Week 06 - Electronics design

This week, we have the following tasks to complete:

• Use the test equipment in your lab to observe the operation of a microcontroller circuit board.
• Use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller.
• Optional: Try another design workflow.
• Optional: Design a case for it.

Group Assignment

The weekly group assignment can be accessed here.

Test Platform

For testing purposes, we used an Arduino Nano with the "Fade" example code from Arduino. This generates a PWM signal on pin 9, cycling in five steps from 0% to 100%. The signal should oscillate between < 0.8V and > 3V, with VCC being approximately +5V.

/*
  Fade

  This example shows how to fade an LED on pin 9 using the analogWrite()
  function.

  The analogWrite() function uses PWM, so if you want to change the pin you're
  using, be sure to use another PWM capable pin. On most Arduino, the PWM pins
  are identified with a "~" sign, like ~3, ~5, ~6, ~9, ~10 and ~11.

  This example code is in the public domain.

  https://www.arduino.cc/en/Tutorial/BuiltInExamples/Fade
*/

int led = 9;         // the PWM pin the LED is attached to
int brightness = 0;  // how bright the LED is
int fadeAmount = 5;  // how many points to fade the LED by

// the setup routine runs once when you press reset:
void setup() {
  // declare pin 9 to be an output:
  pinMode(led, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  // set the brightness of pin 9:
  analogWrite(led, brightness);

  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;

  // reverse the direction of the fading at the ends of the fade:
  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount;
  }
  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}

Measuring 3V3 and +5V Pins

For the first measurement, we used a Fluke 117 multimeter, and for the second, a Rigol DM3068 multimeter, measuring between the GND pin and 3V3, +5V, and VIN. The Arduino was connected via a 30 cm USB 2.0 Type A to USB Mini cable to a laptop. The following readings were recorded:

We powered the Arduino via USB from a laptop, leading to some fluctuations in power delivery. The laptop was running on battery power, and additional voltage drops occurred due to the cable and connection resistances. The probe wires used should have an impedance of 50 Ohms. If powered via the VIN pin from a stable power source, such as a regulated power supply, the results would be closer to 3.3V and +5V. In this case, the LM1117IMPX-5.0 regulator would provide +5V, and the FT232RL would derive 3,3V from the +5V rail, requiring an input voltage between 7-15V, according to the Arduino datasheet.

Power Consumption of the Arduino

For this measurement, we switched to a GW Instek GPS-3303 power supply. The Arduino was powered using cables with insulated banana plugs on one end and crocodile clamps on the other, connected to jumper wires leading to the breadboard and then to the Arduino. The contact resistance between the crocodile clamps and the jumper cables, along with the breadboard connections, had the most significant impact, in addition to the impedance of the jumper cables themselves.

For convenience, we used the same setup to connect the Rigol DM3068 multimeter. In standard practice, both voltage (U) and current (I) are measured to obtain a complete picture of power consumption. However, based on past measurements, we know the power supplies are highly accurate. According to the datasheet, the error is < 0.01% + 3 mV, meaning less than 5 V * 10^-4 + 0.03 V = 0.0305 V. Therefore, we decided not to measure the voltage separately. The setup ensures a correct current measurement. Our goal was to determine the total power consumption of the Arduino Nano board, not just the ATmega328P microcontroller.

We measured -16,1890 mA. The accuracy of the multimeter is impressive, as confirmed by the datasheet.The negative value resulted from reversing the measurement leads. For power consumption calculations, we simply use the absolute value:

5 V * | -16.189 * 10^-3 A | = 80.945 * 10^-3 W.

A similar measurement could be performed while powering the setup from a laptop, but it would be more complicated unless a USB cable is cut in half. This is because a multimeter in current measurement mode must be placed in series, and the input voltage from the laptop would also need to be measured. At this point, one could debate whether it is better to measure voltage or current precisely, or if simply using a power meter would be the more practical approach.

