Mechanical Music Digest  Gallery
You Are Not Logged In Login/Get New Account
Please Log In. Accounts are free!
Logged In users are granted additional features including a more current version of the Archives and a simplified process for submitting articles.
Home Archives Calendar Gallery Store Links Info
MMD > Gallery > Tech > mohrReader

Optical Reader for Music Rolls
Fiber Optics Reader for Music Rolls
by Horst Mohr

mohrReader1a.jpg (59kb)
Demonstration to members of GSM and MBSI at Schloss Bruchsal, 8-10 October 1999.
[Higher resolution image: mohrReader1.jpg (62kb)]

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 diameter to lead the optic fibres a few millimeters 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.  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 diameter and 1/8" spacing distance, the 14th card will go to work for Welte T-100 red rolls.

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. Juergen 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.

Horst Mohr
Fri, 29 Jan 1999 19:52:56 MEZ

More articles by Horst Mohr are indexed at http://www.mmdigest.com/Archives/Authors/Aut248.html
Enjoy the emulated music rolls, as MIDI files, at the MMD Sounds site, http://www.mmdigest.com/Sounds/
Return to MMD Tech site, http://www.mmdigest.com/Tech/


10 January 2000

Home    Archives    Calendar    Gallery    Store    Links    Info   


Enter text below to search the MMD Website with Google



CONTACT FORM: Click HERE to write to the editor, or to post a message about Mechanical Musical Instruments to the MMD

Unless otherwise noted, all opinions are those of the individual authors and may not represent those of the editors. Compilation copyright 1995-2024 by Jody Kravitz.

Please read our Republication Policy before copying information from or creating links to this web site.

Click HERE to contact the webmaster regarding problems with the website.

Please support publication of the MMD by donating online

Please Support Publication of the MMD with your Generous Donation

Pay via PayPal

No PayPal account required

                                     
Translate This Page