Acitvity LED


Joined Mar 14, 2008
Don't know of any such thing.
Anything connected to the high-speed serial USB signal will likely disturb the signal and cause errors.


Joined Aug 7, 2020
I had success on RS485 by replacing the line-termination resistor by a resistor with a smaller value in series with two anti-parallel LEDs, so that the current drawn remained the same. Might be worth a try, but I can't guarantee it would work satisfactorily at USB speeds.


Joined Jan 30, 2016
USB data lines operate with carefully controlled impedance and timing, especially USB3 and are far more critical than RS485. Any loading other than a proper USB transceiver with have a detrimental effect on throughput and error rate.

A better question would explain why you need to monitor activity and what the specific circumstances are so that viable alternative approaches could be suggested.


Joined Aug 21, 2008
I think you would find that the data lines are in constant as the host constantly polls devices on the bus. The rule on the bus is "don't speak until spoken to".

I am sure you can watch the data lines with a commercially available USB analyzer without causing system problems, but it is unlikely you will see anything interesting.


Joined Jan 30, 2016
If its a Windows or Linux system wireshark and USBpCap (IIRC) will give you chapter & verse on what's going to/from a peripheral.