[sdiy] Using a PIC micro as an Octal schmitt buffer with programmable threshold levels..

[Jean-Pierre Desrochers]

Yeah.. I suppose that could make a change.. 
Thanks Roman.

> -----Message d'origine-----
> De : Roman Sowa <modular at go2.pl>
> Envoyé : 4 novembre 2024 07:55
> À : Jean-Pierre Desrochers <jpdesroc at oricom.ca>; synth-diy at synth-diy.org
> Objet : Re: [sdiy] Using a PIC micro as an Octal schmitt buffer with
> programmable threshold levels..
> 
> Lower the optos pull-up supply voltage to 4V and it should improve a bit
> 
> Roman
> 
> W dniu 2024-11-01 o 18:37, Jean-Pierre Desrochers via Synth-diy pisze:
> > Hi list,
> >
> > Long post here..
> >
> > Since I often asked help and suggestions on this forum for many
> > issues,
> >
> > I thought: Here is an idea I'd like to share..
> >
> > Some months ago I talked about a project I was working on
> >
> > to read old piano paper rolls.
> >
> > https://www.youtube.com/watch?v=ZhH9kftuT_A&t=2s
> > <https://www.youtube.com/watch?v=ZhH9kftuT_A&t=2s>
> >
> > This project works well.. but with some paper holes reading issues I
> > had to address.
> >
> > Let me explain:
> >
> > The 88 paper holes are read using IR photo transistors with 100k
> > pullup resistors
> >
> > with the help of 74HCS165 SPI buffers through a PIC micro.
> >
> > A wide Infrared LEDs band is in front of the scrolling paper that has
> > holes
> >
> > punched in it (played notes). Each hole lets the IR beam reach an
> > aligned Phototransistor that has a ‘light pipe’ to ‘conduct’ the light
> > beam to it.
> >
> > Some of the light pipes has more difficulties to get the light flow to
> > its PT..
> >
> > This arrangement causes some PT’s ‘ON’ low state to get too high in
> > voltage values read by the 74HCS165 SPI readers. The PT OFF state does
> > not cause any problem
> >
> > since  it goes high impedance up to 5vdc. Ok. But the ON low state
> > values can go from 0.31v up to 1.7v !!
> > _Because of the very variable 74HCS165 threshold voltage values from
> > chip to chip_
> >
> > this sometimes causes reading problems and loss of some paper hole notes..
> >
> > I tried to use 470k pullup resistors instead of 100k but the system
> >
> > starts to get in an unreliable floating state when no notes detected.
> >
> > Here is my idea..
> >
> > Why not use a small PIC micro to work as an octal schmitt input buffer
> >
> > that has programmed threshold levels at fixed specific values ?
> > Here are the HCS165 threshold levels compared with my PIC threshold :
> >
> > Now the PT’s could have up to 2.5v in their ON (low state) and still
> > be read as a low state by the still in place HCS165 SPI readers..
> >
> > 88 notes means 11 x PIC16F1829..
> >
> > The use of 8 x ADC inputs, applying threshold values while reading to
> > finaly output 8 x standard digital I/O.
> >
> > Voilà !
> >
> >
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