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I am trying to build a small circuit which will connect my phone, laptop and headset with a switch.

So in state 1, the headphone and phone will be connected

and in state 2, the headphone and laptop will be connected.

Just DIY stuff so I need not frequently disconnect/connect headphone from/to each device.

The circuit will have three female audio jack with connection shown in diagram(did not get the right tool. so its not much appealing but gives the over all idea)

Connection

The headphone which I use has 3.5mm TRRS jack so which translates as

Tip --> Left --> L

Ring --> Right --> R

Ring --> Ground --> G

Sleeve --> Microphone --> M

Question:

Which of the below approach can be used?

  1. Connect(Short) every terminal except ground to every other female jacks and toggle ground between headphone/phone and headphone/laptop.

Here I realised that connecting R,L of Phone to R,L of laptop might be an issue as R,L is output port and here I am trying to connect a output of two device back to back. So I came up with point 2.

  1. The connection as mentioned in the diagram. The DPDT switch will toggle R,L between two device and the other will be isolated. This will solve the issue in point 1 but is it okay to connect ground of phone and laptop at all time?

Mic is not a problem(I feel so) as it is always a input port and doesn't matter if my laptop gets the input when I am talking over Phone.

I am confused on which approach I should use and do the circuit and also not blow up my laptop or phone audio device.

Also I would like to hear if there are any other factors to be considered for this circuit.

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Option 2 is the way to go. We'd draw it like this.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Double-pole, double-throw switching.

Connect the mic lines together as you suggest. Both the phone and the laptop will provide a small bias voltage to the mic but it shouldn't cause any trouble.

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You would want 3. For the reason you give for 1, and because floating the ground would not be the best way to do it. But also because you don't really want the ground to be connected on the audio like that due to ground loop issues common with audio and devices that have both internal batteries and are powered via mains adapters. And 2 isn't good because the MIC line is not just a normal input. It can have a phantom power supply which mics need for them to work. Two competing supplies is never good.

3 would be to use a 4 pole Double throw switch so each of the 4 connections is toggled. Less common than normal SPDT or DPDT switches. You could use 2 DPDT switches but that's a bit awkward. Alternatively you can use 2 DPDT relays and use one switch to control both of them. Or use switching ICs designed for audio signals.

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