Hi, I seem to be having an unusual problem. Running Saleae 2.4.22 on NixOS using a Logic 8 device.
On my desktop machine the device is properly recognized and can capture data. Only problem is that it is measuring only noise (or some heavily transformed data). See this image:
The curious thing is that it works on my laptop (also NixOS), same Saleae version:
What could be the potential cause here? Everything else is the same, setup, cables, everything.
Are you getting your grounds messed up? A desktop will have its common for USB and other such I/O connected to mains ground which may not be the ground point you are connecting your analyzer’s “ground” pins to on the DUT. That can short out the DUTs power supply or cause other weird behavior.
A laptop may well be “floating” (not connected to mains ground), depending on how the laptop is being powered. Note that connecting a floating laptop’s “ground” to some random point in the DUT may be lethal to either you, the DUT, the analyzer, the laptop, or all of the above!
Be very sure that you understand how grounds for the DUT and the analyzer’s host device are related to avoid damaging anything and to get sensible signals.
100%. This is why I nearly always use my Logic on a laptop and I do NOT plug that laptop in. Then the laptop is floating and has no real connection to any sort of external ground. Otherwise it’s too easy to have odd grounding issues that mess everything up.
Thank you two, that was definitely it. You’re right, it’s easier if you don’t have to think about what’s connected where.
