Activity light to indicate when sound is playing

Hi! I'm a great fan and long time user of the Hifiberry AMP2. I'm using it in combination with a RPI 3 as an custom built speaker with bluetooth/spotify connect/airplay which works great.

I would like to have a light (in my case it is an ancient light bulb) which turns on whenever sound is playing and turned off whenever the sound stops. Previously I accomplished that using a 'software' approach, i.e. by reading the unix filesystem and setting a RPI pin (in combination with a transistor) accordingly.

However, I don't like that approach and would like to reduce my lines of code within that project. Therefore I am looking for a more 'hardware' like approach and was wondering whether the hifiberry amp2 maybe has some kind of an activity pin or something similar which I could use for that purpose. Or maybe someone has another idea?

Thanks!

Fred blogs January 10, 2022 19:58

There is no binary (ie active or not) pin that can be monitored. But if you look at pin 21 (pin 18 on older firmware), you'll see it's a data pin, so when you see the pin fluctuating between high and low, music is being played, and when it's not changing music is not being played. It can be stationary in either high or low state, so make sure to code around the fluctuating states. My timer is around 500ms, so if no fluctuation for 500ms Playing LED goes out.

Activity light to indicate when sound is playing

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