Chinese USB to USB Isolator Test

[amspire]

Just got my A$15 usb to usb isolators, and they are brilliant. The motivation is that I have always been uncomfortable about testing stuff on the bench while I have equipment directly attached to the device under test plugging directly into my desktop's PC's electronics via a USB cable.

The problem is in both directions - noise from the PC going to the device been tested, and the risk that if the test generates a massive spike, my desktop PC may be damaged.

Anyway, I got two of these from ebay. A search for USB to USB isolator will find them.

I pulled the isolated DC 5V-5V isolator off. Shouldn't be there anyway. It is only 200mA out, it says it is not properly regulated in the data sheet and it is rated only up to 1000V. I will file the board and pads where the isolator was located away to make a proper gap. Removing the DC-DC isolator  means you do need a powered USB hub on the unpowered side of the isolator.

Without the DC-DC isolator, the only things spanning the insulation gap are an Everlight EV817 opticoupler rated at 5000V RMS and an Analog Devices UDuM3160 USM isolator chip rated at 2500V RMS for 1 minute (UL). The unpowered capacitance across the gap was 4pF. It will probably rise to about 12pF to 14pF when powered, but it was a bit hard to measure. Still very good.

Anyway, it is only USB 2.0 High Full Speed (12mBits/sec) so I wasn't sure how it would work.

Tried it with a Hantek DSO-2150 USB scope and a Logicport USB Logic analyser and both worked flawlessly. Very happy. Even the scope had a very good update rate on the screen - hardly noticed a difference. The USB scope noise seemed to be about half what is was when connected to the PC directly. I am sure it will work perfectly with any USB to serial device like Arduino boards.

I will try a HV test, but I have to rig something up for that - do not have any HV testing gear of my own other then a Fluke HV probe.

Just a warning - if you are going to use this to connect to a HV device under test, do not trust your safety on this cheap device. I think it is pretty safe with the DC isolator removed and with the gap filed to a safe size, but assume everything on both sides is live. I am using this to protect my equipment, and lower noise. I will protect myself by not taking risks with anything potentially live. Almost all my work is at low voltages anyway.

Richard

[ebclr]

A Pendrive is a nice device to check speed, try to connect a USB flash and compare the speed with and without the converter

[amspire]

A Pendrive is a nice device to check speed, try to connect a USB flash and compare the speed with and without the converter

That is easy to test.

With a USB3 memory stick plugged into a USB3.0 port: 37Mbytes/sec
Plugged into a USB2.0 port: 30Mbytes/sec
Plugged into the isolator: 1.055MBytes/sec (totally constant)

Happy with that.

[ebclr]

A lot of usb stuff will not run reliable on 1 Mb/s specially programmers and jtags

[amspire]

A lot of usb stuff will not run reliable on 1 Mb/s specially programmers and jtags

True. Also things like logic analysers that dump data to the PC real time.

For me, I haven't touched the Hantek USB DSO for about 5 years, but as a floating scope, it is useful again. The A/D isolator has a common mode immunity greater then 25Kv/us. It is a pretty impressive.

[voltsandjolts]

Thanks for the mini-review. Minor correction for the first post:

Anyway, it is only USB 2.0 High Speed (12mBits/sec) so I wasn't sure how it would work.

The ADuM3160 max rate is USB1.1 Full Speed (12 Mb/sec). USB 2.0 High Speed is 480Mb/sec.

I can recommend this Lindy USB over CAT5 extender which provides isolation (ethernet magjacks) and 100m range, but it's in a different price league (10x):
https://www.lindy.co.uk/usb-firewire-c4/100m-cat-5-usb-2-0-extender-lite-p7368

[amspire]

You are right - got full speed and high speed the wrong way round. Did a strikethough on the high speed with a correction in the fist post to fix it. Thanks.

[Avacee]

This forum needs an extra button next to thanks of "You just cost me £x"

I'd been looking for one of these for my Arduino controlled DC Load and this fits the bill perfectly - extra thanks for the tip about removing the 5V DC-DC 

[amspire]

You do end up with a perfectly useful 5V to 5V converter for free! I have just saved you money.

