TTY - Teletype Terminal

[Luciano]

More info.

Best regards,

Luciano

===========================================

Telecommunications devices for the deaf:

http://www.tutorgig.com/ed/Telecommu...e_for_the_Deaf

Original TDD devices were called TTYs, derived from teletype, and was
invented by deaf-physicist Robert Weitbrecht in 1964. Communications
was through frequency key shifting and single tone, allowing only
one-way (simplex) communication at once. During the mid- 1970s, portable
TTYs were developed and was also the time period when the term "TDD" began
being used, largely by those outside the deaf community. The deaf
community, interestingly, does not usually use the
term "TDD", but instead prefer "TTY".

The original standard used by TDDs is the Baudot code implemented
asynchronously at either 45.5 or 50 baud, 1 start bit, 5 data bits,
and 1.5 stop bits. The TDD/TTY standard is generally incompatible
with standard Hayes-compatible modems. In 1994 the ITU approved
the V.18 standard, an ASCII full- or half-duplex modulation method
which has been widely adopted. Computers can, with appropriate software
and modem, emulate a V.18 TDD. Some voice modems, coupled with
appropriate software, can now be converted to TDD modems by using a
software-based decoder for TDD tones.

* * *

TTY FAQ:

http://www.deafweb.org/tty_faq.htm

* * *

===========================================

The V.18 standard

The V.18 standard gives specifications for the
implementation of text telephones, more commonly
called TDDs (Telecommunications Devices for the Deaf).


http://www.dinf.ne.jp/doc/english/Us...96/page169.htm

http://tap.gallaudet.edu/v18.htm


ITU Recommendation V.18 specifies interworking with
the following TTY protocols:

Baudot @ 45.45 baud (U.S. TTYs).

Baudot @ 50 baud (used in England, Australia, and some other
countries; also known as "international" Baudot).

V.21/text telephone version (used in Sweden, Norway, and Finland).

DTMF (used in Denmark, Holland, and some other countries).

EDT ("European Deaf Telephone," used in Germany, Austria,
Switzerland, and several other countries).

* * *

TWO DSP SOCKET MODEM with V.18 Standard

(Ask which TTY protocols are supported in their implementation of V.18).


MODULATIONS of the DSP SOCKET MODEM:

V.90 (server and client), V.34bis, V.34, V.33, V.32bis, V.32,
V.29, V.22bis, V.22, V22fast (HYPERCOM compatible), V.23,
V.21, V.18, Bell 212A, Bell 103


DSP SOCKET MODEM - SERIAL
http://www.telindusproducts.com/Tap/...ocketmodem.pdf

DSP SOCKET MODEM - PARALLEL
http://www.telindusproducts.com/Tap/...emparallel.pdf

===========================================

Radio Teletype (RTTY)

I am not an expert but RTTY and TTY/TDD are close.
Maybe you can use ideas from Amateur Radio RTTY circuits.
(If you use only the Baudot code at speed 45.45 for your project).

Both TDD and RTTY use five level Baudot/Murray code.
Baudot table:
http://burks.brighton.ac.uk/burks/foldoc/76/10.htm


The first difference I can see:

In TTY/TDD the “mark” tic is defined as 1400 Hz and
the “space” tic is defined as 1800 Hz.
See: "The Protocol Today"
http://www.ciscounitytools.com/HelpFiles/TTYAngel.htm


In RTTY the mark frequency is 2125Hz and the space is 2275Hz.
RTTY is commonly transmitted at speeds of 45.5 bits per second.
RTTY is either transmitted in Baudot or ASCII code.
http://www.roity.com/rc/rtty.html


===========================================


TDD devices:

Non-Printing TTYs:
http://www.phone-tty.com/PRODUCTS/OLD_PAGES/TTYs.htm

PocketComm the POCKET TTY:
http://www.krowntty.com/html/products/pocketcomm.html

===========================================

[Luciano]

Hi,

Tone Generator and Tone Decoder Integrated Circuits.

================================================== ======

The XR2206 and XR2211 are a versatile pair when it comes to modem building.
Their advantage is that they may be set to what ever Mark and Space tones
you like, creating the tone shift desired.


Example of aplication:

http://www.klm-tech.com/technicothica/xr.html


Manufacturer:

Exar Corporation,
Fremont California,
U.S.A.
http://www.exar.com


Where to buy:

http://www.jameco.com

XR2211 IC = Jameco #: 34999 USD 1.79
XR2206 IC = Jameco #: 34972 USD 3.59


Best regards,

Luciano

[Foxx373]

Everyone, thank you for your help. You have all done WAY more than ever expected. You have practically handed me all the data I would have ever need. Even though I allready know a great deal of TTY, I really admire all of you for your outstanding efforts in helping me with this project. Im glad to see that there are still people arround thats willing to go above and beyond the expectations from a call for help. With all that said, let me tell you what i have been cooking up.

