Week-3 Input Devices

Introduction

In this week’s Fab Academy session, we learned about different electronic sensors and how they work in embedded systems. We also used testing instruments like an oscilloscope and a multimeter to observe and measure electrical signals. By comparing different sensors and performing practical experiments, we gained a better understanding of sensor operation, signal measurement, and basic electronics.

Individual assignment

Task:

During this week, my individual assignment was to connect different sensors to the microcontroller board and test their operation. I checked the output of each sensor by reading its values and confirmed that it was working correctly. This activity helped me understand how different sensors are connected, how they communicate with the microcontroller, and how to verify their performance.

Group assignment

Task:

During this week, we learned how to use an oscilloscope to observe analog and digital signals. We also used a multimeter to measure the voltage and current of an IR sensor. In addition, we compared the DHT11 and DHT22 sensors to understand their features and performance. These activities helped us gain practical knowledge of sensors and electronic testing instruments.

Introduction

During this week’s group assignment, we learned about analog and digital signals using the ESP32-C3 microcontroller. We observed these signals by monitoring an LED blinking with an oscilloscope. We also used a multimeter to measure the voltage and current of an IR sensor. In addition, we compared the DHT11 and DHT22 sensors based on their features and performance. This activity helped us understand how the ESP32-C3 works with digital signals and how to use basic electronic testing instruments.

Digital signal

Using led

Hardware components we used:-

1. XIAO ESP32C3
2. LED
3. oscilloscope
4. Connceting wires

Comparative Analysis of DHT11 and DHT22 Sensors.

The DHT11 and DHT22 are both digital sensors used to measure temperature and humidity, but they differ in performance. The DHT11 is less expensive and suitable for basic projects, while the DHT22 provides higher accuracy and a wider measurement range. The DHT22 can measure temperatures from -40°C to 80°C, whereas the DHT11 measures from 0°C to 50°C. For humidity, the DHT22 measures 0–100% RH, while the DHT11 measures 20–90% RH. Because of its better accuracy and wider range, the DHT22 is preferred for applications that require more reliable environmental monitoring.

Feature	DHT11	DHT22
Temperature Range	0°C to 50°C	-40°C to 80°C
Humidity Range	20% to 90% RH	0% to 100% RH
Temperature Accuracy	±2°C	±0.5°C
Humidity Accuracy	±5% RH	±2% RH
Output Type	Digital	Digital
Operating Voltage	3.3V – 5.5V	3.3V – 6V
Sampling Rate	1 reading/second	2 readings/second
Cost	Lower	Higher
Applications	Basic weather stations, simple monitoring projects	Weather stations, greenhouse monitoring, industrial and IoT applications
Overall Performance	Good for basic applications	Better accuracy and wider measurement range

Measurement of IR Sensor Voltage and Current Using a Multimeter.

Voltage Measurement of the IR Sensor.

As part of our group assignment, we connected the DHT1 1 sensor to the Aurdino microcontroller and measured its output voltage using a digital multimeter. The multimeter probes were connected between the VCC and OUT pins, and the measured voltage was 3.80 V. This activity helped us understand how to measure the voltage of an DHT11 sensor and observe its electrical output during operation.

Current Measurement of the IR Sensor

As part of our group assignment, we connected the DHT11 sensor to the Aurdino microcontroller and measured its current using a digital multimeter. The multimeter was connected in series with the sensor circuit to measure the current consumed during operation. The measured current was 1.17 mA. This activity helped us understand how to measure the current of an DHT11 sensor and observe its power consumption while it was operating.

Input devices

Input devices are electronic components that send information or signals to a microcontroller or computer. They help the system detect changes in the environment or receive commands from the user. Examples of input devices include sensors, push buttons, switches, keypads, and microphones. These devices provide the data needed for the system to make decisions and perform different tasks.