Brown-Out Point

The brown-out point refers to the voltage level at which the microcontroller shuts down due to undervoltage. For an externally powered Arduino Nano via the VIN pin, this test determines the minimum required voltage for the LM1117IMPX-5.0 regulator. The datasheet suggests that this point should be slightly below 7V. We confirmed microcontroller functionality using an oscilloscope.

To better visualize, we labeled the green signal as "INPUT" (measuring the Arduino supply voltage) and the yellow signal as "SIGNAL" (measuring pin 9 output).

The video below illustrates the Arduino Nano’s behavior, showing how its PWM output signal changes with decreasing supply voltage.

The PWM amplitude remained between 4,9V and 5,1V above 6V supply voltage. Below 4,4V, the microcontroller shut down entirely, identifying the brown-out point at 4,4V.

Logic Analyzer

Will be there soon.

General Work Advice

Power Supply

Before disconnecting any components, always gradually reduce voltage and current. When using a power supply, the LED indicator will be green in Constant Voltage (CV) mode and red in Constant Current (CC) mode. If it switches to CC mode unexpectedly, check for issues like short circuits.

Multimeter

Turn off battery-powered multimeters after use to prevent rapid battery depletion. Low-cost multimeters may provide inaccurate readings. High-quality multimeters indicate low battery levels. Avoid changing the measurement range mid-series, as impedance differences may lead to inconsistent results.

Choosing an ECAD Program

In high school, I began using Eagle as my first ECAD program. It was a powerful tool that was relatively user-friendly and intuitive to use. At university, I had the opportunity to work with different software, starting with Altium Designer. While Altium was a much more powerful and complex tool, I only used it briefly before switching to Target 3001 v20, which felt much easier to use for me. Shortly after transitioning to Target 3001, I switched again to EasyEDA Std, primarily due to its integration of the LCSC parts library. This feature allowed me to search for components available for assembly at JLCPCB, significantly streamlining the workflow since we ordered most of our PCBs from there.

In 2022, I also explored KiCad, which performed very well. I found its usability quite similar to EasyEDA, but I preferred EasyEDA’s LCSC integration, so I continued using it and eventually upgraded to the Pro version.

For simulation, I used an older version of PSpice, but mostly relied on LTSpice due to its free availability.

For this project, I will start with EasyEDA Pro. If time permits, I will explore another program or workflow. One tool that caught my interest is pcb.py, particularly to see how well it handles polygons and not just traces. While this aspect is not critical for FabAcademy, it was important in my past work involving voltage converters.

Helpful Links

• Altium Designer PCB Design Guidelines
• Multi-CB Trace Width Guide.
• AdvancedPCB Trace Width Calculator
• Texas Instruments WEBENCH Circuit Designer

EasyEDA Pro

When starting EasyEDA Pro for the first time, it will look like this:

The first step is to create a new project. Navigate to File(F) --> New(N) --> Project(J) or press Shift + N. In the new window, set a project name and click Save.

A key aspect of EasyEDA Pro’s shortcuts is that most of them need to be executed in sequence. For example, the shortcut for creating a new project, Shift + N, works as expected. However, for other shortcuts, you need to press each key in order, such as pressing "F", then "N", then "J", similar to how shortcuts work in Blender.

The following window will appear. The Project Design tab on the left displays all boards along with their corresponding schematics and PCB files. By default, a blank board is created.

Schematic

To begin designing a circuit, double-click on the schematic file. The interface will look like this:

To place components, press Shift + F to open the Device/Reuse Block window. From here, you can select the desired component. At the top, you’ll find three tabs:

• LCSC Electronics – This library provides components from LCSC and displays their current stock availability. It helps ensure that selected components are available for direct assembly at JLCPCB.
• EasyEDA – The default EasyEDA component library.
• Reuse Block – This contains pre-saved assemblies and boards, allowing easy reuse in other designs. For example, if you create your own microcontroller board, such as the "fabxiao", you can reference it in future designs.

On the left side, various filters allow you to refine the search:

• System – Displays all parts available in the selected library.
• Personal – Shows manually designed/add it components.
• Project – Lists components used within the current project.
• Favorite – Displays frequently used or starred components.

