Hi,
  I've just salvaged a microcassette mechanism out of an old answering
machine. Reverse engineering the motor segment was easy enough - run the
motor in reverse and the mechanism switches into a fast-rewind mode, run it
the other way and the mechanism switches into record/playback mode.

  I've also identified what appears to be an optoreflector on the controller
board. It's situated under one of the tape drive pulleys, and has three
leads. Two appear to be the LED anode and cathode, the third seems to be an
output of some description. The sensor is SMD, in a clear case. I suspect all
I need to do is feed it 20mA across the LED, then take the signal from the
output pin, but I'm not sure if the output is open-emitter, open-collector or
totem-pole (I suspect it'll be o/c).

  The big problem is interfacing the magnetic head to something. I don't have
the foggiest clue what I need to do to record on the tape. I know there's
supposed to be an AC bias signal fed to the record head and the erase head,
but I can't find any concrete info on how to determine the frequency and
amplitude of that signal. The same applies to playback circuitry - no info on
output levels or required amplification.

  Does anyone have any schematics lying around that I could get copies of?
Most of the stuff I've seen consists of one chip, the heads and a few
passives. Something that's based on common ICs (standard opamps, transistors
and passives) would be great.

Thanks.
-- 
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem@philpem.me.uk              | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.me.uk/          | 48xCD, ARCINv6c IDE, SCSI
... If there's one thing I can't stand, it's intolerance.
-- 
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