Week 6

Electronics design

Week assignments

1. Group assignment:
   • use the test equipment in your lab to observe the operation of a microcontroller circuit board. ✔
2. 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. ✔
   • extra credit: try another design workflow.
   • extra credit: design a case for it. ✔

Group Assigment

None of us had any prior experience with this kind of equipment, so we spent Thursday, February 27th figuring out how to use an oscilloscope, a multimeter, and a power supply. We ran a few tests, which are documented on the group’s page.

Link to week 6 group assignment

I was especially interested in learning how to measure the current draw of an LED strip since I’ll be using quite a few for my final project and will probably need to add extra power points. During the group practice, I learned the basics of using an oscilloscope and a multimeter. Along with the power supply, these will be essential tools for me from now on.

The Basics

My knowledge of electronics is pretty limited for now, and what I learned in my architecture courses on electrical installations doesn’t really have much to do with electronics. That’s why I need to start by going over the basics and making sure I get them before jumping into actually working with them.

Voltage & Current: the basics.

• Voltage: the “pressure” that pushes electrons forward.
• Current: the amount of electrons flowing (measured in Amps).
• Kirchoff’s current law: the algebraic sum of currents in a network of conductors meeting at a point is zero.
• Kirchoff’s voltage law: the sum of the voltages in a loop should be zero.

Water Analogy: imagine two waterfalls with the same power (Watts):
- One is tall and narrow → High voltage, low current.
- The other is short and wide → Low voltage, high current.

Types of Current

• Direct Current (DC): electrons flow in one direction.
• Alternating Current (AC): electrons switch directions back and forth.

The Most Important Formula

Power (Watts) = Voltage (V) × Current (I)
Ohm's Law: R = V / I (Resistance (Ohms) = Voltage (Volts) / Current) (Amps)

Components

• Wires: if possible, bundle them together.
• AWG (American Wire Gauge): defines wire thickness based on resistance.
• Bus: a bunch of signals that belong together (like an 8-wire bundle).
• Unpolarized vs. Polarized:
  • Unpolarized: can go in either direction.
  • Polarized: only works in one direction.

Key Electronic Components

Resistor (No Polarity)

• Acts like a water flow limiter for current.
• SMD numbers: standard-tolerance SMD resistors use a 3-digit code to mark the resistance value on the part. The first two numbers will indicate the significant digits, and the third will be the multiplier. ‘R’ is used to indicate the position of a decimal point.
• Online Conversion Calculators by Digikey

Capacitor (Tiny Power Storage)

• Stores electrical energy (like a mini battery).
• Used for filtering (blocks certain frequencies).
• DC current → Capacitor acts like an open circuit.
• AC current → Capacitor behaves like a resistor.
• Some capacitors are polarized (electrolytic ones).
• Bypass capacitors: always put one next to a microcontroller to filter out noise (caused by magnetic fields around copper traces).

Diode (One-Way Street for Electricity)

• Only lets current flow in one direction.
• LED (Light Emitting Diode): the material determines the color.
• Flip an LED around, and it can detect light.
• Adding a capacitor can help reduce LED flickering.
• Full bridge rectifier: converts AC to DC.
• Forward voltage/current: the minimum voltage/current needed to light up an LED.

Inductor (Magnetic Field Storage)

• Stores energy in a magnetic field (used in relays and motors).
• Helps switch high voltages and currents.
• Always pair with a diode (placed the “wrong way around”) to stop voltage spikes from feeding back into the circuit.

Transistor (The Ultimate Switch & Amplifier)

• BJT (Bipolar Junction Transistor): current-controlled.
• FET (Field Effect Transistor): voltage-controlled.
• Can be used to amplify signals or switch large currents (for motors, speakers, etc.).
• Small signal in → Big signal out.
• MOSFET Types (Metal–oxide–semiconductor field-effect transistor)
  • N-MOSFET: connects to ground.
  • P-MOSFET: connects to the power supply.

Voltage Regulators (Keeping Things Steady)

• Takes in a range of voltages but outputs a stable voltage (e.g., 5V output from 30V input).
• Can be inefficient → DC-DC converters are a better option for efficiency.

