I am using the pictured TRRS connector and want to detect whether a plug is plugged in via the builtin switches (pins 2/3/4). However, the switches seem to be connected to the audio lines as well. Surely connecting a resistor divider/voltages/other sensing would affect the audio signal?

Preferably I don't want to use "overkill" ICs - I don't need any more amplification. I've seen the TI TPA6166A2 mentioned that can do this, but it only seems to be available in BGA (and is far more complex than I think I need). (However, I am willing to find a hand-solderable IC if it is the only way.)

Other answers have mentioned the switches but not specifically how to use them to detect a plug without affecting the audio signal. What sort of circuit would let me detect these switches opening in this way?

Schematic diagram of connector

(I have bridged together Left and Right channels because my audio source is Mono. I have designed this for "Apple"/AHJ pinout jacks.)


1 Answer 1


The thin rectangle between pins 4 and 6 is probably an insulator that provides a mechanical push to open pins 3 and 4.

When the plug is inserted, pins 3 and 4 open.

Connect one end of a resistor to pin 4 and the other end to 5V. Connect pin 3 to ground. When the plug is inserted the voltage on pin 4 will switch from 0V to 5V.

This will not affect the audio signal.

There are many other ways to use this switch.

  • \$\begingroup\$ Out of interest, what would I have to do if there wasn't that separate isolated pair of contacts? \$\endgroup\$
    – Liftyee
    Commented Jan 16 at 20:41
  • \$\begingroup\$ You would have tomonitor the audioncurrents or the circuit impedance. \$\endgroup\$
    – RussellH
    Commented Jan 16 at 20:51

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