Checklist

• Linked to the group assignment page
• Documented what you have learned in electronics design
• Checked your board can be fabricated
• Explained problems and how you fixed them
• Included original design files (Eagle, KiCad, etc.)
• Included a ‘hero shot’

Group Assignment

The objective of this group assignment is to use the available test equipment in the lab to observe and analyze the operation of a microcontroller-based circuit board. This involves understanding how signals behave in real time and how different components interact within the system.

As a minimum requirement, the use of a logic analyzer must be demonstrated. This tool allows capturing and visualizing digital signals, making it possible to inspect communication protocols, timing relationships, and signal integrity between components.

Through this activity, the goal is to gain practical experience in debugging and validating embedded systems using professional measurement tools, reinforcing theoretical knowledge with real-world observation.

All findings, procedures, and results must be documented on the group assignment page. Additionally, each team member should include a personal reflection on their individual page, describing what they learned and how the experience contributed to their understanding of microcontroller systems and electronic testing.

Open Group Assignment

Electronic Circuit Design – LED Roulette (XIAO ESP32-C3)

This circuit is designed to simulate a roulette effect using 7 LEDs controlled by a Seeed XIAO ESP32-C3 microcontroller. The system sequentially activates each LED to create a dynamic visual pattern, similar to a spinning wheel that eventually stops at a random position.

Components Used

• 1 × XIAO ESP32-C3 (microcontroller)
• 7 × LEDs (any color or combination)
• 7 × Resistors (220Ω – 330Ω) (current limiting)
• 1 × Breadboard
• Jumper wires

Pin Configuration

Each LED is connected to a dedicated GPIO pin of the XIAO ESP32-C3:

• D0 → LED 1
• D1 → LED 2
• D2 → LED 3
• D3 → LED 4
• D4 → LED 5
• D5 → LED 6
• D6 → LED 7

Electrical Connections

Each LED is connected in series with a resistor to protect it from excessive current:

• The anode (+) of each LED connects to a GPIO pin.
• The cathode (-) connects to a resistor (220Ω–330Ω).
• The other end of the resistor connects to GND.

This configuration ensures that when a GPIO pin outputs HIGH (3.3V), the corresponding LED turns ON, and when LOW, it turns OFF.

System Behavior (Roulette Logic)

The program controls the LEDs in a sequential loop:

• LEDs turn ON one by one in rapid succession (scrolling effect).
• The speed gradually decreases to simulate a spinning roulette slowing down.
• The sequence stops at a random LED, indicating the final “selection”.

Design Considerations

• Current Limiting: Resistors are essential to prevent damage to LEDs and GPIO pins.
• GPIO Limits: The ESP32-C3 can safely drive multiple LEDs, but total current must remain within limits.
• Timing Control: Delays or timers are used to create smooth animation and deceleration.
• Expandability: The design can be extended with a push button to trigger the roulette or reset it.

Simulation in Wokwi – LED Roulette (XIAO ESP32-C3)

The LED roulette system was first validated using Wokwi, an online simulation platform that allows testing both circuit connections and embedded code before implementing the design in physical hardware.

Step-by-Step Simulation Workflow

1. Create a New Project:
   Access wokwi.com and create a new project selecting the ESP32-C3 as the main microcontroller.
2. Add Components:
   Insert the required components into the workspace:
   • 7 LEDs
   • 7 resistors (220Ω)
   • ESP32-C3 board
3. Wire the Circuit:
   Connect each LED to a GPIO pin (D0–D6). Each LED must be connected in series with a resistor, and all resistors must go to GND. This replicates the real circuit configuration.
4. Insert the Code:
   Open the code editor in Wokwi and paste the Arduino-based program that controls the LED sequence (roulette effect). The code defines pin modes and controls the timing of each LED.
5. Run the Simulation:
   Click the “Start Simulation” button. The LEDs will begin to turn on sequentially, creating the roulette effect. The speed variation (if implemented) will simulate acceleration and deceleration.
6. Validate Behavior:
   Observe that:
   • Each LED turns ON and OFF correctly
   • The sequence follows the programmed order
   • The final stop occurs as expected (random or fixed)
7. Debug if Necessary:
   If any LED does not behave correctly:
   • Check wiring connections
   • Verify correct GPIO pin assignment
   • Review delays and logic in the code

Advantages of Simulation

• Prevents hardware damage by testing virtually
• Allows rapid iteration and debugging
• Validates logic before physical implementation
• Helps understand circuit behavior step-by-step

Using Wokwi significantly improves the development workflow by ensuring that both the circuit design and the program logic are correct before assembling the real system.

