11/26/2025 1 PM - Started basic rp2040 schematic

I started the schematic for the badges! As we're still trying to figure out the base functionality, I just started with the microcontroller. I made the assumption that most people would be more familiar with the RP2040 over other microcontrollers, which is why I decided on that one. I'm still debating adding protection for the USB shield with either a ferrite or RC filter, but for now I'll omit it since the highest frequency on the board is 12MHz (or whatever the eink GDR pin is at).

11/26/2025 8 PM - Added user features

I added the schematic for the e-ink, and I decided to add some configurable buttons and a photoresistor. I'm aiming to have a similar implementation as the Open Sauce badges with the photoresistor! Essentially, there will be a website which strobes the screen to encode data (name, pronouns, slack, ascii art?), and the badge decodes it to save the user's data. I made a small test on my breadboard with an Orpheus Pico, a photoresistor, and a 10k resistor to see if it's sensitive enough. I'd say it worked pretty well :p
Photoresistor test:
20251127-0127-48.0593154

Schematic at this point:

11/28/2025 - Finished schematic

Finally finished the first draft of the schematic! I decided to switch the photoresistor for a photodiode for faster response time. I used a transimpedance amplifier to convert the low-intensity photocurrent into voltage readable by the ADC, biased to 1.65V. I also added an NFC tag as a cool feature! Hoping this could be used to share Slack profiles or websites. I added footprints and put in LCSC parts on all components.

11/30/2025 - Routed the majority of the PCB

Looks like I forgot to log most of the pcb routing...
Anyways, I started by placing the components as subsystems, i.e. placed decoupling capacitors near the MCU, placed switcher circuitry near e-ink. I then brainstormed overall placements of each system, like where the microcontroller, e-ink, photodiode, and nfc coil should go. I then did all of the routing! I tried my best to keep all the traces on the back so I can route power on the front (trying to avoid a 4-layer board). I still need to think about header pins (and need to add a hole for the eink fpc cable).

I spent a decent amount of time calculating the parameters for the NFC coil. I then spent a lot of time looking for plug-ins to make the parameters into an actual kicad footprint. Of course, I finally found the NXP reference designs, which I could just drop right in.

12/2/2025 - Added GPIO

I added some GPIO pins to make this function like a scaled-down devboard after the event so it's not totally useless! I brainstormed potential locations and how to route the most efficiently. Still probably gonna tweak the routing quality though.

12/5/2025 - Finished + ordered

We ended up completely revamping the dimensions to look more like a real badge! Before it was tiny (like 58x58mm), and I've upped it to 80x50mm to give it more shape. I tweaked some components and added the art for the badge! We then hopped on a call at midnight EST to order them through JLCPCB.