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MMD > Archives > February 1999 > 1999.02.02 > 10Prev  Next

Music Wire Fingers for Cheap Roll Reader
By John Kleinbauer

Hi All,  Today I was poking around on eBay.  There I found a small
children's player piano.  I read the description for the item,  but
nowhere did it mention how the piano works.  Through the years I have
taken apart many toys and after awhile you realize how resourceful
companies are.  Parts are melted in place but not glued.  Some
assemblies are held together by bent over tabs that are at the end
of the part.

Now I don't know for sure how this toy piano works, but an idea flashed
by me.  I pictured finger contacts that ride on the paper roll.  When a
hole comes by the finger drops through the hole and touches a metal
plate.  This plate closes the circuit and a solenoid is activated or
the signal goes on to a logic circuit.  The fingers are made out of
.010-inch guitar string [music wire] and the are mounted in a plastic
block with epoxy a set screw or just melt them in.

You can not solder guitar wire,  so you will have crimp on a connection
using a small section of brass tubing.  The reader fingers have to come
in on a 45 degree angle and they should be no longer than 1/2" long.
Since guitar is a type of high quality spring wire it can be shaped and
adjusted for this task.

The output of each wire could then go to a 10-Kohm pull-up resistor
that would feed a gate in a 74LS14 Schmitt trigger chip.  The Schmitt
trigger removes any mechanical bounce from the signal.  The whole
reader could be made for less than five dollars and that includes a
soda and chips.

I do have one question:  What chip is everybody using to change a
single one-of-88-switches-hit into binary?  I though of using an old
computer keyboard chip but that chip does not like more than one switch
pushed at a time.

John "Make it cheap, make it quick" Kleinbauer

(Message sent Tue 2 Feb 1999, 20:53:54 GMT, from time zone GMT-0800.)

Key Words in Subject:  Cheap, Fingers, Music, Reader, Roll, Wire

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