On 18/12/2020 12:41, Terry Coles wrote: > Hi, > > Some of you are aware that I've been re-engineering the Minster Bells and > Music Player at Wimborne Mode Town. Amongst other things I split the > functionality into two Pis (the original Pi 3 and a Pi Zero); both are > equipped with an Adafruit Stereo 3 W Amplifier Bonnet: > > https://thepihut.com/products/adafruit-i2s-3w-stereo-speaker-bonnet-for-raspberry-pi > > The Pi 3 takes care of the music that plays in the Nave and I configured that > first and using a cut-down version of the original code, it has been running > satisfactorily for a week or two. > > I then backed up its SD Card and created a new one using the Music Player > image as a starting point. Again, using a cut-down version of the original > code installed on the pi Zero, I have now got the bells to ring (almost) > perfectly. > > The one problem that I have is the volume setting command. In both programs > I > have a line: > > subprocess.call(['amixer', '-c', '0', 'set', 'PCM', 'playback', nave_vol]) > > In the music program this works perfectly every time, but in the bells > program > it fails intermittently with: > > amixer: Invalid command! > > After this failure alsamixer has no control over the volume level. However, > once the amixer command is working so is alsamixer. > > Any ideas on what I should check? AFAIK there is no difference between the > two > devices other than the underlying Pi type. I've tried all sorts of > combinations of amixer command from the man page, but when it works it works > and when it doesn't it seems to refuse to do anything.
Quick thought: Print out the exact commandline of: ['amixer', '-c', '0', 'set', 'PCM', 'playback', nave_vol] Every time just in case some previous error or something is getting into those variables? You've probably already checked that the commandline is the same when it stops working I guess, in which case this isn't very useful, but it's the first thing I'd try. Hamish
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