[sdiy] About pots, and other things...

[ChristianH]

On Tue, 1 Jul 2008 10:44:03 -0700 "flightofharmony" <flight at flightofharmony.com> wrote:
> 3) Theoretical musing (A.K.A. Has anybody done this?): Embed a small motor
> in a keyboard key for sensing velocity? I tested this out on some scavenged
> drive motors and a cell phone vibration motor and it seems to work nicely.
> Since the voltage induce in a winding is directly proportional to the
> velocity of the magnet's rotation, the generated voltage and/or current
> could be used almost directly. A scaling buffer would be all that is
> required to adapt the output to a given circuit. As a bonus, if the motor is
> large enough, it would also provide tactile feedback similar to the Moog
> keyboard patent which used magnets for that purpose alone. Upon release of
> the key, another circuit could provide a current to force the key back to
> the rest position - eliminating the need for springs.

If you had no springs at all - how would the key know that you have
released it? 
Without a spring, the motor wouldn't generate anything on release,
unless you grab the key an push it up again...

Add to that, the motor only gives relative movement info, so you need to
be careful to somehow recognise "key fully down" and "fully up".
Otherwise any errors in integration of relative output might sum up over
time to either signal bleed-through on a released key, or not reaching
full intensity on a pressed key.

Definitely an interesting idea, but I'm sceptical about practical
usability. May need quite some intensive research. But then, if it was
easy, any geek on the loose would have done it already :-)

If you find out more, keep us informed...

Christian