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AD2 USB Disconnects - EMI, RFI? Solutions?


AlexanderGDean

Question

I'm using my Analog Discovery 2 to try to capture analog echo data from a marine depth sounder using the fly-wire connectors. The problem is that the USB connection from the AD2 to the PC dies after a few seconds or tens of seconds when the sounder is on.

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 I suspect it is noise from the sounder, which drives a piezo transducer at 192 kHz and 36 W RMS, which would imply significant voltage. I noticed that the fly-wires work well to pick up the transmit pulse when disconnected (but a few inches away).

Edit: The problem remains when I replace the fly-wires with a single coax cable (albeit with poorly terminated connections).

Do you have any suggestions on how to keep the USB connection up?

Thanks,
Alex

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Hi @AlexanderGDean,

We have similar issues in our lab. The best solutions I have been able to come up with are to:

1) Use very high quality USB cables with integrated chokes (Tripp Lite USB 2.0 Hi-Speed A/B Cable with Ferrite Chokes (M/M) 3-ft. (U023-003))

2) Build a custom enclosure for the entire AnalogDiscovery - PC system. We have an embedded PC and the AnalogDiscovery inside a custom enclosure.  I recommend protocase (https://www.protocase.com/). We use 50 ohm thru-panel BNC connectors which are grounded to the enclosure to make connections to our input sources. Even in this configuration we have to ensure that there is a very low impedance between each side of the enclosure and ground (1-2 ohms). 

This isn't a perfect solution, but it is a dramatic improvement over the plastic enclosure for the AnalogDiscovery.

As a side note: be careful if you have any sensitive equipment attached to the AnalogOut channels. Disconnecting the USB cable and/or resetting the USB connection in software can cause those channels to go high for ~10ms. 

Please update us if you find any new solutions that improve this issue.

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Thanks for the detailed suggestions!

I figured out a partial solution which reduced the USB crashes enough for me to get the data. I brought the two signals out of the sounder through a short shielded cable (5"), ran it through a clamp filter (https://product.tdk.com/en/search/emc/emc/clamp/info?part_no=ZCAT2035-0930A-BK) and connected the conductors to a small 2x3 female 0.1" socket to plug directly into the analog inputs of the AD2. The separate cable eliminated any fly-wire antenna effects. Looking at the signals on the bench scope it seemed that most of the noise (but not all) was eliminated. I expect my next step will be replacing the USB cable.

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