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Lesson 35: Smart trashcan

This project revolves around the concept of a smart trash can. The primary aim is to have the trash can’s lid automatically open when an object approaches within a set distance (20cm in this case). The functionality is achieved by using an ultrasonic distance sensor paired with a servo motor. The distance between the object and the sensor is continually measured. If the object is close enough, the servo motor is triggered to open the lid.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Universal Maker Sensor Kit	94	Universal Maker Sensor Kit

You can also buy them separately from the links below.

Component Introduction	Purchase Link
ESP32 & Development Board (ESP32 Board)	BUY
Ultrasonic Sensor Module (HC-SR04)	BUY
Servo Motor (SG90)	BUY
Breadboard	BUY

Wiring

Code

Code Analysis

The project is based on real-time monitoring of the distance between an object and a trash can. An ultrasonic sensor continuously measures this distance, and if an object approaches within 20cm, the trash can interprets it as an intention to dispose of waste and automatically opens its lid. This automation adds smartness and convenience to a regular trash can.

1. Initial Setup and Variable Declaration

   Here, we’re including the ESP32Servo library and defining the constants and variables we’ll use. The pins for the servo and the ultrasonic sensor are declared. We also have an array averDist to hold the three distance measurements.

   #include <ESP32Servo.h>
   
   // Set up the servo motor parameters
   Servo servo;
   const int servoPin = 27;
   const int openAngle = 0;
   const int closeAngle = 90;
   
   // Define the minimum and maximum pulse widths for the servo
   const int minPulseWidth = 500; // 0.5 ms
   const int maxPulseWidth = 2500; // 2.5 ms
   
   
   // Set up the ultrasonic sensor parameters
   const int trigPin = 26;
   const int echoPin = 25;
   long distance, averageDistance;
   long averDist[3];
   
   // Distance threshold in centimeters
   const int distanceThreshold = 20;
   

2. setup() Function

   The setup() function initializes serial communication, configures the ultrasonic sensor’s pins, and sets the initial position of the servo to the closed position.

   void setup() {
     Serial.begin(9600);
     pinMode(trigPin, OUTPUT);
     pinMode(echoPin, INPUT);
     servo.attach(servoPin);
     servo.write(closeAngle);
     delay(100);
   }
   

3. loop() Function

   The loop() function is responsible for continuously measuring the distance, computing its average, and then making a decision whether to open or close the trash can’s lid based on this averaged distance.

   void loop() {
       // Measure the distance three times
       for (int i = 0; i <= 2; i++) {
           distance = readDistance();
           averDist[i] = distance;
           delay(10);
       }
   
       // Calculate the average distance
       averageDistance = (averDist[0] + averDist[1] + averDist[2]) / 3;
       Serial.println(averageDistance);
   
       // Control the servo based on the averaged distance
       if (averageDistance <= distanceThreshold) {
           servo.attach(servoPin);  // Reattach the servo before sending a command
           delay(1);
           servo.write(openAngle);  // Rotate the servo to the open position
           delay(3500);
       } else {
           servo.write(closeAngle);  // Rotate the servo back to the closed position
           delay(1000);
           servo.detach();  // Detach the servo to save power when not in use
       }
   }
   

4. Distance Reading Function

   This function, readDistance(), is what actually interacts with the ultrasonic sensor. It sends a pulse and waits for an echo. The time taken for the echo is then used to calculate the distance between the sensor and any object in front of it.

   You can refer to the Principle of the ultrasonic sensor.

   float readDistance() {
       // Send a pulse on the trigger pin of the ultrasonic sensor
       digitalWrite(trigPin, LOW);
       delayMicroseconds(2);
       digitalWrite(trigPin, HIGH);
       delayMicroseconds(10);
       digitalWrite(trigPin, LOW);
   
       // Measure the pulse width of the echo pin and calculate the distance value
       float distance = pulseIn(echoPin, HIGH) / 58.00;  // Formula: (340m/s * 1us) / 2
       return distance;
   }
   

5. Servo Write Function

   This function maps the angle value to pulse width and calls the writeMicroseconds(pulseWidth) function to deflect the servo to a specific angle.

   // Function to make the servo work
   void servoWrite(int angle){
       int pulseWidth = map(angle, 0, 180, minPulseWidth, maxPulseWidth);
       servo.writeMicroseconds(pulseWidth);
   }