Electronics Design – Recreating My Button-Controlled LED in KiCad

During Week 4 – Embedded Programming, I built a Button-Controlled LED Blinking circuit using the Seeed XIAO RP2040 on a breadboard.

This week, instead of depending on photos and videos of the breadboard setup, I recreated the same circuit using KiCad. Honestly, this felt much more practical. Once the model is saved as a file, I can revisit, edit, and reuse it without rebuilding everything physically.

We were first guided step-by-step by our instructor Saheen to create one model together. After understanding the workflow, this is where I designed my own version independently.

Understanding KiCad – The Basic Workflow

KiCad has multiple working layouts (editors). For this assignment, I mainly worked in:

• Schematic Editor
• PCB Editor
• 3D Viewer

Each layout serves a different purpose, and understanding this flow made the process much clearer.

To start, I created a new project by going to File → New Project in KiCad. I selected a location, gave the project a name, and saved it. This automatically created the project folder along with the schematic and PCB files linked to it.

Installing the Fab Library

Before adding components, I installed the Fab library so that we all use standardized components.

1. Open KiCad
2. Go to Plugin and Content Manager

3. Go to the Libraries tab
4. Search for KiCad offical repository
5. Install KiCad FabLib
6. Click Apply Pending Changes This step is essential to download the library.

This ensures everyone uses the same symbols and footprints.

Schematic Editor – Logical Circuit Design

After creating the project, I clicked on the Schematic Editor. When it opened, it looked similar to an architectural drawing template a blank working sheet where I could start placing elements and organizing the layout. This is where I create the logical version of my circuit. It is not about physical placement, but about defining the electrical connections between components.

Adding Components

Shortcut: Press A to open the Add Symbol dialog box.

From the Fab library, I searched and placed:

• XIAO RP2040
• LED (1206)
• Switch
• Resistor
• Ground (GND)
• +5V
• Horizontal SMD
• Vertical SMD
• JST 4 PIN

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Renaming Component

I can double-click on the component's name to edit it. The names can be customized for self understanding, or deleted if not required.

Rotate

The components can be rotated by pressing "R". There is also an option to flip the module. However, when flipping the component, it might become upside down, so that needs to be kept in mind while doing so.

Connecting Components – Two Methods

Method 1: Drawing Wires

Shortcut: Press W.

I can draw wires directly between component pins. This creates visible electrical connections, but can become messy in complex circuits.

Method 2: Using Net Labels (Cleaner Method)

Instead of drawing long wires, I used net labels.

1. Select the Label tool from the right toolbar
2. Place it at the end of a component pin
3. Give it a name

For example:

• I labeled the LED connection as LED
• I labeled pin D3 on the XIAO as LED

If two nets share the same name, KiCad treats them as connected even if there is no visible wire between them.

This keeps the schematic clean and professional.

Adding Multiple Labels

If I need to add many labels:

1. Select the Label tool
2. Enable Multiple Placement

3. Type the first label → Press Enter
4. Type the next label
5. Click OK when done

Understanding the Circuit Logic

Recreating the circuit digitally forced me to think clearly about:

• Where power is supplied
• Where ground is connected
• Why the LED needs a current-limiting resistor
• How the GPIO pin controls HIGH and LOW signals
• How the button interacts with the microcontroller

CIRCUIT CONNECTIONS BY LABEL METHOD – Gallery 1

Click on the images below:

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Earlier, I depended on remembering breadboard placement. Now, I understand the logic behind each connection.

Electrical Rules Check (ERC) Workflow

Before moving to PCB layout in KiCad, I performed an Electrical Rules Check (ERC) to ensure that my schematic follows proper electrical logic. ERC helps me verify that power nets are correctly driven, inputs are not left floating, and pin connections follow valid electrical constraints.

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1. Running the ERC

To begin the verification process, I selected the Electrical Rules Checker icon from the top horizontal toolbar.

• I opened the ERC dialog box.
• I clicked Run ERC.
• Any detected issues appeared under the Violations tab.

When I clicked on an error message, KiCad automatically cross-probed the issue — meaning it highlighted and zoomed into the exact component or net in my schematic that caused the error.

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2. Troubleshooting: "Input Power pin not driven"

One of the common errors I encountered during this process was:

Error: Input Power pin not driven by any Output Power pins

Technical Cause

In KiCad, most power pins (such as VCC or GND) are defined as Power Input pins. According to KiCad’s electrical rules, every Power Input net must be connected to at least one Power Output pin (for example, the output of a voltage regulator).

While using the breadboard, I powered the XIAO board using a Type-C cable connected directly to my system. Since this power supply connection was external, it was not explicitly shown in my schematic. However, I realized that even though the power source is physically provided through USB, it must still be logically represented in KiCad to satisfy the Electrical Rules Check (ERC).

Since I was powering my board directly from a connector or battery, there was no explicit Power Output pin in the schematic. Because of this, KiCad flagged the net as not being properly driven.

