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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

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  • \$\begingroup\$ Do you have a specification sheet or drawing for your audio jack? \$\endgroup\$ – ThreePhaseEel Nov 23 '17 at 21:23
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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.

schematic

simulate this circuit – Schematic created using CircuitLab

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

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  • \$\begingroup\$ Ha! So simple! I feel stupid not figuring that out 😛 \$\endgroup\$ – Ganhammar Nov 24 '17 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 Nov 24 '17 at 11:58
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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.

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