Hi all:
 
I (thanks to a "push" from Jack Hart and Larry Tigue, and info
from Jeff Angus and Jim Haynes) have come up with a VERY simple
RO TTY loop converter using 1 resistor, 2 diodes and the HSR312L
IC chip.
 
This will be a completed PC board ready for hook-up to your loop
and your RS232. (4 connections.)
 
For those who are wondering, The HSR312L employs an active
current limit circuitry enabling the device to withstand current
surge transients.
 
Each PC board is 1 X 1 5/16. (Fits in a relay case if you so
desire.)
 
I have to charge $20 each to cover expenses. This INCLUDES
postage anywhere in the lower 48.
 
If you would like a picture or the schematic please e-mail me off
list at TIL128 at aol.com
 
OR better yet, if you want to be the first in your neighborhood
to own one of these little beauties, let me know and I'll get the
solder fairies working overtime to zip 'em out to you.
 
I will be away today (Thurs.) but will return Friday. 
 

Thomas Tillson 
1 Abbey Road 
Hyde Park, 
NY 
12538

I have an important correction on the PC board;
 
The end of the board where it says "TTY Loop", the designation POS and NEG are reversed. It should be the other way around.
Please keep this in mind when wiring this board.
 
I apologize for any inconvenience this might have caused.
 
Tom Tillson