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

[Jean-Pierre Desrochers]

2 things I forgot to mention:

*	The paper scrolling speed will be derived from one of the PIC’s TIMER interrupts
who’s timeout will be varied from the reading of a pot (ADC) value. (1feet/min to 13feet/min adjusted).

Constant and accurate.

*	The actual vertical size of each holes of the brass reading bar is about the size of the tinny paper studs left

Between each repetitive holes. In a pneumatic situation the passage of these small paper studs are not seen

>From the brass bar reader and interpreted as a continuous note line.

Because of that I don’t know if playing with IR LEDS angle will actually change something..

*	Interesting to see that there are no half tone pair of notes next to each others in the paper rolls I have

Again to keep paper sturdiness.. Always separated by at least one whole tone note paper space !

 

One other thing for me to check for:

Because Infrared light seems to be easily blocked by moving paper
compared to visible light I’m using 940nm wavelength IR LEDS/Photo-transistors.
But to do that I’ll need some kind of PCB bar to hold an array of IR LEDS
over the brass bar row of reading holes --> hidding an horizontal part of the moving paper roll .. Not very cute..
I was thinking of something else that could work..

Heat is Infrared so.. Using a heating element wire over all the brass bar holes
could be seen as a LEDS array but smaller in width (no PCB).
This wire just heated a little could be glued in a plexiglass transparent Bar
placed over the brass reading bar.??
Or use some kind of diffused incandescent light all over the scrolling paper
that has infrared specs close to 940nm.. ?

But I’m about sure heating wire spectral wavelength would be far from my needed 940nm..

Hmmm…

 

 

 

> On Nov 10, 2022, at 5:56 PM, Jean-Pierre Desrochers < <mailto:jpdesroc at oricom.ca> 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 !

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