Schematic Design Process in KiCad – LED Roulette (XIAO ESP32-C3)

The schematic of the LED roulette system was developed using KiCad, an open-source electronic design automation (EDA) tool. This stage is essential to define electrical connections clearly before moving to PCB design or physical prototyping.

Step-by-Step Workflow

1. Create a New Project:
   Open KiCad and create a new project. This generates the main files for schematic and PCB design.
2. Open Schematic Editor:
   Launch the Schematic Editor to begin designing the circuit diagram.
3. Add Components:
   Use the component library to insert:
   • Microcontroller module (XIAO ESP32-C3 or generic ESP32 symbol)
   • 7 LEDs
   • 7 resistors (220Ω)
   • Power symbols (GND)
4. Assign GPIO Pins:
   Connect each LED to a specific GPIO pin:
   • D0 → LED1
   • D1 → LED2
   • D2 → LED3
   • D3 → LED4
   • D4 → LED5
   • D5 → LED6
   • D6 → LED7
5. Wire the Circuit:
   Draw connections between components:
   • GPIO pin → LED anode (+)
   • LED cathode (−) → resistor
   • Resistor → GND
   This ensures proper current flow and protection of the LEDs.
6. Add Labels and References:
   Assign reference labels (R1–R7, LED1–LED7) and optionally name signals to improve readability and organization.
7. Electrical Rules Check (ERC):
   Run the ERC tool to detect errors such as unconnected pins, missing grounds, or incorrect connections. Fix any issues before proceeding.
8. Assign Footprints:
   Link each schematic component to a physical footprint (for PCB design), such as SMD or through-hole LEDs and resistors.
9. Save and Prepare for PCB Layout:
   Once the schematic is validated, it can be transferred to the PCB editor for board design and routing.

Design Considerations

• Current Limiting: Each LED must include a resistor to avoid overcurrent.
• Clear Pin Mapping: Maintain consistency between schematic and code pin assignments.
• Readability: Proper labeling and organization simplify debugging and future modifications.
• Scalability: The design can be extended by adding more outputs or input controls.

This schematic design process ensures a clear and reliable representation of the circuit, serving as the foundation for both simulation, PCB fabrication, and physical implementation.

• Generate Gerber Files
• Generate Drill Files
• Plot F.Cu, B.Cu, Edge.Cuts, F.SilkS, F.Mask

Conclusions, Challenges, and Solutions

Conclusions

This assignment provided a comprehensive understanding of the complete workflow in electronics design, from schematic creation in KiCad to PCB fabrication and embedded programming using the XIAO ESP32-C3. It reinforced key concepts such as GPIO control, circuit design rules, and the relationship between hardware and software.

Additionally, the integration of simulation tools, PCB design, and real-world testing allowed a better understanding of how theoretical knowledge is applied in practical scenarios. The LED roulette system demonstrated how multiple outputs can be controlled efficiently to generate dynamic behaviors.

Problems Encountered

• Incorrect pin mapping: Initial confusion between GPIO numbering and board labeling caused LEDs not to respond as expected.
• PCB design errors: Some traces were too close or incorrectly routed, leading to potential manufacturing issues.
• Simulation vs reality differences: The circuit behaved correctly in simulation but required adjustments when implemented physically.
• Soldering and connections: Poor connections initially caused intermittent behavior in the circuit.

How the Problems Were Solved

• Pinout verification: The official pinout diagram of the XIAO ESP32-C3 was reviewed to ensure correct mapping between code and hardware.
• Design rule checks (DRC/ERC): KiCad tools were used to identify and fix routing and connection errors.
• Iterative testing: The system was tested step-by-step, first in simulation (Wokwi) and then on physical hardware.
• Improved assembly: Connections were reorganized and solder joints were corrected to ensure stability.

Final Reflection

Overcoming these challenges strengthened problem-solving skills and highlighted the importance of iterative design, testing, and validation. The experience demonstrated that successful electronic system development requires careful planning, attention to detail, and continuous debugging.