[GreenKeys] USB to Loop TTY Control Device

[ad7i]

Greeting Greenkeyers --

I've been reading on this group about the discontinued manufacture and
availability of USB to SERIAL (bridge) devices that can run 5 bit 45 baud
data on the serial side.

I can't offer any alternative device suggestions that can do that
USB-SERIAL bridge function natively like the older devices do, but I wanted
to ask the group if anyone had an interest in a device that would accept
USB Serial ASCII and the output would be a loop control switch (like an
opto-coupler) that would key a loop with 5 unit TTY code, as controlled by
the host PC?  It would be also possible for the host computer to send 5
unit code to the TTY by putting the device in mode where it only looks at
the lowest 5 bits of the incoming ASCII code and then sends that 5 unit
code to the TTY (which moves the responsibility of coding of FIGS and LTRS
from the device to the host computer).  That type of functionality would
*not* be compatible with existing PC or Linux code that drives one of the
older USB-SERIAL devices that can run a 45 bps.  But if you had access to
the source code it should be a straightforward task to modify that code to
use the device I describe to drive a 5 unit TTY.  Control of the device
(change mode from ASCII to BAUDOT or BAUDOT to ASCII, set bit rate (45, 50,
75, 100), disable/enable loop control inversion, etc. would be done through
something like an escape character followed by two letters or numbers.  I'd
propose to use the ASCII caret symbol (^,  0x5E) as the escape character.
So to set the loop baud rate to 45.45 bps the host computer would send ^45
(which would not print on the TTY).  To set the code to BAUDOT the host
computer would send ^BA (which would not print on the TTY), etc.  The
particular escape character and the two character command that followed
could be most anything, as long the escape character is not a symbol that a
TTY would print.  The device could also include functionality to send data
from the TTY Keyboad loop to the host PC.

I think something like this device could be constructed for less than $5 in
parts, including the PCB.  Power would be supplied to the device from the
Host computer via the USB cable.

If this might be of interest to you please let me know and we can kick
around the specifics of functionality and specifications.

73, Paul, ad7i
ad7i at ad7i.net
Middletown, NJ
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