Datasheet Of Inputdevices

Sr. No.	Input Device	What it Measures	Output Type	Operating Voltage	Applications
1	AHT2415C Sensor	Temperature and Humidity	Digital (I²C)	2.2V–5.5V	Weather stations, smart home, environmental monitoring
2	Sound Sensor	Sound intensity	Analog / Digital	3.3V–5V	Noise detection, clap switch, sound monitoring
3	MQ-2 Gas Sensor	LPG, Smoke, Methane, Hydrogen	Analog / Digital	5V	Gas leakage detection, fire safety systems
4	Float Sensor	Water level (High/Low)	Digital	3.3V–5V	Water tank level monitoring, pumps
5	Ultrasonic Sensor (HC-SR04)	Distance	Digital	5V	Obstacle detection, distance measurement, robotics
6	Infrared (IR) Sensor	Object detection	Digital	3.3V–5V	Line follower robots, obstacle detection
7	PIR Sensor	Human motion	Digital	5V	Security alarms, automatic lighting
8	DHT22 Sensor	Temperature and Humidity	Digital	3.3V–6V	Weather monitoring, IoT projects
9	MQ-7 Gas Sensor	Carbon Monoxide (CO)	Analog	5V	Air quality monitoring, CO gas detection

What is a Sensor?

A sensor is an electronic device that detects changes in its surroundings, such as temperature, light, pressure, motion, humidity, or sound. It converts these physical changes into electrical signals that a microcontroller or computer can understand. Based on these signals, the system can monitor conditions, display information, or perform specific actions automatically. Sensors are widely used in everyday devices like smartphones, home appliances, automobiles, and industrial automation systems.

Analog Signal

An Analog signal is a continuous signal that changes smoothly over time and can have many different values. It represents real-world physical quantities such as temperature, sound, light, or pressure. Analog signals vary in voltage or current and are not limited to only two states. They are commonly produced by sensors like temperature sensors, LDRs, and microphones.

Digital Signal

A digital signal (digital wave) is a signal that has only two fixed states: HIGH (1) and LOW (0). Unlike an analog signal, it does not change continuously but switches between these two levels. Digital signals are used by microcontrollers and computers because they are more accurate and less affected by electrical noise. Examples include push buttons, switches, and digital sensors.

Sensors

1.AHT2415C

AHT2415C is a digital temperature and humidity sensor designed to measure ambient temperature and relative humidity. It provides calibrated digital output through the I²C communication protocol, enabling accurate and reliable data transmission to microcontrollers such as the ESP32 and Arduino. The sensor features low power consumption, high measurement accuracy, and excellent long-term stability, making it suitable for continuous environmental monitoring. It is widely used in applications such as weather stations, HVAC systems, smart home devices, industrial monitoring, and other projects that require dependable temperature and humidity measurements.

Pin description

• VCC – Connects to the 3.3V or 5V power supply.
• GND – Connects to the ground (GND) of the microcontroller.
• SDA – Data line used to transfer temperature and humidity data.
• SCL – Clock line used for I²C communication.

Internal structure of AHT2415C

The AHT2415C has a compact internal structure that combines a humidity sensor, a temperature sensor, and a digital signal processing circuit inside a 304 stainless steel probe. The humidity sensor measures the moisture in the air, while the temperature sensor measures the surrounding temperature. A PTFE protective filter covers the sensing element to protect it from dust and water while still allowing air to pass through. The built-in processing circuit converts the sensor readings into accurate digital I²C output, making it easy for microcontrollers to read the data.

