I am currently working on a project where I have two GSM modules in a single product. Those modules have each one a mic port and speaker port.

They will not be used simultaneously but they will be both including on the PCB of the device. I need to be able to switch automatically from one module to the other one depending on the gsm network availability. However, our customer have only one mic plug 3.5mm jack and one speaker plug 3.5mm jack.

Hence I need to connect this only plug (one for mic and one for speaker) to a kind of switch to redirect the signal properly to the module which is currently used (face to gsm network availability).

I am a bit confused by which device to use to perform this 'audio switch"

If anyone has idea about the component that woudl be best suited for this...?

Thank you

but only one jack plug for eacc (one jack for mic, one jack for speaker)

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    \$\begingroup\$ HOW are you deciding when to switch between the two GSM modules? Will you be listening for incoming calls on BOTH of the GSM modules? WHY do you even need to switch? Do you want to hear from BOTH of the GSM modules? If you send microphone sound to BOTH of the GSM modules, the one that is "on-hook" (not in use) will simply ignore the microphone video (just like every other cell phone on the planet). \$\endgroup\$ Commented May 27, 2016 at 5:16
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    \$\begingroup\$ Two SPDT solid-state relays like this one, one for the mic, the other for the speaker should work for this. I looked and it doesn't seem that DPDT solid state relays exist in which case you would have needed just one. Note -- they will add some resistance in the circuit, perhaps 20 ohms. If that that is not acceptable, you could use a reed relay. \$\endgroup\$
    – tcrosley
    Commented May 27, 2016 at 5:23
  • \$\begingroup\$ @Richard: We fetch the status of the network via the module. Depending on the status, we switch from one module to the other (and we establish priority on one module on the othe rif both status are on). We need to switch because if the user is a cross border two network operator are used, and unfortunately some work with GSM and other with UMTS, hence we need to be able to switch from one to the other. \$\endgroup\$
    – user92481
    Commented May 27, 2016 at 5:28
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    \$\begingroup\$ @user92481 another possibility, probably a lot cheaper, would be an analog switch, like the 4066. It also has some series resistance built into it, about the same as the solid state relay. \$\endgroup\$
    – tcrosley
    Commented May 27, 2016 at 5:30
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    \$\begingroup\$ have a look on the maximintegrated site, they do specialised switches for audio/USB switching, and they do samples if you only want one/two items for the right price ;-) \$\endgroup\$
    – Neil_UK
    Commented May 27, 2016 at 6:35

1 Answer 1


As rightly said above most of the analog switches should work, because audio and mic signal runs at pretty low speed it should be easily available from multiple vendors. In my previous design, I used two GSM module however it was more sophisticated design with ARM processor and dedicated codec where we used codec with multiple channels do this job and switching was taken care by the software.


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