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

[Paul Heller]

Do keep us posted, Eric!

Paul
KD0DFR

On Jan 5, 2013, at 7:10 PM, epvgk at limpoc.com wrote:

> 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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