If a required component is unavailable, you can create a custom one. This can be useful for special footprints or symbols. For instance, I could not find a suitable model for the Xiao-ESP32C3, so I will create one manually. However, in practical cases, it is often easier to download the symbol, footprint, and 3D model and import them through the corresponding manager at the bottom. I will demonstrate this later using a 3D model.

Creating a Custom Component

To create a new symbol, navigate to File(F) --> New(N) --> Component. In the new window, set a name and, optionally, add a category and description.

The Xiao-ESP32C3 has 14 pins. To create the symbol, use one of the red-marked tools in the toolbar:

• Pin (ALT + P) – Adds a single pin.
• Line Pins – Creates a row of pins.
• RECT Pins – Generates a rectangular arrangement of pins.

This behavior applies to the RECT Pins tool: If the initial placement is compact, only two opposing rows will be created. Expanding it further results in four opposing columns.

After selecting a component, you can adjust its properties in the Property tab on the right. Left-click to select a component, or use Ctrl + left-click for multiple selections. Alternatively, hold the left mouse button and drag from right to left to select everything within the selection box. Dragging from left to right selects all elements that are partially enclosed by the selection box. This behavior applies throughout the software.

For a cleaner schematic, I typically disable Pin Number and only use Pin Name, renaming them according to the datasheet.

To defining component shapes, use the tools next to the pin tools:

• Polyline (ALT + L) – Draws a line.
• Arc (ALT + A) – Creates an arc.
• Bezier (ALT + Z) – Draws a Bézier curve.
• Circle (ALT + C) – Creates a circle.
• Ellipse (ALT + E) – Draws an ellipse.
• Rect (ALT + R) – Creates a rectangle.
• Text (ALT + T) – Adds a text box.

I typically use the Rect tool for defining component shapes.

To improve component identification in designs, the Designator and Device labels are useful. These can be adjusted under the Property tab (not the previous Property tab). By default, the Designator is set to "U?", where the question mark is automatically replaced by an incrementing number. Here are my personal designator conventions:

• C – Capacitors
• D – Diodes
• J – Connectors for wired connections (e.g., Dupont connectors)
• K – Screw terminals and similar wire terminals
• L – Inductors
• R – Resistors
• T – Transistors
• U – ICs and microcontrollers

Creating a Custom Footprint

To place a component on a PCB, a footprint is required. If a suitable footprint is not available, you need to create one. Navigate to File(F) --> New(N) --> Footprint (Y).

The first step is to configure the document settings in the Property tab. I prefer working in millimeters (mm), keeping in mind that many dimensions are multiples of 1.27 mm or 500 mil. While working in mil may be simpler, I find mm more practical, especially for hole placement, board outlines, and general CAD work, which follows later in the process.

The footprint editor functions similarly to the symbol editor but includes multiple layers. For example:

• SMD and SMT components – Typically placed on the top copper layer.
• THT components – Require drilled holes, which involve multiple layers.

Pads are used instead of pins in the footprint editor. Additional elements like vias and silkscreen markings can be added. Shortcuts are identical to the symbol editor.

Unlike symbols, footprint dimensions are critical. For example, the Xiao-ESP32C3 has a pin pitch of 2.54 mm (1000 mil), so hole center distances must match precisely.

To ensure correct placement, use the Rect tool to define outlines. Place markings on the silkscreen rather than the board outline layer unless a cutout is required (e.g., for reverse-mounted SMD LEDs).

Since the Xiao-ESP32C3 has a USB port that extends beyond the otherwise rectangular PCB, creating a small indentation to accommodate and secure it, modify the outline by selecting the rectangle and dragging the green control points.

Place Parts in the Schematic

A symbol and a footprint are the minimum requirements for a part. To use them, open the schematic, navigate to the Device/Reuse Block window, select the personal filter in the EasyEDA library, and click the place button for your chosen part. The same process applies to components from different libraries.

