Electronics
Design

An EDA Tool (Electronic Design Automation Tool) is software used to design, simulate, and analyze electronic circuits and PCBs. These tools allow engineers to create schematics, design board layouts, verify electrical connections, and generate manufacturing files.

EDA tools are essential in modern electronics because they reduce design errors, improve precision, and speed up the development process. Commonly used tools include KiCad, Altium Designer, EAGLE, and Fusion 360.

Designing a development board means creating a PCB centered around a microcontroller for prototyping and testing. It covers schematic design, component selection, PCB layout, and design rule verification — then the board can be programmed for specific tasks, connecting with the embedded programming work from Week 4.

Through-Hole Technology (THT) passes components through drilled holes for strong mechanical support. Surface Mount Technology (SMT) mounts SMD components directly on the surface, enabling smaller designs. In Fab Academy, we primarily use SMD components.

With our instructor, we reviewed the main components of embedded programming — resistors, diodes, transistors, inductors, and push buttons — focusing on their function and interaction within a circuit.

Key Components

• Resistors (110 Ω) — Not polarized. Limit current and protect components.
• LED — Polarized (anode/cathode). Requires a resistor to prevent burnout.
• Transistor — Electronic switch with emitter (E), collector (C), base (B). Fundamental for logic gates.
• Diode — Allows current in one direction only. Protects the microcontroller.
• Inductors — Store energy as a magnetic field.

Push Button & Pull-Down Resistor

Without a resistor, a button input becomes a floating point — unstable, randomly reading HIGH or LOW. A pull-down resistor (10 kΩ) to ground ensures LOW when not pressed, HIGH when pressed.

My Group Contribution: Together with my lab group, we characterized the functionality of fundamental lab equipment including the Prasek Premium PR-85 multimeter and the Siglent SDS 1102CML+ oscilloscope. I documented the DC voltage measurements on various components, led the experiments testing LEDs under different voltage conditions, and recorded the PWM signal behavior analysis on the oscilloscope.

Click each concept to expand its formula and explanation.

The Prasek Premium PR-85 is a digital multimeter that allows measuring different electrical quantities and verifying whether components are working correctly. Each function below is color-coded to match the physical device dial — click any to expand.

01 · DC Voltage (V⎓) +

Scales: 200 mV · 2 V · 20 V · 200 V · 1000 V

Used to measure: voltage from regulated supplies, microcontroller output, LEDs, sensors, etc.

Our experiment: Placed in series with the yellow LED, at the 20 V range, we read approximately 2.93 V being supplied to the LED — dropping to zero when the microcontroller turned the LED off. Although the microcontroller runs at 3.3 V, this lower reading indicates the connected GPIO pin is worn and doesn't supply its full rated voltage.

06 · Continuity Test & Diode Test ➤|— +

This function is found on the same selector position as the diode symbol. It does not work with a numerical scale — it is a quick verification tool.

When there is a connection between two points and the resistance is very low, the multimeter emits a beep. Used to verify that a trace or cable is properly connected.

⚠️ Important: The board must be powered off before using continuity. Place the probes on the copper trace to check the connection.

Diode Test ➤|— Verifies that a diode conducts in only one direction and measures its forward voltage drop. Very useful for identifying anode and cathode before soldering:

• Black probe → Cathode
• Red probe → Anode

💡 LED Experiment — SMD vs THT: We tested green SMD and transparent THT LEDs on a breadboard. To light a LED, the Black probe must go to the Cathode and the Red probe to the Anode. We observed that the voltage the multimeter provides in diode test mode (~2.7 V) is not enough to light the transparent LED, but it does light the SMD green ones.

Unlike the multimeter, the oscilloscope visualizes how voltage changes over time. Y-axis = voltage · X-axis = time. The trigger system stabilizes the signal for clean analysis.

We built a test circuit with a Raspberry Pi Pico W2 and an LED, controlling it via PWM programmed in Thonny:

A low duty cycle (5%) produces short PWM pulses:

A high duty cycle produces longer PWM pulses:

Multimeter Voltage on the Oscilloscope

The oscilloscope detected the multimeter providing ~2.7 V during diode test mode — explaining why components requiring more than 2.8 V won't activate.

⚡ Duty Cycle — The Key Parameter +

The duty cycle is the percentage of time the signal is HIGH within one full period.

Duty Cycle (%) = (Time HIGH / Total Period) × 100

• 50% → equal on/off time
• Higher % → more average power → LED brighter
• Lower % → less average power → LED dimmer

Variable voltage (0–30 V) and adjustable current (0–10 A). Shows consumed current in real time for safe testing. We found the transparent LED's turn-on threshold: 3 V.

Supporting Elements

• Voltage divider — Steps down voltage using resistors (e.g., 12 V → 5 V for a sensor).
• Electrolytic capacitor — Cylindrical, polarized. Filters voltage variations and reduces electrical noise.

I used a 6mm push button and a green LED on the XIAO ESP32-S3. The button simulates each towel dispense — every press blinks the LED and increments a counter. At 10 presses, the system warns that towels have run out and resets automatically.

