I would like to use a cellphone 3 conductor (2,5mm jack) headset
on my laptop and, therefore, buid an adaptor (2,5mm stereo female jack
to a 3,5mm "stereo" male jack for the mic and another 3,5mm male jack
for the headphone.

My understanding is that as it is mentionned in a former message ("4pin
Modular Handset to Cell Phone 3-conductor as headset???"), the
standard 2.5mm cell phone headset jack is connected as follows:
- The common ground (for both microphone and speaker) is on the sleeve
(outside/base ring)
- The positive for the microphone signal is on the tip
- The positive for the speaker is the middle ring.

What about the power signal for the electret then ? Is it a '2 wires'
setting ?

Any help would be greatly appreciated...

Thanks

Since the computer is stereo, you will have to have a means to set the
computer to mono. Use the left side for the earpiece. In mono the left is
the standard to use when only one channel is used.

The middle part of the plug is called the ring. The end is called the tip,
and the ground or main body is called the sleeve.

To have mono from the computer, you can also parallel the tip and ring
together, through a 15 ohm 1/4 watt resistor in series on each side. This is
to allow current limit to protect the output drive of the computer audio
device. This will then give a mono signal from both sides. If you cannot put
the computer in a mono mode, and you do not do this, their may be instances
where you will not hear the sound.

You will need to buy a 2.5 mm stereo type jack, and two 3.5 mm stereo type
plugs.

Wire the tip of the 2.5 mm plug to the tip of the of the 3.5 mm mic plug.
Wire the two sleeves together. On this plug, you should parallel the ring to
the tip. This will allow your mic to work on both the left and right
channels.

Wire the ring of the 2.5 mm plug via a 15 ohm resistor to the tip of the 3.5
mm earphone plug. Wire the same ring on the 2.5 mm plug via a 15 ohm
resistor to the ring on the 3.5 mm plug.

Label the mic plug as Mic, and label the earpiece plug as Ear.

I would not advise you to be bold, and skip the resistors. If you do, there
will be no protection for the isolation of your earpiece and current limit
for the parallel operation. Take extreme care to not short anything.

These resistors should cost about $0.10 to about $0.15 each, at most
electronic suppliers, if they will sell only a few. Normally they are sold
in bulk from the main suppliers.

If you go around to some of the TV service centres they may sell you a few.
Any value from about 12 to 22 ohms should work very well. The TV service
centre may ask a few dollars each for these, because of their overhead, and
cost to sell them. If there are any electronics parts surplus areas in your
area, you may be able to buy these a few at a time.

Did you know that there are dedicated earphones with microphones that are
designed for computers? Ask at your local computer store.

You are going to go to a lot of trouble for this. You will also have to work
out a way to do this job neatly, and so that it is reliable. After buying
all the parts, and spending the time on this, it would be cheaper and of
greater reliability to simply buy the proper earphone for the computer.


--

Jerry G.
==========================


"Larry Doe" ld.nospam_at_free.fr wrote in message
...
I would like to use a cellphone 3 conductor (2,5mm jack) headset
on my laptop and, therefore, buid an adaptor (2,5mm stereo female jack
to a 3,5mm "stereo" male jack for the mic and another 3,5mm male jack
for the headphone.

My understanding is that as it is mentionned in a former message ("4pin
Modular Handset to Cell Phone 3-conductor as headset???"), the
standard 2.5mm cell phone headset jack is connected as follows:
- The common ground (for both microphone and speaker) is on the sleeve
(outside/base ring)
- The positive for the microphone signal is on the tip
- The positive for the speaker is the middle ring.

What about the power signal for the electret then ? Is it a '2 wires'
setting ?

Any help would be greatly appreciated...

Thanks

Thanks for your help. I have built the adaptor, and even added
an 'RC' filter on the mic plug (from 3 contacts GND, SIG, PWR,
to 2 contacts GND and SIG/PWR).
Everything is almost fine except a grounding issue. I have a buzzing
noise (pure 50 Hz + harmonics) on the mic and it disappears if I
touch the GND with my hand.
I'm using a laptop that does NOT have a ground plug.

Anyone would know how to solve this (other than keep touching
the plug with my hand... ;-)

Thanks!