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arthurp
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Oddball question about teletypes.
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Apr 8 06:54 UTC 1996 |
My Ma just got a teletype (she has about a 90% hearing loss) that she
can use with this system to talk to other people over the phone.
It involves talking to a 'court reporter' type in the middle who has
a similar teletype to bridge from people without to my Ma. The deal
is I wanted to talk to her directly with my modem. Problem being
that I found out the specs on this teletype, and it is 45.5 buad.
I think you can all guess that my modem won't go that slow. You
can hear the individual bits when this thing beeps. Anyone know if
a 45.5 baud modem could be gotten for the end of an RS-232 cable?
Where? How much? Just curious. I guess I could sit down with this
thing sometime and listen to it and just whistle into the phone...
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| 116 responses total. |
rcurl
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response 1 of 116:
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Apr 8 07:04 UTC 1996 |
Let me understand this....does the other person talk, and the "reporter"
retransmit the message by the teletype, which is printed out at your
Ma's? Does the other person *hear* your Ma, or is the message sent by
teletype to them, too? What is the modulation? Standard teletype FSK?
It comes to me vaguely that there are available chips for encoding and
decoding teletype, since (some) hams (have) use(d) rtty as a mode.
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srw
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response 2 of 116:
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Apr 8 07:37 UTC 1996 |
75 baud was the slowest modem I could remember. That was a long time ago, too.
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gregc
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response 3 of 116:
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Apr 8 07:48 UTC 1996 |
My ghod, this thing sounds like an real *teletype* machine. And a really
ancient one to boot. I wonder if it uses baudot encoding?
Rane the way I've heard this works is as follows:
1.) Hearing impaired person calls up service center with teletype and
gets connected to go-between person. He/she then tells this person who
they want to talk to.
2.) Go-bewteen then calls other party on voice line.
3.) Hearing-impaired person and go-between carry on printed conversation
while go-between and other party carry on voice conversation with
the go-between acting as a relay. Not useful for really personal calls.:-)
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scott
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response 4 of 116:
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Apr 8 11:05 UTC 1996 |
Damn, if you'd caught me 5 years ago, I would have given you a teletype
somebody gave me.
If I remember when I'm at work, I'll look at a Black Box catalog to see what
they have.
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n8nxf
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response 5 of 116:
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Apr 8 13:43 UTC 1996 |
Welcome to the low-tech, high priced world of the hearing (etc.) impared!
What your mom has is indeed and modern version of the TTY. Often refered
to TDD in the hearing impared world. Yep, 5 bit, 45.5 baud, daudot code
still lives! Ineed, they make TTY modem. $450 a shot but they also do
standard 300 baud! Imagine. I've contacted various modem manufactures
to see if any of them were considering adding TTY capabilities to any of
their modems but no luck.
The service your mom calls is cally a Relay. Here in Michigan it's the
Michigan Relay.
If your in luck, your mom's TDD can also do standard Bell 103, 300 baud.
None of our TTDs are 300 baud capable so I can't tell you how well that
works.
The one nice thing about TTY is that it will tolerate switching between
voice and TTY, other phones on either lines being off-hook, noisy lines,
etc. Try THAT with your 300 to 28.8K baud modem!
I've always though it would be a neat software project to make a regular
old 8 bit sound card do TTY service. I, however, lack the software back-
ground and the time to learn it. I also get the feeling that those in
the TDD business keep a tight fence around their little low-tech egg.
Getting technical information out of some of them is like squeezing grape
juice out of a rock! (Hummm. I think I'll try surfin the web on the
subject ;)
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rcurl
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response 6 of 116:
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Apr 8 14:50 UTC 1996 |
Klaus, standard amateur radio multi-mode data controllers support rtty.
They cost a lot less than $450.The MFJ receive only RTTY/ASCII/CW
interface is only $70. I don't know what modulation it uses, though -
your're the expert 8^}.
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n8nxf
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response 7 of 116:
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Apr 8 14:59 UTC 1996 |
Yea, I'm not sure if it's the same thing. Close though, I suspect. I need
to find some good, solid technical specifications for TDD in the US. I'm
sure its available somewhere... Did find a source for high speed, TTD
compatable modems. No price given on their web page. Will call and find
out. (BTW. I was off on the price of the TTY / 300 baud modem I mentioned
above. It's $498!!!)
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srw
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response 8 of 116:
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Apr 8 17:44 UTC 1996 |
Why don't we get your ma a vt-100 terminal a cheapo modem and an account on
Grex? She could keep her Teletype, too. Just a thought.
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arthurp
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response 9 of 116:
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Apr 8 20:39 UTC 1996 |
I am affraid gregc got the thing right. 45.5 baudot coding... :( I have
been trying for years to get her a terminal and modem to connect to
*anything*, but she is *very* reluctant to use new technology. She has had
the tty for a while now and has only just started to use it. Getting a
dumb-term would be hard to do now that she has the tty, and Grex is a LD call
unless they get a service, and the tty works for my three sisters, but the
term wouldn't.
I'll keep after this, but I am not very encouraged any more. :(
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n8nxf
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response 10 of 116:
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Apr 9 11:58 UTC 1996 |
After looking around the web a bit, I found a Co. that sells a standard
19.2K baud / FAX / TTY modem. Internal modems are $299 and external is
$398. The Co. is NXi and those prices include windoze software that looks
pretty decent. Wow. A practical modem at a almost decent price!
