[GreenKeys] USB to TTY-loop possibility...

[COURYHOUSE at aol.com]

this  shows  great  promise!
I could hang it off the  back of a raspberry Pi....
Ed#
 
 
 
 
In a message dated 1/5/2013 7:10:18 P.M. US Mountain Standard Time,  
epvgk at limpoc.com writes:

Just a  follow-up. I've been using an AVR microcontroller breakout board
called  "Teensy 2.0" from http://pjrc.com/teensy as a USB-to-TTY adapter  
with
ascii/baudot translation. The board is nothing more than a breakout  for the
Atmel ATMEGA32U4 cpu.  To actually connect it to a loop, you  need to 
convert
voltages, etc.  I believe George has tried the  software, or is planning to 
soon. I'm using a Teensy 2.0 with a  breadboarded adapter pretty 
successfully. 

I just did a quick layout of  a PC board to interface it to a TTY loop. 
With 
this plus the "Teensy 2.0"  and the software, you would have a device that 
looks 
to a computer like a  USB serial port and looks to a TTY loop like a 
teletype 
machine, including  ASCII/Baudot conversion, so the computer does not have
to know or care  about weird baud rates or 5 bit characters or Baudot. 
Looks at first  glance like manufacturing cost would be about $15/ea, 
dropping 

to  $10ish in quantity 60. (including parts) You'd still need the Teensy 
board  
from pjrc.com of course, and they're about $16 each. Still not bad.  

Some details and the circuit at  
http://heepy.net/mediawiki/index.php/Optocouplers_for_teletype_current_loop

I'm  happy to send anyone the Eagle files or printable mask images if you  
want
to etch your own and try it. It's a single-sided board and should be  very 
easy
to make. Or wait until i've tested it. :)  

eric




On Fri, Nov 02, 2012 at 12:34:19PM -0700,  epvgk at limpoc.com wrote:
> It seems like lots of folks have been looking  for an easy solution to 
> connecting a computer to a TTY loop... There  are various options like 
> reprogramming the CP2102-based usb-serial  adapters and using PC software
> to generate the baudot code for it.  
> 
> I just picked up a little breakout board for an Atmel cpu  (Atmega32u4)
> which is tiny and has USB support builtin. The whole  board is only like 
> 3/4" by 1" and costs $16.  I've been playing  around a bit writing 
software
> to make it act as a complete USB to TTY  adapter...
> 
> The idea is to make it look to the computer like a  generic USB serial 
device,
> but internally handle all the character set  conversion, shifts, and 
framing,
> and without a large internal buffer.  So you talk to it from the computer
> in ASCII and it ignores whatever  the computer thinks about baud rate, 
character
> size, etc, and produces  correctly timed 7.42 code at 45.45 baud on the 
output
> end, and vice  versa for receiving. It only picks up a new character from 
> the  computer when it's done sending the current one to the loop, to avoid
>  having to wait for a buffer full of data to transmit once you stop  
sending.
> 
> Anyway, it's nowhere near finished but i have the  sending side more or 
less
> working as a proof of concept at least... if  I can get it working well 
I'll 
> make the software available and  anybody who wants to can get one of the 
boards
> and program it with my  code... just thought I'd mention it in case 
anyone is
> interested, and  to motivate myself to make time to finish it :) 
> 
> eric
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