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From: dje@datacube.UUCP
Newsgroups: sci.electronics
Subject: Re: Full duplex intercoms?
Message-ID: <100500004@datacube>
Date: Mon, 30-Mar-87 10:40:00 EST
Article-I.D.: datacube.100500004
Posted: Mon Mar 30 10:40:00 1987
Date-Received: Thu, 2-Apr-87 00:57:22 EST
References: <649@charon.UUCP>
Lines: 23
Nf-ID: #R:charon.UUCP:-64900:datacube:100500004:000:973
Nf-From: datacube.UUCP!dje    Mar 30 10:40:00 1987


Hey, let's get even crude-r.   The  handsets alone  of a conventional
phone (carbon mike, magnetic earphone) can be wired in  series with a
battery to create an intercom.  I learned this  from my  uncle when I
was a budding young nerd of ten.  (Heavy duty nostalgia here).

---Mic---Ear---Battery---switch--------//-------Mic---Ear---
|                                                          |
---------------------------------------//-------------------

If you use a battery, a switch is necessary  to prevent  drain.  With
an AC powered supply you can leave it on always.  

Maybe for ringing, you could use a  Sonalert (DC  low current beeper)
and some reverse polarity diodes.   Current  through the  loop in one
direction causes beep, current in  the other  direction for intercom,
current off for 'off'.

				Dave Erickson
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Datacube Inc. 4 Dearborn Rd. Peabody, Ma 01960 	617-535-6644
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