This past summer I started building a watch. My idea was to combine a simple digital watch display with a nice watch case. Though it was more involved than I anticipated, it's finally fairly complete!
The toughest challenge with this watch was finding a way to use the traditional rotating crown to set the digital time on the watch. After a great deal of experimenting, I attached a magnetic rotation sensor to the PCB and a magnet to the stem (the metal rod extending from the crown), which made it possible to digitize the rotation of the crown.
The sensor is mounted perpendicular to the PCB, using a tiny second PCB that fits into a slot on the main board. This piece can be printed along with the primary circuit board thanks to existing slot in the PCB required for the watch stem. I document the development process and add many more goodies here: http://joesul.li/van/watch/