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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The transistors aren’t diodes. Some (but I accept not all) phototransistors can conduct in either direction as they are being turned on by light, not a bias
current on the base referenced to the emitter.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">N collector<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">P base<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">N emitter<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Isn’t too different to :<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">N emitter<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">P base<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">N collector<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Gain is less in the second instance, but not zero.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Jean-Pierre Desrochers [mailto:jpdesroc@oricom.ca]
<br>
<b>Sent:</b> 15 August 2022 20:26<br>
<b>To:</b> Mike Bryant; Synth-diy@synth-diy.org<br>
<b>Subject:</b> RE: [sdiy] Reading IR phototransistors in a 8X8 matrix<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">></span><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Test the transistors and if this does occur you’ll need to add series diodes with each transistor.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">But if you look at the shown matrix you will see series diodes on each switches (phototransistors in my case).<br>
Or I am missing something on what you say..<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="FR" style="font-size:11.0pt;font-family:"Calibri","sans-serif"">De :</span></b><span lang="FR" style="font-size:11.0pt;font-family:"Calibri","sans-serif""> Mike Bryant <mbryant@futurehorizons.com>
<br>
<b>Envoyé :</b> 15 août 2022 15:12<br>
<b>À :</b> Jean-Pierre Desrochers <jpdesroc@oricom.ca>; Synth-diy@synth-diy.org<br>
<b>Objet :</b> RE: [sdiy] Reading IR phototransistors in a 8X8 matrix<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="FR-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">One possible problem is that the phototransistors turn on just based on light, and so may conduct in the reverse direction. Thus you may find lots of paths
to conduct some of the current through the selected transistor finding its way to ground and reducing the voltage output. Test the transistors and if this does occur you’ll need to add series diodes with each transistor.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Synth-diy [<a href="mailto:synth-diy-bounces@synth-diy.org">mailto:synth-diy-bounces@synth-diy.org</a>]
<b>On Behalf Of </b>Jean-Pierre Desrochers<br>
<b>Sent:</b> 15 August 2022 20:00<br>
<b>To:</b> <a href="mailto:Synth-diy@synth-diy.org">Synth-diy@synth-diy.org</a><br>
<b>Subject:</b> [sdiy] Reading IR phototransistors in a 8X8 matrix<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoPlainText"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">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" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">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" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">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" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US"><img border="0" width="498" height="497" id="Image_x0020_4" src="cid:image001.png@01D8B0E5.D04546B0"><o:p></o:p></span></p>
<p class="MsoPlainText" style="margin-bottom:12.0pt"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">But instead of switches like in this circuit I would use 2 pins phototransistors like this one:<br>
<img border="0" width="153" height="144" id="Image_x0020_5" src="cid:image002.png@01D8B0E5.D04546B0"><o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-CA" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">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" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">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" style="font-size:11.0pt;font-family:"Calibri","sans-serif";mso-fareast-language:EN-US">In the CPU readings..
<br>
Has anybody used PT’s in such a circuit ?<o:p></o:p></span></p>
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