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<p>Hmmmnnn..</p>
<p>I'm wondering if you can accomplish the same by shifting the
photo transistor grounds slightly negative -1 volt or so? <br>
</p>
<p>For example run the photo transistors off of +5V and -1V.<br>
</p>
<div class="moz-cite-prefix">On 11/1/24 12:37 PM, Jean-Pierre
Desrochers via Synth-diy wrote:<br>
</div>
<blockquote type="cite"
cite="mid:000901db2c84$bf4a89c0$3ddf9d40$@oricom.ca">
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<p class="MsoNormal">Hi list,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Long post here..<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Since I often asked help and suggestions on
this forum for many issues,<o:p></o:p></p>
<p class="MsoNormal">I thought: Here is an idea I'd like to
share..<o:p></o:p></p>
<p class="MsoNormal">Some months ago I talked about a project I
was working on<o:p></o:p></p>
<p class="MsoNormal">to read old piano paper rolls.<o:p></o:p></p>
<p class="MsoNormal"><a
href="https://www.youtube.com/watch?v=ZhH9kftuT_A&t=2s"
moz-do-not-send="true">https://www.youtube.com/watch?v=ZhH9kftuT_A&t=2s</a><o:p></o:p></p>
<p class="MsoNormal">This project works well.. but with some
paper holes reading issues I had to address.<o:p></o:p></p>
<p class="MsoNormal">Let me explain:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The 88 paper holes are read using IR photo
transistors with 100k pullup resistors<o:p></o:p></p>
<p class="MsoNormal">with the help of 74HCS165 SPI buffers
through a PIC micro.<o:p></o:p></p>
<p class="MsoNormal">A wide Infrared LEDs band is in front of
the scrolling paper that has holes<o:p></o:p></p>
<p class="MsoNormal">punched in it (played notes). Each hole
lets the IR beam reach an aligned Phototransistor<br>
that has a ‘light pipe’ to ‘conduct’ the light beam to it.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><img border="0" width="894" height="503"
style="width:9.3125in;height:5.2395in" id="Image_x0020_1"
src="cid:part1.oxQO509m.gcof10j3@ix.netcom.com" class=""><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Some of the light pipes has more
difficulties to get the light flow to its PT.. <o:p></o:p></p>
<p class="MsoNormal">This arrangement causes some PT’s ‘ON’ low
state to get too high in voltage values<br>
read by the 74HCS165 SPI readers. The PT OFF state does not
cause any problem<o:p></o:p></p>
<p class="MsoNormal">since it goes high impedance up to 5vdc.
Ok. But the ON low state values can go from 0.31v up to 1.7v
!!<br>
<u>Because of the very variable 74HCS165 threshold voltage
values from chip to chip</u><o:p></o:p></p>
<p class="MsoNormal">this sometimes causes reading problems and
loss of some paper hole notes..<o:p></o:p></p>
<p class="MsoNormal">I tried to use 470k pullup resistors
instead of 100k but the system<o:p></o:p></p>
<p class="MsoNormal">starts to get in an unreliable floating
state when no notes detected.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here is my idea..<o:p></o:p></p>
<p class="MsoNormal">Why not use a small PIC micro to work as an
octal schmitt input buffer<o:p></o:p></p>
<p class="MsoNormal">that has programmed threshold levels at
fixed specific values ?<br>
Here are the HCS165 threshold levels compared with my PIC
threshold :<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><img border="0" width="604" height="505"
style="width:6.2916in;height:5.2604in" id="Image_x0020_2"
src="cid:part2.0uomPYv7.dfBIyO0B@ix.netcom.com" class=""><o:p></o:p></p>
<p class="MsoNormal">Now the PT’s could have up to 2.5v in their
ON (low state) and still<br>
be read as a low state by the still in place HCS165 SPI
readers..<o:p></o:p></p>
<p class="MsoNormal">88 notes means 11 x PIC16F1829.. <o:p></o:p></p>
<p class="MsoNormal">The use of 8 x ADC inputs, applying
threshold values while reading<br>
to finaly output 8 x standard digital I/O.<o:p></o:p></p>
<p class="MsoNormal">Voilà !<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<br>
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