wmsundell
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land line phone

Sat Apr 27, 2013 4:59 am

Hi, I would like to know if there is a way to use my modem on a RaspberryPi. Reason is I am severely hearing impaired and use a TTY modem. I would love to hook it up to my Pi and keep the setup simple. Is there anyone who has done this? Pls advise and I would appreciate it.

ghans
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Re: land line phone

Sat Apr 27, 2013 11:35 am

If you have any links to datasheets , product pages or software etc.
please post them.
Does the device have a RS232 port ?

ghans
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wmsundell
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Re: land line phone

Sun Apr 28, 2013 3:58 am

It's an Intele-Modem, by Ultratec. I don't have any docs to it other than operation manual. It has a DB 9 connector, so, it would be RS 232. The other is the phone connection, a RJ45.

As far as I can resemble, this is very similar to the old HAYES external modem but a few extra LEDs to give the visual signal to user if the phone is dialing and or ringing at the other end. I assume it is a 2400 baud normal setup, but this modem is made for communicating to other TTYs in BAUDOT, which is about 45 baud.

Bill

sdjf
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Re: land line phone

Sun Apr 28, 2013 3:11 pm

Sadly, my dialup modem uses USB to connect to the Pi. I would guess that you can use the GPIO serial pins, but have no idea how to do that.

The connection would be made from the command line, but you might have to use something like screen or minicom, not sure.

I am using ppp-on from command line, I would guess that setting that up to use your serial line would be possible, but not necessarily simple. A lot of people like using WVDial to automate the process, that is available in the repositories and can be run from the regular command line.

Not sure how much sense I am making, there are two issues here. One is how to attach your hardware, the other is which software to use to get online. I believe you can use the same software to get online over RS232 that those of us doing that with USB modems can use, but I am only sure of that if your modem uses Hayes command set to dial out.
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ghans
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Re: land line phone

Sun Apr 28, 2013 3:16 pm

You need a RS232-to-TTL (3v3) adaptor.
Lots of places sell them. But you might get problems if your
modem does indeed uses all pins on the DB9 connector , because
the Pi only features a simple UART.

ghans
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btidey
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Re: land line phone

Sun Apr 28, 2013 5:34 pm

The modem claims to have DTR and CTS on its interface in addition to the TX and RX. If it uses them at all then they could be driven (via RS232 level converters) from a normal couple of GPIO pins. DTR would normally tell the modem that the equipment (Pi) is active. CTS is normally from the modem saying it is OK to send characters.

Some of the 3.3V to RS232 converters handle a couple of extra lines in addition to TX,RX but you might need to adjust the pin connections.

http://www.ebay.co.uk/itm/RS232-Serial- ... 5655b4de25

Most of the converters I have seen have socket connectors which, unfortunately, is the same as the modem so you would need a cable anyway and that can be used to get the pin out right.

wmsundell
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Re: land line phone

Sun Apr 28, 2013 11:59 pm

I have one of those USB to DB 9 adapters that has its own circuit in it. Would that work?

Bill

wmsundell
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Re: land line phone

Mon Apr 29, 2013 12:14 am

Also, I ordered a daughter board for the Pi but has not arrived. I was gonna try that, but don't know if it would be wise to do that.

Bill

coyotebush
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Re: land line phone

Mon Apr 29, 2013 2:04 am

Some ways to hook up a modem to a PI:
- Use a USB to RS232 adapter. ($3 on e-bay)
- Buy an external USB modem. ($10 on e-bay), or
- add a Max232 circuit to the PI's serial port ($3 on ebay)

Unless I was particularly fond of the existing modem, I'd probably buy the USB modem. USB modems are very compact compared to their predecessors.

coyotebush
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Re: land line phone

Mon Apr 29, 2013 2:20 am

Rethinking ...

Yes, your existing USB-RS232 connector should work fine. You may have to install driver software depending on the brand, but most adapters are well supported by Linux. (When in doubt, buy FTDI brand adapters which work everywhere.)

I don't know if the new USB modems support baudot. A USB modem may not do the job for you.

The Max232 approach could be made to work, but you'd have a lot of issues dealing with modem control lines. It isn't worth the trouble.

sdjf
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Re: land line phone

Mon Apr 29, 2013 2:55 am

coyotebush brings up an important point. any device attached - I think other than one that uses the serial I/O pins - has to have a driver to work on the Pi. I have learned that the hard way with a number of peripherals on my Pi and other Linux devices.

It would probably be wise, if you want to use your old modem and not use the GPIO serial interface on the Pi, to google around to see if anyone has been able to get it recognized by a driver on any Linux box. That would give you a driver name to look for, if I understand this stuff.

Same is true for any new device you get, make sure that it will have a driver that is already on the Pi, otherwise you get stuck compiling one for yourself or trying to find some kind soul to do it for you.

Drivers are what enables the system to interact with the device. Most new USB modems should be recognized, if they are current, older ones may not.

