Temperature Control with a Relay

Components Required

• 1 x Arduino (any model)
• 1 x DS18B20 Temperature Sensor
• 1 x 10kΩ Resistor
• 1 x Relay Module
• Jumper wires
• Breadboard
• Fan or Heater (connected to the relay)

Wiring Diagram

Connect the components as follows:

• DS18B20 Temperature Sensor:
• VCC to 5V on Arduino
• GND to GND on Arduino
• Data pin to digital pin 2 on Arduino (with a 10kΩ resistor between data pin and VCC)
• Relay Module:
• IN pin to digital pin 7 on Arduino
• VCC to 5V on Arduino
• GND to GND on Arduino
• Connect the appliance (fan or heater) to the relay as per the module's specifications (refer to relay documentation for high-voltage connections).

Code Explanation

The system reads the temperature using the DS18B20 sensor and compares it to a predefined threshold. If the temperature exceeds the threshold, the relay will activate to turn on the appliance.

Key Functions

• digitalWrite(pin, state): Turns the relay on or off by sending HIGH or LOW to the relay control pin.
• sensors.getTempCByIndex(0): Reads the temperature value from the DS18B20 sensor.
• if(): A conditional statement to check if the temperature exceeds the threshold.

Arduino Code

Here’s the Arduino code for temperature-based control using a relay:

#include 
#include 

#define ONE_WIRE_BUS 2

OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);

const int relayPin = 7;
const float thresholdTemp = 30.0;

void setup() {
    Serial.begin(9600);
    sensors.begin();
    pinMode(relayPin, OUTPUT);
    digitalWrite(relayPin, LOW);
}

void loop() {
    sensors.requestTemperatures();
    float currentTemp = sensors.getTempCByIndex(0);

    Serial.print("Current Temperature: ");
    Serial.print(currentTemp);
    Serial.println(" °C");

    if (currentTemp >= thresholdTemp) {
        digitalWrite(relayPin, HIGH);
        Serial.println("Appliance ON");
    } else {
        digitalWrite(relayPin, LOW);
        Serial.println("Appliance OFF");
    }

    delay(1000);
}
                

Upload and Test

1. Connect your Arduino to your computer and upload the code.
2. Open the Serial Monitor in the Arduino IDE to view the current temperature.
3. As the temperature exceeds the threshold (e.g., 30°C), the relay will turn on, powering the connected appliance.
4. When the temperature drops below the threshold, the relay will turn off.

Applications

This system can be applied in several real-world scenarios:

• Smart home automation, such as climate control.
• Overheating prevention for devices or systems.
• Temperature-sensitive industrial processes.

Conclusion

This project demonstrates how to use a relay to control an electrical appliance based on temperature readings from a DS18B20 sensor. You can adapt this system for various automation and control applications to save energy or enhance convenience.