We wanted to play around with productization of something we use around the shop (more often than we thought we would): a simple reflective tachometer to replace an Amazon-bought cheapo model.
This was an acts-as prototype for an upcoming kit based on a project in MEMO#001: Arduino, Interrupted, but it's quite usable as-is delta needing a USB power bank and a really short USB cable. It's provided as a platform for your own experimentation.
Note the OLED is rotated the "wrong" way in this picture; we weren't paying attention. We'll post a complete case once our kit design is complete, but unless we end up going with a semi-custom PCB or PCB carrier, you can build the entire thing yourself with off-the-shelf parts and our code that'll be up on Github.
Or you can buy the mini-book and kit and make sure we eat another day!
Preliminary build blog post: