Failing Analog Discovery 2

[Rob Randall]

I have been using an Analog Discovery 2 in a automated python test setup for some time, but it is now failing.  I am just using a few of the digital outputs for static and pulsed enable signals, but they are just driving logic inputs, so very little current required (no external power supply, just relying on the USB for power).  I am also using one of the scope channels.

The symptoms I was seeing was that I would intermittently get timeouts trying to read back the analog scope waveform.

I tried directly connecting to the AD2 via waveforms (rather than our test software), and saw a variety of error messages (see "Digilent errors test station.jpg").  Note that we use an older version of waveforms (for compatibility purposes) on the testing station.

I had been using the test setup for several hours a day for weeks leading up to this, and made no changes to the setup.  The setup itself is pretty benign, the highest voltage in the system is 19 V.  The AD2 digital outputs are connected to other 3.3 V logic circuits and have no mechanism by which they could be connected to something higher.  The AD2 scope input is monitoring a current sense amplifier output that outputs maximum 16 V and has minimal ability to drive any current.  The power supplies are all positive, and all grounds and 0 V in the system (DUT, AD2, PC, PSU) are tied together, so there is no opportunity for something to exceed.  I double checked all the PSU and ground connections, and there are no loose cables that might have caused something to float unexpectedly.

I also tried connecting on my laptop (which has worked fine in the past) with nothing connected to the AD2 (just the USB) and continued to see errors ("Digilent error laptop.jpg") .  Finally, I installed the latest version of waveforms (downloaded mid last week) on a desktop PC and tried using all of the different back panel USB ports and continued to see errors ("Digilent error desktop.jpg").

As you can see from the errors, sometimes it was able to connect, but reported errors when trying to use the scope functionality, while other times it will not connect at all (maybe reporting insufficient USB power).  However, as I said it has been working properly for weeks without any changes to the test setup, and shows the same error when connected to multiple USB ports on multiple PCs without any connections to the AD2 at all.

So it seems clear to me that the AD2 is broken.  This device is only about 6 months old, so I'd like to return it for warranty repair / replacement.

Thanks,

Rob
 

[attila]

Hi @Rob Randall

The AD2 analog circuitry may be damaged by high voltage and when this (AVCC) is enabled the consumption increases, voltage drops causing device disconnect/reset.
Such errors could be also caused by USB contact issue. You could try using different cable, powered hub or 5V DC AUX supply.

For warranty and replacement contact support.digilent@ni.com, specifying the Date of Purchase, Seller and Purchase Order/ Web order Number.

The AD2 is probably out of stock and be replaced with AD3 which is an upgraded version of the device, with more features. Software-wise is compatible but few things may need to be adjusted in the custom application, like the open device name/id if used, default buffer size is larger and if this is not adjusted by the app the capture will take longer...

 

[Rob Randall]

Attila,

Thanks for the response.

As I mentioned, the highest voltage in the system is 19 V, being provided by a proper lab DC power supply.  Also, the analog scope port on the AD2 was connected to the output from a current sense amplifier, with will only output at most 15-16 V and there is no mechanism by which this voltage could exceed this at this node.  There isn't any violent switching of inductive loads or anything like that (and lots of bulk capacitance to soak up any load changes) so there isn't really any possibility of transients that would exceed the nominal voltage.  So I'm very confident the voltage has always been within spec for the AD2.

Indeed, this is a duplicate of a setup we use in our production test, and we have run these tests literally hundreds of times with the AD2 there with no issues.

I neglected to mention, as part of my experiments I not only tried multiple USB ports on three different computers, but also three different cables, including a nice short one with 24 AWG for power.  Also, it doesn't even connect with just the AD2 by itself on USB - so if the AD2 with no external circuitry connected requires an external power adapter just for basic functionality, you should not market it as if the 5V is optional.

I will proceed with the warranty claim.

Thanks,
Rob