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MMD > Archives > January 1999 > 1999.01.29 > 09Prev  Next


Reading Music Rolls Using Pneumatic Switches
By Craig Brougher

After reading Wayne Stahnke's article on a very clever photoelectric
switch using pouches, I had an idea of something else using no pouches
at all.  It seems as though it should be practically instantaneous, but
as with all my "bright ideas," there is usually something I didn't
consider, and I have to make allowances or solve the problems first.
Of course, that's design work in a nutshell.

Anyway, my suggestion is this: Thinking about Wayne's 3AG glass fuse
bodies, I wondered why the little glass fuse tube couldn't be partly
filled (say, 1/4" high in each tube) with a very thin oil like kerosene
that doesn't congeal or evaporate quickly  (somebody could come up with
something perfect for this purpose, I'm sure, like very thin silicone
oil) and use the property of bubbles from an open trackerbar tube with
vacuum above the tube to disturb the fluid?

Make them just like tiny little "bubble jars."  The tubes would simply
"hang" down from a manifold or mount between two manifolds, from which
supply vacuum and trackerbar air flowed through into each respective
tube.  (Then we simplify further and do the whole thing out of clear
plastic sheet goods).

The speed of "relaxation" of the chain of bubbles would be similar
to the speed of relaxation of a pouch, adjustable through its bleed.
I don't foresee a problem there.  And bubble jars, as you know, are
"adjustable," sensitivity-wise.  All of which can be machined easily,
en-masse into the manifold block they all mount into.

Monitoring this disturbance would be a photo switch, whose sensitivity
is adjustable.  Any bubble would turn it more reflective (less trans-
missible), or conversely, add a bit of an oil soluble dye (like indigo
blue) that is opaque to infrared and let the bubbles open the circuit.
Sensitivity adjustment should be all that is needed, and probably not
even individually if the latitude between on and off is great enough.

I haven't through about how to prevent spillage in a portable model
yet, but I thought of a additional "false floor" for the liquid.  When
not in use, it is drawn out of all the tubes into a reservoir through
little needles -- just like little syringes would do it.  All the
"syringes" plungers are connected together.

Some advantages might possibly be: Quicker.  No bounce at all,
measuring flow more directly instead of indirectly.  Easier to adjust
precisely.  Smells funny all the time.  (No-- forget that last
advantage).

Does this possibility compute to anybody? Or should I turn off-a
the "bubble machine?"

Craig Brougher

 [ Your basic idea is good: to sense the change in the transmissivity
 [ of a medium as the result of pressure change.  A fluid has a lot of
 [ mass, though; I wonder if a gas exists with this property?  It might
 [ be something like water vapor at saturation -- when the pressure is
 [ reduced the vapor condenses into a fog!  -- Robbie


(Message sent Fri 29 Jan 1999, 14:56:19 GMT, from time zone GMT-0600.)

Key Words in Subject:  Music, Pneumatic, Reading, Rolls, Switches, Using

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