Old-Time PIClisters --
    I need your help in developing a new device -- a piezoelectric servo.
Remember the crystal (or ceramic) phono cartridge, where, if something (like a
phono record) wiggled the needle, you got a voltage on the output terminals?
Shouldn't it also work backwards?  That is, if I put a voltage on the
terminals, shouldn't it wiggle the needle?
    If I tie the terminals of an Astatic 310T phono cartridge to a scope and
"twang" the needle, I get a 3-volt peak output followed by a damped sine wave:
2500 Hz, damping to half-amplitude at a rate of about 1 cycle.  The needle, I
think, is resonating.
    Suppose I tie the terminals to an I/O pin on a PIC12C671.  Program the pin
for digital output, and hit the cartridge with a 3-volt pulse for, say, 100
microseconds.  Now switch the pin to analog input and read the response at,
say, 1000 samples per second.  What do I get?
     If the needle wiggles, I've got the makings of a solid-state servo.
Program the PIC to keep it going at its resonant frequency.  Using a stereo
cartridge, with the PIC driving the two channels at a phase difference of 90
degrees, the needle will go in a circle, at 2500 revs per second.  I could
drive something with that!
    From what I hear, Astatic has long since gone out of the phono cartidge
business; but the gadgets are still available in the antique eletronics
market.  Do any of you old-timers know how they really work?  Or know any
retired Astatic engineers who might like some consulting work?
-- Mel Evans    mevans1027@aol.com      727-595-7685      fax: 727-595-7680