LiDAR Learning
LiDAR learning was my senior design project in my final semester at Purdue. I worked as an electrical engineer on a team of 4 with three computer engineering students. My responsibilities were to guide and lead the team as well as develop the power system for the project and design the PCB for our end product.
Please see below for more details on the project!
Project Photo
Project Overview
The primary goal of this project is to design a device that assists teachers in identifying potential threats outside their classrooms without compromising their safety. The device integrates a camera mounted on a servo motor, a LiDAR sensor, and a light sensor to provide a comprehensive monitoring system. The camera captures real-time video, while the LiDAR sensor detects the location of subjects outside the classroom. This data is processed by a microcontroller, which controls the servo motor to keep the subject centered on the monitor inside the classroom. Additionally, an LED light is activated in low-light conditions to ensure clear visibility.
Demo Video
Inspiration
The Oxford High School shooting during my Fall 2021 internship in Michigan took place nearby and deeply affected me. As an engineer, I immediately began thinking about how technology could help mitigate such tragedies. My initial concept involved a comprehensive defense system using strategically placed LiDAR sensors throughout a school to track individuals in real-time. This LiDAR tracking data would be the input for a neural network designed to identify potential threats and, based on its analysis, control the building's doors. By analyzing movement patterns, the system could identify potential threats and quickly and safely contain them, limiting their mobility. This would allow students and staff in unaffected areas to evacuate safely while the threat was isolated.
Budget Constraints
Due to a limited budget of approximately $400, the project scope had to be significantly reduced. This constraint prevented the team from developing the multiple-device system and incorporating the machine learning capabilities of multiple scanners that my original vision entailed. Despite these limitations, we successfully created a functional safety device using a single 2D LiDAR scanner and a camera.
Key Features and Design Requirements
LiDAR Sensor: The RPLiDAR sensor scans the hallway and detects moving subjects. It provides accurate distance and angle measurements, which are used to control the camera's movement.
Camera and Servo Motor: The camera pedestal rotates to follow the moving subject as indicated by the LiDAR mapping. This ensures continuous monitoring of potential threats.
Light Sensor and LED: A photoresistor detects the brightness of the environment and activates an LED fixture if the hallway is too dark. This feature ensures that the camera can capture clear video even in low-light conditions.
Power Supply: The device is powered by a standard wall outlet, making it easy to install and use in any classroom.
User-Friendly Interface: A TFT display inside the classroom receives continuous live video feed via WiFi connection. An on/off switch is located next to the display for easy control.
System Integration and Operation
The system is designed for easy mounting outside classrooms and is powered by standard wall power. The LiDAR sensor continuously scans the surrounding area, tracking the closest object and rotating the camera to the corresponding angle. During a lockdown, the integrated illumination system activates, ensuring clear visibility for the camera. The video feed is then wirelessly transmitted to a display inside the classroom, allowing teachers to monitor the situation without exposing themselves to potential threats.
System Block Diagram
System Block Diagram Explained
The 5 Subsystems
RPLiDAR - Self-contained LiDAR, controlled by ESP32-S2
ESP32-S2 - Main controller, processes LiDAR data, controls hardware
ESP32 - Camera/controller interface, Bluetooth communication
Camera Support - Servo-driven camera mount, light sensor, lighting
Power System - AC/DC converter, 3.3V buck converter
My Responsibilities:
As the EE guy on the team, my main responsibility was to design the power system for the project. The +3.3V rail powers the ESP32-S2 and its USB interface components, while the +5V rail powers the remaining components and sensors. The external display is powered via a dedicated +5V DC cable.
Power Subsystem Block Diagram
Buck Converter
I designed a buck converter voltage regulator using TI's LMZ10504. Prototyping on a copper clad board proved challenging. After resoldering two times, I was confident it wasn't a soldering issue or design flaw. Throughout the process, I used an oscilloscope to verify inputs and outputs and double-checked my feedback loop design. Despite the resistors being within the datasheet's specified range, my testing pointed to the feedback loop as the problem.
Confused, I consulted our lab mentor, a retired circuit designer with over 40 years of experience. He independently diagnosed the issue as the feedback resistors, specifically R1 and R2. While the datasheet values seemed appropriate, they were too high, preventing sufficient current from reaching the IC's feedback pin for proper regulation. We lowered the resistor values, and the regulator then functioned as expected. This taught me a valuable lesson of the importance of experience; sometimes, theory and datasheets just aren't enough.
PCB Design
During one of my internships, I gained experience reading schematics and PCB layouts, and sat in on a design review where experienced avionics designers critiqued a junior designer's work. Those two hours were a crash course in PCB design.
For our senior design project, I volunteered to design the PCB, which involved consolidating subsystem schematics and tackling the puzzle of component placement. Our focus was on placing components according to physical interface locations, not size or efficiency. While I wouldn’t want to do it 100% of the time, I find PCB design, like coding, to be a rewarding exercise.
Whether through luck or thorough preparation, our PCB and components worked perfectly after assembly. Teammates 3D-printed camera and controller enclosures, and we had a laser-cut enclosure fabricated. We were quite happy and proud of how our final product turned out!