In Global Open Time chat, Adrian shared this link, Getting Started in Electronics by Forres M. Mims, III. It’s great for getting started with electronics. Thanks, Adrian.

Individual Assigment

KiCAD

A few weeks before this FabAcademy cycle started, our instructor Luis had introduced us to KiCad, an open-source Electronics Design Automation Suite. On Thursday the 27th, with his help, we revisited that initial training—this time focusing on designing our first PCB.

Now, in this sixth week, I’m starting to get a clearer picture of some basic requirements my Final Project will need in the future. On one hand, I’ll need to control an LED matrix to display the bending moment diagram. On the other hand, I’ll need to process input from four load cells, which will be placed under each of the (initially) nine seats of the bench.

KiCad version 9 was recently released. I already had version 8 installed, and I don’t really like using new versions before their first update. So, for this week’s assignment, I’ll stick with version 8.

First, I need to download and install the FabLab libraries from this link: gitlab.fabcloud.org
Just click on “Code” > “Download source code” > “zip”. I saved the zip file in the Users\myuser\Documents\KiCad folder and unzipped it there too, so it’s always in the same place and easy to update whenever needed.

Next, I need to set up the path so KiCad can find the libraries we just loaded, and I also have to add the path to include them in the symbol and footprint libraries.

• Configure Paths…: Global libraries:
  ¨+¨ Name: fab Path: C:\Users\josev\Documents\KiCad\kicad-master
• Manage Symbol Libraries: Global libraries
  ¨+¨ Nickname: fab Library Path:${FAB}/fab.kicad_sym
• Manage Footprint Libraries:
  ¨+¨ Nickname add: fabLibrary Path: ${FAB}/fab.pretty

It is now time to create my first project in KiCad. My plan is to design a PCB using a XIAO ESP32C3 module, incorporating an LED_1206, an R_1206 resistor, and SDA and SCL connections for an I2C OLED display as well as a power supply with PWR_5V and PWR_GND. Additionally, I will later need to add an input for data acquisition from a series of load cells.

Schematic Editor

The following steps outline the process for defining the project in KiCad’s Schematic Editor:

1. Adding the XIAO ESP32C3 Symbol
   I click on the right column to add the XIAO ESP32C3 symbol or use the shortcut “A”.
   

2. Adding the LED_1206 Symbol
   I click again on the right column or press “A” to add the LED_1206 symbol.
   

3. Adding a Resistor (R_1206)
   I press “A” to add a resistor. I search for "r fab" and select R_1206.
   

4. Adding a Ground Connection (PWR_GND)
   I click on the Power button located just below the symbol addition button, or press “P”, then search for "fab power" and select PWR_GND.
   

5. Disabling unused ESP32C3 Outputs
   To disable unused pins, I select the Cancel option from the right column. In the image, pin 21 is deactivated.
   

6. Connecting Components with Wires
   I start connecting components using the “W” shortcut to place wires.
   It is good practice to add TAGS to identify and link different symbols and their input/output pins.
   

7. Running the Electrical Rules Checker (ERC)
   After adding the wires, I check for errors by clicking Inspect > Electrical Rules Checker.
   In this case, an error appears on pin 13, indicated by a red arrow.
   

8. Fixing the ERC Error with a Power Flag
   This is a common beginner’s mistake—a power flag is missing at that point.

• I press “P”, search for "fab Power", select Pwr_Flag, and connect it between pin 13 and PWR_GND.
• I run the Electrical Rules Checker again, and the result should show no errors.
  

9. Save the Project and Expand the Design
   I save the project as MyProjectEvolution_01 and continue adding symbols and connections for an LED strip and an I2C OLED display. Below are multiple images showing the expanded design:
   

PCB Editor

Now I can switch to the PCB Editor. It’s a bidirectional workflow, as it is common to return to the Schematic Editor to add or modify the schematic and then go back and update PCB with changes made to schematic.

I have liked Vera’s work since the first time I saw it while preparing for my first week at FabAcademy. On Saturday, I reviewed it again and followed her recommendations for the Board Setup.

