> Actually, if using a mechanical reduction, you might as well use a  
> rotary pot for this

I guess, although the track in a slider pot would be a little longer

> That now makes me think of using a series of IR LED's in a line with  
> one IR sensor under the "switch"

I've added a reflective IR sensor to the motor train and painted the
drive pulley half-white half-black so that the PIC can tell if the cylinder
is turning before it enables the sound

If each LED had its own individual and accurate frequency that could
be quite easily determined with CCP

Another detail - the machine has two lead screws. One is the same
fine pitch as the grooves on the cylinder. This is used to move the stylus
along, rather than the grooves themselves, which is what would have
happened originally. The other lead screw is much coarser and is used
to return the stylus back to the home position. When playing, a spring
pulls a plastic guide (which has a fine thread on one side and a coarse
thread on the other) onto the fine screw. At the end of travel, a micro-
switch, via the PIC, energises a solenoid to pull the guide off the fine
thread and onto the return thread, which is rotating the opposite way
because of the gearing

Something like that could be done with the selection thread, with a
solenoid enabling song selection only at a particular time. Any other
time the crank could be spun around without the pointer moving

wbr
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