Not Hall effect, since there is no magnet involved. Most likely
something about (or some part of) the rubber is conductive - silicon
rubber can be made conductive. Perhaps the degree of conduction changes
when the rubber is squished.

It is also possible that it is capacitive sensing - the layers form a
capacitor, whose value changes when the rubber is deformed to bring the
conductors closer together. Sounds pretty elaborate, though.

Bill
---------------------------
DaveC wrote:

Underlying the key mechanisms is a double-sided film with concentric circuit
pads (for each key) on either side of the film. The key cap pushes down a
little inverted cone of what looks like silicone rubber to touch the film.

This isn't a contact switch; the top of the film has just one pad, as does
the bottom of the film; no electrical connection is being made.

Is this hall effect? I can't see anything on the end of the cone, unless
there's something impregnated in it.

The connector to the motherboard is a 40-pin flexible mylar cable.

What technology is used in this kind of keyboard? With 40-pins going
off-board, I presume all matrix processing is done on the motherboard?

Google didn't turn up any in-depth descriptions of keyboard technology.

Thanks,