6. Electronics Design

• Group assignment
  • Use the test equipment in your lab to observe the operation of a microcontroller circuit board (as a minimum, you should demonstrate the use of a logic analyzer)
  • Document your work on the group work page and reflect what you learned on your individual page
• Individual assignment
  • Use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller

Group Assignment

For the group assignment we explored the test equipment in the lab and used them to observe and analyse a working microcontroller circuit.

Multimeter (ZOYI ZT301) used for checking continuity across traces, measuring voltage on the 3.3V and 5V rails, and verifying resistor values.

Oscilloscope (OWON TAO3104A) used a XIAO RP2040 as a function generator to output different waveforms via PWM and observed them live. Since the RP2040 outputs digital PWM, waveforms like sine and triangle are approximations, zoom out on time/div to see the full envelope.

Logic Analyser (Saleae Logic 8) captured and decoded real communication protocols from the RP2040. UART decoded "hello world!" at 9600 baud, and I²C captured communication to an SSD1306 OLED display.

Bench Power Supply provides clean regulated DC power for testing. Set voltage and current limit before powering up.

Full group docs: https://fabacademy.org/2026/labs/kochi/group_assignmetns/week06/

Individual Assignment

Using Wokwi Extension in VSCode

To set up the .json config file, rename it to .txt, paste in the code from the online Wokwi simulator, then rename it back to .json.

In Arduino IDE, go to File → Preferences and enable "Show verbose output during compile". Select the correct board and compile. Once done, the output terminal will show the path to your build directory — navigate there to find the .uf2 and .elf build files.

The output terminal displays the location of the build files. You can either point the .toml directly to that path, or just copy both files into your Wokwi project root folder.

These are the two build files found at the compiled output path.

If you copy both files into the Wokwi root folder, the relative path in your .toml is just the filename itself.

Alternatively, you can skip copying and just link the full absolute path to both files directly in the .toml.

ELF (Executable and Linkable Format) is the standard binary file format on Linux/Unix systems. It acts as a container for machine code and metadata, letting the OS load, link, and execute programs. The three formats compared:

1. BIN — a raw byte-for-byte image of what goes into target memory. No gaps, no extras.
2. HEX — a text representation of the binary with addresses and checksums, so it can be sparse.
3. ELF — the full build output, containing the code plus symbol and debug info. BIN and HEX are both generated from the ELF.

With that set up, we can now simulate!

Electronics Basics

Power = V × I

For example, my laptop charger runs at 170W — input is 220V at 0.7A, and the output is 20V at 8.5A, which is what the laptop actually needs to run.

SMD Resistor — Surface Mount Device. Sits flat on the PCB surface rather than having legs that go through holes.

The Fablab Kerala inventory of components and materials can be found at: https://inventory.fablabkerala.in/

Transistor — three terminals: Base, Emitter, Collector.

MOSFET — three terminals: Gate, Source, Drain. The insulating layer inside is formed from SiO₂ (silicon dioxide), which is what separates it structurally from a standard BJT transistor.

Crystal Oscillator — a circuit that generates a stable oscillating frequency using a quartz crystal instead of a tuned LC circuit.

Ceramic Resonator — works the same way but uses ceramic as the piezoelectric material instead of quartz. Cheaper and smaller than a crystal oscillator, but slightly less precise.

Voltage Regulator — maintains a stable output voltage regardless of input fluctuations. Uses an internal reference voltage, an error amplifier, and a pass transistor to continuously compare and adjust the output, providing a stable DC voltage from an unregulated source.

Zener Diode — allows current to flow in reverse at a precise breakdown voltage. Used for voltage clamping and regulation.

Buck Converter — a switching regulator that steps voltage down efficiently by rapidly switching current through an inductor, using far less power than a linear regulator.

Boost Converter — a switching regulator that steps voltage up efficiently.

Buck-Boost Converter — can both step voltage up and down depending on the input and load conditions.

Voltage Rail Naming:

• VCC — Voltage at Common Collector. Positive supply for BJT circuits.
• VDD — Voltage at Drain. Positive supply for MOSFET and digital logic circuits.
• VEE — Negative supply in BJT circuits, associated with the emitter terminal.
• VSS — Voltage at Source. Ground or negative supply in MOSFET circuits.
• GND — Ground. The 0V reference point for everything in the circuit.

PCB design on KiCAD

To add a component symbol in KiCAD, click the diode icon in the right toolbar to open the symbol picker.

Once the schematic is complete, switch to the PCB editor to convert it into a physical board layout.

The blue lines are air wires (ratsnest) — they show logical connections from the schematic that haven't been routed as physical traces yet and still need to be connected.

Route the connections using Route → Route Single Track, or just press X as a shortcut.

To set the board boundary, select the Edge.Cuts layer in the Appearance panel and draw a rectangle around your components to define the physical edge of the PCB.

Once the board is laid out, you can open it in the 3D viewer to see a rendered preview of the final PCB.

Downloading the KiCAD FabLib Library

Open the Plugin and Content Manager, search for "KiCAD FabLib", then download, install, and apply pending changes.

UPDI — Unified Program Debug Interface. The single-wire interface used to program and debug the chip.

FTDI — a company whose serial connectors are widely used for USB-to-Serial communication. Socket is female, header is male.