Applications

• Weather stations
• Smart home systems
• HVAC systems
• Environmental monitoring
• Industrial automation
• IoT projects

Here is the code I used:-

                            
#include <Wire.h>
#include <Adafruit_AHTX0.h>

Adafruit_AHTX0 aht;

void setup() {
  Serial.begin(115200);

  Wire.begin(8, 9);   // SDA = GPIO8 , SCL = GPIO9

  if (!aht.begin()) {
    Serial.println("AHT sensor not detected");   
  }

  Serial.println("AHT sensor ready");   
}
 

void loop() {

  sensors_event_t humidity, temp;
  aht.getEvent(&humidity, &temp);


  Serial.print("Temp: ");
  Serial.print(temp.temperature);
  Serial.print(" °C  ");

 
  Serial.print("Humidity: ");
  Serial.print(humidity.relative_humidity);
  Serial.println(" %");

  
  delay(2000);     
}

2.Sound sensor

Pin description

A sound sensor is an electronic device that detects sound waves in the surrounding environment using a microphone. Inside the sensor, the microphone converts sound into small electrical signals, which are then amplified and processed by a comparator or signal conditioning circuit. The sensor provides either an analog output (showing the sound level) or a digital output (indicating whether the sound exceeds a set threshold). This makes it useful for projects such as clap switches, noise detection systems, and security alarms.

• VCC – Connects to the 3.3V or 5V power supply.
• GND – Connects to the ground (GND).
• DO – Digital output that gives a HIGH or LOW signal based on the sound level.

The structure of sound sensor

The structure of a sound sensor consists of a microphone, an amplifier circuit, a comparator, and input/output pins mounted on a small circuit board. The microphone detects sound waves and converts them into electrical signals. The amplifier increases the strength of these weak signals, while the comparator checks whether the sound level is above a preset threshold. Finally, the processed signal is sent through the output pins as either an analog or digital signal, making it easy to connect the sensor to a microcontroller like an Arduino or ESP32.

Applications

• Noise level monitoring
• Clap switch projects
• Security and alarm systems
• Home automation
• Smart devices
• Robotics and IoT projects

const int soundPin = 2;    // D2 (GPIO2)
const int buzzerPin = 3;   // D3 (GPIO3)

void setup() {
  pinMode(soundPin, INPUT);
  pinMode(buzzerPin, OUTPUT);

  digitalWrite(buzzerPin, LOW);
  Serial.begin(115200);
}

void loop() {
  int sound = digitalRead(soundPin);

  if (sound == HIGH) {
    Serial.println("Sound Detected!");
    digitalWrite(buzzerPin, HIGH);   // Buzzer ON
  } else {
    Serial.println("No Sound");
    digitalWrite(buzzerPin, LOW);    // Buzzer OFF
  }

  delay(200);
}

3.MQ2 Sensor

The MQ-2 gas sensor is an electronic sensor used to detect the presence of gases such as LPG, methane, propane, hydrogen, and smoke in the air. It works by sensing changes in the concentration of these gases and converting them into an electrical signal. The sensor provides analog and digital outputs, making it easy to interface with microcontrollers like Arduino and ESP32. It is widely used in gas leakage detection systems, smoke alarms, fire safety devices, and air quality monitoring projects due to its low cost, high sensitivity, and simple operation.

Pin description

• VCC – Connects to the 5V power supply.
• GND – Connects to the ground (GND) of the microcontroller.
• AO – Analog output that provides the gas concentration value.
• DO – Digital output that gives a HIGH or LOW signal when the gas level exceeds the preset threshold.

The structure of MQ2 Sensor

The MQ-2 gas sensor is made up of a sensing element, a heating coil, a stainless steel mesh, and connecting pins. The sensing element is made of tin dioxide (SnO₂), which changes its electrical resistance when exposed to gases such as LPG, methane, smoke, and hydrogen. A small heating coil inside the sensor keeps the sensing material at the correct operating temperature. The stainless steel mesh protects the sensing element from dust and other particles while allowing gases to enter. The sensor then sends the detected gas concentration as an analog or digital output to a microcontroller like an Arduino or ESP32.

