[sdiy] Reading IR phototransistors in a 8X8 matrix

[Jean-Pierre Desrochers]

Yes I know that project..
But I want a self running unit (no PC needed).
Stuff that I’ll use:

Microchip uPC

MP3 player to play the paper roll notes (88 playable ‘Honkytonk piano’ wavefiles) on stereo audio outputs

MIDI output for any external device.. like a synth for instance !



I think so far the matrix way to read the notes could be the easiest way
with the less components used.

 

 

De : Ben Stuyts <ben at stuyts.nl> 
Envoyé : 15 août 2022 19:05
À : Jean-Pierre Desrochers <jpdesroc at oricom.ca>
Cc : Synth-diy at synth-diy.org
Objet : Re: [sdiy] Reading IR phototransistors in a 8X8 matrix

 

Have you seen this project? It uses a webcam to read the piano roll:

 

https://github.com/nai-kon/PlaySK-Piano-Roll-Reader

https://www.youtube.com/watch?v=8lkMRsoG9cg

 

Ben

 





On 15 Aug 2022, at 21:00, Jean-Pierre Desrochers <jpdesroc at oricom.ca <mailto:jpdesroc at oricom.ca> > wrote:

 

I'm designing a piano Roll reader/player (yes antique paper piano rolls !)
that will read holes on a scrolling paper and play the actual musical notes
using MIDI standards..
This has already been done in the past but with very few documentations left
for DIYers like me.

So.. I'm thinking of using IR (940nm) LEDs, phototransistors and aligned short optical fibers
to read the actual scrolling holes. 90 phototransistors will be used as 'bit' readers.
I would use IR because paper is mostly opaque to 940nm wavelength
compared to visible light that could get through it.

Because of that high quantity of PT’s to be read I was thinking of using
rows/columns matrix of switches like keyboards in synths like this:

 

<image004.png>

But instead of switches like in this circuit I would use 2 pins phototransistors like this one:
<image001.png>




The resistors could be around 10K and this configuration would use only 2 x 8 bits ports.

But I was wondering about using PT’s in a matrix like that would bring glitches or noise

In the CPU readings.. 
Has anybody used PT’s in such a circuit ?

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