DigiTekXplorer - Capstone Project

A mind map is a diagram used to visually organize information into a hierarchy, showing relationships among components of the project. It is often drawn as an image and associations of the system components or concepts.  Components or concepts are represented as circles with arrows or lines all leading to the center or the main concept. 

The second level components or concepts are:

• System Requirements
• Design Process
• Real-Time Operating System: Multitasking
• Communications
• Inputs and Outputs
• Project Coding Language
• Code Build Process
• Software Version Control
• Schematic Capture and PCB Design

System Requirements

Engineering system requirements are a set of specifications that detail the precise functions, performance, and constraints of a system. They serve as the foundational document for the entire engineering process, guiding design, development, testing, and deployment.

System requirements are a fundamental part of the system design process and should be defined before starting a new project. In our case, the B_Bot system, we define simple requirements to guide the development process. The following items are requirements for our system.

1. Low cost (less than $150)
2. Low power 
3. Mobile
4. Communications
   1. Serial: UART, I2C
   2. Wireless (Bluetooth)
5. Programmable
6. Easy to use software development environment
7. Microcontroller Multitasking (FreeRTOS)
8. Main Controller: Raspberry Pi Pico W (or Pico 2 W)
9. Collision avoidance (ultrasonic ranging)
10. Software version control (GitHub)
11. Hardware development
    1. Chassis & motors
    2. Motor drivers
    3. Power supply
    4. Ultrasonic sensor (HC-SR04)
    5. Connectors and cables
12. Positive learning experience (Have Fun!)

Desgin Process

 Here is an overview of the engineeing design process

• Define the Problem
  • B_Bot system requirements
• Conduct Research
  • started with a previous design (A_Bot)
• Brainstorm & Conceptualize
  • used mind maps
• Create a Prototype
  • several subsystem prototypes were created
• Select & Finalize
  • selected final electrical components
• Product Analysis
• Improve Product Design

In our informal design process, we did not adhere to all steps of the design process.  For example, a product analysis was not performed.  The final step, improve the product design, is an ongoing step that may continue for an extended period. 

Real-Time Operating System: Multitasking

A "real-time operating system" (RTOS) is a specialized operating system designed to manage and prioritize tasks within strict time constraints, guaranteeing timely responses to events and making it suitable for critical applications where fast and predictable processing is essential. Essentially, it ensures tasks are completed within specified deadlines, often measured in milliseconds, by prioritizing tasks based on their time sensitivity.

FreeRTOS was used in the B_Bot's Pico W.  FreeRTOS is a market-leading embedded system RTOS supporting many processor architectures, including the Pico's RP2040, with a small memory footprint, fast execution times, and cutting-edge RTOS features and libraries. It’s open-source and actively supported and maintained. 

Communications

Serial Interface (wired):  Universal Asynchronous Receiver / Transmitter (UART)

Wireless: Bluetooth Low Energy (BLE)

Inputs and Outputs

Microcontroller Input/Output (IO)

Outputs: LEDs, motor control, SSD1306 display, HC-SR04 ultrasonic module trigger, and UART TX.

Inputs:  Ultrasonic module echo, pushbuttons, battery voltage analog level, and UART RX.

Project Coding Language

The Raspberry Pi Pico supports two high-level languages (C and MicroPython) and assembly language.  For the B_Bot project the C language was selected because FreeRTOS and BTstack are written in C therefore the coding environment is naturally easier to configure in C.

Code Build Process

Because C was chosen as the project language, we needed a build process that would support C.  There are several tools and build processes that also support the Raspberry Pi Pico.  Two examples are Visual Studio Code (VSC) and the Makefile process.

Software Version Control

We use Git and GitHub to maintain version control for the B_Bot project.

Schematic Capture and PCB Design

We used KiCad for schematic capture and Printed Circuit Board (PCB) design.

The B_Bot top-level block diagram shows the key electrical components or modules.

The Raspberry Pi Pico W (or Pico 2 W) is at the center of the diagram and is the most important device in the system. The motor driver module is connected to control signals from the Pico W and outputs bi-directional power lines to both DC motors. The ability of the motor driver to provide bi-direction current to the motors allows us to move the vehicle forward and backward. The motor driver also provides a higher voltage, and much higher currents required to drive the motors.

The HC-SR04 ultrasonic module accepts a trigger signal from the Pico W (or 2 W) and returns an echo signal indicating the distance to an object in front of the vehicle. The DC-DC converter takes in a battery voltage from 5V to 30V and regulates an output voltage of +5V with an output current of 1.5A.

KiCad V8.0 was used for the B_Bot's Printed Circuit Board (PCB) design.   The PCB is a two-layer board with 3.0 x 3.1 inch dimensions.  

The B_Bot PCB was fabricated at PCBWay.