What was the reason to use your older modem, was it just because you know it works on dialup and want to save money, or is there something else special about it that the other devices recommended may not do?
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coyotebush
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Re: land line phone

Mon Apr 29, 2013 5:52 am

> What was the reason to use your older modem, ... is there something else special
> about it that the other devices recommended may not do?

This is a special modem for the deaf. It communicates to TDDs (Telecommunication Device for the Deaf) using a 5-bit Baudot character set over a 50 or 45.5 baud connection. Modern modems generally use the ASCII character set and run at a minimum of 300 baud.

There are open source and commercial products which use modern "voice" modems to simulate TDD signals. It isn't trivial. Basically, you have to synthesize and recognize the signal's wave form directly. You end up using the voice modem more as a sound card than as a modem.

sdjf
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Re: land line phone

Mon Apr 29, 2013 9:04 am

Hmm, I am aware of TDDs, am disabled myself. What I am wondering is what would be better about attaching your TDD modem to the phone via the Pi instead of just attaching it directly to the phone line? I thought TDDs just attached directly to the phone line and worked that way.
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wmsundell
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Re: land line phone

Sun May 05, 2013 4:27 am

Wow... Thanks all of you... That's a lotta info... Well, today, I bought a Linksys phone adapter and router. Its model number is SPA2102-R. What would this unit do for me? I have no docs to it and have no idea what its purpose is. I was hoping to find something like this with a DB9 connector on the unit but to no avail. Although, the Intlele modem has phone jacks on it and wonder if the Linksys could just use the Intele modem's phone connection to do the on screen communications. I haven't tried it yet, I want to know if anyone has tried it this way. The Linksys has Ethernet connections so I can hook it up to the Pi. Any ideas???

Bill

wmsundell
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Re: land line phone

Sun May 05, 2013 4:32 am

By the way, The Intele-Modem is not old stuff. I bought it last year due to its Baudot capability. I am hoping to use it with my Pi to do the communicating. I have tried many PC platforms of software using the computer's modem of many kinds and prevents me from communicating with actual TDDs on the other end of the line/s. It's because all the TDDs use Baudot code and standard modems do not have this capability.

Bill

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Paul Webster
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Re: land line phone

Sun May 05, 2013 6:19 am

From their manual at
http://www.ultratec.com/manuals/Intele-Modem_Manual.pdf
It looks like the modem is doing the character conversifroze tween Baudot and ASCII - which is good otherwise you might have been stuck.
It says that you must set the serial connection to it as 300 baud, 8N1 (8 bit, no parity, 1 stop bit) .... but maybe that is not right because you said you thought 2400 baud works.
In any case, it is not clear whether or not it is using hardware flow control because the wording is imprecise.
The manual certainly says no software flow control (I.e. xon/xoff or ctl-s/ctl-q).
Looping together the 2 pins in the DB9 plug might work anyway if it needs a signal and you can't generate one. (pin numbers are standard and are listed at the end of the manual).

FYI I started my computing career on TTY (Teletype - not TDD) writing applications and device drivers to handle slow speed serial comms and remember having to generate test messages on paper tapes. Some of the systems had "fractional speed" trans-atlantic links where the 50 baud connection was split between 3 terminals at the far end ...
Biggest system we did was to support 192 asynchronous connections from a PDP-11 84 - with the slow speed links going out to teletypes on oil rigs.

timmo11
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Re: land line phone

Tue Dec 24, 2013 3:10 pm

Hi there wmsundel

First of all - this is a project that intersts me as well.

For all those others out there, Baudot for all its slowness has one advantage over the ASCII modem standards - it does not require a carrier signal.

This means that you can mix voice and data on the one phone line.

Why would you want to do this? Because for example you can hear but you cant speak. So you type, but the called party doesnt have to.

There seem to be two approaches to doing this.

One is the special (usually expensive) modem you have bought which does it in hardware.

The other is to do it in software via a V.90 modem after having switched it into Voice mode.

So - back to your situation...

I have some tips but by now I am more curious to know how you got on.

I will start a new thread on what I am trying to achieve.

Tim

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FLYFISH TECHNOLOGIES
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Re: land line phone

Tue Dec 24, 2013 3:58 pm

Hi,
timmo11 wrote:I have some tips but by now I am more curious to know how you got on.
Isn't internet access nowadays so widely available, that it is questionable to start development on merging both voice and "digital" communication through a single channel ?
I see this more like a configuration task to configure (and then use) a text chat program in parallel to voice call.
timmo11 wrote:I will start a new thread on what I am trying to achieve.
I'm looking forward to. ;-)


Best wishes, Ivan Zilic.
Running out of GPIO pins and/or need to read analog values?
Solution: http://www.flyfish-tech.com/FF32

timmo11
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Re: land line phone

Wed Dec 25, 2013 2:13 am

FLYFISH TECHNOLOGIES wrote:
timmo11 wrote:I will start a new thread on what I am trying to achieve.
I'm looking forward to. ;-)
here you go:

http://www.raspberrypi.org/forum/viewto ... 39#p474139

Merry Christmas :)

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