I noticed when I touched the blue lead of a tricolor led and it lit up faintly despite not being connected to anything.
So I grabbed my multimeter, and it says that there's around 4 microamps flowing from me (anywhere on my body really, finger, arm, face) to the arduino. I tried measuring the voltage, but it fluctuates too rapidly. Depending on what's between me and the arduino, the frequency of these fluctuations changes, but is typically 30-40 kHz.
I've tried connecting the yun to different power sources, and it happens consistently. The current does not appear dependent on orientation, so I don't think it's me acting as an antenna.
This doesn't not happen when the yun doesn't have power, but begins immediately (as far as I can tell) after I power it.
What's happening here?
What kind of shoes are you wearing?. Is the -main- electrical system well isolated?
Sounds like a high efficiency LED!
The body does act like an antenna, emitting energy. One of the reasons for not having unconnected inputs without a pullup (generally the internal one) or a pulldown resistor is to keep the input from oscillating when it sees that 4uA - CMOS inputs only need 1uA max to make them change from high to low or low to high.
You haven't described how the LED is wired up, so its not clear how the Yun comes into play here.
Sounds like a high efficiency LED!
I'd lean toward the leakage theory 
I uploaded a video.
The LED has a common anode, so I have just that connected to the arduino.
I realize that this isn't apparent in the video, so I can do a better one tomorrow, if you guys want.
I suspect that the reason that it glows brighter than one would think for 4 uA is that the voltage fluctuates higher than 5v for brief periods of time.
I should really see if I can get a hold of an oscilloscope.
This occurs when the arduino is plugged into my laptop, or a usb hub. I'll try a usb battery to see if it has to do with the power grid.
I can't observe this behavior with any of my unos.
jamesbiederbeck:
I uploaded a video.
Current flows between body and Arduino Yun - YouTube
::::SNIP::::
This occurs when the arduino is plugged into my laptop, or a usb hub. I'll try a usb battery to see if it has to do with the power grid.
I can't observe this behavior with any of my unos.
jamesbiederbeck,
I'm not an electrician, nor do I pretend to be one on TV.
But seriously, not all laptops are configured to "true" ground; that is an earth ground. Three prone plugs generally indicate "earth ground", but not always. If the electrician did not set the outlet tos some ground ("specification"), it is not. Homes are notorious for not being wired correctly, hence the specification. AAMOF server rooms require certification; and even then most good system administrators will double check things.
FWIW, you could spend a lifetime studying the incorrect ways to not have "ground".
More importantly, someone in the next few posts, will tell us how to achieve a "good ground", then someone else may give us a better explanation that I can.
The point of course being, you did not show any evidence of proper "groundness" in the video.
Jesse
