Lecture 3 – Sensors and Actuators

IoT sensors and actuators their types, calibration, and signal handling with practical lab exercises using DHT22, ultrasonic sensors, and PWM outputs.

Introduction

Sensors and actuators are the heart of the Internet of Things (IoT). They bridge the physical and digital worlds sensors detect and measure changes, while actuators perform actions in response to those measurements.
In this lecture, you’ll explore how these components work together and learn to use them through practical lab activities.

What Are Sensors?

Sensors are devices that convert physical quantities (like temperature, light, motion, or pressure) into electrical signals that microcontrollers can process.

Types of Sensors

Type	Description	Example
Analog Sensors	Produce continuous signals that vary with the measured quantity.	Temperature Sensor (LM35), LDR
Digital Sensors	Output discrete (ON/OFF or numeric) signals that can be directly read by microcontrollers.	DHT22, Ultrasonic Sensor

Key Difference: Analog vs Digital

• Analog sensors output voltage that changes smoothly with the measured value.
• Digital sensors send data as binary pulses or packets, making them more accurate and less affected by noise.

Lecture 2 – IoT Architecture and TCP/IP Model

What Are Actuators?

Actuators are devices that convert electrical signals into physical actions such as movement, rotation, or light.

Type	Description	Examples
Electrical Actuators	Use electricity to produce motion.	Motors, Relays
Mechanical Actuators	Produce linear or rotary movement.	Servo motors, Gears
Electromechanical Actuators	Combine both electrical and mechanical properties.	Solenoids, Robotic Arms

Actuators help IoT systems “respond” to their environment for example, turning on a fan when a sensor detects high temperature.

Sensor Calibration and Signal Handling

Before sensors can produce accurate data, they must be calibrated that is, adjusted to ensure their readings match real-world values.

Calibration Steps

1. Measure the actual value using a reliable instrument.
2. Compare it to the sensor’s reading.
3. Adjust constants or offsets in your code to correct differences.

Signal Handling involves cleaning, amplifying, and converting sensor signals so they can be read accurately by a microcontroller (for example, converting analog voltage to digital values using ADC).

Laboratory Exercise Working with Sensors and Actuators

Objective

To explore how sensors gather data and how actuators respond, using DHT22, an ultrasonic sensor, and PWM control.

Hardware Required

• Arduino UNO or ESP32
• DHT22 Temperature and Humidity Sensor
• Ultrasonic Sensor (HC-SR04)
• LED or Servo Motor for PWM Output
• Breadboard and Jumper Wires

Step 1 – Read Temperature and Humidity (DHT22)

Use the DHT22 sensor to measure real-time temperature and humidity.

#include "DHT.h"
#define DHTPIN 2
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  dht.begin();
}

void loop() {
  float t = dht.readTemperature();
  float h = dht.readHumidity();
  Serial.print("Temp: "); Serial.print(t); Serial.print("°C ");
  Serial.print("Humidity: "); Serial.print(h); Serial.println("%");
  delay(2000);
}

This shows how a digital sensor transmits clear numeric data over a single pin.

Step 2 – Measure Distance with Ultrasonic Sensor

#define trigPin 5
#define echoPin 18

void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  long duration = pulseIn(echoPin, HIGH);
  float distance = (duration * 0.034) / 2;

  Serial.print("Distance: "); Serial.print(distance); Serial.println(" cm");
  delay(1000);
}

This demonstrates time-of-flight measurement converting sound-wave timing into distance.

Step 3 – Actuate Using PWM Output

Now, use PWM (Pulse Width Modulation) to control an LED’s brightness or a servo motor’s position.

int led = 13;
void setup() { pinMode(led, OUTPUT); }
void loop() {
  for (int i=0; i<255; i++) { analogWrite(led, i); delay(10); }
  for (int i=255; i>0; i--) { analogWrite(led, i); delay(10); }
}

This simulates how actuators respond to processed sensor data.

The approach followed at E Lectures reflects both academic depth and easy-to-understand explanations.

Summary

After completing this lecture and lab, you will be able to:

• Differentiate between analog and digital sensors.
• Connect and calibrate sensors for accurate data.
• Generate PWM signals to control actuators.
• Understand how IoT systems sense and act simultaneously.

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