Group assignment
Use the test equipment in your lab to observe the operation of a microcontroller circuit board
For the group assignment, I didn’t have a proper place to carry out the activity, so I contacted a friend, Omar, who had the necessary equipment at his house. He has been helping me with some of the equipment he owns and with key concepts to better understand electronics. This helped me a lot, as he had the equipment required for the assignment, which allowed me to see its utility and gain a clearer understanding of various aspects of electronics.
Here is the link to learn more about the group project.
I currently work at Fab Lab iFurniture as a Fab Manager, so whenever we have visitors or organize training sessions, I am responsible for leading this workshop on risk prevention and workplace safety. For this reason, I have organized a group invitation to my colleagues from Fab Academy to participate in this workshop.
What is displayed on the screen is the result of configuring the LED to trigger every 0.1 seconds. Each pulse or square on the screen represents 100 millivolts. In my LED, the voltage is 200 millivolts, so each square represents 50 milliseconds. In practice, I have 2 squares, which equal 100 milliseconds.
In the signal analysis, the Pk-Pk (peak-to-peak) value I obtained is 212.00 mV. The sampling rate is 20.0 MSa/s (million samples per second), with a memory depth of 14.0 Mpts (million points per channel). This indicates that the oscilloscope is sampling at a high rate and has sufficient memory capacity to capture complex and high-resolution signals.
For this exercise, the microcontroller must be connected to a power source in order to use the oscilloscope. This is necessary because the oscilloscope measures the electrical signals generated by the microcontroller, and it needs the microcontroller to be active and functioning in order to obtain accurate readings.
Now I will use the multimeter to measure the resistance. For this, the component must be disconnected from the power source to make an accurate measurement. The reading obtained in ohms is 217.07 Ω.
To measure the LED, it must be connected to a power source. Then, we perform the same process with the multimeter, and the reading obtained was 0.94 V. This value corresponds to the voltage drop across the LED when it is operating. The LED typically has a voltage drop that varies depending on its type and color. In this case, the 0.94 V reading indicates that the LED is functioning correctly within the expected range, as the typical voltage drop of common LEDs is usually between 1.8 V and 3.2 V, depending on the type of LED.
Reflections
During the measurement practices with the oscilloscope and the multimeter, I was able to understand the importance of these tools for analyzing and diagnosing electronic circuits.
The oscilloscope allowed me to observe the waveform of signals in real-time, which is crucial for understanding how signals behave in circuits.
On the other hand, the multimeter helped me measure components like resistances and voltages, ensuring that the circuit was functioning correctly. These tools are essential for developing practical skills and improving my understanding of electronics.
Individual Assignment:
1. Prerequisite steps
Select your operating system; in my case, it is Windows.
I selected the GitHub option, and the program started downloading immediately (this took a little while).
I followed the installation steps.
Here, I can configure KiCad. In my case, I didn't make any custom settings since it's my first time working with these tools, so I started with the default settings.
Here, I simply follow the process and click on "Yes!".
And that's it! Now I have the program enabled and ready to start.
2. I start designing with KiCad.
I am starting a new project.
I save the project to keep it.
Once the project is saved, two files will appear in the KiCad interface:
projectname_pcb
projectname_sch
Now, I clicked on the schematic editor, which is the first thing we will work on.
Here, I select 'Copy default global symbol library table' (recommended) and click 'OK'.
I recognize the program's interface. The section highlighted in the green box contains important tools that we will use (from top to bottom):
Select elements
Add symbols
Add power symbols
Add a wire
Now, in the KiCad program, in the Symbol Editor, I add the downloaded library.
I select 'Global' to use the downloaded library in all the projects I create and click 'OK'.
I search for the file in the folder where I saved it, select 'fab.kicad_sym', and open the library.
To use EDA and design a development board that utilizes components from the inventory to interact and communicate with an integrated microcontroller, the first step is to learn how to use the software. For this, our instructor Ulises held a 4-hour masterclass, where he taught us how to design and create our electronic boards.
For this, I had already installed the KiCad software beforehand, so the masterclass was conducted in a practical manner.
Here is the link to the masterclass recording. Click here.
Here is a list of the components I will be using:
4 resistance 1206 - 1.2 x 10^6 Ω
2 Led - Led Blue 1206 SMD
4 Conectors - Header 1x5
1 Microcontroller - XIAO-RP2040
Component Considerations for PCB Design
To determine the proper resistance, LEDs, connectors, and microcontroller values in terms of voltage and resistance to ensure your PCB works correctly, consider the following:
Resistors (1206, 1.2 MΩ)
The 1.2 MΩ resistors are suitable if you're using them to limit current to components like LEDs. Calculate the resistance value to ensure the LED doesn't receive more current than it can handle. The value will depend on the supply voltage and the LED's voltage drop.
LEDs
Blue LEDs typically have a voltage drop of 3.0 to 3.2 V. To calculate the appropriate resistance, use the formula R = (Vsupply - VLED) / ILED, where ILED is the recommended current for the LED, typically between 10 mA and 20 mA.
Header Connectors (1x5)
Header connectors generally do not directly affect resistance or voltage, but ensure they can handle the signals and power that will pass through them.
Microcontroller (Xiao RP2040)
The Xiao RP2040 operates at 3.3V, so make sure the circuit components do not exceed this voltage. Use voltage regulators if you're powering from a 5V source.
For each component, ensure you consider the voltage drop and appropriate operating current.
