On 6/17/2013 4:12 PM, Mouse wrote:
  Depending on what it's to be connected to, I
could come pretty close to
 an async serial interface using discrete transistors.  I'd need a lot
 of them, probably nearly a hundred by the time it's all done, but it's
 not out of reach.  USB probably _is_ out of reach. 
 Mechanical would be more fun. 
:-)
Actually, I think a maechancial RS232 interface is impossible too.
Electromechanical, sure. You could switch a polar relay fro man RS32
signal and use the contacts of that to operate the receive magnet in your
asynchronous receiver (e.g. ASR33 selector unit)
But I doubt you could make a receiver magnet that could be driven
directly from an RS232 line and which would have enough force to driectly
operate a similar selector mcchanism.
-tony