DONE

I figured the design could look really cool with a keychain so I added that, I also populated the model with 3d parts and, with the exception of the neopixel, the secure element, and the USB C connector, have gotten everything ready to be fabricated! I'll add some silkscreen art before I send it out tho :3

REDESIGN

I was hating how the current design looked, so I ended up rebuilding it, as well as adding pull up resistors to both I2C lanes, swapping the USP-C plug to a receptacle for more flexibility, and adding a more defined power lane. I also am going to be adding some silkscreen art to the back, and a few other fun things.

I also took this time to perform a comprehensive DRC check, which took a few hours as I tweaked tolerances and minumum design rules to find the best balance between smart design practice and efficiency. Ultimately I think I did a good job at this, and have only a few parts I actually need to worry about design wise.

I also resized it to fit the OLED screen more effectively, and did a few last rewords of smaller aspects like the secure element (swapped to a smaller footprint) and the connector (found one that was like 10 cents cheaper and a bit smaller.

PCB PAIN

I got the original pcb routed, I had a few issues but I ended up adding a SSD1306 Oled and 2 neopixels for fun! It's a mess rn but DRC is saying yes and frankly that's good enough for me. I honestly might redesign it around 4 layers, because it is really reLLY BOTHERING ME.

Schematics!!

I started off by creating the main power system, including a polyfuse, USB-C connector, and a ESD protection circuit (can never be too careful, esp with security) I also added a security module and the main STM-32 chip, there's a spare I2C pair I have on this, so I might take advantage of the overkill amount of memory to add an LCD screen to this, for a fun twist!

Planning and prep

I started by spending a few hours exploring potential options, protocols, and security solutions! This took a bit, and I ended up going down a cryptography rabbit hole exploring all of the abusrdly cool options available. In the end I decided to go for a simple design, using a USB-C plug for simplicity, and avoiding the fingerprint sensor, because the cheapest one I can find is 20$ and I need to trim the fat off of these so I can order a few for testing, in case I accidentally brick it in firmware development.