7. Electronics design

This week is all about Electronics Design. The task for this week is to design a board that uses parts from the Fab Inventory to interact and communicate with an embedded microcontroller. I decided to use this as an opportunity to try multiple workflows. I settled on Using KiCad and Autodesk Fusion.

The Individual assignment for this week:

• Use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller.

Group Assignment

See Reykjavik Site

KiCad EDA

KiCad is a surprisingly powerful Open Source Electronic Design Automation (EDA) tool. I decided to remake a board Andri made in a tutorial series on the Reykjavík youtube channel. The board in the tutorial is a button controlling an LED using an Attiny412. I ran through the videos at 2x speed first then followed along pausing as I went. I recreated Andri’s board 1:1 before restarting and making a variation using the RP2040 and two LEDs. The idea being pressing the button alternates which LED is lit.

Starting in KiCad

First thing to do is to add the Fab Library. I followed Andri’s tutorial and the installation instructions on the Library’s Gitlab page. After that I moved on to setting up the Schematic

Page Settings:

Set the page settings:

The Schematic

The schematic is fairly simple. The Attiny in Andri’s tutorial needs a capacitor to smooth out power but the Xiao RP2040 gets power through the USB-C port so I can skip that.

Labeled the everything while marking the unused connections:

ERC

Running the Electrical Rules Checker. It throws an error:

"Error: Input Power pin not driven by any Output Power pins"

Tried several things:

• Replaced my “GND” label with a PWR_GND symbol from the FAB Library.
• Also added values for the resistors. 1k
• Didn’t fix the Input Power error but I think this is just due to the way KiCad treats inputs and outputs in the schematic properties.

Ended up telling KiCad to exclude the violation for now.

PCB Design

As soon as I got to PCB Design I realized the current setup would require me to solder the Xiao straight to the board. This would be a massive waste so I did a bit of searching and found a Socket version of the footprint in the fab library.

• Replaced the “Module_XIAO-RP2040” with the “Module_XIAO_Generic_SocketSMD”.
• Didn’t delete any of the other symbols. Just the XIAO itself as they line up perfectly.

Here’s the finished schematic after switching the Xiao:

Here’s a comparison of the two in the PCB Editor:

Adjust the layer visibility. KiCad’s default can be cluttered and hard to read. I settled on the following:

• F.Cu
• F.Silkscreen
• Edge.Cuts
• F.Courtyard

Design Rules

I copied Andri’s design rules for the bits we use in the Roland MDX20 here in Reykjavík:

Routing

Now to route the board. I got the rough layout first then connected everything up. This was surprisingly tricky and also gave me vivid flashbacks of routing conveyor belts in Factorio, a factory simulation game I’ve spent hundreds of hours on. Definitely a transferrable skill there.

Here’s the layout I settled on:

Main priority here was keeping it as compact as possible to save material while also keeping it relatively easy to solder. I think I managed to strike a decent balance but I think the USB-C port on the Xiao might cover up the text. Oh well.

DRC

After routing I run the Design Rules Checker. This checks for spacing between traces and components, Unconnected items and outlines.

Running the Design Rules Checker returns one error:

@Footprint component type doesn't match footprint pads (expected 'SMD'; actual 'Through hole')

I’m fairly certain this has to do with the way the footprint is defined in the fab library. The socket component itself is an SMD footprint but going into the footprint editor and the specific Footprint Properties I notice the Component Type is set to “Through Hole”:

The footprint itself is correct in terms of manufacture so the error doesn’t have any real effect on the board’s functionality.

Exporting for production

Time to export:

I’m using KiCad 9. Andri’s Tutorial was for KiCad 8. After a bit of digging around in the UI I found a “plot” button next to the “print” button.

The Plot menu lets me choose the format, I’m going for SVG. It lets me choose which layers to export.

These are the settings I used:

This resulted in two separate files for the two layers. “Edge.Cut” and “F.Cu.” I brought both into Inkscape and made some adjustments to prep it for exporting to PNG.

