Week 6: Electronics Design

Date: February 25 - March 4, 2026 Status: ✅ Complete

What I Did This Week

This week I learned electronics design. I simulated a circuit and designed a PCB using EDA software.

Tools I used: - Falstad — Circuit simulation (web tool) - KiCad — Schematic and PCB design

📋 Assignment

Group Assignment

✅ Use test equipment to observe how a microcontroller works

Individual Assignment

✅ Simulate a circuit ✅ Design a microcontroller board using EDA software

🔬 Group Assignment: Logic Analyzer

Our lab used a Saleae Logic 8 Pro logic analyzer to observe the operation of a microcontroller circuit board.

Setup: - Channel 0 → SDA line - Channel 1 → SCL line - USB connection from analyzer to PC

Procedure: 1. Opened Saleae Logic 2 software 2. Started signal capture 3. Powered on the microcontroller 4. Recorded the I2C communication signals between the microcontroller and its peripherals

We could see the SDA and SCL signals on the screen. This showed how the microcontroller sends data using the I2C protocol.

📎 Group Work Page

💻 Individual Assignment 1: Circuit Simulation

I used Falstad Circuit Simulator to simulate the LED circuit from Week 4.

Tool: Falstad (free web tool, no install needed)

Circuit

I built a simple LED circuit:

3.3V → R1 (1kΩ) → LED → GND

This is the same circuit I made on a breadboard in Week 4.

Step 1: Build and Run the Circuit

I placed a voltage source (3.3V), a resistor (1kΩ), and an LED. Then I clicked RUN / Stop to start the simulation.

The yellow dots show the current flowing through the circuit. The LED lit up.

Falstad Circuit LED circuit running in Falstad

Step 2: Check the Values

I clicked on the LED to see the simulation data.

Falstad Result LED values shown by Falstad

Results:

Item Value
LED voltage (Vd) 1.612 V
Current (I) 1.688 mA
Power (P) 2.721 mW
Resistor voltage 1.688 V (= 3.3V − 1.612V)

What I Learned

I first tried a 10kΩ resistor. The LED did not light up. The current was too small (0.13 mA). I changed it to 1kΩ. The LED lit up at 1.688 mA. This matches the Week 4 circuit.

Simulation is useful. I can test values before building the real circuit.

🖥️ Individual Assignment 2: PCB Design with KiCad

I designed an embedded microcontroller board based on the Week 4 circuit. The board uses a Seeed XIAO SAMD21 as the MCU. It has a tactile switch and an LED.

All parts (resistor, LED, switch) are from the Fab Lab inventory.

Board name: Test Board MCU: Seeed XIAO SAMD21 (represented by two 7-pin headers)

Step 1: Draw the Schematic

I opened KiCad and drew the schematic.

Components:

Reference Part Value
J1, J2 PinHeader_1x07 XIAO SAMD21 (left/right pins)
SW1 Tactile switch Button
R1 Resistor 1KΩ
D1 LED Red

The XIAO SAMD21 does not have an official KiCad symbol. So I used two 7-pin headers (J1 and J2) to show the left and right pin rows of the XIAO board.

Schematic Step 1 Early stage — components placed, before wiring

I connected the pins with net labels: - D1 label → J2 pin 2 (D1 on XIAO) → SW1 pin 1 - D7 label → J1 pin 7 (D7 on XIAO) → R1 → LED anode - GND and +3V3 power symbols connected to each component

Schematic Completed schematic

Circuit logic: - Button (SW1) connects D1 to GND. XIAO uses INPUT_PULLUP mode. - D7 drives current through R1 (1KΩ) and LED to GND. - This is the same circuit I tested in Week 4.

Step 2: ERC (Electrical Rules Check)

I ran the ERC to check for errors.

ERC Warnings Two warnings found

Warnings I fixed:

Warning Cause Fix
5V and GND on same net Wrong label on J1 pin Corrected the label
No-connect flag on connected pin Extra X mark on D1 pin Deleted the X mark

After fixing, the ERC showed Errors: 0 / Warnings: 0.

Step 3: Assign Footprints

I assigned THT (through-hole) footprints to each symbol.