I had to find a replacement for the XR Encoder/Decoder. It works the same, just different passive components. I will try and use the NJM-2211 ( http://www.njr.co.jp/pdf/be/be06008.pdf ) for the CODECs. I would try and use the simple socket modem stated in earlier posts, but i have dealt with that modem before and for a simple project as TTY (heh... SIMPLE he says) the modem is too costly, and it way more powerful than whats needed. Im trying to keep this project simple, and inexpensive. As for a keyboard, i will probabbly just use a Mini-AT 86 Key keyboard i have laying arround. Im going to try and use an old 4x16 green LCD that has been sitting arround.
Im going to try and use parallel LCD functions if i can for now. I dont want to build a Serial LCD Backpack and make this project more expensive, but i will if i have to.

Im still a little dazed and confused on how im going to code this. This is going to be my 1st PIC project. I know im jumping into the deep end on this project, and I am way over my head, but im sure I can figure this out.

As for a simple hardware layout, this is what i have in mind

[Headset]-[LM 386 OP Amp]-[FSK En/DeCoder]-[PIC]-[LCD+Keyboard]

[Dwayne]

Hello Foxx,

Foxx>>Im still a little dazed and confused on how im going to code this. This is going to be my 1st PIC project. I know im jumping into the deep end on this project, and I am way over my head, but im sure I can figure this out.

As for a simple hardware layout, this is what i have in mind

[Headset]-[LM 386 OP Amp]-[FSK En/DeCoder]-[PIC]-[LCD+Keyboard]<<

Looks good!...If you have a scope, it will make tuning a little easier <g> if you are in the USA, I may be able to help you. if you have a telephone recorder, I could call and send some "A"'s and B's and other letters over my TDD (tty), so that you may verify and "smoothout" your reception.

Audios! and good luck.

Dwayne

[Foxx373]

Thanks, ill keep that in mind. I have some TTY Apps for the PC, and I have a program that can make a *.WAV of TTY messages. Ive also recorded some TTY tones a few years ago.

Im going to see what i can do about piecing the hardware together, and get started on the software. I was hoping to have a scroll back buffer, but I dont know how to do that yet...

I dont have an O-Scope, but i do have Frequency function on my Multimeter. I do have a chunk of software that lets me use my PC as a simple sound-based O-Scope.

[Luciano]

Hi,

About sound card as Digital Oscilloscope.

If your sound card is embedded in the motherboard then put
a second sound Card in the PCI bus and use it as Oscilloscope.
(It is very easy to burn your sound card when trying to
investigate some signal with unknown amplitude and DC offset).

Need more than 20 Hz to 20 kHz bandwidth?

Virtins Sound Card Oscilloscope
Bandwidth: 20 Hz - 96 kHz (depending on Sound Card)
US$24.95, 7 day evaluation time.
http://www.virtins.com/page2.html#Oscilloscope

* * *
SEE "Sound card input protection circuit":
(Scroll down the web page).
http://www.virtins.com/
* * *
Sound Card Interface For PC Test Instruments:
(Full schematic and description + PDF files,
the web server is sometimes busy).
http://www.siliconchip.com.au/cms/A_30518/article.html
* * *
Example of Sound Card 96 kHz:
(Ask Virtins Technology if OK with the SW).
CREATIVE SOUND BLASTER LIVE 24-BIT
Sound card - 24-bit - 96 kHz - 7.1 - PCI
Where you can buy it:
http://www.cdw.com
CDW# 713157 US$30.43

Please add your location in your forum profile.
(Example "USA" or "IL, USA" or "Vernon Hills, IL, USA").
If you do that I know which URLs are appropriate when I
send you a link where to buy HW/SW.

Best regards,

Luciano

[Foxx373]

Hi everyone,

I havent written any code fr this project yet. I am trying to figre out the easiest way to implement and deal with this project. Im also having a lot of trouble finding the time to hunt down resources. Here is what ive been trying to do...

I have decided to try and use only one PIC if possible, perhaps a 16F84. I will try and use a Hitatchi based LCD in 4 bit mode. I will have 2 pins for the TTY Encode/Decode features. I want to try and use a small PS/2 keyboard as the input. That will need 2 I/O pins (data and clock). I have to figure out how to clock the keyboard with the PIC, take the keyboard data, process it into 5 BIT ASCII (baudot format) and have the PIC use a lookup table to generate the proper "deedles" for TTY, or pass the 5 bit data to a TTY encoder chip.

I am concerned about the speed of the PIC. Will the pic be able to keep up? It will need to use a few lookup tables to convert the PS/2 Data into 5 bit and make it TTY Format, then take the data from the TTY Decoder, pass it through a lookup table, then convert it to 4-Bit LCD data. I am also worried about typing too fast for the little guy. TTY Terminals dont send the data very fast, i can out type most terminals now. What will happen to the PIC? Will it have a "queue" by default, or will i have to tell the program to store what i type into memory? What about a scrollback buffer? I was hoping to add a simple SPI Serial memory of some kind that i can use to save the conversations to, then use HyperTerminal to download them... if possiblle.

Any advice and code samples on lookup tables, memory access, "scroll buffer", how to interface an AT keyboard and data conversions would be nice. Again, thanks for taking the time to help me.