Key Formulas for PCB Design
1. Resistor for LED
The formula to calculate the resistor for limiting the current in an LED is:
R = (Vsupply - VLED) / ILED
- R: Resistance in ohms (Ω)
- Vsupply: Supply voltage in volts (V)
- VLED: Voltage drop across the LED (typically 3.0 to 3.2 V for blue LEDs)
- ILED: Current through the LED in amperes (A), typically between 10 mA and 20 mA (0.01 A - 0.02 A)
2. Power Dissipation in a Resistor
The power dissipated by a resistor is given by:
P = I2 * R
- P: Power in watts (W)
- I: Current in amperes (A)
- R: Resistance in ohms (Ω)
3. Current Consumption of the Microcontroller
The current consumed by the microcontroller can be calculated by:
Imicro = Pmicro / Vmicro
- Imicro: Current consumed by the microcontroller in amperes (A)
- Pmicro: Power consumed by the microcontroller in watts (W)
- Vmicro: Operating voltage of the microcontroller (typically 3.3V)
4. Voltage Divider
The formula for calculating the output voltage in a voltage divider is:
Vout = Vin * (R2 / (R1 + R2))
- Vout: Output voltage
- Vin: Input voltage
- R1 and R2: Resistors in ohms (Ω)
With these more detailed elements, we can proceed with the board design.
For this exercise, we chose the Xiao RP2040 microcontroller, which is exactly the microcontroller I have been working with.
For this, we opened the KiCad software and accessed the "Schematic Editor."
The symbols are opened, and I select the module_XIAO-RP2040.
When the symbols are added, they immediately appear on the workspace.
I select the symbols to add to my board, including pins, LEDs, and switches.
I create labels for the pins. This helps to:
Clearly identify the signals of each pin.
Facilitate the connection of components within the schematic.
Avoid errors when connecting the pins correctly in the design.
Improve the organization of the circuit, especially in complex designs.
Now I assign a footprint. OK
Now the microcontroller is ready with the resistors, LEDs, and switches.
To update, I go to "Tools" and click on "Update PCB from Schematic.
Now, in KiCad, I enter the PCB Editor.
In the PCB Editor, I update by going to "Tools" and selecting "Update PCB from Schematic." Another way to update is by pressing F8, but it is necessary to save first.
All set, now we click on "Update PCB."
Once the PCB is updated, I can see my design on the board.
Now, to set the track width and start designing and connecting, I go to "Edit Pre-defined Sizes."
The track width in a PCB design is very important to ensure proper performance and avoid manufacturing issues. The minimum of 12 mils recommended by instructor Ulises is due to several reasons:
Electrical resistance
Manufacturing
Reliability
Thermal capabilities
I select the track width.
Now I start organizing the ports so that the mesh on the PCB looks a bit more organized and the tracks can be more efficient. For this, Ronal has been supporting me, as he is an expert in this area.
It took me a while to understand the layout of the circuits, but I managed to do it and I really liked it. There were details I noticed along the way, as something important to consider is that the tracks should not have obtuse angles or be at 90°. It is recommended that the angles be open, or alternatively, a triangulation can be made at those angles to ensure the current flows properly.
Now, to add the 3D model to my design, I access the "Footprint Properties" and search for the 3D model within the Xiao RP2040 libraries.
"To access the libraries in KiCad and search for the 3D model of a component, follow these steps:
- Open KiCad: Launch the program and open your project.
- Access the "Footprint Editor":In the main KiCad window, click on the "Footprint Editor" icon or select the corresponding option from the "Tools" menu.
- Access the footprint properties:In the "Footprint Editor", select the component to which you want to add the 3D model.Right-click on the component and select "Properties" or "Footprint Properties".
- Add the 3D model: In the footprint properties, look for the option to assign a 3D model. Click on the 3D model field, and a dialog box will open where you can browse the local libraries.
Navigate to the Xiao RP2040 library folder or the relevant one depending on your setup. If you don’t have it, you can manually add it in KiCad’s configuration.
- Select the 3D model: Once you find the 3D model in the library, select it and apply it.
- Save and verify:After adding the 3D model, save your changes and verify that the model displays correctly in the 3D view of the PCB."
This information is taken from ChatGPT.
In the PCB, I designed the board in the shape of a leaf.
In the PCB design within KiCad's "PCB Editor," to access the 3D view, I go to the top menu and click on "View." In the dropdown menu, I select "3D Viewer." Once in the 3D view, I can move the model using the mouse to rotate it and view the design in three dimension.
The first thing I do to verify if the track is correct is go to the "Inspect" menu and then click on "Design Rules Checker".
I have 2 errors and 11 warnings.
Reflections
The installation of KiCad was the first important step in the process. Although it's a very comprehensive software, it wasn't difficult to set it up on my computer, thanks to clear instructions and the resources available online. This allowed me to quickly dive into board design and learn how to use its tools.
The learning process with Ulises was incredibly enriching. In his masterclass, he not only taught me how to use KiCad effectively, but also shared valuable advice on circuit organization and best practices when working with designs. His practical and clear approach helped me better understand how each tool worked and how to apply the knowledge gained in real-world projects.
Regarding the creation and design of the board, the process was challenging but rewarding. At first, it was a bit difficult to understand how to organize circuits and connections, but with practice and Ulises' support, I made progress. Designing the board was not only a technical exercise, but also a creative process. I had to think about the placement of components, track width, and 3D model integration to ensure everything fit properly.
In summary, this project allowed me to develop valuable technical skills in PCB design and gave me a deeper understanding of the process of creating electronic circuits. Without a doubt, it was an experience that reinforced my interest in electronics and motivated me to keep learning more about this fascinating field.
To verify if my design was correct, I did a review, which resulted in 2 errors and 11 warnings. This could be an observation that needs to be corrected, such as tracks that are too thin or some connection error that I need to fix.