The file in Inkscape:

And here are the settings for exporting:

• Export Selection
• 1000 DPI
• Quadruple check that the images are the exact same dimensions

That’s it for KiCad. After finishing up I noticed a discussion in the Mattermost Channel mentioning issues with the KiCad 9 .svg export compared to KiCad 8. I didn’t notice anything personally, scale was correct and adjusting the colors while tricky wasn’t too hard.

Autodesk Fusion EDA

I decided to give Fusion a try since I already use Fusion for 3D design regularly. The ability to do Autorouting was also enticing. The Electronics workspace was like entering an old bookstore. There’s parts of the UI that feel ancient but overall It’s fairly polished. Probably a case of “If it ain’t broke, Don’t fix it”

Fusion Fab Library

Getting the fab library installed into Fusion was a bit trickier. The Gitlab page doesn’t include any instructions. I had to get help from Addi (of cereal spoon fame). He uses Fusion’s EDA regularly.

I downloaded the library from Gitlab:

I went to “File > New Electronics Library”

Once that was open I navigated to “Create>Open Library Manager”

This opens a window where I could “import from local disk”.

Setting up the library was not as pain-free as in KiCad.

Fusion Schematic

First thing was setting the Design Rules.

Located in Design>Design Rules (Or CTRL+D)

I based these off the ones from KiCad and set them as follows:

I started off trying to recreate the RP2040 schematic I made in KiCad but I noticed the Fab Library doesn’t have the SMD Header footprint for the Xiao RP2040 like in KiCad so I decided to recreate Andri’s Attiny design from the tutorial.

I decided to recreate KiCad’s schematic layout with the nice page. Fusion has the page as a Schematic component named “Frame”. There’s several to choose from and I ended up going with “A4L-LOC”. The Library also didn’t include the same 1x3 header so I had to use a 1x6 instead. After netting and labelling everything I ran the ERC and it passed with no warnings or errors.

Here’s the completed schematic:

Fusion PCB

Starting off adjusting the layer visibilty. Just like in KiCad it can get a bit cluttered with everything enabled. There’s a few profiles for the layers. I found “PresetTop” to suit the work I was doing here.

I laid everything out in a way I felt made sense based off the KiCad routing. Now it’s time to test out the Autorouting. Starting Autoroute opens this window:

The options on the left seem to be separate layers of the PCB and the right hand side lets me set the performance settings. I turned it all the way up. I didn’t build this PC for light work. The autoroute finished so fast I thought it failed. I closed the window. Autorouting looks good. I think it’s a tool like any other. Definitely something to be used as an augment instead of something to be relied on. If I hadn’t gotten a sense for the layout from KiCad the AutoRoute could’ve been disastrous.

Here’s the board after routing:

Once I was satisfied with the routing I added an outline and some text.

Here’s the finished board:

Fusion ERC

Fusion’s ERC seems to be more of a live-warning system compared to KiCad’s manual running. Fusion is more aggressive in stopping you from doing things you shouldn’t. I didn’t get any ERC errors or warnings after the autoroute. But just to test it I messed the design up on purpose. Here’s the spaghetti-fied routing:

After the Spaghettification I ran the Rules Checker and it returned 67 errors and 2 Warnings. 52 Overlap errors and 15 copper clearance errors. The warnings are for the two wire stubs.

Clicking on an error or warning highlights it on the board:

I think I prefer KiCad’s ERC UI. It gives more detail on each error, Fusion only defines the category and exact criteria. The overlap errors are all either labelled “Wire-Wire” or “Smd-Wire”. Which is fairly explanatory but KiCad’s I prefer KiCad’s more verbose explanations.

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Fusion Export

Exporting from Fusion to a black and white fabmodules compatible format is done through “Document > Print”

This opens up a fairly standard print menu. I set it to “Print to File (PDF)” and ticked “Black” in the options on the left. I also noticed that the default Output file path was a temp folder in %LocalAppdata%. Not exactly easily accessible so make sure to change that.

I take the .pdf file from Fusion and open it Inkscape. Fusion places these crosshairs at the center of the file so I had to delete those before exporting as .PNG

Here’s the Fusion board ready to export in Inkscape:

Design Files for this week:

Filename	Type	Program	Link
KiCadReRun	.zip	KiCad	Link
BlinkyThingy	.f3z	Fusion	Link