The puzzle is the product

Before the NAS enclosures and the parametric CAD, there was this: a wooden box that won’t open until you solve it. It’s the oldest project on this page (2021) and still one of my favorites — a small, complete product with hardware, firmware, and a user experience, built at my desk.

How it works

The lid hides a bank of toggle switches wired into an Arduino. Set them to the right combination and the box reacts: an LED strip gives you feedback as you get closer, a piezo buzzer chirps at you, and when you finally land the correct sequence, a servo pulls the latch and the box pops open. Wrong guesses get you nothing but the buzzer’s opinion of your reasoning.

The build

Everything in the box is hand-soldered point-to-point — no custom PCB, no connectors kit, just wire, flux, and patience:

• An Arduino-compatible board running the whole show: reading the switch bank, driving the lights, and deciding when you’ve earned the latch.
• A WS2812 LED strip glued down the center line, shining through a row of holes drilled in the face of the box.
• A bank of micro toggle switches, each one soldered inline and zip-tied into the harness.
• A servo on the latch — the single moving part, and the entire payoff.
• A repurposed hinged wooden box with brass hardware, because a puzzle box should feel like furniture, not a project enclosure.

Why it holds up

This build predates my CAD era — there’s hot glue in there, and I’d route the wiring very differently today. But I still like what it’s built around: the electronics don’t matter much if the moment doesn’t land. Everything in the box exists to serve one interaction — the click of that latch letting go.