Symbol Footprint
J1, J2 Connector_PinHeader_2.54mm:PinHeader_1x07_P2.54mm_Vertical
SW1 Button_Switch_THT:SW_PUSH_6mm_H5mm
R1 Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal
D1 LED_THT:LED_D3.0mm

Step 4: PCB Layout

I opened the PCB Editor and placed the components.

Board settings:

Setting Value
Track width 0.5 mm
Clearance 0.5 mm
Board size ~100 × 80 mm
Mounting holes MountingHole_3.2mm_M3 × 4
Copper fill GND (F.Cu)

I set the pin header spacing to 11.4 mm between J1 and J2. This matches the actual XIAO SAMD21 board width.

PCB Layout PCB layout with GND copper fill

Step 5: DRC (Design Rules Check)

I ran the DRC to check the PCB.

DRC Result DRC result — Errors: 0, Warnings: 0

The board passed with no errors.

Step 6: 3D View

I checked the 3D view to see the component placement.

3D View 3D view of the finished board

Note about component side:

All components are THT (through-hole). I plan to mount them from the back side of the board. So I designed all PCB patterns in mirror image (left-right flipped).

The 3D view shows components on the front (pattern) side. But in real use: - Components go in from the back side - Pins come through the holes to the front (pattern) side - Soldering is done on the front side

This is a common approach when making single-sided PCBs with a milling machine at a Fab Lab.

📦 Design Files

All files are in docs/files/week06/Test_Board/.

File Description
Test_Board.kicad_pro KiCad project file
Test_Board.kicad_sch Schematic
Test_Board.kicad_pcb PCB layout

🔗 Connection to Final Project

This week helps my Smart Reptile Habitat System project:

  • PCB design skills → Design a custom sensor control board
  • EDA workflow → I can add temperature, humidity, and UV sensors in the future
  • KiCad practice → Useful for Week 8 (Electronics Production)

🔧 Problems and Solutions

Problem 1: XIAO SAMD21 symbol not in KiCad library

What Happened: I could not find the XIAO SAMD21 symbol in KiCad's standard library.

How I Solved It: I used two Conn_01x07 pin headers (J1 and J2) instead. Each header represents one row of the XIAO's 7 pins. I added net labels for each pin name (D0, D1, D7, GND, 3V3, etc.).

What I Learned: In KiCad, pin headers are a simple way to show modules that don't have official symbols.

Problem 2: ERC warnings after wiring

What Happened: The ERC showed two warnings — a 5V/GND label error and a no-connect flag on a wired pin.

How I Solved It: I corrected the wrong label and deleted the extra no-connect mark.

What I Learned: Always run ERC after wiring. Small mistakes like wrong labels are easy to miss but quick to fix.

⏱️ Time Management

Activity Time Spent
Group test equipment work 1 hour
KiCad schematic 1.5 hours
KiCad PCB layout 1.5 hours
Documentation 1 hour
Total 5 hours

✅ Evaluation Checklist

Group Assignment

  • [x] Used test equipment (Saleae Logic 8 Pro)
  • [x] Observed I2C signals (SDA/SCL)
  • [x] Results on group work page

Individual Assignment

  • [x] Circuit simulation (Falstad)
  • [x] KiCad schematic completed
  • [x] Footprints assigned
  • [x] PCB layout completed
  • [x] DRC passed (Errors: 0)
  • [x] 3D view confirmed

Documentation

  • [x] Screenshots included
  • [x] Design files in repository
  • [x] Images compressed (under 500KB)

💭 Reflection

What Went Well

KiCad was easier than I expected. Using pin headers for the XIAO was a smart solution. The DRC passed on the first try after fixing the ERC warnings.

What I'd Do Differently

I want to make the board smaller next time. The current layout has a lot of empty space.

Lessons Learned

  • EDA tools make it easy to check for errors before manufacturing.
  • Net labels are very useful for keeping schematics clean.
  • Always run ERC and DRC before finishing.

For Next Week — Computer-Controlled Machining

  • Learn about CNC toolpaths and feeds/speeds
  • Plan what to machine for the final project

📚 References

Last updated: March 4, 2026