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ajax
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response 11 of 116:
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Apr 9 17:53 UTC 1996 |
It beats $500 for a 300 baud modem, but I can't bring myself to agree
that that's a decent price, considering some internal V.34 modems are
under $100! Since many computerists want V.34 now, it would still
mean having two modems, so whether it tops out at 19.2k or 300 baud
would matter little.
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scg
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response 12 of 116:
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Apr 10 07:22 UTC 1996 |
You could get your mom a vt-100 terminal that would connect directly to your
computer, without Grex, and tell her to think of it as just a long distance
phone call, and the terminal as just another TTY.
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arthurp
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response 13 of 116:
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Apr 10 11:36 UTC 1996 |
My intent was to figure out some way to use hardware we both have already.
I do think it might be a neat project to build something to play the tunes
from my serial port, and write a little ditty to control it. That's on a
burner way way in the back, though.
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n8nxf
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response 14 of 116:
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Apr 11 11:24 UTC 1996 |
Using a sound card would be the way to go. Just add microphone and speaker
in some old ear-cups and write some software ;) (I need to drag out the
specs for my sound card some time...)
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arthurp
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response 15 of 116:
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Apr 11 12:23 UTC 1996 |
I (gasp) don't have a sound card, but I have a CD-ROM now (couple days old)
so I wouldn't be too opposed to getting one. That does seem like an easy way
to do it now that you metion it. I was thinking of building two circuits that
play a steady tone and then gating one or the other (or neither) into the
output speaker based on the level of the serial data line. I am not too sure
about how easy it would be to mix digital and analog circuits, though. I've
only ever worked on digital circuits before.
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n8nxf
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response 16 of 116:
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Apr 11 18:20 UTC 1996 |
I'm not sure how many tones are used in a TDD. Each tone may even be a
combination of tones as used in DTMF touch tones. Your gating idea my work
OK but you might run into problems when you gate a tone somewhere other
than at a zero crosing. It may be necessary to do some filtering or switch
on zero crossing to elimitate any distortion.
I have a TDD sitting here on my desk. When I listen to the tones, it first
seems to put up a carrier and then put the tones on top of that. When I type
a continious string of characters the carrier is continious, with the tones
on top. When I stop typing the carrier drops after about half a second. it's
hard to tell if there are one or two tones besides the carrier but the carrier
seems to be around 1000 Hz.
I'm not sure if one can do all that with a sound card, but it's worth looking
into when a used 8 bit card can be had for $15 or less!
If you do build your own hardware, you may want to consider using the parallel
port. It has 8 bidirectional data bits, plus some handshaking, you can tweek.
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arthurp
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response 17 of 116:
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Apr 12 23:51 UTC 1996 |
Yeah, I started thinking about it and parallel came to mind as a possibility.
I am not sure how much trouble a half wave distortion will be when you can
hear the duration of a single bit, though. I don't know. I didn't realize
I could get sound at that price, either. Hmm.
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gull
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response 18 of 116:
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Apr 14 04:31 UTC 1996 |
If it's the same as 45.45 baud RTTY, I think there are just two tones,
'mark' and 'space.' God knows what the frequency shift would be,
though. If it's standard, you might be able to pick up one of those old
C64 RTTY interfaces cheap at a hamswap, and hook it up to an acoustic
coupler or something. :)
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arthurp
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response 19 of 116:
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Apr 14 21:39 UTC 1996 |
As in Commodore? So there are a couple sources out there to get these things
other than the company that sold one to my Ma. Cool...
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scott
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response 20 of 116:
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Apr 14 22:53 UTC 1996 |
The tech is certainly old enough. Heck, if you dig into those project books
for electronics, you might find one. I've got a CMOS design for a 300 baud
modem some where...
(I wouldn't be at all surpised, now that I'm thinking about it, to find a
single chip somewhere that does it...)
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n8nxf
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response 21 of 116:
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Apr 15 13:38 UTC 1996 |
I looked through the manual that came with my sound card but it did not
touch on writing software for the things, other than IRQs and register
addresses. There was a lot of TTY stuff written for the Commodore but
I don't have one of those and I don't intend to ;)
I recall seeing a book on programing and sound cards at work. I'll have
to see if I can find it again. After playing with my sound card and some
canned software, it seems that an 8 bit card sould be capable of doing the
job. I'll try recording some TTY tones and playing them back to the TTY
(TDD) to see if it can recognize them.
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arthurp
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response 22 of 116:
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Apr 16 00:28 UTC 1996 |
Can you get input from a sound card and convert it into a spectrograph output
so I could tell what tones the TDD on the other end is playing? I didn't
know you could do that kind of input with a sound card. There seem to be a
few references to SoundBlaster in my Ralf Brown Interrupt list. I am sure
some of those are about port addresses and driver functions. Maybe I'll be
able to find out something useful in there.
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n8nxf
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response 23 of 116:
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Apr 16 13:45 UTC 1996 |
Now there's an idea! I'll bet there is software out there that can use
a sound card as a crude audio spectrum analyzer. I'll have to browse some
of the local BBSs.
Sound cards have a microphone input (Standary 600 ohm dynamic) and speaker
output jacks. You don't even need to amplify the audio output if you don't
require room-filling sound. Interfacing the sound card to phone could be as
simple as gutting an old 300 baud modem with ear-cups.
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arthurp
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response 24 of 116:
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Apr 16 22:52 UTC 1996 |
Yeah, I think the sound card certainly has lots of the circuits needed, but
I would have to have some way to distinguish between no bits, low bits, and
high bits coming out of my phone as well as being able to generate bits into
the phone. If a SB can't do that, requiring me to build, I might be just as
far ahead to build all. If I can avoid learning to program the SB... ;)
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