In today's DIY-friendly world, building an automatic temperature controller is a fantastic project for hobbyists and anyone interested in home automation. Imagine having a system that automatically regulates the temperature to keep a room or an incubator at a stable, precise temperature—perfect for plant nurseries, homemade incubators, or even a simple climate control system in your workspace. In this article, we’ll go through how you can build an automatic temperature controller using an Arduino, a temperature sensor, and a heating element.
Why Build an Automatic Temperature Controller?
Automatic temperature controllers can be useful in a variety of applications:
- Incubators for hatching eggs or growing plants
- Climate-controlled enclosures for reptiles or plants that need precise temperatures
- Homemade sous-vide cooking machines for controlled, low-temperature cooking
- Greenhouse automation to maintain ideal growing conditions for plants
Our design will use a PID (Proportional-Integral-Derivative) control algorithm to achieve smooth, automatic temperature control. PID control is commonly used in industrial applications due to its ability to fine-tune output based on feedback, making it ideal for home automation projects.
How Does a PID Temperature Controller Work?
PID control uses three elements—proportional, integral, and derivative—to control the output:
- Proportional (P) adjusts output based on the difference between the setpoint and the current temperature.
- Integral (I) accumulates past errors to fine-tune long-term accuracy.
- Derivative (D) reacts to the rate of change, smoothing out sudden changes.
By using all three components, the PID algorithm can keep temperature stable without constantly overshooting or oscillating around the setpoint.
Materials Needed
To build this project, you’ll need:
- Arduino Uno (or any compatible board)
- LM35 Temperature Sensor – This sensor measures the current temperature.
- 12V Bulb or Heating Element – Acts as the heater.
- IRF540 N-channel MOSFET or similar MOSFET
- Power Supply – A 12V power supply for the bulb and Arduino.
- Wires and Breadboard
Setting Up the Circuit
LM35 Temperature Sensor: Connect the VCC pin of the LM35 to the Arduino’s 5V pin, GND to ground, and the output to the analog pin A0. This sensor will send temperature readings to the Arduino.
Heating Element: Connect the positive terminal of the 12V power supply to one of the terminal of the heating element. Connect the other terminal of the heating element to the drain of the MOSFET transistor IRF540N.
MOSFET: Connect the gate pin of the IRF540 N-channel MOSFET to a digital output pin on the Arduino (e.g., D9) via 1kohm resistor for control, connect 10kohm resistor between the gate and the source as shown in the circuit diagram. Connect the source to the common ground where the negative terminal of the 12V battery is connected and the Arduino ground is also connected. The drain of the MOSFET is connected to the heating element terminal.
Code for the Temperature Controller
Here’s the code for the PID-based temperature controller. This will measure the temperature from the LM35 sensor and adjust the power to the heating element to maintain a set temperature (25°C) using a relay.
// Pin Definitions
const int tempSensorPin = A0; // LM35 Temperature Sensor connected to A0
const int heaterPin = 9; // Heater connected to PWM pin 9
// Parameters for optimal control
float Kp = 2.5; // Proportional gain
float Ki = 0.5; // Integral gain
float Kd = 0.1; // Derivative gain
// Variables for control
float setPoint = 30.0; // Desired temperature in °C
float currentTemp = 0.0; // Current temperature reading
float error = 0.0; // Error value
float previousError = 0.0; // Previous error for derivative term
float integral = 0.0; // Integral accumulator
float output = 0.0; // Output PWM value
void setup() {
Serial.begin(9600);
pinMode(heaterPin, OUTPUT);
Serial.println("Automatic Temperature Controller");
}
void loop() {
// Read temperature from LM35 sensor
int sensorValue = analogRead(tempSensorPin);
currentTemp = (sensorValue * 5.0 / 1023.0) * 100.0; // Convert to Celsius
// Calculate error
error = setPoint - currentTemp;
// Calculate integral term
integral += error;
// Calculate derivative term
float derivative = error - previousError;
// Compute control output
output = Kp * error + Ki * integral + Kd * derivative;
// Limit output to PWM range (0-255)
output = constrain(output, 0, 255);
// Apply control to heater
analogWrite(heaterPin, output);
// Update previous error
previousError = error;
// Print for monitoring
Serial.print("Temperature: ");
Serial.print(currentTemp);
Serial.print(" °C, Output: ");
Serial.println(output);
// Delay for stability
delay(1000);
}How the Code Works
Temperature Reading: The Arduino reads the temperature from the LM35 sensor. This value is converted from an analog reading to a voltage, then to degrees Celsius.
PID Calculation: The PID controller calculates the output based on the current temperature and the setpoint. If the temperature is lower than 25°C, the controller increases the output (more power to the heater). If the temperature is higher, it reduces the output (less power to the heater).
Relay Control: The relay is controlled by the output value of the PID. Since the relay is digital, the Arduino may use PWM (Pulse Width Modulation) to vary the heating level or turn it on and off in bursts, effectively simulating power adjustment.
Maintaining the Set Temperature: The PID controller works continuously, adjusting the heating power to maintain the temperature close to the setpoint. As the temperature reaches the setpoint, the PID will gradually reduce the power to prevent overshooting.
Tuning the PID Constants
Tuning the Kp, Ki, and Kd constants is essential to achieve smooth temperature control:
- Kp: Affects the speed of response. Higher values increase the speed but can cause overshoot.
- Ki: Helps eliminate steady-state error but can cause slow oscillations.
- Kd: Reacts to sudden changes and helps dampen overshoot.
Start with small values and incrementally adjust until the temperature is stable.
Benefits of Using a PID Controller
A PID controller is particularly effective because it adapts to changing conditions, providing:
- Precision: Maintains the temperature close to the target value.
- Smooth Control: Avoids rapid oscillations that can occur with simpler on-off control systems.
- Flexibility: Can be applied to a wide range of temperature-sensitive projects.
Applications for Home DIYers
With this setup, you have a basic but powerful temperature control system with Arduino that can be adapted to a range of applications:
- DIY Incubators: Create a warm, stable environment for egg incubation.
- Greenhouse Automation: Maintain optimal conditions for plant growth, automatically adjusting temperature as needed.
- Aquarium Heaters: Regulate water temperature to provide a comfortable environment for tropical fish.
- Sous-Vide Cooking: Although this is a more advanced use, you can adapt the system to control water temperature for cooking.
Conclusion
Building an Arduino-based PID temperature controller is an excellent way to explore automated control systems and bring a professional touch to your DIY projects. This setup is flexible enough to be adapted to many applications, allowing you to create a temperature-stable environment for everything from growing plants to caring for pets and more. With a few components and some tuning, you’ll have a fully functional automatic temperature controller for your home projects!
To further explore control systems, check out various control system such as adaptive control systems, Neural Network Control with Arduino, feedforward control with Arduino, Fuzzy Logic control with Arduino to expand your knowledge and applications.
If you’re ready to optimize your next project, Arduino and optimal control are the perfect pair to achieve outstanding results!
