Path: utzoo!attcan!uunet!aplcen!uakari.primate.wisc.edu!zaphod.mps.ohio-state.edu!tut.cis.ohio-state.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request
From: gtisqr!toddi@yang.cpac.washington.edu (Todd Inch)
Newsgroups: comp.dcom.telecom
Subject: Re: How Does a Telephone Receiver Work?
Message-ID: <10027@accuvax.nwu.edu>
Date: 22 Jul 90 23:25:52 GMT
Sender: news@accuvax.nwu.edu
Organization: Global Tech International Inc.
Lines: 28
Approved: Telecom@eecs.nwu.edu
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 10, Issue 507, Message 3 of 11


In article <9849@accuvax.nwu.edu> dave%westmark@uunet.uu.net (Dave
Levenson) writes:

>Your telephone receiver may act in reverse, as a low-level microphone.

In fact, you can build a "high-tech" tin-can quality phone by
connecting two of these telephone handset "speakers" together with a
pair of wires.  No amp, no battery.  They just provide enough of a
miniscule signal to drive one other and will act as either a
microphone or a speaker.  Amazing.

They're also great for crystal radios because they're so sensitive.

Using the speaker as a microphone is quite common in inexpensive
push-to-talk station intercoms such as the $15 two-wire type from
Radio Shack.  One end has the amp and battery, the other end is just a
speaker (plus a push button which shorts a DC-blocking capacitor to
signal the "base") and the push-to- talk button on the base unit
essentially just swaps the two speakers.

I've also seen PA systems on boats that use a horn-type speaker on the
mast to talk to land or another ship which also allow eavesdropping,
er, listening via the same horn speaker.


Todd Inch, System Manager, Global Technology, Mukilteo WA  (206) 742-9111
UUCP: {smart-host}!gtisqr!toddi    ARPA: gtisqr!toddi@beaver.cs.washington.edu