How to Use 2 Telephone HANDSETS as Intercom?

Guest
I understand how to use 2 telephones (USA) with 9v battery and
resistor and possibly .47mfd cap across resistor to make 2 station
intercom
BUT
How do you use two HANDSETS(USA modern not old carbon type) to make an
intercom? I cannot get into the handsets to see if earphone and the
mic are connected to anything such as a diode. I have a red & green
lead that I believe is earphone and a yellow (+) and black leads is
mic. I have tried experimently to connect them as if they were phones
and failed. I don't need much (gain/amplificarion if any) they will be
connected across 5 feet of wire.

PLEASE REPLY TO NEWSGROUP-MY SPAN FILTER IS VERY AGRESSIVE.
 
colklink@newsguy.com wrote:

I understand how to use 2 telephones (USA) with 9v battery and
resistor and possibly .47mfd cap across resistor to make 2 station
intercom
BUT
How do you use two HANDSETS(USA modern not old carbon type) to make an
intercom? I cannot get into the handsets to see if earphone and the
mic are connected to anything such as a diode. I have a red & green
lead that I believe is earphone and a yellow (+) and black leads is
mic. I have tried experimently to connect them as if they were phones
and failed. I don't need much (gain/amplificarion if any) they will be
connected across 5 feet of wire.
Click to expand...
You need to amplify the signals from the mics and feed it to the
earphones. But the sound from each mic needs to be fed to both earphones,
because you need to hear yourself as well as the other person in your
earphone. The sound which reaches your ear becomes very confusing if you
do not hear your own voice as well as the other person.

You can use a transformer to mix all input signals and create the sum of
all signals for all the outputs. Use separate windings for each input and
each output. The mic signals need to be amplified before the mixing in
the transformer, and maybe amplification for the output signals too.

I think there is an even simpler solution, mix all input (mic) signals
using an op-amp, and connect all earphones to the output of the op-amp.


--
Roger J.
 
"Roger Johansson" <no-email@home.se> wrote in message
news:Xns9595BEEF61A2886336@130.133.1.4...
But the sound from each mic needs to be fed to both earphones,
because you need to hear yourself as well as the other person in your
earphone. The sound which reaches your ear becomes very confusing if you
do not hear your own voice as well as the other person.
Click to expand...
^^^^
As far as I can tell, there are a lot of cell phones out there that don't
provide this 'sidetone,' and people don't seem to get too confused using
them.

---Joel
 
"Joel Kolstad" <JKolstad71HatesSpam@Yahoo.Com> wrote:

The sound which reaches your ear becomes very confusing if you do not
hear your own voice as well as the other person.

^^^^
As far as I can tell, there are a lot of cell phones out there that
don't provide this 'sidetone,' and people don't seem to get too
confused using them.
Click to expand...
Yes, I realize now that you are right about that.

That is the reason why inexperienced cell phone users often shout into
the phone.

The old telephone system had this sidetone, for reasons which were judged
to be important. You could hear your own voice, so you could adjust the
volume of your voice through feedback.

Okay, it is up to the constructor to decide if he thinks the sidetone is
important or not. I explained two ways to realize it, in any case, so he
knows how to do it if he wants it.


--
Roger J.
 
Joel posted:

<< "Roger Johansson" <no-email@home.se> wrote in message
news:Xns9595BEEF61A2886336@130.133.1.4...
But the sound from each mic needs to be fed to both earphones,
because you need to hear yourself as well as the other person in your
earphone. The sound which reaches your ear becomes very confusing if you
do not hear your own voice as well as the other person.
Click to expand...
^^^^
As far as I can tell, there are a lot of cell phones out there that don't
provide this 'sidetone,' and people don't seem to get too confused using
them. >>
--

The only time sidetone causes confusion is when there is echo. The combination
causes one to stutter.

The advantage of sidetone is that it helps you regulate the loudness of your
speech. Without sidetone you will talk louder, just as a hard of hearing
person does.

By the way, *all* cellphone connections include digital echo cancelation.
there is so much transmission delay in cellular switching and transmission, the
echo would make it almost unusable otherwise.

Don
 
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