Code

#define BUTTON_PIN D4
#define LED_PIN D3

int count = 0;

void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  Serial.println("Hello world!");
  Serial.println("Hygiene dispenser ready!");
  Serial.println("Counter: 0/10");
}

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    count++;
    // LED blinks 3 times as confirmation
    for (int i = 0; i < 3; i++) {
      digitalWrite(LED_PIN, HIGH);  delay(200);
      digitalWrite(LED_PIN, LOW);   delay(200);
    }
    if (count >= 10) {
      Serial.println("✅ Dispenser activated!");
      Serial.println("⚠️  Limit reached! Resetting...");
      count = 0;
      Serial.println("Counter: 0/10");
    } else {
      Serial.println("✅ Dispenser activated!");
      Serial.print("Counter: ");
      Serial.print(count); Serial.println("/10");
    }
    delay(500);
  }
}

This was my first time designing a PCB. I was excited to create a custom board for the HigiBox project. I used Autodesk Fusion 360 to design both the schematic and the PCB layout. The design included all components integrated directly on the board: an LED indicator, a power button, pull-up resistors, an N-Channel MOSFET for motor control, and a Schottky diode for motor protection.

Before starting, I downloaded the Fab Academy component library: gitlab.fabcloud.org/pub/libraries/electronics

My schematic included: GPIO connections, power distribution, sensor connector header, and motor control circuit with MOSFET and flyback diode.

After placing all components and routing the traces, I ran the Design Rules Check (DRC) in Fusion 360 to validate that the design was manufacturable.

PCB Layout View:

The DRC report showed the extent of the failures:

This design was not fabricated. It required a complete redesign that led to PCB Version 2 in Week 8.

During Week 6, I designed my first PCB — but it wasn't good enough. For the Week 8 assignment, I decided to completely redesign the board from scratch. In the first version, I made the critical mistake of integrating 15+ components directly on the PCB. After analyzing the failed design and feedback from my instructor, I realized that several of these components could instead be connected using available free pins through header connectors.

Including everything on the board was unnecessary, created a cramped layout, and caused copper traces to cross each other — which could lead to short circuits and fabrication failures during the milling process.

Before & After Comparison

❌ Before — Version 1 (Week 6)

186 DRC Errors
15+ integrated components
Traces crossing (shorts)
Dense, unroutable layout
Not fabricated

✅ After — Redesigned (Week 8)

DRC Passed ✓
Simplified core circuit
Clean trace routing
Modular header design
Successfully fabricated

A critical part of the redesign was creating custom SMD header connectors. The same four-step procedure was followed to create the pin connectors: 1×3, 1×4, and 1×6. Here's the detailed process:

1 Configure Component Properties

The component editor opens in Fusion 360. On the right panel, fill in the Name field (e.g., "CONN_1X3_SMD") and Prefix field (e.g., "J1" for the first connector). Click Añadir símbolo to link an existing symbol from the library, and click Nueva huella to create the PCB footprint.

💡 Pro Tip: Always name components descriptively ("CONN_1X3_SMD") and use the prefix system (J for connectors, U for ICs, R for resistors). This makes schematic reading and BOM generation much easier.

2 Verify Symbol and Associate the Footprint

The left panel in Fusion shows the hierarchical component structure with three levels: component (top level), symbol (schematic representation), and footprint (PCB layout representation). Each level can be edited separately by clicking on it. Verify that both the symbol and footprint are properly assigned before proceeding.

⚙️ Component Hierarchy: The component is the overall object. The symbol is its schematic icon (how it appears when drawing circuits). The footprint defines the physical pads and outline for PCB manufacturing.

3 Edit the Footprint in the Footprint Editor

Fusion 360 automatically opens the HUELLA (Footprint) tab when you edit the footprint. You can see the SMD pads laid out and numbered 1 to 6 (for a 1×6 connector), vertically aligned on the ct Top copper layer. The pads are rectangular SMD pads optimized for hand-soldering.

📏 Pad Sizing Guidelines: For hand-soldering SMD components, pads should be approximately 3mm × 1.5mm. Pin-to-pin spacing should match standard header spacing (2.54mm/100mil for standard connectors). Too small = cold joints; too large = wasted space.

After the Week 6 failure, I completely redesigned the PCB for Week 8. This version was simplified, optimized for fabrication, and successfully fabricated using the Roland Modela Pro II MDX-540 CNC milling machine.

Week 8 PCB Journey: Schematic → Traces → Fabricated Board → Design Rules ✅ Passed

By Week 15, I had identified additional improvements needed for system integration. The third PCB version was designed with more header outputs, better organization, and full pin management for all HigiBox subsystems.

Week 15 PCB Journey: Enhanced Schematic → Improved Routing → Final Integration → Design Rules ✅ Passed

The final PCB design for HigiBox integrated all lessons learned from previous iterations. This version connected every subsystem seamlessly: sensors, motors, display, power management, and microcontroller, all working in perfect harmony.

Week 20 Final PCB: Complete Schematic → Final Traces → Manufacturing Ready → Design Rules ✅ Perfect