💻 Programming Code

🎯 Lesson Objective

In this lesson, students will learn:

• How to program the Smart Dustbin using ESP32
• How the ultrasonic sensor measures distance
• How the ESP32 processes the sensor data
• How the servo motor opens and closes the lid
• How the complete automation logic works

By the end of this lesson, students will be able to upload the program and run the Smart Dustbin system.

1️⃣ Complete Copy-Paste Code

Students can copy and paste the following code directly into Arduino IDE.

#include <Servo.h>

int trigPin = 5;
int echoPin = 18;

long duration;
int distance;

Servo dustbinServo;

void setup()
{
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);

dustbinServo.attach(4);

Serial.begin(9600);
}

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

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

digitalWrite(trigPin, LOW);

duration = pulseIn(echoPin, HIGH);

distance = duration * 0.034 / 2;

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

if (distance < 20)
{
dustbinServo.write(90);
delay(3000);
dustbinServo.write(0);
}

delay(200);
}

2️⃣ Program Logic

The program follows a simple automation logic:

1️⃣ The ultrasonic sensor measures the distance.
2️⃣ ESP32 reads the sensor value.
3️⃣ If a hand is detected within 20 cm, the servo motor opens the lid.
4️⃣ The lid stays open for 3 seconds.
5️⃣ The servo motor closes the lid.
6️⃣ The program repeats continuously.

3️⃣ Library Explanation

This line imports the Servo library.

The Servo library allows the ESP32 to control a servo motor easily.

Without this library, controlling servo motors would require complex PWM programming.

4️⃣ Pin Declaration

These variables define the pins connected to the ultrasonic sensor.

• Trig pin sends ultrasonic signals.
• Echo pin receives the reflected signal.

These variables store the sensor data.

• duration stores the time taken for the ultrasonic signal to return.
• distance stores the calculated distance in centimeters.

This object allows the program to control the servo motor.

5️⃣ Setup Function Explanation

void setup()
{
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);

dustbinServo.attach(4);

Serial.begin(9600);
}

The setup() function runs once when the ESP32 starts.

pinMode()

These commands configure the ultrasonic sensor pins.

• Trig pin → OUTPUT
• Echo pin → INPUT

Servo Attach

The ESP32 will send control signals through this pin.

Serial Communication

It allows the program to display distance values in the Serial Monitor.

6️⃣ Loop Function Explanation

The loop() function runs continuously.

This allows the dustbin to constantly check for a hand.

Step 1 — Trigger the Ultrasonic Sensor

digitalWrite(trigPin, LOW);
delayMicroseconds(2);

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

digitalWrite(trigPin, LOW);

This sends a 10 microsecond ultrasonic pulse.

The sensor emits a sound wave that travels through the air.

Step 2 — Measure Echo Time

This time represents the travel time of the ultrasonic wave.

Step 3 — Calculate Distance

Explanation:

Speed of sound = 0.034 cm per microsecond

The signal travels to the object and back, so we divide by 2.

Step 4 — Print Distance

This prints the distance in the Serial Monitor.

This helps during testing and debugging.

Step 5 — Check Hand Detection

If true, the dustbin lid opens.

Step 6 — Open the Lid

The servo rotates to 90 degrees.

This opens the dustbin lid.

Step 7 — Keep Lid Open

Step 8 — Close the Lid

This closes the lid.

7️⃣ Final Working Process

The Smart Dustbin works like this:

1️⃣ Ultrasonic sensor detects a hand.
2️⃣ ESP32 calculates the distance.
3️⃣ If distance < 20 cm → lid opens.
4️⃣ After 3 seconds → lid closes.
5️⃣ System continues monitoring.

This creates a fully automatic dustbin system.

8️⃣ Common Mistakes

Students may face the following issues:

⚠ Servo not moving → Check servo signal pin
⚠ Sensor always shows 0 → Check echo pin connection
⚠ Lid opens randomly → Adjust distance threshold
⚠ Servo shaking → Ensure proper power supply

Always verify wiring before debugging the code.

🚀 What Happens Next

Now that the program is uploaded and working, the final step is to test the system and explore improvements.