Telephone Audio Interface

[Oakton]

I searched the forum, so I know this topic
was discussed before.

I need something very specific for a relative
who is hearing impaired. He's tried various
hearing aids, and several other devices that
are suppose to assist his hearing. I knew
nothing about hearing disorders until this
relative developed hearing problems. If you
read some of the posts at the larger medical
forums, you'll realize how many people never
successfully adjust to devices like hearing aids.
It can be a real nightmare!

The only time he hears everything clearly
is when he uses a pair of IR or RF headphones
while watching TV. With that in mind, I
purchased an expensive cordless phone that
came with 2.5mm and 3.5mm jacks. He had
tried other phones that did not have a jack to
plug-in headphones. Both jacks in the phone
I purchased for him had problems. One had
weak contacts, and the other was misaligned
with the plug. Unfortunately, this is a common
problem with many audio devices that come
with jacks.

I think I have a possible solution. One of the
many hearing assist gizmos I purchased for
him is called the "PockeTalker." Its a small
amplifier with two 3.5mm jacks. It has a
volume and tone control. A small microphone
element is plugged into one jack, and pair of
headphones into the other. It sits on a shelf
collecting dust, but maybe it can be given a
new life.

If the microphone jack could be plugged into
a telephone audio interface it would allow
him to use almost any phone he chooses with
a pair of headphones. I found a schematic in
"Encyclopedia of Electronic Circuits," volume 6,
page 625, figure 90-8. Its a reprint from the now
defunct Popular Electronics. Like most of these
reprinted magazine schematics, very little info
is provided. For instance, it shows a 1uf capacitor,
but it doesn't specify the type, voltage rating, etc.

I don't have the time to breadboard numerous
circuits until I find one that works. When I was
teenager, breadboarding circuits was an addiction.
I still like experimenting with circuits that may or
may not work, but in this case I really want to build
something that will allow my relative to use the
phone again. Right now, his wife makes all his
phone calls for him and its driving her nuts! A kit
would be perfect, since most kits are thoroughly
tested before they're sold to us electronic folks.

 

[crutschow]

You can buy inductive pickups that connect to the telephone for listening or recording purposes (although they don't work with all electronic phones). Is that what you're looking for?

 

[Oakton]

Hi crutschow.

I was looking through an old Radio Shack
catalog that showed an inductive pickup.
It looks like a little suction cup.

My relative tried a traditional touch tone
office phone with the keypad in the base.
They sell amplifiers that plug-in to the
handpiece at one end, and the base at the
other. I think these inductive pickups work
best when the keypad is in the base.

99% of the modern phones sold today, have
the keypad in the handpiece. I'm not sure
I know what they mean by an "electronic phone."
The handpiece in a traditional office phone
is not stuffed with complex circuitry. It seems
like an inductive pickup would work best with
this type of phone. Am I correct?

 

[crutschow]

The older phones have an electromagnetic earphone speaker which generate an output that can detected by an inductive pickup. Newer "electronic phones" use electronics to amplify the sound and use an earphone that may not generate enough magnetic field to be detected. Some phones are specified as "hearing aid compatable" which, I believe, means they are designed to output a sufficient magnetic field that can be picked up by hearing aids designed for this. I suspect they would also work with a inductive pickup.

 

[Super_voip]

The hearing aid needs to have a "T" setting which is to be used with a telephone with inductive coil in the earpiece.

 

[Oakton]

Its almost embarassing to admit how much
stuff I've purchased for this relative related
to his hearing impairment.

He has at least two or three phones that
are hearing aid compatible. Maybe an
inductive pickup will work with one of
them.

I know why he can hear almost normally
when he puts on a pair of closed cup
headphones. Like most hearing impaired
people, each ear can detect a different
range of frequencies, tones, etc. By
combing both ears through a pair of
binaurial headphones, he hears the same
sounds through both ears at the same
instant in time.