Suggestion by Eric Barbour (metasonix.com)
If you want a key sensor with two degrees of analog sensing freedom, here is an idea that can be implemented
with off-the-shelf hardware and (probably) minimal cost.
Take one of those tiny Alps video-game joysticks.
Mount it sideways, and attach an arm that pokes upwards, with a key on the end, to the stick. It could be as simple as
a metal rod with a hole and setscrew on one end, to attach to the stick, and a key or button glued to the other end.
So, when you push down on the key, the resistance changes on one of the built-in pots, and if you push the key sideways,
the other built-in pot changes.
Sense the resistance changes as needed—an analog circuit can derive keydown, pressure, and velocity in both planes of motion
for a single key. This would have an advantage in that it would be faster than microprocessor scanning. It would be suitable
as-is for controlling an analog synthesizer. Simply OR the trigger outputs together to derive a single trigger, and add the
pressure voltages together to derive a single control voltage as needed.
Or a microprocessor can scan a bunch of joysticks at once and derive keydown, pressure and velocity. A fast processor with
loads of analog-voltage inputs would be a necessity.
There's probably no cheaper and easier way to do this, at least that I have found. Mechanical design is relatively simple, and a
large number of these devices can be crammed into a small keyboard because of the small size and PCB mountability of the
joysticks. The joysticks are 22.7mm wide, but you could cram them into a smaller space by offsetting them alternately.
A single PC board would be required for each rank of keys, and could hold the analog circuitry as well as the joysticks.
The joysticks come in two forms, one with just two pots and another with two pots and a tact switch that is activated by
pressing the stick down. This keyboard would use the version without the tact switch. (Or, if you prefer, you could use the
tact-switch version, mount it in the normal way, and put a key on the end of the stick. Then you push down for a simple
trigger, sideways for one analog change, and forward-back for another analog change.)
If anyone implements this, don't forget to credit me……