Christmas 2024 and I was back home in Belfast. When it came to presents for everyone, I knew my niece and nephews just wanted cash. I thought it was sad that kids so young had no interest in receiving and unwrapping toys and gifts and it felt very hollow to just hand over an envelope with cash or some kind of gift voucher in it.
Jump forward to October 2025 and I had recently built a project called “AC_thing” which was an iPhone app and physical, ESP32-powered box for controlling air conditioners. That was done and I was trying to think of my next project.
I cast my mind back to the Christmas prior and the handing over of cash and thought it would be fun that, if I was just going to be handing over an envelope again this year, it would be fun to at least put a challenge behind it and that a puzzle box, which when solved dispenses their cash, would be perfect.
So I got to work…
A Word About the Rest of This Series
This project generated a lot of material, so these posts are split into separate deep-dives covering different aspects of the build. Feel free to jump to whichever topics interest you most, though I recommend starting with the Full Playthrough post, as it provides the context needed for many of the later sections.