Introduction

This tutorial focuses on controlling thermal actuators with an Arduino, a unique approach to motion control that leverages heat-induced expansion or contraction. Thermal actuators, such as wax-based or bimetallic devices, convert temperature changes into mechanical movement, offering a simple yet effective solution for applications like valves or switches. In this experiment, you’ll learn how to interface a thermal actuator with an Arduino, use a heating element or relay to control its temperature, and test its actuation. This guide is perfect for hobbyists and engineers interested in heat-driven actuators.

Unlike motorized actuators, thermal actuators operate silently and with minimal power once activated, though they respond more slowly. We’ll use an Arduino to regulate power to a heating element, demonstrating precise control over the actuator’s movement in this hands-on setup.

Components Required

To control a thermal actuator with Arduino, you’ll need the following components:

• Microcontroller (e.g., Arduino Uno): Controls the power to the actuator’s heating element.
• Thermal Actuator (e.g., wax actuator or bimetallic strip): The heat-responsive device that moves when heated.
• Heating Element (e.g., resistor or Peltier module): Generates heat to activate the actuator (e.g., a 10Ω power resistor).
• Relay Module or MOSFET (e.g., IRF540): Switches or modulates power to the heating element safely.
• Power Supply (e.g., 12V, 1A): Powers the heating element, separate from the Arduino’s 5V supply.
• Connecting Wires: Jumper wires for secure connections.
• Breadboard or PCB: For prototyping the circuit.
• Optional: Temperature Sensor (e.g., DS18B20): Monitors the actuator’s temperature for precise control.

Schematic

The schematic illustrates how to wire the thermal actuator’s heating element to the Arduino via a relay or MOSFET:

Basic connection overview: - Connect the heating element (e.g., power resistor) in series with the thermal actuator to the relay’s normally open (NO) terminal or MOSFET drain. - Wire the relay’s control pin or MOSFET gate to an Arduino digital pin (e.g., D9) through a 10kΩ resistor (for MOSFET). - Attach the power supply (e.g., 12V) to the heating element circuit, with the relay/MOSFET source connected to GND, sharing a common ground with the Arduino. - If using a temperature sensor, connect its data pin to an Arduino pin (e.g., D2) with a 4.7kΩ pull-up resistor.

Note: Ensure the heating element matches the actuator’s thermal requirements (e.g., 5W-10W for a small wax actuator). Use a heat sink with the MOSFET if driving high currents.

Steps

Follow these steps to build and test your thermal actuator control system:

1. Assemble the Circuit: Connect the heating element and thermal actuator to the relay’s NO terminal or MOSFET drain, and wire the control pin to Arduino D9.
2. Power Connections: Attach a 12V power supply to the heating circuit, and power the Arduino via USB, ensuring a shared GND.
3. Upload the Code: Load the Arduino sketch (see "Code Example" below) to regulate the heating element.
4. Test Activation: Run the code to heat the actuator and observe its movement (e.g., extension or bending).
5. Test Deactivation: Turn off the heat and verify the actuator returns to its resting state as it cools.
6. Add Feedback (Optional): Integrate a temperature sensor and adjust the code to maintain a target temperature for consistent actuation.

Code Example

Below is an Arduino sketch to control a thermal actuator by switching a heating element via a relay or MOSFET:

                
// Define control pin for relay or MOSFET
const int HEAT_PIN = 9;  // Digital pin

void setup() {
    pinMode(HEAT_PIN, OUTPUT);
    Serial.begin(9600);  // For debugging
}

void heatOn(int duration) {
    Serial.println("Heating ON");
    digitalWrite(HEAT_PIN, HIGH);  // Activate relay or MOSFET
    delay(duration);               // Heat for specified duration
    digitalWrite(HEAT_PIN, LOW);   // Turn off
    Serial.println("Heating OFF");
}

void loop() {
    heatOn(10000);  // Heat for 10 seconds
    delay(15000);   // Cool for 15 seconds
    heatOn(5000);   // Heat for 5 seconds
    delay(15000);   // Cool for 15 seconds
}
                
            

This code alternates heating periods (10s and 5s) with cooling pauses (15s) to actuate and relax the thermal actuator. Adjust `duration` based on your actuator’s response time and heat requirements.

Applications

Controlling thermal actuators has practical uses in various real-world scenarios, including:

• Automation Systems: Regulates valves or vents in HVAC systems.
• Prototyping for Robotics: Drives silent, low-power mechanisms in small robots.
• Educational Experiments: Teaches thermal expansion and control principles.
• Home Automation: Operates thermostat-controlled devices or window actuators.
• Automotive Systems: Controls flaps or vents in engine cooling systems.