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

Jean-Pierre Desrochers jpdesroc at oricom.ca
Wed Jan 11 23:39:57 CET 2023


Winter.. what a good time to work on my electronic projects!

I'm taking the opportunity right now to polish up my old piano roll reader project

for earlier mechanical piano. This project will be able to read the scrolling vintage music paper rolls

containing piano notes and hear them using an external MIDI player.

My prototype takes up a large part of my desktop space,

but it's going well so far.. A big challenge to take up..

>From the start I faced 2 problems: First, The IR beams reading strength of each holes

to be read. I managed it using short 2mm ‘light pipes’ between the photo-transistors

and the IR emitting leds to ‘channel’ the light. Second, The SPI parallel to serial

74HC165’s have no Schmitt trigger inputs so… LOTS of jitter readings making the holes readings

Completely unreliable. The solution.. inserting 74HC14 schmitt inverters between

The photo-transistors and the HC165 inputs. Voilà !

Of Note: The bottom photo shows the paper roll installed and ready to play.. 

notice the little purple lights above the paper.. 

these are infrared LEDs invisible to the naked eye but visible to the camera..


Have a nice 2023 beginning everybody !



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