Author Topic: USB oscilloscopes and usb isolation  (Read 1846 times)

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Offline Thelosouvlakia

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USB oscilloscopes and usb isolation
« on: December 22, 2016, 11:09:12 am »
Hey there folks, I'm about to start assembling my own electronics lab as I'm a computer engineering student and I would like to have some equipment at home since I can get access to the lab only if the prof is there and I have to ask him for permission

So I've watched that video about the 300$ lab Dave uploaded and he mentioned those Hantek usb oscilloscopes but they are not isolated. I know that a mistake on my side might lead to catastrophic results for my hardware so I wanted to ask, is there a way I can make or buy a usb isolation circuit. I've found some items on ebay that say "USB Isolator 1500V etc etc etc" however I don't know if this is what I'm looking for AND/OR whether those circuits actually offer some protection.

Any reply would be appreciated..

Thank you,
Thelosouvlakia
 

Offline Gyro

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Re: USB oscilloscopes and usb isolation
« Reply #1 on: December 22, 2016, 11:37:59 am »
Welcome to the forum.  :)

Unfortunately there isn't a way of USB isolating the Hantek USB scopes because they need to use the full bandwidth of the USB2 interface to get the data to the PC fast enough. I don't think (somebody might correct me) that there are currently any USB2 isolation devices (ICs) available. The only USB scopes in a 'similar' price range are the OWON VDS series (specifically the 'I' for Isolation suffix) which Mike also mentioned. They are able to do it because they do all their high speed processing in the scope itself rather than in the PC sofware (they only use it for display and UI) so they can use a lower speed USB1.1 isolated interface.

P.S. Correction, I have seen the odd reference to 'unique' USB2 isolator on the web - you need to check the spec carefully for full 480Mbps data rate and sufficient current to power the Hantek. You should also compare the combined price against a scope with USB isolation built in.
Chris

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Offline Thelosouvlakia

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Re: USB oscilloscopes and usb isolation
« Reply #2 on: December 22, 2016, 11:47:21 am »
Thank you for your quick reply. I want specifically one of the hantek ones I can't find an owon one that has a logic analyser, which is essential to me basically
 

Offline Gyro

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Re: USB oscilloscopes and usb isolation
« Reply #3 on: December 22, 2016, 12:07:49 pm »
Quote
I can't find an owon one that has a logic analyser, which is essential to me basically

No, unfortunately you won't. Your other alternative would be to pick up one of the very cheap 8 bit USB logic analysers on ebay and use it with sigrok. Unfortunatley you will run into the same problem as the hantek though because they also are just basic streamers that need to use full USB bandwdth (You could at least have scope isolation though).



Edit: Here's the link I found for the true 480Mbps USB2 Isolator (It's $200 though ::)). There are several other hits for isolators that claim to be USB2 compatible but only support USB Full Speed (12Mbps) when you read the small print.

http://www.coolgear.com/product/usb-isolator-high-speed

It apparently uses the Silanna ICE08USBC chip, which is a new one on me, Analog Devices said it couldn't be done. Interesting. (search links on the chip and company don't seem to work).
« Last Edit: December 22, 2016, 01:04:03 pm by Gyro »
Chris

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Online BrianHG

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Re: USB oscilloscopes and usb isolation
« Reply #4 on: December 23, 2016, 05:26:04 am »
I guess you could just end up using a cheap used 200$ lap-top on battery power.  If you want to see the display and control it from your main PC, you can use the WiFi, or, preferably 1GB lan (Ethernet is transformer coupled isolated) with remote viewing & control software like VNC.  (1 Gb lan works really smooth with VNC even in 1080p)

The battery power laptop will give you that isolation from the wall AC on that side.  I know this might not be perfect for you, but, if you are going to spend 200$ on an isolator, this might be a workable alternative...

It's too bad there isn't a 1GB lan version of the USB scope.

BG.
« Last Edit: December 23, 2016, 05:42:56 am by BrianHG »
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