Audio input possible issue - approx. 5V on the cable

[Andrew]

Hi everyone!
I encounter e strange issue when I try turning on my mp3 player with the audio cable inserted and it doesn’t start. If I remove the audio cable, I can turn on the mp3 player just fine, plugged in and is all good from here. Out of curiosity I measured the voltage on the audio cable and I found out that when the 2B is powered on it has approximately 5v on the line. I’m not an electrical engineer, so I ask you, is this normal? To have 5volts on an audio cable? I’m worried that I’ll fry the mp3 player or worse, damage the 2B unit.
Apart from this issue, the 2B works just fine with no problems. I’ve also attached some pictures with the measurements I took.

[admin]

Its part of the monitoring system as there is a shared serial port. It's very low current, and is turned off in the Beta firmware releases. It only causes issues with so called intelligent devices which share input ports like speakers and mics. The ones who ask when you plug in a set of headphones - is this a set of headphones??? Really? They then think its an input when its not. The outputs of an amp driving a speaker or line out are far more powerful than the serial port. The simple answer is as you found is to plug in after you turn the MP3 player on. Or use a beta firmware.

Si

[Andrew]

I totally forgot about the serial port as it needs 5v for data communication. So it's all good. Thanks for the info!