Tools Used for this step

• Add symbols: to add new components such as microcontrollers, resistors, capacitors, among others.
• Add Power Symbols: to add voltage and ground to each component as needed. It is important to connect each component to ground and voltage since it will create the paths that will be used later to connect all the components in the PCB.
• Add a wire: or you can use the shortcut “x” to create connections between components.

I followed the next photo

1. I added the Attiny 45 and connected it to 5 volts and ground.
2. I connected one resistor to the reset pin on the Attiny and to voltage. From the same “Reset” pin the button was connected, as well as to the ground.
3. The capacitor was left alone and connected to voltage and ground.
4. The second resistor I connected it to voltage, then to the led and finally the led to ground because it needed to create a closed circuit.
5. The first 6 pins were conected to voltage and ground and then to the other 3 pins on the microchip. These pins were Reset, SCK, MOSI and MISO.
6. The second pins were connected to voltage, ground and pin 7 on the Microchip since it is Din.
7. The neopixels needed to be connected each to voltage and ground. Only the first neopixel on the circuit had to be connected to Data. All the neopixels are connected between each other by DIN and DOUT.

PCB editor

Once the sketch was done I selected the " Open PCB in board editor" on the top menu bar to create the tracks. Then I selected on the "tools" feature on the main menu and clicked on "Update PCB from schematic" so that the sketch that I had already done can be imported into the editor.

Once it was imported, I proceeded to arrenge the different components and created the tracks by using the "x" shortcut. The objective was to create the tracks without them interfearing with others. This was quite challenging.

In the 'File' drop-down menu, I selected ‘Board Setup’ so that I could modify some parameters in the 'Constraints' under ‘Design Rules’. I set the minimum clearance to 0.4 mm and the minimum track width to 0.7 mm.

Exportin in Kicad

Once the design is done in order to export it I selected the File, export as, SVG I selected only the ‘User.Drawings’ layer for milling and the ‘F.Cu’ layer for the cutting.

Making sure to design a good PCB

Even though this was my first time designing a PCB, I quickly learned some essential design rules the hard way. Here are a few key guidelines to follow before milling and cutting the board:

• Clearance: Pay close attention to the distance between tracks to ensure there is enough room for soldering.
• Width: Ensure there is enough space for the current to flow effectively.
• Footprints: Select the correct footprints for your components, making sure to distinguish between surface-mount and through-hole components.
• Power and Ground: Keep your power and ground tracks separate to avoid short circuits.
• Design: If you're using components like a Xiao RP2040 that need direct connection to a computer, ensure there are no obstructions. This applies to all components; make sure there's enough space for connections and easier soldering.
• Components: Consider how components interact. For example, if you're using a button, ensure you include a resistor in your design.

Selecting the track´s width

Selecting the appropriate track width for a PCB design is crucial for ensuring reliable electrical performance and manufacturability. Here are the key criteria to consider when determining the track width:

• Ampacity: The track width must be sufficient to carry the intended current without overheating. Thicker tracks are needed for higher currents.
• Standards and Calculations: Use IPC-2221 standards or online trace width calculators to determine the appropriate width based on current and acceptable temperature rise.
• Voltage Drop: Wider tracks help reduce voltage drop across the PCB, which is crucial for low-voltage designs.
• Insulation and Clearance: High voltage requires wider tracks to ensure adequate clearance and avoid arcing or breakdown.
• Minimum Track Width: The manufacturing capabilities of your PCB fabricator will dictate the minimum track width and spacing.

Here are some general widths that can be used:

• Low current signals (up to 0.5A): 0.1524 mm - 0.254 mm
• Moderate current (0.5A to 1.5A):0.254 mm - 0.508 mm
• High current (above 1.5A): +0.508 mm

Getting ready the document for milling

In order to cut first the document has to be in the right format so that the machine can read it. For that, I used Mod Project Org where I changed some parameters such as it has been done on week 4.

Step	Photo	Description
1.		Open Mods Project Org
2.		Choose “Programs”
3.		Click on “Open program”
4.		Then you have to select the milling machine you are going to use, in my case I selected the Roland/ SRM 20 mill/ Mill 2d PCB
5.		It may look like a lot but a handy tip is to start from the left and then go all the way to the right
6.		In the “Read png pink label” import your png file by clicking “Select png file”
7.		After this in the “Convert SG image” option DON’T FORGET TO CLICK “ INVERT”. This is really important since it will invert the colors on the png so that the machine can read the file. If you skip this step the cut will not fit the original size of the file (Trust me I made this mistake)
8.		Then in the “ Set PCB defaults” pink label click “Mill traces 1/64” so that the png is read as individual vectors to follow throughout the milling process. For the cutting file I selected the "Mill outline 1/32".
9.		In the “Mill raster” feature I chose a “2 offset number” and finally clicked “calculate”
10.		Don’t forget to click “on” in the “on/ off” option
11.		Once you finished adjusting the settings return to the “Mill raster” section in step 9 and click “Calculate” so that it automatically saves your file

How to use the cutting machine

I used the MONOFAB SRM-20 Milling machine

1. Connect the machine to your computer
2. Lock your PCB into the machine using the 4 screws and the correct Allen key
3. Close the machine’s door
4. Turn on the milling machine
5. Open the software
6. Adjust the X, Y origin by clicking the arrows on the program (Use the cursor step “Continue” for a faster movement)
7. Once the end mill is really close to the PCB you can place a Post-it note between it and the PCB, once you can't move the Post-it note, it means the end mill is in the correct Z position
8. On the gray part of the window click the “X/Y” button as well as the “Z” one to tell the machine the position in which the end mill currently is, is going to be the new X,Y and Z origin. So that when it starts milling it’ll start on those coordinates.
9. Take out the piece of paper and close the machine
10. Select the file you want the machine to follow by clicking “cut” which will take you to another window where you can select the file you already edited on Mods Project online
11. Press “on” in the spindle feature and click “Z” in the “Move to origin” feature to check if the “Z” position is correct. When you see the material starting to wear out then move down the “Z” origin .1 mm by clicking “x1 in the cursor step feature” and then set that new position as the Z origin (remember this is possible by clicking the “Z” button in the gray space)
12. Finally, click “CUT”