This week’s group assignment covers the usage of tools such as power supply, multimeter, oscilloscope and logic analyzer.
To download KiCAD, we go to their website and download the latest installment.
After downloading KiCAD, we need to install the Fab library, so we can work with the specific parts that we have available in the lab. To do this, we go to the Fab Electronics Library for KiCAD repository. We can clone this repository with Git, so any updates done can easily be adapted to.
To add this library to KiCAD, we can follow the instructions outlined in the repository:
Clone or download this repository. You may rename the directory to fab.
Store it in a safe place such as ~/kicad/libraries or C:/kicad/libraries.
Run KiCad or open a KiCad .pro file.
Go to “Preferences / Manage Symbol Libraries” and add fab.kicad_sym as symbol library.
Go to “Preferences / Manage Footprint Libraries” and add fab.pretty as footprint library.
After we install our library, we can start designing our part. We create a new project and make sure to check “create a new folder for the project.”
The place symbol command allows us to place electronic parts into our designs. We make sure to choose our parts from the Fab Library. First, we add the XIAO board.
Using the add power symbol command, we should add a power input and ground to the XIAO board. At this point, we should also pay attention to the type of grid we are using. For now, we will stick with the default one (1.27mm).
Then, we add the LED and resistor pieces from the same Fab Library
We can connect these parts together with the XIAO board using wires. We can also put custom names to parts by right clicking and edit main fields/ edit value.
We need to calculate the value that we give to the resistor. For this, we need to know the specifics of the LED that we are going to use. We can check the LED’s data sheet through the right click menu. But at this case, it was just a generic LED datasheet, so we checked the Fab database. Through there, we found the details in the product page.
We learned that the recommended forward current in 30 mA. The information that we need is the “forward current” and “forward voltage”.
Then, we start our calculations. In KiCAD, we can add text through the add text command on the right menu. What we need to find is the required resistance. For this, we use the formula “V=I*R”, where V is voltage (volts), I is current (amps), and R is resistance (ohm). We need to convert the mA values to A for this to work.
We find 43 ohm as the required resitance. We dont have exactly 43 ohms in the inventory but we can use 49.9 instead, as the closest one.
Next, we added a button. We use the same process for adding a part. But this time, we will not connect it straight to the board in the schematic, but modularize it. For this we can use the net label command on the menu. We put the button cable somewhere else and label it. This is how we can modularize schematics.
If there are pins that are not connected, we add “no connection” flags to them, so the electronics rules checker does not see them as errors. These are displayed as small blue crosses.
We can run the electronics rule check now, but it fails. Because there is no power input to the circuit. For this, we need to add power flags to the 3.3V output and ground. We add it though the add power symbols. After this, the rule check is succesfull.
After completing the tutorial, I decided to try adding the neopixel component. After adding it through the Fab Library, I checked out it’s datasheet.
I assumed I should hook it up to one of the analog pins, because I want to send a range of data, not only on or off. So I chose D3 as it’s data pin. Since it requires 5V, I hooked it up to the 5V power pin. I ran electrical rules check but got two errors.
I deleted the pwr flag connected to neopixel ground, one of the errors went away. The other error said DOUT pin not connected. According to the schematic, it doesn’t have to be connected, so I added a “no connection” flag, which solved the problem.
But when I tried to update it in the PCB board editor, it said no footprint. So I went back to the place symbol menu and relized I had not selected a footprint. The error got solved when I added this.
My idea was to make the neopixel be controlled by a potentiometer and map it to the RGB values. So when I turn the knob, I can move through the RGB spectrum. After looking at the data sheet, I connected one end to 5v, one end to GROUND and one end to an analog pin.
The next step is to use the “PCB Board Editor” workspace. After opening the file, we should execute the “update PCB from schematic” command. If there are no errors, our schematic is imported.
We need to flip the board, since we are making a shield for the XIAO, and it makes sense to place the components to the other side of the board. We select board, press f. The pins turns blue. In this context, F means front and B means back.
In the PCB board editor, there are many layers we can use to draw different parts of the design. For the actual shape of the board, we use “edge cut”. Edge cut allows us to make any shape we want out of the board.
The faint blue lines between, called a rats nest, shows connections between the components. We can move the components around, rotate them with “R” and place them wherever we like. Don’t forget to switch to “1mm” grid when doing this.
Before adding connections between our placed parts, we need to edit pre-defined sizes. These are limiting values that depend on our manufacturing method. We wrote the values according to CNC milling, which is the method that we are going to use.
We go to edit pre-defined sizes thorugh the upper menu and select net classes. We changed the first three values: “clearance”, “track width” and “via size” to the values below.
Now we can start adding connections. We can change the grid to 0.1mm to allow for more flexibility. We then switch to “Front Copper Layer” to add the connections.
We can use the connect tool and connect the components manually. We can go a certain point an hit F to connect the rest auromativally. Or if we select a pad and click shit+F that completes the whole route automatically.
It is very important to edit net classes before we start drawing, because it will not update by itself.
At this point, I experimented with different connection configurations. Since it was my first time doing this, it was very hard to actually find a connection setup that did not interrupt each other’s paths. It was like a game of escaping a maze.
Most of the configurations I tried did not work at all. Finally, I found a placement that allowed me to connect everything together.
The final step is to run “design rules checker”. However, I had an issue here: The footprint of the neopixed LED doesn not seem to be in accordance with our milling rules.
Why does the footprint cause issues in the design rules checker? Should I have used a different one?
What part is the “header connector”? There are many of them in the Fab Library, which of those should I have connected?
Is the potentiometer and neopixel LED connected correctly?
After receiving answers to these questions from Kris, I was ready to export. Before exporting, I decided to make some changes in my circuit board.
My last design featured a neo-pixel LED, however I realized after talking to Kris that we did not have it in the FabLab inventory. I accidentally used something from the default KiCad libraries.
I found the neopixel LED that was present in the lab, but couldn’t figure out how to wire it. I will have to ask it later in this week’s review. Anyway, I decided to not use the neo-pixel for this assignment.
My updated design consists of LEDs(x2), resistors(x2), button(x1) and potentiometer(x1). I also changed their orientation to make the paths simpler.
To export our design as a gerber file, we follow these steps:
At this point, I got an error saying “width correction constrained”. I closed the windows, did it again, and it solved itself.
For drilling the holes, we do the following:
This will create two files: “plated through holes” and “non-plated through holes”. Plated through holes are taken into account in the milling process in Coppercam. Non-plated through holes are used for mechanical purpoeses. So the only file we need is the PTH file.
We can now close the window and go to gerber viewer in KiCad, and do the following:
At this point, I realized that the gerber file I created had only consisted of the lines between the components. This would work fine, but the milling process would take longer since it would have to mill the whole surface but the connection lines.
In order to fix this, I learned that I would have to create a “ground plane” in KiCad. This way, I could avoid unneccessary connection lines for connecting to ground since the whole surface would be ground. This would also save a lot in milling times.
To do this, I went back to the PCB editor and added a “copper zone”. I selected the front copper layer and “PWR_GND”. Then, we just have to draw an outline for the copper zone.
I went back and re-did the same steps, and exported my gerber files.