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Auto switching 3.5mm circuit

I currently have my phone connected to my car stereo via 3.5mm audio cable on the aux input for music playback

I would also like to connect my UHF radio to the car stereo as the internal speaker is not very loud/clear.

I would like it set up so that the music is playing and it auto switches to the UHF when someone is broadcasting.

I'm not sure if such a thing is possible (DIY) or if a product existing on the market already.

I would appreciate any help on the subject

Cheers 

Use a clap circuit to detect audio coming across the UHF. From the LED on the clap circuit attach a transistor to the LED so when the LED comes on the transistor triggers 12V from the car to activate a relay shutting off the audio of the phone and allowing audio of the UHF to go through. You'll need a SPDT 12V relay.