Assignments

This week we learned about.

Table of Contents

• Group Assigment
• Individual Assignment
• DHT 11 sensor
• Ultrasonic sensor
• Final Project Development

Roadmap



Group Assignment

-Probe an input device(s)'s analog levels and digital signals
-Document your work on the group work page and reflect on your individual page what you learned

For this week's group assignment, we had to test instruments like multimeters and oscilloscopes to observe the signals produced by a sensor.

Learned to visualize electrical signals and waveforms using an oscilloscope.Gained experience in writing and debugging Arduino code for sensor data acquisition.Improved skills in setting up experiments, diagnosing issues, and accurately measuring signals.

Individual Assignment

Measure something: add a sensor to a microcontroller board that you have designed and read it.

Before we upload the code via a USB, we must download certain libraries. For this firstly I had to switch my board to Xiao Esp32 c3 from Arduino Uno and then install dht11 sensor.



The DHT11 is a commonly used Temperature and humidity sensor that comes with a dedicated NTC to measure temperature and an 8-bit microcontroller to output the values of temperature and humidity as serial data.

Image source



This is a code generated by Chatgpt when given the prompt "Write a Xiao esp32 c3 program to read temperature and humidity using a DHT11 sensor. Use the DHT library, define the GPIO pin connected to the sensor, and output the readings to the serial monitor every 2 seconds. "

                                
                                
#include 
#define DHTPIN 4     // Define the GPIO pin where the DHT11 is connected
#define DHTTYPE DHT11 // Define the sensor type

DHT dht(4, DHTTYPE);

void setup() {
    Serial.begin(115200);  // Start serial communication
    dht.begin();           // Initialize the DHT sensor
}

void loop() {
    float humidity = dht.readHumidity();
    float temperature = dht.readTemperature(); // Default is Celsius

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

    Serial.print("Humidity: ");
    Serial.print(humidity);
    Serial.print("%  Temperature: ");
    Serial.print(temperature);
    Serial.println("°C");
    
    delay(2000); // Wait 2 seconds before the next reading
}

There was a unstable connection between the sensor and the GPIO pin, thus it caused temporary read failures before the connection stabilized.



Ultrasonic sensor

An ultrasonic sensor is an electronic device that measures the distance of a target object by emitting ultrasonic sound waves, and converts the reflected sound into an electrical signal. Ultrasonic waves travel faster than the speed of audible sound (i.e. the sound that humans can hear).
Image source



How an Ultrasonic Sensor Works (HC-SR04)

An ultrasonic sensor (like the HC-SR04) has two main parts:

• Trigger (TX) – sends out the ultrasonic sound.
• Echo (RX) – receives the sound when it bounces back.

How it works: [This part is fully credited to AI because I asked it to explain the working mechanisms in simple terms.]

1. Triggering: You send a short 10-microsecond HIGH pulse to the trigger pin. This makes the sensor emit an 8-cycle ultrasonic burst at 40 kHz.
2. Wave travels: The sound wave travels through the air.
3. Reflection: If it hits an object, the wave reflects (like an echo) and comes back.
4. Echo pin goes HIGH: The echo pin stays HIGH for the time it takes for the echo to return.
5. Measure time: Your microcontroller measures how long the echo pin stays HIGH — that’s the round-trip time.
6. Calculate distance: Use the formula:
   
   Distance = (Time × Speed of Sound) / 2

In the code that I've used, no external libraries are used. It only relies on built-in Arduino core functions that are available by default in the Arduino IDE.



const int trigPin = 2;
const int echoPin = 3;
long duration;
int distance;

void setup() {
  Serial.begin(115200);         // Start the Serial communication at 9600 baud rate
  pinMode(trigPin, OUTPUT);   // Set the trigPin as an output
  pinMode(echoPin, INPUT);    // Set the echoPin as an input
}

void loop() {
  // Clear the trigPin by setting it LOW for 2 microseconds
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Send a 10µs pulse to trigger the sensor
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Measure the time it takes for the echo to return (in microseconds)
  duration = pulseIn(echoPin, HIGH);

  // Calculate the distance in cm
  // Speed of sound is 0.034 cm/µs, and we divide by 2 because the pulse travels to the object and back
  distance = duration * 0.034 / 2;

  // Debugging: Print the duration for troubleshooting
  Serial.print("Duration: ");
  Serial.println(duration);

  // If the duration is 0, it means the sensor did not receive any echo, so we print a warning
  if (duration == 0) {
    Serial.println("No echo received.");
  } else {
    // Print the distance to the Serial Monitor
    Serial.print("Distance: ");
    Serial.print(distance);
    Serial.println(" cm");
  }

  delay(500);  // Wait for half a second before taking another reading
}

Recollection: During the electronics design week, I tested a soil moisture sensor with arduino Uno. This time, I tested DHT11 sensor with my very own board!!