TTY - Teletype Terminal

[Foxx373]

I am new to PicBASIC, and im not too sure how to work this out right now, but i would liek to make a TTY Terminal. TTY is used by deaf people to place calls through a relay operator. TTY Terminals work by using the BAUDOT protocol. There is a set of tones that has to be decoded and turned into characters on an LCD display. Im sure i can figure out how to generate the tones, and place them on an LCD display, but how can i decode Multi-Frequency tones? Any ideas?

[mister_e]

2-3 way... COUNT and PULSEIN. will return you some value to play with for low frequency. Or using interrupts to count exaclty the period of each frequency with internal TIMER/Counter.

[Foxx373]

Since TTY deals with soundwaves, i was thnking about using the on board Analog-Digital Converter. I just have no idea how to do that. im sure if i use the COUNT or PULSEIN command, i will have to take the sound coming from the headset, make it a digital signal with a simple op amp, or transistor based logic converter, then pass it to the designated input. Does this sound right?

How do I use interrupts? Liek i said, im really new to PicBASIC, but not to programming.

[mister_e]

Since TTY deals with soundwaves, i was thnking about using the on board Analog-Digital Converter.

without any external of frequency to voltage converter you'll not be able to do it. A/D converter return a valu that correspond to the voltage at a specific input.

im sure if i use the COUNT or PULSEIN command, i will have to take the sound coming from the headset, make it a digital signal with a simple op amp, or transistor based logic converter, then pass it to the designated input. Does this sound right?

depending of the signal amplitude, a simple capacitor with 2 resistor as voltage divider can do the job too. 10 cents solution
OR if you want to feel very very safe, using a OP-AMP or Voltage comparator to make the signal as sqaure as a real TTL- CMOS can also be used... i'll prefer that one to avoid some probale odd interrupt causes.

How do I use interrupts? Liek i said, im really new to PicBASIC, but not to programming.

depending of your PIC look into your datasheet under INTCON register... If you want some code example using interrupt... there's a load of those in the forum. Do a search with interrupt will gives you a bit less result than SEROUT. BUT, i did one example for lamp-dimming. Using interrupt to synchronise on AC power line.

Click Here

[Dwayne]

Hello Foxx,

Fox>>I am new to PicBASIC, and im not too sure how to work this out right now, but i would liek to make a TTY Terminal. TTY is used by deaf people to place calls through a relay operator. TTY Terminals work by using the BAUDOT protocol. There is a set of tones that has to be decoded and turned into characters on an LCD display. Im sure i can figure out how to generate the tones, and place them on an LCD display, but how can i decode Multi-Frequency tones? Any ideas?<<

Ah ha!...My area of field <g>. I was making these in the 1990's with Philips 752's. Then went through a bad divorce. Then 3 years later, ended up becoming deaf myself!

A couple of things to remember.. TDD does not use Standard RITTY code. It also does not use standard 8/7 bit data exchange.

I can't remember the exact "tones" it uses. You can use a chip to decode each of the tones (which I did) or possibly use your PIC with PULSE in and timeout. Or maybe use a interupt and measure the time between the pulses.
If I remember correctly it is a 3 to 1 ration on tones.
I used a Lookup Table for decoding of the bits.

You will have a problem for decoding between the two tones. lets say we have the tones "descriminated".

Using two bytes, you can "shift" the 5 charactoristics into the bytes.

Dots var byte
Dash var byte

Loop:
Dots =0;
Dash=0;
.....
.....
if Tone=true
if(Tone=low)
Dots[0]=1
endif

if(Tone=High)
Dash[0]=1
endif
Dots<<1
Dash<<1
endif

With this, you have the exact layout of the mark and stop of the 5 bits...representing the letters/numbers. How you look it up in the table is
up to you...If you need help in this, maybe I can dig up some of my notes from 15 years ago, or give you some ideas to go on.

One other thought...Most TDD operators can do standard ASCII from your computer. I use my computer modem at work to TDD to certain people.

Dwayne

[Foxx373]

Thats some very helpful info! Thanks a million. I didnt realize there were TTY Tone Decoder chips. Do you have any info on those? I think it would just be easier for me to use the tone decoder chip and process the data through the PIC, instead of making the PIC do all the work. Trying to "Descriminate" the audio levels are gonna be a bit unreliable. I am aware that a computer can be used to dial-in to the Relay Service, but a phone line isnt always available, and all that can be found is a payphone headset.

Also, any ideas on what i can do about a small keyboard? Ive seen really cheap palm keyboards for 15 bux, think that can be used on a PIC? I would like this thing to be as small as possible, so no full AT keyboards... hummm... unless i build the terminal INTO the keyboard...

[Luciano]

Hi,

Maybe you can use these for debugging purpose.


* * *

CallTTY 1.10
(See software and schematics)
http://www.dxsoft.com/en/products/calltty/

* * *

The tool TTY Angel:

Manual:
http://www.ciscounitytools.com/HelpFiles/TTYAngel.htm
Download:
http://www.ciscounitytools.com/App_TTYAngel.htm

* * *

ActiveX Controls.

(See Online doc and Trial copy download).

http://www.tapiex.com/ToneEncoder.htm
http://www.tapiex.com/PhoneToneDecoder.htm


* * *


Best regards,

Luciano

[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