Thought folks here might be interested in this: I was taking apart a RailDriver, which is a specialist game controller for railway simulators, for work, and I found an interesting arrangement in the middle of the main processing board(s). The first attached photo is a photograph of the controller itself.
I was trying to work out how the actual levers on the top of the thing communicated their position to the computer, so that we might be able to hack it into doing some other stuff. It turns out that the levers were directly mechanically plumbed into little plastic washer things on the main board sandwich. When I desoldered the board sandwich apart, I found the second photograph.
This appears to be variable capacitors constructed with two PCB copper planes and plastic that slide in and out between them: and as the plastic slides in and out it varies the capacitance between the two plates. This is backed up by the fact that the little rotating grommet things were labelled CAP1/CAP2...CAPn on the silkscreen on the front board.
I've not really seen this way of doing things before, especially in USB game controller type applications! I mean it works, and works well: the controller is lovely and responsive in actual use, but it struck me as a bit unusual. So thought I'd pass it on here as a slight curiosity. :-)
