[GreenKeys] Loop to RS-232 and RS-232 to TTL circuits

[ralph irish]

GreenKeys

I put out info on these circuits earlier, but not really certain how long back.  

Back in the late 1970s, I saw ads from a company named Electronic Systems.  In
1977 they were located in Burlingame, California.  The following year, they had
moved to San Jose, California.  They kept the same phone number.  

Original:

Electronic Systems
P. O. Box 212
Burlingame, CA  94010
(408) 374-5984

After relocation:

Electronic Systems
P. O. Box 4691
San Jose, CA  95157
(408) 374-5984

I will be more than happy to send scans of the schematics and photos of the finished
items to anyone on GreenKeys who can find a way to make them available to the group with
just a few mouse clicks.  They seem to be quite simple, and in recent weeks, there has
been some discussion of this general type of circuitry.

- - - -

Here are the descriptions which came with each device:

Part No 600   RS-232/TTY INTERFACE
This board has two separate circuits.  One converts
RS-232 to 20 mA current loop, the other converts
20 mA current loop to RS-232.

Parts List:

330 ohm 1/4 Watt
6.8K 1/4 Watt
560 ohm 1/2 Watt
1.2K 1 Watt
.001 uF disc
2N2222
1N4148

Copyright 1978

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(No part number)  RS-232 to TTL/TTL to RS-232
The RS-232 board has two separate circuits.
One converts RS-232 to TTL.  The other converts
TTL to RS-232.   The board has a ten pin edge
connector.  Power requirement is +12 and -12 volts.

Parts List:		Edge Connector

R1   6.8K		PIN
R2  15K			 
R3  10K			 1- GND
R4  15K			 2- RS-232 in
R5  10K			 3- TTL out
R6  15K			 4- +12V
R7  2.7K		 5- RS-232 out
R8  330 ohm		 6- -12V
C1  100pf		 7- NC
Q1` 2N2222		 8- NC
U1  741 mini dip	 9- TTL in
CR1 1N4148		10- GND

Copyright 1977

-   -   -   -   -   -   -   -   -   -   -   -   -   -   -   -

I have seen too many instances on GreenKeys where people attached something and it somehow
got zapped before the GreenKeys list was published.  That is why I will hold back on that
and wait for someone to get in touch with me.  I will send this person or maybe more than
one person the scans of the items described above and photographs of the two boards, front
and back.  The object being having the items show on GreenKeys or be made available on some
website where they can be downloaded for local use.

73,

Ralph - W8ROI

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