Thank you, Wayne Stahnke, for bringing the subject of roll reading
to MMD again.

As you will probably remember, my 88er roll reader, built in 1990,
used 100 photo transistors in a tracker bar, read-out by a computer
7 bit-wise.  The light emitting diodes were regulated together by
voltage, but the photo transistors were only once adjusted by selected
resistors.

Now I made a new approach with fibre optics.  I use a plastic rod with
drillings of 2.2 mm to lead the fibres some mm above the moving punched
paper.

The other ends of the fibres end in photo transistors (infra red) with
matching holes.  They are mounted on cards in a 19" card cage: 13 (14)
cards each with 8 photo transistors, 2 voltage expanding gates and a
74LS245 IC to connect via flat cable to the card with a 8255 PIO in
the computer.

At the visible card ends are trim-pots for the photo transistors.  Now
the light emitting diodes under the roll are still regulated en bloc by
voltage, but the photo transistors are tuned singly by trim-pots.  This
way it is possible to read even the semi-translucent paper rolls of
Dr. Hocker.

By the way, since the card cage unit uses its own 5- and 12-volt supply
I damaged my computer when I switched it off and forgot to switch off
the card unit before.  Now it runs on the monitor outlet and is
switched off this way simultaneously.

The plastic rod was drilled 1/9" in line very precisely, thanks to
Dr. Walter Tenten.  When I someday get a rod drilled with 110 holes
of 2.2 mm 1/8" spacing distance, the 14th card will go to work for
Welte T-100 red rolls.

May I send an example MIDI-file to MMD ?

Best regards,

Horst Mohr
mohr@nemeter.dinoco.DE  D-51515 Kuerten 02268/1561

 [ Please do, Horst.  A good roll for evaluation is Ampico 57504,
 [ Prelude in C-sharp Minor, played by Rachmaninoff.  Wayne Stahnke
 [ has made a precision transcription of this available to MMDers.
 [ I will prepare a special web page at MMD for these contributions.
 [ -- Robbie