I hope this is the correct forum for this question, I don't have a background as a electrical engineer, just a hobby.

I have a problem that I can't figure out. I have two audio sources, one default and one 3.5mm mono audio jack. The plan is to use the default source as long as a cable isn't connected to the audio jack. The audio jack has three pins; ground, audio, and a pin that is connected to the middle pin as long as a cable isn't inserted in the audio jack. I plan to use a Raspberry Pi as the micro controller for the project and the Pi is the default audio source.

I might have misunderstood the mono jacks pins, see image below.

The audio jack

  • \$\begingroup\$ Do you have a specification sheet or drawing for your audio jack? \$\endgroup\$ Commented Nov 23, 2017 at 21:23

2 Answers 2


Pin1 (The one closest to where the plug goes in) is the ground, Pin 2 (middle one) is the input, Pin 3 (other one) is the default signal.

As shown below.


simulate this circuit – Schematic created using CircuitLab

When you push in the plug, the switch opens, leaving the default source disconnected.

  • \$\begingroup\$ Ha! So simple! I feel stupid not figuring that out 😛 \$\endgroup\$
    – Ganhammar
    Commented Nov 24, 2017 at 8:04
  • \$\begingroup\$ @Ganhammar :) Don't feel that way, I'm pretty sure we all had that question at one point. For some reason it instinctively feels odd having the internal signal switch, and be left hanging, inside the connector. It is of course perfectly appropriate. \$\endgroup\$
    – Trevor_G
    Commented Nov 24, 2017 at 11:58

Assuming the left most pin is the switched audio, you connect the RPI to that pin, which routes the music through to the middle pin. When you insert a 3.5mm connector, it breaks the switch, so the connector's audio routes to the middle pin.

See this schematic for how it works electronically.

enter image description here

RPI to 3, Audio Out to your speaker/audio circuit to 2, Ground to 1.

Make sure your RPI audio ground is also connected to 1.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.