[sdiy] Reading IR phototransistors in a 8X8 matrix

[Ben Stuyts]

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

https://github.com/nai-kon/PlaySK-Piano-Roll-Reader <https://github.com/nai-kon/PlaySK-Piano-Roll-Reader>
https://www.youtube.com/watch?v=8lkMRsoG9cg <https://www.youtube.com/watch?v=8lkMRsoG9cg>

Ben


> On 15 Aug 2022, at 21:00, Jean-Pierre Desrochers <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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