A simple inline case for an Adafruit Trinket Mini or M0. I designed this with a friend when she was building an automatic fish feeder. The Trinket fits in very snug (it can be challenging to remove) and the case snaps closed without hardware but can be easily pried apart using a fingernail. The OpenSCAD source is available if you'd like to adjust the wire opening, tinker, modify, remix, etc.

Trinket M0: https://www.adafruit.com/product/3500 Trinket Mini 5v: https://www.adafruit.com/product/1501 Trinket Mini 3.3v: https://www.adafruit.com/product/1500