I would like to add some additional engineering details to anyone who is
contemplating building a "brush-type" hole sensor.

I did some experiments years ago and build a small 20-note Door-bell
organ using silver wire brushes.  I found out quickly that any sort of
dirt or lint would prevent the contact wire from making contact.  This
happened because the contact pressure was kept to a minimum (to prevent
too much drag on the paper).  The drag can add up as the number of
contacts increases.

So because of the low contact pressure, there were many times a note
would not sound or would be late due to a piece of paper lint.  To solve
this problem, I replaced the silver plate that the contacts came down on
with a copper tube of about 3/4" in diameter which would rotate away from
the contacts at the same speed as the paper and in the direction of the
paper flow.  This solved the problem because any lint or dirt would soon
be pulled away from the contact points.  A soft felt wiper would prevent
the dirt from reappearing as the roller turned.

A mechanical lifting mechanism would allow one to tilt up the contacts
and replace the paper.

If I were to work on such a project I would use the roller once again but
I would silver plate it this time because the copper eventually darkens
with age and I suppose (I can't say for sure because I gave the mechanism
away) the oxidation might have prevented contact closure.

There is also the matter of contact point shaping.  I used the end of
the wire in my device.  Although it did not rip the paper, I was always
worried that it might.  I think I might form the bottom of the contact
to a "V" shape so that the paper rides on a radius rather than the sharp
edge of a wire.

Silver wire can be purchased from organ supply houses.  Pipe organ pedal
contact blocks might work for experimental use but the wire used is too
heavy.  About .020" diameter wire seemed to work well.

I used 2-inch wide adding machine paper for my music roll.  It was laid
out by hand and punched with a hand punch assembly.  "Long, Long Ago"
was the first and only song I perforated.

If anyone is building a roll reader using brushes,  I would love to hear
of your progress.

Andy LaTorre
LaTorre Orgue Mecanique
Sylva, North Carolina, USA