A number of people have asked about technical details of my MIDI piano
roll player. Here is a bit more info for those who may be interested.

The hole sensing is done using an array of IR light-emitting diodes
(LEDs) and IR detectors [phototransistors] arranged in a line just like
a tracker bar. There is one LED and one detector per note. The LEDs and
the detectors are "through the hole" discrete components only 2.2 mm
wide. They are rather unusual and very inexpensive components from
China. The part numbers are SR2424 and SGPT2424. They are mounted onto
custom printed circuit boards that have 9-to-the-inch spacing.

The encoder circuit board takes a 5-volt signal from each activated
detector. It is a 96-note commercially available encoder from Christian
Blanchard: https://orgautomatech.fr/ 

Christian has done an amazing job of programming into his encoder most
of the functions that are wanted for a piano roll player, e.g., sustain,
snakebite boost, volume, de-bridging, etc etc. The 96-note encoder is
fairly new and is not yet shown on Christian's website.

Phil Dayson
Vancouver, British Columbia, Canada