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3. Resolution: Using the PWR_FLAG

To resolve this issue, I used the PWR_FLAG symbol.

The Fix

• I placed a PWR_FLAG from the symbol library.
• I connected it to my power nets (such as VCC and GND).

The Result

By adding the PWR_FLAG, I informed the ERC that these nets are being driven by an external power source. This satisfied KiCad’s pin type requirements and cleared the error successfully.

PCB Editor – Physical Board Layout

After completing the schematic and clearing all ERC errors, I moved to the PCB Editor in KiCad.This is done by clicking the last icon "Switch to PCB Editor" on the horizontal tab If the schematic is the logical blueprint of the circuit, the PCB Editor is the physical construction site. This is where the circuit transforms from connections on paper into a manufacturable board.

Unlike the schematic, PCB layout is about:

• Physical placement
• Real-world dimensions
• Routing copper traces
• Board shape and structure
• Design for fabrication

This step felt very similar to moving from concept drawings to working drawings in architecture.

1.Applying Design Constraints

Before importing the components, I first defined the manufacturing constraints. This step is critical because the PCB must follow the fabrication limits of the milling machine or board house.

• Go to File → Board Setup
• Navigate to Design Rules → Constraints
• Set the following values:

• Minimum Clearance: 0.4 mm
• Minimum Track Width: 0.4 mm
• Minimum Connection Width: 0.4 mm

These constraints define the minimum spacing between copper features and the minimum width of traces. Setting them early ensures that routing decisions automatically comply with fabrication safety limits.

2. Importing the Schematic into PCB Editor

After setting constraints, I clicked the Update PCB from Schematic icon from the top horizontal toolbar (or pressed F8).

In the dialog box, I confirmed the update. The components were then imported into the PCB Editor in their real footprint size.

Understanding Footprints

In the schematic, components are symbols. In the PCB editor, they become footprints — the actual physical pads and dimensions that will be soldered.

• XIAO RP2040 footprint defines USB position, pin spacing, and mounting orientation.
• 1206 LED and Resistor footprints define pad size, spacing, and soldering area.

Choosing the correct footprint is very important because it determines whether the component will physically fit on the board.

Board Setup

• Track width
• Clearance rules
• Copper layer settings
• Board thickness (default settings used)

This ensures that the PCB follows fabrication constraints.

3. Component Placement Strategy & Routing

Creating traces is not as simple as just drawing lines. It is a back-and-forth process — rotating components, moving them slightly, rethinking paths, and sometimes even going back to the Schematic Editor to correct something. Then I return to the PCB Editor and press Update PCB from Schematic (F8) to sync the changes.

Shortcut: Press M to move components, R to rotate.

Keep in mind

Component placement is not random. It has to be placed based on the components logic and functionality:

• XIAO RP2040 placed centrally for accessibility.
• LED placed near the edge for visibility.
• Switch placed where it can be easily pressed.
• Resistor placed close to LED to minimize trace length.
• JST connector placed at board edge for external connections.

While placing components, I considered short trace paths, clear routing space, no overlapping footprints, and logical grouping of related components.

Core Actions I Do During Routing

• Press X to activate Route Single Track.
• Follow the ratsnest (blue guide lines) to connect pads.
• Keep traces short and direct wherever possible.
• Rotate components (R) and move them (M) to reduce crossings.
• Press U to select a full track path, then Delete if rerouting is needed.
• Re-run DRC if necessary to verify no rule violations.

If I try to overlap traces from different nets, KiCad immediately blocks it because of the clearance rules. If pads belong to the same net, copper continuity is allowed. This automatic rule enforcement prevents accidental short circuits.

When a connection is successfully routed, the corresponding blue ratsnest line disappears. That visual feedback helps me track which nets are completed and which still need work.

Placement Thinking (Before Final Routing)

• Position frequently connected components closer together.
• Keep power traces wider when required.
• Avoid unnecessary 90° corners.
• Leave space between traces for manufacturability.
• Place connectors and power ports along board edges.

Reflection – What I Learned

Initially, I forgot to properly consider the placement of the XIAO module. When I checked the design in the 3D Viewer, I realized the USB port alignment was not practical. That small step of viewing the board in 3D made a big difference.

I went back, adjusted the placement, updated the PCB, and re-routed the affected traces.

At this stage, routing became slightly fun — almost like solving a puzzle. It is not just about connecting pins anymore. It is about thinking physically: accessibility, spacing, fabrication limits, and how the board will exist in real life.

Extras That Help

• Use the 3D Viewer to check component alignment.
• Zoom in closely when routing tight areas.
• Keep checking the board edges and mechanical fit.
• Update from schematic whenever changes are made.

This workflow ➜ move, route, check, adjust, update ➜ repeats until the board is clean, logical, and manufacturable.

3. 3D Viewer – Final Visualization

After routing, I opened the 3D Viewer.

This helped me check:

• Component orientation
• Board thickness
• Overall physical structure
• Any visible placement errors

At this stage, the board feels real and ready for fabrication.

Reflection