Week 5

For this week's assignment, I'm trying to reproduce this "hello world" circuit board:

circuit board schematic

I started working on it in KiCAD and as of Saturday 2018-10-06, I have been able to narrowly snatch victory from the jaws of defeat.

I started with the circuit schematic in KiCAD using the fab library. In my first attempt at a schematic, I tried to connect everything manually, and wound up with a snarly ugly diagram, like this:

Then I remembered what I had seen in the tutorial video that I watched to get started, and how the guy in the video used labels instead of direct connections, and tried that. That came out better:

neater circuit diagram with labels

This is when the trouble started, switching to PCB design. I generated a net file from my schematic, and then tried to switch into PCB design. I opened the PCB layout editor, opened my net file, and was greeted with this screen:

screenshot with several error messages on the bottom indicating that footprint libraries are missing

I tried going through the “Footprint library editor” into Preferences –> Manage Footprint Libraries… and importing my downloaded library through Browse Libraries…, both the “fab.pretty” folder and the “kicad_fab.mod” file, but neither changed the error messages that I’ve been getting. I had run the tool to “Apply PCB footprints to schematic symbols”, and found that all of the symbols had associated footprints. However, as I was revisiting the menu while writing this, I noticed that there were errors saying that the footprints could not be found. With the fab libraries now available because I had added them as footprint libraries, I was able to find the footprints and re-associate them. It looks like the names of the footprints were correct, but they weren’t prefixed with “fab:”, which the software wanted, apparently.

In this screenshot, you can see the mostly correct footprints, with the "fab:" prefix, and one LED I added separately, which does not, and therefore doesn't work yet. You can also see how I've highlighted the correct footprint, in order to correctly associate it.

screenshot of interface showing all but one schematic correctly aligned

In setting up the board, I realized that I had the wrong footprint for my 2x3 header as I was putting in my traces, because I didn’t seem to have as much room as the example board that I had been looking at. I was able to route my traces with only a minimum of frustration, and no 0 ohm resistors.

In exporting to PNG, I ran into an issue inverting the image, since it had saved as a PNG with a transparent background, which couldn’t be inverted, but I eventually solved that by changing the background color in the document properties in Inkscape.

Milling the board the first time was fairly painless, at least until I went to assemble the board and found this:

photo of milled copper circuit board with microprocessor seated on pads much too large for it, while a 6 pin header and capacitor fit comfortably in their pads

The footprint for the microprocessor was very much the wrong size, seemingly for some other 14 pin component. I was able to find the right footprint in the kicad library (the only other 14 pin component) and re-route my board, but that burned through the rest of the time that I was able to put into the project, so I was only able to mill the board, and haven’t been able to attach the components yet.

Also, as I was vacuuming the dust off of the board, the vacuum stuck to it a bit and pulled it up. I thought that I re-secured it firmly, but I was proven wrong when milling the edges, as the board came unstuck and started getting pushed around by the bit. Enough of the edges were cut that I was able to cut it out with a box cutter, but it looks fairly messy.

photo of two boards, one with an oversized microporcessor footprint in the middle, another with ragged edges. They both have small shrug emojis on them

At least I was able to add shrug emojis to them in Inkscape, which helped keep me sane amidst these failures.

For the curious, here are svgs for my copper traces and my edge cuts, as well as a pdf of my circuit diagram