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

[Jean-Pierre Desrochers]

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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