A useful feature in schematics is the Text tool, which allows you to annotate your schematic easily. For example, you can document which cables need to be connected to specific terminals or note parameters such as minimum and maximum voltage input/output. These annotations will only be visible in the schematic and will not transfer to the PCB.

List of helpful tools:

• Wire (ALT + W) - Connect two or more pins.
• Bus (Alt + B) - Create a bus to bundle multiple signals into one line, useful for connecting many different pins from two parts.
• VCC - Create a symbol for the VCC net and name connecting signals accordingly.
  • +5V - In the dropdown menu under VCC, functions the same way as VCC for +5V.
  • GND (G) - In the dropdown menu under VCC, functions the same way as VCC for GND.
  • AGND (A) - In the dropdown menu under VCC, functions the same way as VCC for AGND.
  • PGND (P) - In the dropdown menu under VCC, functions the same way as VCC for PGND.
• IN (I) - Marks separated signals as one without using a wire or bus (input).
  • OUT (O) - In the dropdown menu under IN, functions the same way as IN but for output.
  • BI (B) - In the dropdown menu under IN, functions the same way as IN but bidirectional.

For the VCC and IN dropdown menus, the ribbon will always display the last used tool from this menu in the project.

I just designed a small dimmer circuit needed for my final project: a modular smart lighting system.

Create Custom Part

Before updating the PCB (which is currently empty), go to Tools (T) and open the Footprint Manager... (Alt + F) to link the created symbol with its corresponding footprint. I also used some additional terminals that were not included in the standard library, requiring me to create them manually. The "Footprint Manager" highlights in red any parts that are not currently linked to a footprint. You can then select one or multiple parts, choose the correct footprint, ensure that the pin numbers are correctly assigned, and click "Update."

DRC

Next, we check if our design adheres to the specified rules. Navigate to Design (D) --> Check DRC. The program will analyze your schematic and provide a message if there are any issues. It cannot determine if your circuit will function but ensures that the design meets the design rules. In my case, I had some floating pins, and the DRC (Design Rule Check) flagged that U2 (an opto-isolator) and U3 (the Xiao) had floating pins. Always review these messages and verify whether they require correction.

To edit the text field, go to the Property tab on the right side and navigate to Title Block.

PCB

To transfer your designed schematic to a PCB, navigate to Design (D) --> Update/Convert Schematic to PCB (Alt + I). If you work in an iterative development process, this will be one of your most frequently used shortcuts. EasyEDA will automatically open the corresponding PCB file and prompt you to confirm which changes from the schematic should be applied to the PCB. If you make changes, it will always ask you to confirm them. In most cases, you will want to apply all changes, so simply click "Apply Changes." You will then see all the components from your schematic placed in the PCB window. The blue lines connecting the pads represent the electrical connections that need to be routed.

Before making any connections between components, I organize them into functional assemblies. This circuit is not the best example since it does not contain many different assemblies. However, it can be roughly divided into a sensor assembly, a processing assembly, and an output assembly. The input is at terminal K1, and all components between K1 and the Xiao belong to the sensor assembly. Processing occurs on the Xiao, making it a single-component assembly. The output is at K2, and the components to the left of the Xiao form the output assembly.

Once the components are grouped into assemblies, I arrange them within each assembly for optimal placement. Considerations include connections to other assemblies, board position, board size, and accessibility. At this stage, potential improvements to the layout can already be identified to simplify routing.

For example, K1 should be placed in a specific orientation because otherwise, the cable opening would face inward rather than outward, making it impractical. To fix this, I swap pins 1 and 2 on K1 to avoid crossing connections to R1 and R2. Important: This modification is only feasible for components without polarity. To do this, I go back to the schematic, remove the wires from K1, mirror K1 horizontally using the right-click menu or by pressing X, and reconnect the wires to the opposite pins.

• Y mirrors a component vertically.
• Space rotates a component counterclockwise.

After making these adjustments, I update the PCB using Alt + I and apply the changes.

This results in a much cleaner and easier-to-route PCB.

