[mcp6453[_2_]]

Sort of off-topic, but I need to interface a Bellsouth BLS-420 multi-line
speakerphone to a recording console for a project. The original idea was to use
the headset jack to grab the caller and feed the mix-minus audio. I've done this
many times before. However, this telephone is too smart. If I press the headset
button with no headset connected, it generates an error. If I plus a 2.5mm
stereo cable into the headset jack, it generates the same error. Someone, the
phone is able to detect that a real headset is not connected.

The phone may be sensing that there is no electret mic element, which the
headset uses. Does anyone know what I could use to fool the phone into thinking
a headset is connected?

I know that there are many ways to build or buy a telephone interface, including
a Telos digital hybrid, but I need to nail this one since the phone is part of
an existing telephone system.

[Charles Tomaras]

"mcp6453" wrote in message
...
Sort of off-topic, but I need to interface a Bellsouth BLS-420 multi-line
speakerphone to a recording console for a project. The original idea was
to use
the headset jack to grab the caller and feed the mix-minus audio. I've
done this
many times before. However, this telephone is too smart. If I press the
headset
button with no headset connected, it generates an error. If I plus a 2.5mm
stereo cable into the headset jack, it generates the same error. Someone,
the
phone is able to detect that a real headset is not connected.

The phone may be sensing that there is no electret mic element, which the
headset uses. Does anyone know what I could use to fool the phone into
thinking
a headset is connected?

I know that there are many ways to build or buy a telephone interface,
including
a Telos digital hybrid, but I need to nail this one since the phone is
part of
an existing telephone system.


Look at www.jkaudio.com Lots of solutions at a variety of prices.

[Scott Dorsey]

mcp6453 wrote:
Sort of off-topic, but I need to interface a Bellsouth BLS-420 multi-line
speakerphone to a recording console for a project. The original idea was to use
the headset jack to grab the caller and feed the mix-minus audio. I've done this
many times before. However, this telephone is too smart. If I press the headset
button with no headset connected, it generates an error. If I plus a 2.5mm
stereo cable into the headset jack, it generates the same error. Someone, the
phone is able to detect that a real headset is not connected.

It's probably impedance. Try putting a shunt resistance on both the receiver
and the transmitter.. use a pot and see which one needs to be adjusted where
to make the phone pick up. It could be looking for a receiver load, not a
transmitter... and if so you can just leave the receiver hooked up.

You can also probably buy a box from Plantronics that is specific to that
phone and intended to interface it with a Plantronics headset. That may
also be worth trying if you get desperate.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[[email protected]]

On 10/18/2010 9:51 AM, Scott Dorsey wrote:
wrote:

It's probably impedance. Try putting a shunt resistance on both the receiver
and the transmitter.. use a pot and see which one needs to be adjusted where
to make the phone pick up. It could be looking for a receiver load, not a
transmitter... and if so you can just leave the receiver hooked up.

You can also probably buy a box from Plantronics that is specific to that
phone and intended to interface it with a Plantronics headset. That may
also be worth trying if you get desperate.

It turns out that the phone looking for a load on the receiver. I put a
coupling transformer on the output pair and the transformer was enough
load to fool the phone. The problem now is that there is a very clear
hum on the audio feed even though the audio is transformer-isolated. I'm
going to try a different transformer as telephones normally do not like
being connected to audio equipment. Unless this transformer has an
unusual amount of leakage at 60 Hz (not likely), this phone is noisy.
It's possible the wall wart is bad and is providing dirty DC.