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I would like to connect my Motorola phone, which is having common USB plug to charge and connect headset, to connect to laptop's mic and headphone.

So what I want is to connect

  • mobile's audio (output signal) to computer's mic jack (input singal) and
  • mobile's mic (input signal) to computer's headphone(output signal)

It's very practical but do we get a cable to connect it ... or do we have to make our own?

If products are available in market are there

  • mini USB to 2x3.5mm (male) jack or
  • 2.5mm 4 pole TRRS (male) jack to 2x3.5mm (male) jack

I do have an Imate phone which has a 2.5mm dedicated headset socket so even if I can get a cable of 2.5mm 4 pole TRRS (male) jack to 2x3.5mm (male) jack that will help me.

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2 Answers

There are three problems to overcome:

Signal-level mismatch and Impedance mismatch

The simplest way to pass audio signals between devices is to connect line-in to line-out. Your devices lack line-in and line-out ports, so this isn't possible.

The signal needed to drive headphones is larger than the signal produced by a microphone. You should expect a lot of noise and clipping. It might be feasible to use a potentiometer to attenuate the signal.

The usual solution is a Direct Injection Box but you could try a pair of Attenuating Dubbing Cords.

Stereo vs Mono

You also need to convert stereo headphone signals to a mono microphone signal. Use a stereo to mono adapter

Feedback Loop

By creating a signal loop, you run the risk of creating feedback (howl-around). Make sure the laptop outputs are not monitoring the microphone input.

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I don't think I've seen any 3.5mm to 2.5mm cables, but there are many 3.5mm to 3.5mm cables available in most electrical stores. A quick Google Shopping search yields some for £1.

I have found this though:

3.5mm To 2.5 mm Audio Headphone Jack Adpater Cable

You may be able to place this between the 2.5mm jack and the 3.5mm to 3.5mm cable - but I have no idea if it'll work, and if it does, what sort of quality you'll end up with.

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