Electronic – How to switch this audio jack, using its own mechanical switches, without creating feedback


I've spent a few hours inside my car radio and I've found that when I short a hidden pin called AUX-ON to VCC, I can pipe music right into the it and it's treated like a regular AUX input. Great success.

Now, I have a switched jack that I'd like to use to short VCC to AUX-ON whenever I plug in a cable. The jack I'm using is Radio Shack 274-0246, the diagram is below. I can't figure out any way to do this without having the potential of grounding the audio to the vehicle ground (which could, I assume, distort quality) or without having the potential of sending 12v back through the audio cable into the phone. I know there MUST be a way to do this with a semiconductor or two, but I don't even know where to start. All I know is I need to pass current from pin 2 to 3 (or 4 to 5) and when that current stops (the jack mechanically separates the contacts when plugged in) then VCC can go to AUX.

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EDIT: I forgot to mention, the unit is expecting balanced inputs, however.. I don't think I've ever seen an ipod or phone with balanced outputs. Should that be taken into consideration with this circuitry?

Best Answer

You don't even need a semiconductor.

Audio jack insertion detect

In this circuit, when no jack is connected, GPIO will be pulled down to (almost) ground R4. When you insert the jack, R4 becomes disconnected, and R2 weakly pulls GPIO up to AVDD.

In your case you'd have VCC instead of AVDD. And you'd have AUX-ON instead of GPIO.