Newsgroups: sci.electronics.misc
Subject: Re: Telephone to Sound Card Interfacing Question
References: 
Bill Richman  writes:

> I have recently installed an old Toshiba Strata XXe phone system in our
> house, and would like to interface my home-control system with it.  I am
> using "Mister House" (www.misterhouse.net) for the basis of it, and would
> like to have it be able to talk through the phone system's "page" or "all
> call" option.  I can handle having it "push the buttons" on the phone to
> make the call, using some analog switches or even DIP relays to close the
> various contacts, but getting the audio into the system is a little more
> challenging.  I did quite a bit of searching on the web and came up with
> very little that applied to what I want to do.  Finally, I went to Radio
> Shack and bought a couple of the "telephone recording attachments" that they
> sell, which go between the handset and the base of the phone.  The device
> has a "play/record" switch and a plug that's meant to connect to a cassette
> player's "earphone/mic" jack depending on the position of the switch.
> You're supposed to be able to record conversations and then play them back
> through the handset.  By placing two of these devices in series, one set to
> "play" and the other set to "record", and plugging them into the correct
> jacks on the home control PC's sound card, I've been able to get some audio
> in and out of the phone system, but it's very faint and has a loud hum in
> the background.  

Your problem is those adapters! 

Any telephone line adapters which you use to connect between
telephone line and any other electronic device should have
a galvanic isolation between the telephone line and the output.
This is a mandatory regualtory need in adapters sold in
many European countries! The isolation is needed for
the following reasons:
- safety (for both you and telephone line repairing persons)
- avoid humming because of different grounding point of line and your home
- avoids potential damages to equipments
- provides overvoltage protection

Trying to use an adapter without this kind of isolaition is not
adviced by me! 

For your application I recommend you to return those recording adapters
to the shop and getting money back. They are not suitable for your
application! They are potentially dangerous to try to use.

> I'm wondering if there's anything better that I could use
> to accomplish this, 

Good quality telephone recording adapters which provide gavanic
isolation are definately suitable for recording telephone conversations
using your sound card. Some of them are even suitable for sound playback.

For more technical information on this topic take a look at
http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html

> short of taping a speaker and a microphone to the
> handset on the telephone.  

I have also seen telephone recording/playback adapters which
plug to this interface. You have to search youself where
you can find those. And the adapters which go also to this
place have the same need: they have to provide galvanic isolation
from the telephone line.

> I'd also like to be able to connect my Voice
> Direct 364 (www.voicedirect.com) speech recognition board to the phone
> system, so I can give verbal commands to the system using the hands-free
> phones that came with the Toshiba phone system.  I'm assuming that whatever
> will work for the sound card's audio input will probably also be suitable
> for this card.  

I quess that. Just a quess, I haven't sene or used their products.
And their web site didn't no work, so I could not check if
they had any technicla data on-line (I just got "Coming Soon!"
page which does not promise much in this web cyberspace).

> Any suggestions would be appreciated!

Hopefully my suggestions were useful to you.

> 
>       -Bill Richman ([email protected])
>        Web Page: http://incolor.inetnebr.com/bill_r
>        Home of the COSMAC Elf Microcomputer Simulator, Fun with 
>        Molten Metal, Orphaned Robots, and Technological Oddities.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/