Project: Automated Optical Sorting - Ariana Sadeghi (#1014)

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Co-authored-by: Omer Genan <81963672+genan2003@users.noreply.github.com>

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Co-authored-by: POPAGEORGEMATEI <119328898+POPAGEORGEMATEI@users.noreply.github.com>
Co-authored-by: Omer Genan <81963672+genan2003@users.noreply.github.com>

Author: 3 people

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+# Automated Optical Sorting System
+An automated system designed to identify and sort objects based on their optical properties and weight using an STM32 microcontroller and Rust (Embassy).
+
+:::info
+**Author:** Ariana Sadeghi \
+**GitHub Project Link:** [GitHub Repo](https://github.com/UPB-PMRust-Students/acs-project-2026-arianasadeghi)
+:::
+
+## Description
+The project consists of an industrial-style sorting line that uses a TCS34725 color sensor to detect the RGB signature of objects and an HX711 load cell for weight validation. Based on the sensor data, a custom calibration algorithm classifies the items. A mechanical arm (SG90 servomotor) acts as the sorting mechanism, while a stepper motor drives the conveyor belt continuously. The system's status and detected colors are visually fed back in real-time through an SPI TFT display.
+
+## Motivation
+I chose this project to explore the integration of multiple digital communication protocols (I2C, SPI) and precise motor control (PWM and Stepper sequences) in a real-time automation scenario using the Embassy async framework in Rust.
+
+## Architecture
+**Main Components**
+* **Sensing Module:** TCS34725 Color Sensor (I2C) for optical recognition and HX711 Amplifier with a Load Cell for weight detection.
+* **Control Logic:** Continuous polling loop acting as a state machine for detection, classification, and precise timing delays.
+* **Actuation Module:** 28BYJ-48 Stepper motor (with ULN2003 driver) for the conveyor belt and an SG90 Servomotor (PWM) for the sorting arm.
+* **User Interface:** TFT LCD display controlled via SPI to show current calibration data and detected colors.
+
+## Log
+* **Week 5 - 11 May:** Project idea selection and hardware requirements gathering. Basic component testing (Stepper and Servo motors) and pinout planning.
+* **Week 12 - 18 May:** Color sensor (TCS34725) I2C integration, TFT display SPI setup, and writing the initial color calibration logic.
+* **Week 19 - 25 May:** Finalizing the state machine integration in Rust, fine-tuning the RGB calibration thresholds for specific object colors, adjusting servo timings to sync with the conveyor belt, and completing GitHub documentation.
+
+## Hardware
+The system is built around an STM32 Nucleo board programmed in Rust. 
+The main peripherals include:
+* **TCS34725:** RGB Color Sensor for object detection.
+* **HX711:** Load cell amplifier with a 1kg/5kg load cell.
+* **1.8" TFT Display:** SPI-driven screen for visual feedback.
+* **28BYJ-48 Stepper Motor & ULN2003:** Drives the conveyor belt.
+* **SG90 Servomotor:** Acts as the sorting arm.
+
+## Schematics
+![Schema Hardware](./diagrama_pm.svg)
+
+## Physical Implementation
+Below are the layout views of the fully assembled automated sorting system, showcasing the conveyor alignment, sensor housing, and mechanical integration.
+
+![Overall System Assembly](./project.webp)
+*Figure 1: Overall assembly of the conveyor belt line and electronics integration.*
+
+![Sensing Zone and Optical Shield](./color_sensor.webp)
+*Figure 2: Close-up of the TCS34725 color sensor featuring a custom paper shield to block ambient light reflections.*
+
+![Sensing Zone with Object](./object_sensor.webp)
+*Figure 3: Color sensor actively scanning an object passing underneath on the conveyor belt.*
+
+![Stepper Motor Drive](./step_motor.webp)
+*Figure 4: The 28BYJ-48 stepper motor and mechanical coupling driving the conveyor belt.*
+