Applications

• Gas leak detection
• Smoke detection systems
• Fire safety systems
• Home and industrial safety
• Air quality monitoring
• IoT and automation projects

Here is the code I used:-

#define MQ2_PIN 4
#define LED_PIN 2
#define BUZZER_PIN 5

void setup() {
  pinMode(MQ2_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);

  Serial.begin(115200);

  digitalWrite(LED_PIN, LOW);
  digitalWrite(BUZZER_PIN, LOW);
}

void loop() {
  int smoke = digitalRead(MQ2_PIN);

  if (smoke == LOW) {   // Smoke detected
    digitalWrite(LED_PIN, HIGH);
    digitalWrite(BUZZER_PIN, HIGH);
    Serial.println("Smoke Detected");
  } else {
    digitalWrite(LED_PIN, LOW);
    digitalWrite(BUZZER_PIN, LOW);
    Serial.println("No Smoke");
  }
}

4. Float Sensor

A float sensor is a device used to detect the level of liquid in a tank or container. It works using a floating object (float) that moves up and down as the liquid level changes. When the float reaches a certain level, it activates an internal switch to send an ON/OFF signal to a microcontroller or control system. Float sensors are commonly used in water tanks, sump pumps, industrial equipment, and automatic water level control systems because they are simple, reliable, and easy to use.

Pin description

• VCC – Connects to the power supply (if required by the module).
• GND – Connects to the ground (GND).

The structure of Float Sensor

The internal structure of a float sensor consists of a hollow float, a reed switch, a permanent magnet, and connecting wires. The float moves up and down with the liquid level and contains a small permanent magnet. Inside the sensor stem, a reed switch opens or closes when the magnet comes close to it. This action changes the electrical signal, which is then sent to a microcontroller or control circuit to indicate the liquid level.

Applications

• Water level monitoring
• Water tank automation
• Overflow protection systems
• Industrial liquid level monitoring
• Pump control systems
• Smart irrigation systems
• IoT water management projects

Here is the code I used:-

const int floatPin = 2;     // D2 (GPIO2)
const int buzzerPin = 3;    // D3 (GPIO3)

void setup() {
  pinMode(floatPin, INPUT_PULLUP);  // Enable internal pull-up
  pinMode(buzzerPin, OUTPUT);

  digitalWrite(buzzerPin, LOW);

  Serial.begin(115200);
}

void loop() {
  int sensorState = digitalRead(floatPin);

  if (sensorState == LOW) {
    Serial.println("Water Detected!");
    digitalWrite(buzzerPin, LOW);   // Buzzer OFF
  } else {
    Serial.println("No Water");
    digitalWrite(buzzerPin, HIGH);  // Buzzer ON
  }

  delay(500);
}

4. Ultrasonic Sensor

The internal structure of an ultrasonic sensor consists of a transmitter, a receiver, a control circuit, and connecting pins. The transmitter sends out high-frequency ultrasonic sound waves, while the receiver detects the waves that bounce back after hitting an object. The control circuit measures the time taken for the echo to return and calculates the distance to the object. The processed data is then sent to a microcontroller through the output pins, making the sensor useful for distance measurement, obstacle detection, and automation projects.

Pin description

• VCC – Connects to the 5V power supply.
• GND – Connects to the ground (GND).
• TRIG – Trigger pin used to send an ultrasonic pulse.
• ECHO – Echo pin used to receive the reflected pulse from the object.

The structure of Ultrasonic Sensor

The structure of an ultrasonic sensor consists of two main transducers: a transmitter and a receiver, along with a control circuit and connecting pins, all mounted on a small circuit board. The transmitter emits high-frequency ultrasonic sound waves, while the receiver detects the reflected waves after they hit an object. The control circuit processes the echo signal and calculates the distance based on the time taken for the sound to return. This design allows the sensor to accurately measure distance and detect obstacles in robotics, automation, and embedded system projects.