Next, I use the Rect tool to create a board outline. To do this, it is necessary to select the correct layer before adding the rectangle. I typically configure this in the context menu, as shown in the screenshot below. Alternatively, you can switch the active layer manually in the Layer tab on the right. The rectangle will then be automatically assigned to the correct layer. The board outline can be adjusted in the same way as the silkscreen rectangle.

In my case, I aim for a narrow board, so I arrange the components in a way that minimizes trace lengths and reduces unnecessary curves. The goal is to maintain a grid layout with 45° curves.

To prevent tombstoning during reflow soldering—mainly an issue with small components—it is best practice to route traces straight out of the pads in both directions. This ensures that components are pulled evenly during soldering. Small surface-mounted components sometimes lift on one side, resembling a tombstone, which is why this phenomenon is called the tombstone effect or tombstoning.

While routing traces, I noticed that something was missing—it felt like there were too few connections. I realized that I had forgotten to add certain connections in the schematic. After correcting the schematic, I updated the PCB again.

At this stage, all components are correctly placed, and all connections are completed. Now, I rearrange the component designators to ensure they are:
- Placed consistently relative to their components
- Uniform in size
- Oriented in the same direction

Although this is not crucial for milling since a printed silkscreen will not be used, it is generally good practice. A well-structured silkscreen makes assembly faster, easier, and less error-prone.

In the next step, I inspect the PCB for design flaws—either issues affecting manufacturability or aesthetic concerns.

For example, Q1 (a MOSFET) is connected from the side using a relatively wide trace leading to a narrow pad. This causes the trace radius to extend beyond the pad. To fix this, I use a small Copper Area on the top copper layer. This ensures that the trace terminates before the pad and the copper area provides a clean connection. Removing the last part of the trace improves clarity and simplifies the design.

To create a copper area, it must be named and assigned to a corresponding net. By default, copper areas may appear fragmented, which is not ideal.

To fix this, select the copper area, then go to the Property tab on the right. Navigate to Rule Setting, create a new rule, and change the Connection Type to Direct. Apply the changes and finalize the trace routing.

To add mounting holes, I use the Circle tool. I ensure that they are correctly defined as slot areas in the Property tab, where size and position can also be adjusted.

I made a mistake—I initially planned to use THT socket strips but forgot that we would be milling our PCBs. Since vias can be more challenging to create manually, I decided to move the Xiao to the bottom layer. To do this, I selected the Xiao, went to the Property tab, and changed its layer to Bottom Layer. I repeated this step for K1 and K2.

Some rewiring and repositioning was necessary. Normally, I avoid placing SMD components underneath other boards, such as the resistors in my previous design. However, after moving the Xiao to the bottom layer, additional space became available. I also updated the schematic to reroute the I/O pins for easier trace routing. In the end, the revised layout looks as follows:

On the left side of the ribbon menu, you can open the 3D rendering of your PCB. If components include 3D models, they will be displayed in the rendering.

To add a 3D model for a manually designed component or import an external model, navigate to Library → 3D Model → Add. In the new window, select the file, specify the correct unit, and save it.

Right-clicking allows you to link the 3D model to a component. In the pop-up window, simply select the corresponding component and save the changes.

In my case, the 3D model had an incorrect orientation. To fix this, I selected the Xiao, went to Property → 3D Model Title, and clicked the three dots. In the 3D Model Manager, I adjusted the rotation and position of the model relative to the footprint.

What I learn this week

• CEM-1 and CEM-3 PCB materials exist. Previously, I was only familiar with FR-1 to FR-4, along with aluminum-core, flex, and rigid-flex base materials.
• A well-structured MkDocs syntax improves readability and highlights sections effectively in VS Code.

What I want to improve next week

• Continue documenting the group assignment as early in the week as possible.
• Better distribute the documentation workload for the group assignment. It improved this week but can still be optimized.

Design Files

dimmer

To create this page, I used ChatGPT to check my syntax and grammar.

Copyright 2025 < Benedikt Feit > - Creative Commons Attribution Non Commercial

Source code hosted at gitlab.fabcloud.org