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From: dave@dlb.uucp (Dave Buck)
Newsgroups: sci.electronics
Subject: Re: Phones used as intercoms
Message-ID: <1990Nov14.180524.3459@dlb.uucp>
Date: 14 Nov 90 18:05:24 GMT
References: <1990Nov12.181746.5465@syssoft.com>
Reply-To: dave@dlb.UUCP (Dave Buck)
Distribution: na
Organization: D.L.Buck & Associates, Inc.; San Jose, Calif.
Lines: 64

In article <1990Nov12.181746.5465@syssoft.com> len@syssoft.com (Len Galasso) writes:
>
>I live in a four-bedroom, split-level house which has at least one phone
>jack in each room.  What I'd like to do is to allow the phone "network"--
>if you will--act like a local intercom when it isn't being used as a
>regular phone system.
> ...
>I suppose some sort of intelligent isolation device would have to be placed
>between the main feed from the Phone Company into my house.  This would have
>to sense the command set defined--at this point only the special ring. And
>then when the "intercom mode" is finished it would reconnect the whole system
>back to Ma Bell.

I'd have to consider purchasing a "KSU" -- Key Service Unit, which is like a
PBX typically used by small businesses, and allows multiple lines and intercom
functions between all telephones plugged into the KSU, which is itself plugged
into Ma Bell's RJ11 jacks.

However, most KSUs use special telephones, not your standard telephone,
with leds and buttons for all the special functions (Hold, Transfer, Intercom,
Speed Dial, Speakerphone, etc).  Using regular phones is possible on many
as a special feature.
AND the big heavy bad news is that it's intended for business users, so the
retail prices are towards the thousands of dollars range.  Maybe $1,000, but
still substantially more than you'd pay for a simple intercom system.

>The way this came about is that I was going to install some sort of an
>intercom, using either the power-line carrier or FM wireless variety and
>I got to thinking that I *already* have an intercom system: the
>telephones.  Any user would not have to learn how to yet another piece
>of electronic equipment.

First of all, your users are your family, so we're talking about something
controllable here.  Second, intercoms are pretty simple, aren't they?  I haven't
seen one that requires a college degree to operate.  Third, dialing #*55 to
activate it is certainly a special procedure that has to be taught, so there's
some learning even though it is using the same handset and keypad.
Fourth, the wireless intercoms often don't require that the callee go to the
intercom and press a button ... they can hear and answer from across the room,
only having to go to the intercom to be a caller.  Fifth, I most often use
an intercom to tell someone else that they have a call.  If your system
disconnects Ma Bell when used, then what do you do?  Tell the caller to hang
up, wait 60 seconds and call back, so that you can use the intercom to tell
your wife the next call will be for her?  Sixth, there are other advantages
to intercoms over telephones ... most can be used in a monitor mode, so you
have a built-in nursery monitor from any intercom location.

>+------------------------------+-------------------------------------------+
>|  Len Galasso                 | "Just a machine to make big decisions     |
>|  Systems and Software Inc.   |  Programmed by fellows with compassion    |
>|  len@syssoft.com             |  And Vision"                              |
>|  (714) 833-1700              |    Donald Fagen, "IGY", _The_Nightfly_    |
>+------------------------------+--------+----------------------------------+

Personally, I use a KSU and associated special telephones that were obsoleted
when my company bought a new phone system.  The retail value of the used KSU
system was low, so my cost, other than some installation pains, was low.
I could justify it as I have more than one phone line coming into the house,
and I can answer calls to any line from any phone.  And the special telephones
have built-in speakerphones for intercom use, so I have the advantages of
a regular intercom plus regular telephones.
-- 
Dave Buck	{aeras,amdahl,ames,ardent,daver,netcom,sun,zygot}!dlb!dave
D. L. Buck and Associates, Inc.; San Jose, California 95119; (408)972-2825