Phototransistor Music Roll Reader
By Spencer Chase
A description follows of the roll reader that I intend to build. I would appreciate any comments and suggestions that might help this project along.
The reader will initially be built with a reader head for Duo-Art and 88-note rolls. It will be built to accommodate wider paper and to allow reader heads for other formats to be substituted easily. The reader head will consist of .010-inch acrylic fiber optic threads sandwiched between Teflon bars. This provides a smooth continuous surface that is virtually immune to the effects of dust, etc. Individual fibers can be sorted and bundled to represent hole positions, or channels can be cut in the hole positions only and filled with fibers. The collected fibers will impinge on individual phototransistors, one per hole position.
The phototransistors can stay in place in a rack and various scan heads can be substituted by having their fiber bundles held in a matching rack. I have experimented with this approach and it seems to be able to detect minute paper displacements. Because the sensitivity is very high, detecting the onset of round holes should not be a problem even with minor tracking errors. I plan to experiment with detector window width to determine the optimal size for minimizing tracking error and adjacent hole reading.
The output of the transistors will be connected to an array of 8- or 16-input analog multiplexers depending on whether an 8-bit or 16-bit word size is chosen. The outputs would be fed to an array of comparators with variable threshold to allow for varying opacities of paper. (This could be dynamically adjusted through computer control of a D-to-A converter.) This would produce either 6 16-bit words per scan line or 12 8-bit words per scan line. This data would be fed to a digital input-output (I-O) board in a PC. The multiplex addressing and paper stepping would be controlled by the same board. I believe this approach would be quite fast as far as the hardware is concerned. Scanning 200 steps per inch should not be a problem.
I have several concerns regarding the software to control the data acquisition. I do not have experience with this and would appreciate the opinions of those who do. If a high level computer language were used to control the I-O board and write the data to a file, would this slow down the scanning to a crawl? Robert Hopp suggests that he collects data and converts it to MIDI format and plays it simultaneously. I would love to do this too, but I don't want to spend my life writing assembly code to do it. If rolls are to be scanned and archived, it is important to have confirmation that the collected data is accurate. Does anyone (Robert Hopp?) have software that they would like to share that does this.
I am willing to devote the time to develop an easy-to-build, reliable, and not very expensive scanner that can be used by a number of people to help preserve a musical heritage that is rapidly falling to dust. My only reluctance is also having to develop the software, especially if it has already been done by someone who is willing to share their efforts.
Spencer Chase
[ Editor's note:
[
[ Our member Horst Mohr built a phototransistor reader with stepper
[ motors, similar to your description, Spencer, and I hope that you and
[ Horst can discuss your project together.
[
[ By the way, I substituted "reader" for "scanner" in your article,
[ because the term "reader" has been associated for decades with parallel
[ data devices such as punched paper tape and punched cards.
[
[ The term "scanner", in the parlance of industry, is used mostly
[ for devices which move a single element across the object field,
[ for example, (a) the cathode-ray scanning beam of a TV or video
[ monitor, and (b) the single-point scanner of Robert Hopp's "Amadeus".
[
[ The "parallel reader head", seen in both player pianos and Hollerith
[ machines, is used to achieve the greatest possible speed (e.g., frames
[ per second while scanning music rolls).
[
[ Robbie Rhodes
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(Message sent Sat 7 Dec 1996, 21:16:56 GMT, from time zone GMT-0800.) |
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