+![Sorting Servo Arm](./servo_in_action.webp)
+*Figure 5: SG90 servomotor configured as the sorting arm, positioned to intercept rejected items.*
+
+![TFT Interface](./object_display_color.webp)
+*Figure 6: The 1.8" SPI TFT display providing real-time visual feedback of the detected colors.*
+
+![TFT Interface Close-up](./display.webp)
+*Figure 7: Close-up view of the TFT screen displaying active color recognition.*
+
+![STM32 Nucleo Wiring](./stm32.webp)
+*Figure 8: The STM32 Nucleo board handling all I2C, SPI, and PWM signals asynchronously.*
+
+
+## Bill of Materials
+
+| Device | Usage | Price |
+|---|---|---|
+| STM32 Nucleo Board | Main Microcontroller | - |
+| TCS34725 Module | Optical/Color Sensing | 22,68 RON |
+| HX711 | Weight Sensing | 4,57 RON |
+| Load Cell | Weight Sensing | 12,80 RON |
+| 1.8" TFT Display | User Interface | 40,62 RON |
+| 28BYJ-48 | Conveyor movement | 10,29 RON |
+| ULN2003 | Conveyor movement | 4,97 RON |
+| SG90 Servomotor | Sorting Arm | 9,49 RON |
+
+## Software
+
+**Concurrency & Async Execution**
+The software architecture leverages the cooperative multitasking model provided by the Embassy framework in Rust. Since the stepper motor requires precise step impulses every 3ms to maintain constant conveyor speed, a traditional blocking approach (`delay_ms`) would freeze sensor polling and screen updates. By utilizing `async/await` and asynchronous hardware timers (`Timer::after_millis`), the system interleaves the conveyor drive loop, the I2C color polling, and the SPI screen drawing tasks seamlessly. This ensures zero jitter for the motor and deterministic real-time execution without the overhead of a traditional RTOS.
+
+**System State Machine**
+The control loop operates as a finite state machine (FSM) with the following operational transitions:
+* **IDLE / SCANNING:** Conveyor belt runs continuously; the system polls the TCS34725 Clear channel waiting for a threshold drop.
+* **COLOR_IDENTIFICATION:** Object detected; RGB channels are sampled and evaluated against the software-defined calibration boundaries.
+* **WEIGHT_VALIDATION:** The system captures data from the HX711 load cell using a moving average filter to determine and validate the mass.
+* **SORTING_ACTION:** A specific PWM duty cycle is sent to the SG90 servomotor after a precise kinematic delay, moving the arm to sort the object.
+* **RESET:** The servo returns to its default position (0°), the TFT display resets to idle status, and the FSM returns to the scanning state.
+
+**High-Level Logic**
+Practically, the software follows these stages during a successful sorting cycle:
+1. **Movement:** The stepper motor runs continuously using a non-blocking sequence to drive the conveyor belt.
+2. **Detection:** Continuous polling of the TCS34725 sensor via I2C to read Clear, Red, Green, and Blue light channels, alongside weight readings from the HX711.
+3. **Decision:** Comparing RGB values against preset, fine-tuned thresholds to identify specific colors (e.g., White, Yellow, Pink, Purple, Brown).
+4. **Action:** Updating the TFT display with the detected color and triggering a precise PWM sequence to extend and retract the Servo arm at the exact moment the object passes.
+
+**Libraries and Drivers**
+
+| Library | Description | Usage |
+|---|---|---|
+| `embassy-stm32` | Hardware Abstraction (HAL) | Peripheral control (I2C, SPI, PWM, GPIO) |
+| `embassy-time` | Time Management | Delay management and timing for the stepper/servo |
+| `defmt` / `defmt-rtt` | Logging Framework | Real-time debugging and color calibration output |
+
+
+## Links
+* [Embassy Rust Documentation](https://embassy.dev/)
+* [TCS34725 Color Sensor Datasheet](https://cdn-shop.adafruit.com/datasheets/TCS34725.pdf)
+* [HX711 Datasheet](https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/hx711_english.pdf)
+* [Laboratories text](https://embedded-rust-101.wyliodrin.com/docs/acs_cc/category/lab)