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I'm building a car stereo using a Raspberry Pi, a touch screen and half of an existing car radio. I've remove the front screen from the car radio and hooked the Raspberry Pi in to the correct circuits to mimic a user turning the volume control. That all works fine.

I'm running OpenAuto on the Pi which has an onscreen volume control UI. When you change the volume in OpenAuto it sets the master volume of the alsa audio device.

What I would like to do (if possible) is to create some virtual alsa device so that when I change the volume in OpenAuto, I can leave the Rasperry Pi's master volume to 100, but trigger a process which will toggle some GPIO pins and set the volume of the car radio circuitry.

Does anybody know if such a thing is possible?

Marcus Müller
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CoximusPrime
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  • bit surprised! Would have expected that clicking on a Android Car head unit's volume buttons would change the Android device's volume settings, not the one of the head unit. – Marcus Müller Jan 27 '23 at 12:52
  • Sorry for the confusion, this isn't an Android Car head unit, this is essentially a Raspberry Pi running OpenAuto connected to the AUX input of a basic car stereo. What I want to do is instead of controlling the system volume when using the UI volume interface, trigger some code to control the external amp of the stereo, but OpenAuto is not open source, so I need to do something lower-level – CoximusPrime Jan 28 '23 at 09:05
  • OpenAuto is open source; I mean, I even added a link to GitHub repo containing the GPL sources... Also, if anyone shipped you an OpenAuto binary (other than the original author(or plural authors of they all agree), who might use dual-licensing, e.g. you can always have the GPL version, but if you want I can give you the non-gpl version for money), you're entitled to receiving the source code and ask scripts needed to build a working version of exactly the same. GPL and stuff. – Marcus Müller Jan 28 '23 at 09:59

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