What it does The “Smart Bin” is an automated trash receptacle that opens its lid automatically when it detects a user's hand approach. Additionally, it continuously monitors the internal trash level, providing comprehensive feedback through an LCD display (showing the exact fill percentage and system status), an LED interface (Green, Yellow, Red for quick visual capacity indication), and an active buzzer (emitting an auditory warning while refusing to open if the bin is completely full).

The purpose of the project The main purpose is to create a hygienic, hands-free waste disposal experience while preventing the common issue of overfilling the bin.

The initial idea The idea stems from the everyday inconvenience of disposing of messy waste (e.g., while cooking) without dirtying the bin's lid. Furthermore, in shared spaces (offices, kitchens), bins often get overfilled because people don't realize the capacity is reached until they force the lid open. Combining motion-sensing opening with a precise, screen-based capacity-monitoring system solves both issues effectively.

Why it is useful This project is highly useful for improving hygiene and sanitation in environments like hospitals, kitchens, or public restrooms by eliminating cross-contamination. For the user, the addition of an LCD display provides clear, precise data regarding the bin's status and when it's time to empty the trash, ultimately promoting better waste management habits.

The system is built around a central microcontroller (AVR ATmega328p) which acts as the main processing unit, orchestrating the inputs and outputs through a non-blocking state machine design. The main loop evaluates sensor data every 500ms to ensure real-time responsiveness without overloading the processor.

Interaction Flow: The system operates in three main states: CLOSED, OPEN, and COOLDOWN.

• Input Layer: Two HC-SR04 ultrasonic sensors act as the “eyes” of the system. The exterior sensor continuously scans for a user's hand (triggering at a distance of ⇐ 20cm). The interior sensor, mounted under the swing-top lid, measures the distance to the trash. To ensure accurate readings (since the sensor tilts when the lid opens), the internal measurement is continuously polled only while the system is in the CLOSED state.
• Processing Layer: The microcontroller receives the distance data. It features a self-healing logic failsafe: if the interior sensor reads a distance greater than the bin's physical depth, it clamps the value to prevent state deadlocks. It calculates the internal trash percentage dynamically. If a hand is detected, it evaluates this percentage to decide the next state.
• Output Layer: * Mechanical Action: If the bin is not full, the microcontroller sends a PWM signal to the SG90 Micro Servo Motor, which acts as a mechanical lever to push the swing-top lid open to 180 degrees. It waits for the user to remove their hand, initiates a 4.5-second timer, and then closes. A 1.5-second cooldown follows to let the lid mechanically settle.
  • Textual Feedback: A 16×2 LCD Display connected via an I2C module shows real-time information, such as the exact trash percentage and system status. The I2C module drastically reduces the number of pins required to interface the screen with the microcontroller (using only SDA and SCL pins).
  • Visual & Auditory Warnings: If the bin is full (>= 85%), the system locks the opening mechanism. The Red LED lights up, and an Active Buzzer emits an error sequence. The fullness level is continuously displayed using 3 LEDs (Green < 50%, Yellow < 85%, Red >= 85%).

To build this project, the following hardware components are used:

• 1x ATmega328p XPlained Mini Microcontroller Board
• 1x Small Swing-Top Plastic Trash Bin
• 2x HC-SR04 Ultrasonic Sensors
• 1x 16×2 Character 1602A LCD Display
• 1x I2C Serial Interface Module for LCD
• 1x SG90 Micro Servo Motor
• 3x LEDs (Green, Yellow, Red)
• 3x 220Ω Resistors
• 1x TMB12A05 Active Buzzer
• 1x Breadboard
• Assorted Dupont Jumper Wires (Male-to-Male, Male-to-Female)

The project is currently in the advanced breadboard prototyping phase. All critical hardware subsystems (distance measurement, visual/auditory feedback, and PWM mechanical actuation) have been successfully wired, integrated, and validated against the microcontroller's logic. The finite state machine correctly drives the hardware inputs and outputs without blocking the CPU execution. The next planned step is the physical mechanical assembly onto the bin chassis and soldering the I2C backpack to the LCD module for the final interface integration.

• ATmega328P Xplained Mini: The main processing unit executing the state machine, reading sensors, and driving actuators.
• HC-SR04 Sensors: Used as digital inputs. The exterior one triggers the bin opening, while the interior one acts as a dynamic level gauge.
• SG90 Servo: Used as a mechanical output to transform the PWM signal into a 180-degree physical rotation for the lid mechanism.
• LEDs & Resistors: Provide immediate visual feedback. The 220Ω resistors are strictly required to limit the forward current (~15mA) and prevent overloading the microcontroller's GPIO pins or burning the LEDs.
• Active Buzzer: Acts as a critical error indicator (auditory output) when a user tries to interact with a completely full bin.
• LCD 1602 + I2C Module: Provides the detailed Human-Machine Interface (HMI). The I2C backpack serializes the data, translating it into parallel instructions for the HD44780 controller on the screen.

The hardware pinout was carefully designed to map specific components to their required internal AVR hardware modules, while explicitly avoiding the SPI pins (PB2-PB5) to prevent programming (ISP) conflicts during development.

The electrical circuit utilizes the breadboard's side power rails as a central power distribution bus.

• Power Bus: The 5V and GND pins from the ATmega328p board are connected directly to the red (+) and blue (-) rails of the breadboard. All sensors and actuators draw power from these rails in parallel to ensure uniform voltage and avoid stressing a single ground pin on the microcontroller.
• Protection Circuits: Each LED anode is connected to a PD GPIO pin, while the cathode routes through a 220Ω current-limiting resistor to the common GND bus.
• I2C Architecture: The LCD module is connected in parallel on the I2C bus (PC4/PC5), taking advantage of the microcontroller's internal pull-up resistors for the serial communication lines.

The images below demonstrate the successful wiring and the functional proof of the hardware logic running on the microcontroller.

1. General Breadboard Prototyping Setup

Explanation: This image presents the complete hardware prototype. The components are wired using the power rails for optimal cable management. The HC-SR04 sensors, the servo, and the LED/Buzzer sub-circuit are successfully interfaced with the Xplained Mini board.

2. Proof of Functionality: The Interlocking Logic (Full Capacity)

Explanation: This test validates the interlocking safety state. An obstacle is placed physically close (< 7cm) to the interior ultrasonic sensor (simulating a trash capacity of > 85%). The microcontroller correctly processes the echo timing, updates the logic state, and physically turns on the Red LED. Simultaneously, the active buzzer is triggered on pin PD5, and the servo motor is software-locked, proving that the hardware responds accurately to environmental inputs.