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</o:shapelayout></xml><![endif]--></head><body lang=FR-CA link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoPlainText><span lang=EN-CA>I'm designing a piano Roll reader/player (yes antique paper piano rolls !)<br>that will read holes on a scrolling paper and play the actual musical notes<br>using MIDI standards..<br>This has already been done in the past but with very few documentations left<br>for DIYers like me.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA>So.. I'm thinking of using IR (940nm) LEDs, phototransistors and aligned short optical fibers<br>to read the actual scrolling holes. 90 phototransistors will be used as 'bit' readers.<br>I would use IR because paper is mostly opaque to 940nm wavelength<br>compared to visible light that could get through it.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA>Because of that high quantity of PT’s to be read I was thinking of using<br>rows/columns matrix of switches like keyboards in synths like this:<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA><o:p> </o:p></span></p><p class=MsoPlainText><span lang=EN-CA><img width=498 height=497 style='width:5.1875in;height:5.177in' id="Image_x0020_4" src="cid:image004.png@01D8B0B6.9A1910A0"></span><span lang=EN-CA><o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA>But instead of switches like in this circuit I would use 2 pins phototransistors like this one:<br><img width=153 height=144 style='width:1.5937in;height:1.5in' id="Image_x0020_5" src="cid:image001.png@01D8B0B7.B9CD68A0"><br><br><o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA>The resistors could be around 10K and this configuration would use only 2 x 8 bits ports.<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA>But I was wondering about using PT’s in a matrix like that would bring glitches or noise<o:p></o:p></span></p><p class=MsoPlainText><span lang=EN-CA>In the CPU readings.. <br>Has anybody used PT’s in such a circuit ?<o:p></o:p></span></p></div></body></html>