Week 6 Assignments - Electronics Design

Group Assignment

The group assignment for this week was to:

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 multimeter and oscilloscope)
Document your work on the group work page and reflect what you learned on your individual page

Outcomes

Link to Group Site

The group assignment page for this week is on the 2025 Charlotte Super Fab Lab group site for Week 6 - Electronics Design.

What Was Learned

In the group assignment, we considered the use of a multimeter and of an oscilloscope to observe the operation of a microcontroller circuit board. For the multimeter, we considered how to use it in order to measure / observe both fixed and variable voltage outputs from the XIAO microcontroller. For the oscilloscope, we considered how to use it in order to measure / observe power voltage signal and noise levels, as well as changes in output signals for digital (blink) and analog (PWM) outputs.

This provided us the experience on:

How to use test equipment to measure these types of input signals
What to look for in these types of signals as part of assignments and project work going forward

Individual Assignment

The individual assignment for this week was to:

Use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller

Outcomes

I selected KiCad as the Electronic Design Automation (EDA) tool to use for designing a development board.

Learning KiCad - Tutorial

I had not used KiCad previously, so I began with KiCad's own Getting Started in KiCad introduction and tutorial. I found this tutorial to be fairly comfortable fit as introductory material - covering the concepts with a straightforward example.

The tutorial covered basic concepts and developed a straightfoward board for a battery powered LED. The first main part of the tutorial covered concepts an practices for development of the schematic.

The second main part of the tutorial covered concepts and practices for layout of the PCB. The tutorial went over a 2-sided board design, but I wanted to focus on 1-sided board design, so kept the elements on 1 side.

With the completed board design, it was very helpful to be able to see the outcome as a 3D view.

XIAO ESP32C3 Development Board

With the experience of the tutorial, I began work on designing a development board that uses parts from the Fab inventory.

I began by adding the Fab electronics component library to the KiCad project environment. This involved adding both the symbol library for schematic design, as well as the footprint library for PCB layout.

I planned to use a XIAO family board as the development board, and I selected the XIAO ESP32C3 as the target board. I had several main design goals in mind for the board:

Central XIAO ESP32C3 microcontroller
External access to XIAO pins using connectors to support module connections
Multiple external access connectors for power / ground to support module connections
Basic onboard I/O - allowing for button input and LED output elements

Design organization considered the pin layout for the XIAO ESP32C3 (from Getting Started with Seeed Studio XIAO ESP32C3)

The final schematic design included:

External connectors were separated into different categories, with physical separation to serve as a reminder on function
- Block of 4 for general inputs (A0-A2, D0-D3)
- Block of 2 for I2C communication (also D4/D5)
- Block of 3 for SPI communication (also D8-D10)
- Block of 2 for 5V
- Block of 2 for GND
- Block of 2 for 3.3V
Pin D7 used for dedicated onboard pushbutton input connection (with 10K pulldown resistor)
Pin D6 used for dedicated onboard LED output connection (with 50 ohm series resistor)

KiCad Schematic for XIAO ESP32C3 Development Board

With the schematic in place, the PCB design was opened and updated to bring in the component footprints. Arrangement of the external connectors was relatively straightforward. Using the rats nest connections as general guidance, it took a bit more time and exploration to settle on the arrangment for the button, LED, and resistors that would be sensible for trace routing.

KiCad PCB Layout for XIAO ESP32C3 Development Board

With the components in place, a board outline was finalized in the edge cuts layer with dog bone corners to soften the basic rectangle.

KiCad PCB Layout with Edge Cuts for XIAO ESP32C3 Development Board

Routing presented the greatest challenge for the design. Main problems that needed to be addressed were:

Placement of connector blocks in the schematic wound up with crossover in the rats nest pin connection lines in the PCB for trace routing. This seemed to be a result of mirroring for left vs. right orientation. Some blocks needed to be replaced and use only rotation for orientation in order to get relatively straight rats nest connections.
Initial routing traces seemed to be too narrow. Adjusting a bit to large caused issues with clearance constrants from the footprints. The board setup needed to be revised for larger than default values that balanced track width and clearance constraints with the component footprints.

Once the basic routing was in place, I explored a number of refinements on routing. This included:

Adding filets to routing for a more rounded design
Adding teardrops to pads for better potential connections

KiCad Trace Routing for XIAO ESP32C3 Development Board

Design Rules Checking

KiCad includes settings for design rules to validate board designs. The design rules have default settings, but can also be configured for the project. The rules cover a variety of aspects, including constraints and sizes. The severity of a design rule violation can also be characterized as error, warning, or ignore.

A PCB design can be checked against the specified rules for the design using the KiCad Design Rules Checker functionality. Running the Design Rules Checker will show a listing of potential issues for the design. Issues are shown as Errors, Warnings, or Ignored, as specified in the Design Rules Settings.

For the XIAO ESP32C3 Development Board Design, I ran the Design Rules Checker. A number of issues were identified, but they were not functional errors that required a change in the design. The first set of issues were warnings about silkscreen labels. Since the board is planned to be milled in the lab without silkscreen, these did not impact the functional design. If the board were sent for fabriction, these would likely need to be addressed.

Design Rules Checker Warnings for XIAO ESP32C3 Development Board

The second set of issues were missing connection errors. These identified connections across the pushbutton, where the activated pushbutton would complete the connections. So, these did not need to be revised.

Design Rules Checker Connection Errors for XIAO ESP32C3 Development Board

Turning off the warnings, the Design Rules Checker shows no violations, so it should be possible for the board to be fabricated.

Design Files

https://wiki.seeedstudio.com/XIAO_ESP32C3_Getting_Started/ ↩