Applications

• Distance measurement
• Obstacle detection
• Robot navigation
• Water level monitoring
• Parking assistance systems
• Smart dustbins
• IoT and automation projects

Here is the code I used:-

#define TRIG_PIN 4
#define ECHO_PIN 5
#define LED_PIN 2

void setup() {
  Serial.begin(115200);

  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
}

void loop() {
  long duration;
  float distance;

  // Send ultrasonic pulse
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);

  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);

  digitalWrite(TRIG_PIN, LOW);

  // Read echo time
  duration = pulseIn(ECHO_PIN, HIGH);

  // Calculate distance in cm
  distance = duration * 0.0343 / 2;

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

  // LED control
  if (distance > 0 && distance <= 20) {
    digitalWrite(LED_PIN, HIGH);
  } else {
    digitalWrite(LED_PIN, LOW);
  }

  delay(200);
}

5. Infrared Sensor

The structure of an infrared (IR) sensor consists of an IR LED (transmitter), an IR photodiode or phototransistor (receiver), a signal processing circuit, and connecting pins, all mounted on a small circuit board. The IR LED emits infrared light, and the receiver detects the light reflected from nearby objects. The signal processing circuit analyzes the reflected signal and generates an analog or digital output. This simple structure makes the IR sensor suitable for obstacle detection, line-following robots, object detection, and automation projects.

Pin description

• VCC – Connects to the 3.3V or 5V power supply.
• GND – Connects to the ground (GND).
• OUT – Digital output pin that sends a HIGH or LOW signal to the microcontroller when an object is detected.

The structure of IR Sensor

The structure of an IR (Infrared) sensor consists of an IR LED (transmitter), an IR receiver (photodiode or phototransistor), a signal processing circuit, and connecting pins, all mounted on a compact circuit board. The IR LED emits invisible infrared light, while the receiver detects the light reflected from nearby objects. The signal processing circuit amplifies and processes the received signal to determine the presence of an object. Finally, the sensor sends the result as an analog or digital output to a microcontroller such as an Arduino or ESP32.

Applications

• Obstacle detection
• Object detection
• Line-following robots
• Automatic doors
• Security systems
• Industrial automation
• Robotics and IoT projects

Here is the code I used:-

const int irPin = 3;
const int ledPin = 2;   // D2

void setup() {
  pinMode(irPin, INPUT);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  if (digitalRead(irPin) == LOW) {
    digitalWrite(ledPin, HIGH);  // Object detected
  } else {
    digitalWrite(ledPin, LOW);   // No object
  }
}

6. PIR Sensor

A PIR (Passive Infrared) sensor is an electronic sensor used to detect the movement of people or animals by sensing changes in infrared (heat) radiation. Unlike other sensors, it does not emit any signals; instead, it detects the natural heat produced by living objects. When a person or animal moves within its detection range, the sensor sends a digital HIGH or LOW signal to a microcontroller such as an Arduino or ESP32. PIR sensors are widely used in motion-activated lights, security alarms, automatic doors, and smart home systems because they are reliable, energy-efficient, and easy to use,

Pin description

• VCC – Connects to the 5V or 3.3V power supply.
• GND – Connects to the ground (GND).
• OUT – Digital output pin that sends a HIGH signal when motion is detected and a LOW signal when no motion is detected.

The structure of PIR Sensor

The structure of a PIR sensor consists of a Fresnel lens, a pyroelectric sensor, a signal processing circuit, and connecting pins, all mounted on a compact circuit board. The Fresnel lens collects and focuses infrared radiation onto the pyroelectric sensor. The pyroelectric sensor detects changes in heat energy caused by the movement of people or animals. The signal processing circuit amplifies and processes these signals and sends a digital output to a microcontroller such as an Arduino or ESP32 when motion is detected.

