<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div>I humbly suggest using higher-voltage CMOS Schmidt triggers to reduce noise. </div><div>Or to use a darlington phototransistor. </div>Making everything work on 3.3v is a hobbling constraint.<br id="lineBreakAtBeginningOfMessage"><div><br><blockquote type="cite"><div>On Nov 1, 2024, at 1:37 PM, Jean-Pierre Desrochers via Synth-diy <synth-diy@synth-diy.org> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Hi list,<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Long post here..<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Since I often asked help and suggestions on this forum for many issues,<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">I thought: Here is an idea I'd like to share..<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Some months ago I talked about a project I was working on<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">to read old piano paper rolls.<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><a href="https://www.youtube.com/watch?v=ZhH9kftuT_A&t=2s" style="color: blue; text-decoration: underline;">https://www.youtube.com/watch?v=ZhH9kftuT_A&t=2s</a><o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">This project works well.. but with some paper holes reading issues I had to address.<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Let me explain:<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">The 88 paper holes are read using IR photo transistors with 100k pullup resistors<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">with the help of 74HCS165 SPI buffers through a PIC micro.<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">A wide Infrared LEDs band is in front of the scrolling paper that has holes<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">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></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><span id="cid:image002.jpg@01DB2C63.37C01040"><image002.jpg></span><o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Some of the light pipes has more difficulties to get the light flow to its PT.. <o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">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></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">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></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">this sometimes causes reading problems and loss of some paper hole notes..<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">I tried to use 470k pullup resistors instead of 100k but the system<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">starts to get in an unreliable floating state when no notes detected.<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Here is my idea..<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Why not use a small PIC micro to work as an octal schmitt input buffer<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">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></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><span id="cid:image006.jpg@01DB2C63.37C01040"><image006.jpg></span><o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">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></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">88 notes means 11 x PIC16F1829..<span class="Apple-converted-space"> </span><o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">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></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;">Voilà !<o:p></o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div><div style="margin: 0cm; font-size: 11pt; font-family: Calibri, sans-serif;"><o:p> </o:p></div></div><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;">________________________________________________________</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; 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