[GreenKeys] Interface board for Model 15 with 60mA current loop

[John Nagle]

     I've designed an interface board for the old 60mA machines,
to do level conversion from RS-232 to 60mA 120V current loop.

http://www.animats.com/nagle/images/teletype/pcboardv1.png

It's fully opto-isolated; there's no electrical connection, not even
a common ground, between the high voltage and low voltage sides.
The optoisolators are Fairchild HSR312L parts, which have more
than enough voltage and current rating to do the job.

     I should know in a week if this will work.  The board is
out being fabbed.  Once I get this working I'll make the board
design and parts list available.  All parts are current Digi-Key
stocked items, unlike some of the older designs.

     A 120VDC supply is still required.

				John Nagle