Luis mentioned that the best approach is to set a default value of 0.4 to connect pins and 0.8 for tracks connected to power. I select the tab under Constraints called Predefined Sizes and add a new width in the Tracks menu. I enter 0.8 millimeters and press OK. I start by routing power wires with a 0.8 mm track width.

I initially worked on MyFirstProject and gradually incorporated more components while arranging the connection wires.

In my first project, I worked with a simple circuit consisting of a single resistor and an LED. I drew some connection lines and then clicked on the “Design Rules Checker” to validate the design.

The check returned a list of numerous errors. The first error was expected, as I had not defined a border for the board. However, the other errors were primarily due to beginner mistakes. For instance, I drew lines instead of proper tracks, a common error for those new to PCB design. After making this mistake, I aim to avoid repeating it in future projects.

In KiCAD, components are organized by layers. In this first project, I utilized two specific layers:

• F.Cu (Front Copper Layer): This layer was used for the copper traces and component placement on the front side of the board.
• Edge.Cuts (Edge Cuts Layer): This layer was used to define the physical boundaries of the PCB.

Additionally, the elements I defined in the Schematic Editor were automatically placed on the F.Fab (Front Fabrication) layer. This layer is typically used for documentation purposes, such as component outlines and reference designators.

As a test to define the board outline in my first project, I drew a rectangle with rounded corners.

During the PCB design process, I encountered an issue where the outputs of pins 4 (SDA) and 5 (SCL) were crossing to connect to the I2C OLED. Luis helped me resolve this by explaining how to incorporate a 0-ohm resistor to create a bridge, effectively solving the crossover issue.

At that moment, I followed the following process: I checked for the absence of errors using the Electrical Rules Checker (ERC).

Since no errors were found, I switched the KiCAD environment to PCB Editor and updated the design from the Schematic. I then incorporated the bridge, arranged the tracks, and verified the absence of errors using the Design Rules Checker (DRC). However, when running the DRC, a significant number of errors were detected. The first issue was the lack of defined board boundaries. Additionally, several errors were related to missing GND connections. Following Luis’ recommendation, I will create a filled zone on the PCB to connect all GND pins.

I clicked the ‘Add filled zones’ button (shortcut: Shift+Ctrl+Z). Selected the PWR_GND net in the right-side menu.

Then I clicked at one corner of the PCB an outline the entire board. Double click to close the shape.

Finally, click ´B¨ (or select ‘Update Zones’ from the menu) to fill the ground plane.

And this would be the first render of my PCB. To manufacture it, I need to export the design in SVG format. Another option would be Gerber files if I wanted to send the PCB for fabrication abroad.

I have generated two SVG files: one with the trace of the F.Cu layer and another with the trace of the Edge.Cuts layer. Luis recommends opening the first file in GIMP and exporting it as a PNG with a resolution of 1000 DPI to later vectorize it in a 2D drawing program.

In my case, I will vectorize the bitmap in VCarve Pro, which will be the software I will use to define the toolpaths for milling the board.

extra credit: design a case

I could have created a box from the file MyProjectevolution_010-Edge_Cuts.svg; however, I found it more interesting to test KiCad’s export capabilities and generate an Step file of the PCB with its components.

I imported the STEP file into Rhinoceros, and from there, the process will involve integrating it into the Grasshopper workspace, creating a bounding box around its elements to define the enclosure that should protect the PCB.

In the end, I think I got way too tangled up and made the mistake of over-parametrizing the design. Starting with the geometric definition of the board’s edge and its mounting holes would have been a much more logical and sensible approach. Lesson learned!

It’s been a busy and really interesting week! The concepts I learned back in week 3 about embedded programming have been super helpful as a foundation for this week’s tasks, and now I’m getting closer to the PCB manufacturing stage. I think changing the order of the weeks compared to previous years was a great idea!

Files week 6

MyProjectEvolution_010.zip
MyProjectevolution_010-Edge_Cuts.svg
MyProjectevolution_010-F_Cu.svg
PCBCase_v02.3dm Rhinoceros 8
PCBCase_v02.stl