BlacKnight

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BlacKnight last won the day on October 1 2014

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About BlacKnight

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  1. Hi Folks Although the Analog Discovery has fully differential analog (scope) inputs, the Discovery BNC adapter board does NOT! For some reason the negative inputs of both analog channels have been connected to the Analog Discovery ground. Therefore, they form a short circuit between any conductors they are connected to. Why is this important? I just found out the hard way, when I connected the scope leads from the Discovery BNC adapter board to parts of a circuit at very different voltages. I was expecting each channel to measure the differential voltage across each probe. Instead, there was a crack, a flash, and a little jet of molten metal, as the clip on one of my scope probes vaporised! IMO this is a safety hazard, because adding the Discovery BNC adapter board to the Analog Discovery changes its electrical behaviour in a significant way (from differential to single ended) but there is no mention of this in the Discovery BNC adapter board reference manual. Users should be warned in BIG LETTERS about this change in behaviour, perhaps printed on the PCB as well. I was lucky, but providing users with a warning about this could save somebody's life one day. I can see that grounding the negative inputs could make sense, in that it makes the analog inputs behave more like a conventional oscilloscope, where the probe shields are usually returned to Earth. However, if you're going to do this you should at least warn users about what you've done. IMO it would be better to provide 4 sockets for scope probes, with each connected to one of the differential inputs, and all the scope shields returned to Analog Discovery ground. Then the Discovery BNC adapter board could be used for fully differential measurements. You could also provide jumpers to select single ended behaviour instead, by shorting the negative inputs to ground. At least that would give the user a choice about whether to operate as differential or single ended inputs.
  2. Update - OK it's working now. I needed to add an external power supply because the Analog Discovery was drawing too much power from the bus for the isolator to supply (>400mA). It works with an Olimex USB isolator with an external power supply.
  3. Hi Folks I'm using an Analog Discovery. For my current project I need to isolate it, but it doesn't work when I try to connect it with a USB isolator. According to the manual... I've tried USB isolators from 2 different manufacturers. The Analog Discovery doesn't work with either of them. When the device connects I get an error message during device configuration (image attached). Is it possible that the software has changed so that it now doesn't work correctly with a USB isolator? It may be a timing issue during configuration, since the isolator only runs at 12Mbps. If so, is it possible to download an old version of the software that does work with a USB isolator? Any help would be appreciated.