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I'm trying to design an audio input card that only need to support TRS format.

I was hoping to use TRS + 1 switch (to indicate if a plug is inserted) but because of mechanical constraints all I could find was CUI SJ5-43502PM TRRS which is a TRRS jack.

On my schematic, I have the jack wired as below.

  • Pins 1 (TIP) and 2 (RING) for left and right
  • Pin 3 (RING) used as a switch to indicate a plug is inserted (signal is fed to an FPGA)
  • Pin 4 (SLEEVE) as a GND which is also tied to chassis GND.

-When nothing is inserted, pin 3 will be pulled high to indicate a plug is not present.

-When a TRS plug is inserted, pins 1, 2 and 4 will act as a normal TRS jack and pin 3 will be pulled low to indicate a plug is present.

So I think the wiring works for TRS plug. SJ5-43502PM wiring

However I'm not sure what happens if a user accidently plugs in a TRRS plug.

-If a CTIA TRRS plug is inserted, GND of the plug will pull pin 3 low to indicate a plug is inserted. However pin 4 will pull down MIC of the plug. Is this okay? What happens if there's an MIC bias voltage from an audio source?

-If an OMTP TRRS plug is inserted, GND of the plug will make contact with pin 4 which is also GND. However MIC will make contact with pin 3 of the jack which is tied to an FPGA. If there's an MIC bias voltage from an audio source then pin 3 will not be pulled down or even worse could damage the FPGA.

TRRS

I'm not an audio circuit expert so I'm not sure if my reasoning about how TRRS works is correct. Will above wiring work for both TRRS plugs? If not, is there a way to make sure CUI SJ5-43502PM TRRS would accommodate both TRS and TRRS (CTIA and OMTP)?

My design only needs to support TRS (unbalanced audio) but I want to make sure nothing bad happens when a TRRS is connected.

Any comments or feedback would be appreciated. Thank you!

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  • \$\begingroup\$ maybe you should first compare what would happen with a CTIA/OMTP plus if you were able to use a switched TRS socket. I assume the issues with be similar. \$\endgroup\$
    – RJR
    Jan 7 at 8:40

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