Applications

• Motion detection systems
• Security and burglar alarms
• Automatic lighting
• Smart home automation
• Occupancy detection
• Energy-saving systems
• Robotics and IoT projects

Here is the code I used:-

const int pirPin = 2;      // PIR sensor connected to D2
const int buzzerPin = 3;   // Buzzer connected to D3

void setup() {
  pinMode(pirPin, INPUT);
  pinMode(buzzerPin, OUTPUT);

  digitalWrite(buzzerPin, LOW);

  Serial.begin(115200);
}

void loop() {
  int motion = digitalRead(pirPin);

  if (motion == HIGH) {
    Serial.println("Motion Detected!");
    digitalWrite(buzzerPin, HIGH);   // Turn buzzer ON
  } else {
    Serial.println("No Motion");
    digitalWrite(buzzerPin, LOW);    // Turn buzzer OFF
  }

  delay(500);
}

7. DHT22 Sensor

The DHT22 sensor is a digital sensor used to measure temperature and humidity with high accuracy. It contains a capacitive humidity sensor and a thermistor to detect environmental conditions. The sensor processes the measured values internally and sends the data as a digital signal to a microcontroller such as an Arduino or ESP32. It is commonly used in weather stations, smart home systems, greenhouse monitoring, and environmental monitoring projects because of its accuracy, reliability, and low power consumption.

Pin description

• VCC – Connects to the 3.3V or 5V power supply.
• DATA – Sends temperature and humidity data to the microcontroller.
• GND – Connects to the ground (GND).

The structure of DHT22 Sensor

The structure of the DHT22 sensor consists of a capacitive humidity sensing element, a thermistor (temperature sensor), a signal processing chip, and connecting pins, all enclosed in a protective plastic casing. The humidity sensor measures the moisture in the air, while the thermistor measures the surrounding temperature. The signal processing chip converts the sensor readings into a calibrated digital output. The processed data is then transmitted through the data pin to a microcontroller for further use.

Applications

• Weather stations
• Smart home systems
• HVAC systems
• Greenhouse monitoring
• Environmental monitoring
• Industrial monitoring
• IoT projects

Here is the code I used:-

#include <DHT.h>

#define DHTPIN 13      // DHT22 DATA pin connected to GPIO 13
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(115200);
  Serial.println("DHT22 Sensor Test");
  dht.begin();
}

void loop() {
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();

  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("Failed to read from DHT22 sensor!");
    delay(2000);
    return;
  }

  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.print(" °C\t");

  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.println(" %");

  delay(2000);
}

8. MQ 7 Sensor

The MQ-7 gas sensor is an electronic sensor used to detect carbon monoxide (CO) gas in the air. It works by measuring the concentration of carbon monoxide and converting it into an electrical signal. The sensor provides analog and digital outputs, making it easy to interface with microcontrollers such as Arduino and ESP32. It is widely used in carbon monoxide detectors, air quality monitoring systems, industrial safety equipment, and smart home applications.

Pin description

• VCC – Connects to the 5V power supply.
• GND – Connects to the ground (GND).
• AO – Analog output that provides the carbon monoxide concentration value.
• DO – Digital output that gives a HIGH or LOW signal when the CO gas level exceeds the preset threshold.

The structure of MQ7 Sensor

The structure of the MQ-7 sensor consists of a tin dioxide (SnO₂) sensing element, a heating coil, a stainless steel mesh, and connecting pins. The sensing element detects carbon monoxide by changing its electrical resistance when exposed to the gas. The heating coil maintains the required operating temperature for accurate sensing. The stainless steel mesh protects the sensing element from dust and other particles while allowing gas to pass through. The sensor then sends the detected gas concentration as an analog or digital output to a microcontroller.

Applications

• Carbon monoxide leak detection
• Home safety systems
• Industrial gas monitoring
• Air quality monitoring
• Fire safety systems
• Smart home automation
• IoT and environmental monitoring projects

Here is the code I used:-

#define MQ7_PIN 4
#define LED_PIN 2

void setup() {
  Serial.begin(115200);

  pinMode(MQ7_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
}

void loop() {
  int gasState = digitalRead(MQ7_PIN);

  // Most MQ-7 modules output LOW when gas is detected
  if (gasState == LOW) {
    digitalWrite(LED_PIN, HIGH);
    Serial.println("Carbon Monoxide Detected!");
  } else {
    digitalWrite(LED_PIN, LOW);
    Serial.println("Air is Normal");
  }

  delay(200);
}