Circuit Documentation

Summary of the Circuit

This circuit is designed to control a 12V fan using an Arduino UNO based on humidity readings from a DHT11 sensor. The fan is powered by a 12V battery and its speed is controlled through a PWM signal from the Arduino, which is interfaced with an NPN transistor acting as a switch. A resistor is used to limit the current to the base of the transistor, and a diode is included to protect against reverse voltage spikes when the fan is turned off.

Component List

Arduino UNO

• Microcontroller board based on the ATmega328P
• Provides I/O pins for interfacing with various sensors and actuators
• Includes power supply pins and a reset button

120mm Fan (12V)

• A 12V DC fan used for cooling
• Operates at 12V and requires a ground connection

NPN Transistor

• A bipolar junction transistor used as a switch to control the fan
• Has three pins: Emitter (E), Collector (C), and Base (B)

Resistor

• A 1kΩ resistor used to limit the current to the transistor's base

KY-015 DHT11 Temperature and Humidity Sensor

• A digital sensor that measures ambient temperature and humidity
• Has a data pin, power supply pin, and a ground pin

12V Battery

• Provides the power source for the fan
• Has a positive (VCC) and a negative (GND) terminal

1N4007 Rectifier Diode

• A diode used to prevent reverse voltage spikes from the fan
• Has an anode and a cathode

Wiring Details

Arduino UNO

• GND connected to the ground of the DHT11 sensor and the emitter of the NPN transistor
• 5V connected to the 5V pin of the DHT11 sensor
• D9 connected to one end of the 1kΩ resistor
• D2 connected to the data pin of the DHT11 sensor

120mm Fan (12V)

• 12V+ connected to the cathode of the rectifier diode and the collector of the NPN transistor
• GND connected to the ground of the 12V battery

NPN Transistor

• E (Emitter) connected to the ground of the Arduino UNO
• C (Collector) connected to the anode of the rectifier diode and the 12V+ pin of the fan
• B (Base) connected to the other end of the 1kΩ resistor

Resistor (1kΩ)

• One end connected to the D9 pin of the Arduino UNO
• The other end connected to the base of the NPN transistor

KY-015 DHT11 Sensor

• 5V connected to the 5V pin of the Arduino UNO
• S (Signal) connected to the D2 pin of the Arduino UNO
• GND connected to the ground of the Arduino UNO

12V Battery

• VCC connected to the cathode of the rectifier diode
• GND connected to the anode of the rectifier diode, the ground of the fan, and the collector of the NPN transistor

1N4007 Rectifier Diode

• Cathode connected to the VCC of the 12V battery and the 12V+ pin of the fan
• Anode connected to the collector of the NPN transistor and the ground of the 12V battery

Documented Code

#include "DHT.h"

// Pin definitions
#define DHTPIN 2      // Pin connected to the data pin of the DHT sensor
#define FANPIN 9      // PWM pin connected to the base of the transistor

// DHT sensor type
#define DHTTYPE DHT11 // Use DHT11 or DHT22, depending on the sensor

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  pinMode(FANPIN, OUTPUT); // Set fanPin as an output
  dht.begin();             // Initialize the DHT sensor
  Serial.begin(9600);      // Start serial communication for debugging
}

void loop() {
  // Read humidity from the DHT sensor
  float humidity = dht.readHumidity();
  
  // Check if the reading is valid
  if (isnan(humidity)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  // Print the humidity value for debugging
  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.println("%");

  // Map humidity to a PWM value (0-255)
  // Assuming you want the fan to run faster at higher humidity
  int fanSpeed = map(humidity, 30, 100, 0, 255);  // Adjust 30 (min humidity) and 100 (max humidity) as needed

  // Make sure fanSpeed stays within the 0-255 range
  fanSpeed = constrain(fanSpeed, 0, 255);

  // Set the fan speed using PWM
  analogWrite(FANPIN, fanSpeed);

  // Wait before the next reading
  delay(2000);  // Read every 2 seconds
}

This code is responsible for reading the humidity level from the DHT11 sensor and controlling the speed of the fan accordingly. The humidity level is mapped to a PWM value which is then used to set the fan speed. The fan is controlled via a transistor that is driven by the PWM signal from the Arduino's D9 pin.