RE: Re: Husband Automation ?

["Paul Gale" <p-gale@xxxxxxx>]

If you want some kind of hands free duplex (i.e. both talk at the same
time) system - won't you have to have some circuitry to prevent feedback
like most hands free phones have?



Paul.



-----Original Message-----
From: the_home_automator <db@xxxxxxx> [mailto:db@xxxxxxx]
Sent: 03 March 2003 23:39
To: ukha_d@xxxxxxx
Subject: [ukha_d] Re: Husband Automation ?



--- In ukha_d@xxxxxxx, "Alex Monaghan" <ha@m...> wrote:
> Good idea, I had thought of that, however I tend not to answer the
phone as
> it's never for me :-)

Ahh.. but thats the beauty of it.  It only rings if its an external
call; for an incomming intercomm call it just goes beep and then pops
straight into handsfree phone mode.  Thats when SWMBO speaks :-)

> I was thinking of something a bit more primitive, a few
transistors, a few
> push buttons and a speaker/mic and a chance to burn my fingers with
a
> soldering iron.

Oh good grief.  Make something?  Well, its not imposible; most
speakery type intercomms use  a simple amplifier, a push to talk
button, and some switching (or relays) to use speakers as
microphones. The only unusual bit is getting a decent impedence match
>from
impedence.  a mic matching tranformer is the answer.

The last bit of the jigsaw is a call button; If you are willing to
run more cores it all becomes trivial.  To do it all on just one
pair, the trick is to put a cap (100uf non-polarised elec) in series
with the speaker.  Put the call button across the cap.  In standby
mode, switch the remote speaker connection into the supply line of an
oscialator.  With the cap in series, no current flows.  Pres the
utton, dc path made, oscilator squeaks.

For some ideas of that you can do with his type of technology with a
few relays, look at the yankee nutone intercomms.  Tim Allen fitted
one (with the appropriate goings wrong, includng a big electrical
flash, butthats all optional) in the kitchn in Home Improvement; the
big black thing on the wall.   Never seen them use it, mind you...

David

(Happy owner of a Panasonic KXTA624 system, which SWMBO has no
trouble summoning me with!  Highly recommended.)