Hello, Walter Tenten.  Using one-shot multivibrators instead of simple
R-C circuits might be a solution but is more complex, requiring many
integrated circuits, and anyway R-C components.

In both solutions, you must determine the exact amount of delay required
for the contacts used.  Contacts are not the same, each kind of contact
has its own bouncing time.  Some contacts, using conductive rubber, are
nearly bounce-free.

The R-C components (and their tolerance) should be chosen accordingly.
Excessive delay should be avoided, because it may affect accuracy of
piano performance.

Leonardo Forti
Rome, Italy

 [ Richard Tonnesen, Custom Music Rolls, found that digital
 [ "de-bouncing" worked well for his pneumatic roll reader, with equal
 [ time delay across all 100 ports.  The biggest problem, he told me,
 [ was the instability of the phosphor bronze pouch spring.  At least
 [ twice each year he would adjust the contacts with pliers, to achieve
 [ consistent response.  See the photo, Figure 9, in the article at
 [ http://www.mmdigest.com/Gallery/Pictures/tonnesen.html 
 [ -- Robbie