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

[Roman]

Yes, I agree with Don. You should do it the way original pneumatic roll worked, make sensing device large enough to never be fully covered by a gap between holes. It may be not so easy with tiny LEDs and optotransistors, but if you add 2 optos in a distance that is half the distance between holes, it will work.

Why bother with tunable filters or counters if you can do it the right way from the start like it was invented 100 years ago.

Romn

PS. Who am I to say "I agree with Don". I can only be happy that I think the same way as the master himself :) 

---- Użytkownik Donald Tillman napisał ----

>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 !
>
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