ERGO 16 Hz oscillation: bug or feature?

[RSteinhauser]

Dear BioSemi team,

For the first time I've paid attention to the ERGO sensor of our Lab's ActiveTwo system (because for the first time, I need to save some audio from a mic in my bdf file).

What I find strange: There is a very powerful (about 70 milliVolt!) continuous oscillation of exactly 16 Hz on our ERG1 channel (see image attached). This oscillation occurs independently of whether there is something plugged in into the ERGO sensor. When I plug in the mic cable, the 16 Hz oscillation seems to vanish for a few (1-2?) seconds but then appears again.

This is not a huge problem for me because I can notch filter the 16 Hz out offline, but that's of course not a perfect solution...

So, Is this some kind of feature or is our box broken in some way?

Best regards and thanks for your help
Robert

[Coen]

When nothing is connected to the ERGO, then the floating inputs may pick up interference (50 Hz form the mains, or 16 Hz from the GSR circuit). This is normal.

However, when a signal source is properly connected to the ERGO, then there should not be 16 Hz interference. Please check the microphone connector, see viewtopic.php?f=1&t=931&p=2854 (pin 4 to MIC signal, pin 5 and pin 2 to MIC ground). If the problem remains, then sent the AD-box for checking and repair (a connection to the ERGO input may be loose)

Best regards, Coen (BioSemi)

[RSteinhauser]

Dear Coen,

thank you so much for your help! It took me some days to get the chief electrician of my (small) university to help me, but he figured it out quickly based on your reply, the pin layout and a voltage meter

Maybe for other noobs with the same problem: The issue was that I had used a stereo audio cable and a stereo 5-pin DIN plug. Those use a different pin layout, which apparently caused the issue with the 16 Hz oscillation from GSR.

It now looks a lot better again.

Thanks again and best regards
Robert