[sdiy] Reading holes (voids) on piano paper rolls.. using Photo-transistors and PIC micro..

[Donald Tillman]

Interesting problem.

Try setting up the light source and phototransistor for an aperture width of exactly the distance between sequential holes.  Ie., one hole plus one space.

  -- Don
--
Donald Tillman, Palo Alto, California
https://www.till.com

> On Nov 10, 2022, at 5:56 PM, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:
> 
> Hi all,
>  
> My Player piano reader project is going fine so far..
> Some little robotics stuff (stepper motors, sensors, etc..) going on now..
> I’m now in the process of reading the small holes scrolling
> with the music paper rolls ‘sandwiched’ between Infrared leds and 88 x Photo transistors (see the image below).
> The actual music data appears on the paper as parallel lines of small successive holes
> shown in blue below. Because of the need of paper sturdyness for long duration notes the original paper punches
> made small successive holes in the same note line instead of a steady cut in paper
> that could eventualy be damaged over time..
> That is shown by the blues dots below (successive holes).
> Now I need to read these constant note ‘ignoring’  all the occuring small holes
> during these long  duration notes..
> The second line shows what the reading Photo transistor ‘sees’
> and the third line shows an ideal reading stored in the micro.
> So far there are 2 ways I found to get close of the ideal reading :
> #1  Place a capacitor in parallel with each Photo transistors to get rid of the ‘pulsating holes’ on a continuous note
> #2  Use software with separate counters to ‘skip’ the incoming small pulses just enough not to miss any ‘real’ short notes.
> My challenge here is that the paper roll speed will be a variable one
> which could be varied from  1feet/min  up to  13feet/min.
> That’s a  1 to 13 ratio !!
> So method #1 using caps in parallel with the photo-transistors (fixed RC time)  will not be feasable (I think).
> Is there another way you could think of to get rid of these small pulses
> when necessary ? 
> Thanks !