[amspire]

More parts can come off the board.

If you do not need USB Low Speed mode (1.2Mbits/sec), take the switch and optocoupler off the board. They are only there to allow you to select Low Speed mode on both sides of the AD chip.

Here is what I have left. I have cut away the DC-DC Isolator tracks. Decided to remove the switch since I never want it accidentally in slow mode, and I want to cover it again in heatshrink tubing.

Electrically, there is no big advantage in removing the switch and optocoupler - the capacitance of that optocoupler is really low so it will not matter if it stays on.

Some of the through hole solder joints could be better.

[tomeo.gonzales]

Hi,
Can you post the link to ebay seller?
Thank you.

[amspire]

I didn't do a link just because there are so many suppliers. Just do a search for USB isolator in eBay,  aliexpress,  or whatever you use.

[fki82]

I'v got a slightly different version.
There is no switch and no optocoupler.
The DCDC converter is a mornsun b0505s-1wr2.
The USB-isolator is a ADuM4160. Max speed 12Mbps.
Some USB thumb drives seem to not like it, some work fine with it.
The max speed is as expected about 1 MByte/s.

[amspire]

That is a very odd looking layout for trying to get a decent isolation gap.

These USB Isolator devices keep using DC-DC converters that in their specs state that is it for applications where  "Regulated and low ripple noise is not required". They only claim 15% regulation accuracy at maximum output (200mA) so that means it could drop to 4.25V - probably not enough to reliably run a memory stick. So it is not the greatest power source.

Also many of these isolators claim 1500V isolation, and yet these Mornsun isolators only claim 1000V DC isolation.

I am just providing my own 5V on the far end - often a USB battery pack.

[xrunner]

Just got my A$15 usb to usb isolators, and they are brilliant. The motivation is that I have always been uncomfortable about testing stuff on the bench while I have equipment directly attached to the device under test plugging directly into my desktop's PC's electronics via a USB cable.

The problem is in both directions - noise from the PC going to the device been tested, and the risk that if the test generates a massive spike, my desktop PC may be damaged.

Hmm I'm intrigued. I didn't know about these, but I'm wondering ... My ham radio rigs are connected to my PC via USB. I wonder if these might be a good thing to isolate any computer noise from getting back into the rig?

[amspire]

Should help. The Analog Devices isolator chip is rated to have a 10pF capacitance across the isolation gap. That should really help you. The DC-DC converter is a noise source and also has over 30pF of capacitance - definitely get rid of it. The optocoupler is only a few pF, but I got rid of that too. It wouldn't matter if you left it on the board.

[xrunner]

Should help. The Analog Devices isolator chip is rated to have a 10pF capacitabce across the isolation gap. That should really help you. The DC-DC converter is a noise source and also has over 30pF of capacitance - definitely get rid of it. The optocoupler is only a few pF, but I got rid of that too. It wouldn't matter if you left it on the board.

Yea so I'm looking at the datasheet regarding how it works. Uses "iCoupler" technology. Reading up on that now but I think this thread just cost me some bucks ... but it's all good! 

[HoracioDos]

Just got my A$15 usb to usb isolators, and they are brilliant. The motivation is that I have always been uncomfortable about testing stuff on the bench while I have equipment directly attached to the device under test plugging directly into my desktop's PC's electronics via a USB cable.

I was thinking to buy some of them to isolate the Feeltech FY3200 DSG, a Korad KA3005P PSU and a ZKE EBC-A05 Electronic Load.

[fki82]

That is a very odd looking layout for trying to get a decent isolation gap.

I added a picture of the bottom side.
Looks like they tried to squeeze it into the case.

[amspire]

At least if you take off the DC-DC isolator, you could grind of the tracks to make a reasonable isolation gap. Definitely fine right now for under 100V - all you need for isolating low voltage electronics.

[lisafig]

Is the conclusion of this thread that the cheapest USB to USB Isolator on ebay (≈8€) will do their job ? (Will they my computer protect against  24v or 220v ―to go extreme?)