[GreenKeys] HRS312 TTY Interface

[Duncan M. Brown]

I've been thinking about making a HV interface for a computer to drive a
TTY loop for some time, but never had gotten around to it. This would
mainly be for a RO demo system that could drive a M15 from ITTY or
HeavyMetal in the Museum.

Then last month someone mentioned the HRS312 MOSFET optocoupler and that
looked like the heart of a very simple interface.  Jon Schlegel and I have
been playing with the HRS312 and  it seemed like the circuit was so simple
that it could be placed inside the 9-pin D-connector's housing.  I found I
had some AMP 745854-3 housings. There is room for a 5/8" x 3/4" board,
which is plenty big enough (point-to-point wiring).

Hopefully this small picture will come through.

 Jon measured 500v spikes coming off a M28 selector magnet, so we added
back-to-back, 200V zener diodes (1N5956) across the output of the HRS312.


Have fun,

Duncan, K2OEQ