Clear the second row
    lcd.setCursor(0, 1);
    lcd.print("                "); // Clear the second row by printing spaces
    
    // Set the cursor to the second row, first column
    lcd.setCursor(0, 1);
    
    // Print the temperature to the LCD
    lcd.print(temperature);
    lcd.print(" C");
    
    // Update the previous temperature
    previousTemperature = temperature;
  }
  
  // Add a small delay to avoid flickering
  delay(50);
}

This code initializes the LCD and DHT11 sensor, reads the temperature from the sensor, and displays it on the LCD. The display is only updated if the temperature changes, and a small delay is added to avoid flickering.