[sdiy] Reading IR phototransistors in a 8X8 matrix

[Jean-Pierre Desrochers]

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:

 



But instead of switches like in this circuit I would use 2 pins phototransistors like this one:




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 ?

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20220815/5fba3144/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image004.png
Type: image/png
Size: 159091 bytes
Desc: not available
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20220815/5fba3144/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 13562 bytes
Desc: not available
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20220815/5fba3144/attachment-0001.png>