albert@ucbarpa.Berkeley.EDU.UUCP (03/25/87)
Why is it that most intercoms and speaker phones are half duplex? They usually require a push to speak button. Does anyone know of any intercoms which are full duplex, i.e., both parties can speak at the same time with no button to push? Anthony Albert ..!ucbvax!ucbarpa!albert albert@ucbarpa.Berkeley.EDU
f12008ad@deimos.UUCP (03/25/87)
Concerning the half-duplex situation with intercoms... I believe the reason why only one person can talk at once is simple. Most intercoms have a flush-mount speaker, as opposed to a headset. If there were dulex communications going on, the other party would here their own voice relayed back to them. There also might be one heck of a feedback own voice relayed back to them. There also might be one heck of a feedback problem. Isolated microphones/speakers would solve the problem, but then you might as well use a telephone. might as well use a telephone. Hope I'm correct with this assumption! Ollie - N6LTJ
gene@cooper.UUCP (03/27/87)
> Does anyone know of any intercoms which are > full duplex ... ? Sure. Take two junk telephones (that still work, just maybe a dead bell or something) connect them in series with a 9V battery, and Voila! an intercom! Of course, there may not be an easy way to call the other end, as with a ringer, but the connection is FULL duplex with just two wires (red and green) going from station to station. (A few years back, we did this in work to talk from the stock room to the selling floor. It worked then...) Gene ...!ihnp4!philabs!phri!cooper!gene "Mourn for us, so pressed with fear. Chained and shackled, we all found Freedom choked, in dread we lived Since Tyrant was enthroned." - RJAH
dje@datacube.UUCP (03/30/87)
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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[ihnp4 | mirror]!datacube!djehenry@utzoo.UUCP (Henry Spencer) (03/31/87)
> Why is it that most intercoms and speaker phones are half duplex? They usually > require a push to speak button. Basically, because the manufacturers are cheap. A half-duplex intercom can be just an audio amplifier, a speaker, and a switch or two. To make it work full-duplex, you need some way to prevent feedback, which gets more complex. > Does anyone know of any intercoms which are > full duplex, i.e., both parties can speak at the same time with no button to > push? Not commercial ones. Circuits for such things have been published here and there. Not inordinately difficult, as I recall, but non-trivial. -- "We must choose: the stars or Henry Spencer @ U of Toronto Zoology the dust. Which shall it be?" {allegra,ihnp4,decvax,pyramid}!utzoo!henry
henry@utzoo.UUCP (Henry Spencer) (03/31/87)
> ...Not commercial ones....
Our electronics man tells me I'm wrong, that full-duplex intercoms do exist
on the commercial market.
--
"We must choose: the stars or Henry Spencer @ U of Toronto Zoology
the dust. Which shall it be?" {allegra,ihnp4,decvax,pyramid}!utzoo!henry