Introduction to IoT
Unit 5: Actuators & Motors
From DC motors to servos and relays — master the output side of IoT. Make things move, spin, and switch using Arduino.
⏱️ Time to Complete: 6–8 hours | 💰 Build a DIY Robot Car for ₹500 | 📝 30 MCQs (Bloom's Mapped)
💼 Skills unlocked: Motor control, PWM speed regulation, Servo positioning, Relay switching, H-bridge driver circuits
What are Actuators?
🔧 Sensors See, Actuators DO
In Unit 3 and 4, you learned how sensors let your Arduino "see" the world — temperature, light, distance, motion. But what good is sensing if your system can't act on it? Actuators are the muscles of IoT. They convert electrical signals into physical motion, force, or action.
When your smart fan turns on because the temperature crossed 35°C — that's an actuator (motor). When your automatic door opens — that's an actuator (servo). When Alexa turns on your tube light — that's an actuator (relay). Without actuators, IoT would just be "I" — the Internet of sensors staring at data, doing nothing.
Types of Actuators in IoT
⚡ Actuator Classification
An actuator is a device that converts an electrical signal into a physical output — motion, rotation, linear displacement, sound, or switching.
| Actuator Type | What It Does | Example | IoT Use Case |
|---|---|---|---|
| DC Motor | Continuous rotation | Fan, car wheel | Robot car, conveyor belt |
| Servo Motor | Precise angular rotation (0°–180°) | Robot arm, door lock | Automated gate, camera pan/tilt |
| Stepper Motor | Discrete step rotation (precise) | 3D printer, CNC | Precision positioning |
| Solenoid | Linear push/pull motion | Door lock, valve | Automatic door lock |
| Relay | Electrical switch (ON/OFF) | Light switch | Home automation (AC appliances) |
| Piezo Buzzer | Produces sound | Alarm beep | Alert system, doorbell |
| LED | Produces light | Indicator | Status display, smart lighting |
In this unit, we'll focus on the three most important actuators for IoT beginners: DC Motors, Servo Motors, and Relay Modules. These three cover 90% of all student IoT projects.
DC Motor Basics — How It Works
The Science Inside a DC Motor
A DC motor converts electrical energy into mechanical rotational energy. Inside, it has a coil of wire (armature) sitting inside a magnetic field. When current flows through the coil, it creates a force (Lorentz force) that makes the coil spin. The direction of spin depends on the direction of current.
🔄 DC Motor Key Parameters
| Parameter | What It Means | Typical Value (Small Hobby Motor) |
|---|---|---|
| Operating Voltage | Voltage needed to run the motor | 3V – 12V |
| Current Draw | Current consumed when running | 100mA – 300mA (no load), up to 1A (stall) |
| RPM | Rotations Per Minute — speed | 3000 – 15000 RPM |
| Torque | Rotational force | Low (needs gearbox for heavy loads) |
| Stall Current | Current when motor is blocked/stuck | 500mA – 2A (dangerous!) |
Why You CANNOT Connect a DC Motor Directly to Arduino
This is the #1 mistake every beginner makes. Let's understand why:
Arduino digital pin can supply: Maximum 20mA (recommended), 40mA (absolute max).
DC motor needs: 100–300mA minimum, up to 1A when starting or stalling.
That's 5–50× more current than Arduino can provide. Doing this can burn out the ATmega328P chip permanently. Additionally, motors generate back-EMF (voltage spikes) when turning off, which can fry the microcontroller.
The Solution? Use a motor driver IC like the L293D. The motor driver acts as a middleman — it takes the small control signal from Arduino and uses a separate power supply to drive the motor with the current it needs.
Analogy Think of it like this: Arduino Pin = TV Remote (sends signal, tiny power) Motor Driver = AC Power Socket (provides actual power) DC Motor = Television (needs real power to work) You use the remote to CONTROL what happens, but the TV gets its POWER from the wall socket. The motor driver is that wall socket for your motor.