A Cordless Phone & Headphones

[rotatepod]

I hereby promise, this the last time I will post about this subject!

I opened a box and found a cordless phone that I used a few years
ago. It was meant to be used in front of your desktop, and keep
both hands free. It consists of a small rectangular case, no handpiece.
You plug-in a pair of headphones that have a flexible microphone
element. I looked at the plug and noticed immediately it was
divided into three sections. This type of plug is normally used
to separate the left and right channels in a stereo recording. In
this case, I'm guessing that the extra channel is used for the
microphone. As far as I know, there is no need for binaural
sound seperation when you're using a telephone.

This phone got me thinking about my dad's hearing problems.
The only time he hears clearly is when is uses a pair of closed
cup IR or RF headphones while watching TV.

One of the many gizmos I purchased for him is called the
"PockeTalker." It a small, but powerful amplifier. It has two
3.5mm jacks. A small microphone element is plugged into
one jack and a headphone into the other. Both jacks are
monaural.

Naturally, I started thinking about combining the PockeTalker
with the phone and how simple it would be to connect them
together with a patch cord. You plug one end of the cord into
the headphone jack on the cordless phone. The other end
would go where the microphone element would normally be
plugged in on the PockeTalker. My dad has mentioned that
this PockeTalker amplifies soft and higher pitched sounds
better than anything he has tried so far.

After a few minutes I realized it probably couldn't be done. The
headphone jack on the phone is binaural, while the microphone
jack on the PockeTalker is monaural. Wiring the patch cord to
combine both channels is not going to work because you need
that extra channel to hear as well as speak. The PockeTalker
amplifier is not going to do the job. Am I thinking clearly about
this problem? In this case, I would be very glad to be wrong!

Thanks guys.

[Bigglez]

*** Redacted by poster ***

[rotatepod]

Hi Bigglez.

I've got plugs, cables, and a zillion other parts I'll probably never use.
When I was in my teens and twenties I was completely addicted to
electronics. 90% of the stuff I purchased was never used. I just
wanted to have all these boxes of parts within easy reach. Kind of
crazy, but that's the way I was years ago.

When you say, "split out the cables" I think I'm going to need a diagram
unless you can explain exactly how to wire these patch cords.

[jaem]

Hi rotatepod,

I don't know off the top of my head, but here's what I do know (or think I do, anyways). If the headset plug has 3 conductors, then I don't see how it could be binaural, due to the need of a ground connection. It's likely set up with a monoaural audio connection, a mic connection, and a ground. IIRC, a standard headphone phono plug has the ground on the base of the plug (the cable end, that is), so it might be the same. It should be a just a problem of finding the common conductor with a meter, then figure out which of the other two is which (tip: the speaker makes noise ). "split the cables" was referring to splitting the (ground/speaker/microphone) into (ground/speaker)/(ground/microphone) As for how well patching them together would work, I don't know. The one other thing is that plugging in something to the headset jack on the phone will probably mute both the handset speaker *and* microphone, so you'll need to wire an external microphone up to the phone's jack too. Since you have it, you may as well do more or less the same thing on the other end, and hook up the headset speaker to the amplifier, and the microphone to the handset jack.

Last minute note: if it's a standard wiring scheme, this is probably all online somewhere, but I thought I'd go the education/diy route rather than tell you to Google it

Hope that helps,
Jeff

[dyarker]

On 3 conductor plugs (Tip, Ring and Sleeve (AKA TRS)):

For binaural (or stereo); tip is left, ring is right and sleeve is common.

For headsets with mic and earphone, tip is mic, ring is ear and sleeve is common (mic and ear could be swapped, but that would make nasty popping in earphone when plugging in while wearing headset.)

For microphones with push-to-talk switch; tip is probably mic, ring is probably switch, sleeve is common.

For balanced communications circuits and Hi-Z mics (twisted pair); tip is signal, ring is return and sleeve is shield if used.