Designed a simple circuit in the schematic editor.

Used net labels instead of drawing wires between components to keep the schematic clean. Then switched over to the PCB editor to start layout.

0.4mm is the standard trace width used at the Fablab.

Go to Board Setup and configure the design constraints to match the PCB etching machine's capabilities — set all values before starting layout so your traces and clearances are within what the machine can physically produce.

To select an entire trace, click any part of it then press U to select the full connected path. Keep all traces at 45° angles for clean, reliable etching.

A zero ohm resistor is essentially a wire in resistor form, used to jump over another trace when routing gets tight.

Run DRC (Design Rules Check) to validate the board — got a couple of errors, one for overlapping components and one for a trace too close to the board edge. Fixed both and re-ran until clean.

On a real PCB, the green coating is the solder mask — it insulates and protects the copper traces, only exposing the solder pads where components need to be soldered. The white text and markings on top are called silkscreen, used for labels, component outlines, and pin indicators.

No errors, DRC passed clean!

Export the Gerber files and upload them to PCBWay to preview the board visually — and if everything looks good, you can go ahead and order prints directly from there.

This is the tool that generates trace images for the in-house PCB milling machine — it takes the Gerber files and produces a PNG that the machine uses to etch away the copper from the blank PCB board.

Downloading a Component from SnapMagic

Use SnapMagic/SnapEDA to download free symbols, footprints, and 3D models for components not in the default library.

Connector Types and Pitches:

• Header pin — soldered directly onto the board, 2.54mm pitch (standard, breadboard compatible)
• JST connector — better fit and more secure than a plain header. Seeed Studio I²C JST is 2mm pitch. Only horizontal orientation available, so the footprint needs to be added to the library manually
• USB-C — an example of a horizontal connector with an overhang/pivot style mounting
• Terminal block — 3mm or 5mm pitch

Downloaded zip contents:

• .sym — schematic symbol
• .mod — PCB footprint
• .step — 3D model

Auto Routing — go to Net Classes and set all trace width and clearance values before running. Differential pairs (e.g. USB D+/D-) are two traces that must be kept the same length.

To add parts: Preferences → Manage Symbol Libraries and Manage Footprint Libraries.

Press V to place a via and jump a trace between copper layers.

Head to SnapEDA (snapeda.com) and search for the part you need. In my case I needed a 4-pin right-angle SMD JST header — part number S4B-PH-SM4-TB.

After downloading, the zip contains:

• .kicad_sym — schematic symbol
• .kicad_mod — PCB footprint
• .step — 3D model

To add them to KiCAD, go to Preferences → Manage Symbol Libraries and Manage Footprint Libraries, and add both by linking their respective file locations.

For the footprint library, the entire folder is added rather than individual files.

To attach the 3D model, double-click the part in the PCB editor, go to the 3D Models tab, and add the path to the .step file — ideally stored in your project folder under libraries/3d models. It almost never positions correctly by default, so use the offset and rotation controls to manually align it onto the footprint using the pin holes as reference.

Final Board Design

In Inkscape I designed the Monado sword outline from Xenoblade — since it's a simple PCB I wanted it to have some meaning to it. Exported it as an SVG, then imported it into Fusion 360 since KiCAD needs a DXF for custom board outlines. In Fusion, cleaned up the outline to make sure it was a proper closed path so it exports correctly to DXF.

In KiCAD, import the DXF as a graphic via File → Import → Graphics.

Make sure to import it onto the Front Copper layer so the milling machine knows to cut it out. Since this is a trial PCB, all communication interfaces are broken out to jumper headers so everything is accessible for testing.

UART (Serial)

• TX → D6 (GP0)
• RX → D7 (GP1)
• Group these 2 pins + GND + 3V3 into a 4-pin header (standard FTDI layout)

I²C

• SDA → D4 (GP6)
• SCL → D5 (GP7)
• Group with GND + 3V3 into a 4-pin header (matches Stemma QT / Qwiic convention)

I play a lot of Super Smash Bros and one of the characters I main is Shulk from the Xenoblade Chronicles game series.

He has a special sword called the Monado where you can choose certain aspects to boost like speed, power, and defence — the sword changes colour to indicate which mode is active.

Since the assignment was to design a PCB with an LED circuit and a switch, I thought I'd make it so the LEDs show which mode you've chosen for Shulk to fight with.

First designed all the circuits in the schematic editor.

Then ran ERC to confirm there were no errors.

Switched to the PCB editor.

Made all the traces — focused on the communication traces first and kept them short to minimise noise, then connected all GPIO giving them second priority.

Tested all connections using DRC — no errors.

The 3D model of the PCB came out looking great.

Exporting the Files

To export the Gerber files, go to File → Fabrication Outputs → Gerbers.

To export the 3D model, go to File → Export → Step.

Building a Case for the PCB

To mount the PCB inside the case, first add mounting holes in the schematic editor by placing them as components, then route them through to the PCB layout.

Now there will be two holes in the final output.

Imported the STEP file of the PCB into Fusion 360 and designed a case around it, leaving holes for the XIAO Seeed RP2040 and the I2C header pins.

Left a small hole on the top clear acrylic layer so the switch can be clicked.

Project Files

Download here