I've been using the following schematic to use an IR Led and photo-detector transistor for my touch panel (sorry about the bad drawing):
This is a cheap alternative to proximity sensors and works great for finger detection on my Plexiglas panel.
Now I have a project that requires 42 "touch" areas and I'm trying to figure out the simplest way to multiplex them.
My plan (below) is to use shift registers to turn on each IR led one at a time, and take a reading from the respective photo-detectors:
would it be safe to hook all the transistors together or should I power them one at a time also?
I'm still an electronics novice and not sure whether photo-transistors consume power at all.
I don't mind soldering an extra bunch of shift registers if I have to, but I figured the experts might have a better plan to share
Again, sorry about the foggy explanation/schemo and many thanks for any insight!