The box needs a servo-activated lock to allow it to open at the correct point.

The simplest solution would have been a servo rotating a catch into a hole inside the box, similar to how has been implemented for many reverse-geocache projects.

But I decided I wanted to replace the catch that came with the box with an external locking mechanism; it feels much cooler, and provides an external visual feedback that the box has been unlocked.

This design was inspired I'm sure by something I've seen in a computer game somewhere.

The lock parts are cut from 6mm ply. I would have been much easier with a laser cutter, but I've not got one, so it was done by hand. The pegs are cocktail sticks (2mm dowel). Note that they've not been sanded down yet.

Here's the box closed. The central 'lozenge' shape is attached to the body of the box, and the two 'c' shapes are attached to the lid.

The 'c' shapes run in two slots in the lid, so they can slide outwards to release the catch. I'll use a servo to control this.

Detail of the lock; the rubber bands are a temporary option to use it as a manual lock. I've not trimmed the dowels as I'm not sure how long I'll need them for the servo.