ivp wrote:
> The client has indicated he'd like the slider moved by a brass crank. !!!!
> This probably means that the slider will be on a lead screw and several
> turns of the crank will move the pointer from one item to the next
> 
> The reason being that this is a museum exhibit of a 1906 Edison cylinder
> player, which has been motorised but originally was wound up with a
> crank, so he wants to keep some of that feel to it. The selector is to pick
> a song to play from a bank of WAV files

Interesting!

Did you know that there are people who are still making wax cylinders for
Edison machines? I recently saw a presentation in which they were re-creating
an old-time acoustic recording session. You wouldn't believe the gyrations
they went through while recording in order to get a decent-sounding playback.
Between the lousy dynamic range (high noise floor) and terribly non-flat
frequency response, you basically had to do a lot of "pre-compensation" of
the sound balance just to get something recognizable back out.

> My idea with a long PCB is that it would have fixed resistors and solid
> detentes, thus turning the crank is a WYSIWYG. It's for public use and
> something I'd rather not have to service or field complaints about

If I were you, I'd seriously consider non-contact solutions, such as
capacitive sensing.

For example, the brass crank could move a brass "pointer" along the surface
of the PCB, almost but not quite touching it. Sensor pads built into the PCB
artwork (sealed underneath the soldermask) would detect the presence of the
pointer at particular locations.

There are many ways to do multi-point capacitive sensing with low parts
count these days, anything from dedicated chips to ordinary I/O pins on
general-purpose microcontrollers. Usually, you just need one or two passive
components per point sensed, which compares favorably with your resistive
divider.

-- Dave Tweed
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