Simple USB Isolator

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Simple USB Isolator

Postby TomKeddie » Fri Mar 21, 2014 2:21 pm

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In one of the earlier SMD workshops I've running at http://vancouver.vanhack.ca I managed to temporarily kill my new macbook pro when I plugged in a partcipant's prototype. I revived it by removing the back cover and disconnecting the battery - all the time chanting to myself, must get a usb isolator, must get a usb isolator, must get a usb isolator…..

This is a nice simple soldering project that does exactly that, isolates your USB port from connected devices. There are two input usb connectors, one carries data and power from the computer the other supplies power to the output. The output comes from a 3rd USB A connector. There is no power/ground/data connection between the computer and connected devices other than through the isolator chip. This board has two grounds, two power supplies etc.

The isolator chip is an ADUM3160, it is most of the cost of this workshop – “The ADuM3160 is a USB port isolator, based on Analog Devices, Inc., iCoupler® technology. Combining high speed CMOS and monolithic air core transformer technology, this isolation component provides outstanding performance characteristics and is easily integrated with low and full speed USB-compatible peripheral devices.”

I did manage to get some samples from http://www.analog.com/en/interface-isol ... oduct.html. We’ll be getting the ADUM3160 from Farnell/Element14, you can see more details on the isolator at http://www.element14.com/community/docs/DOC-50978/l/analog-devices-eval-adum4160ebz-usb-isolator-board-for-the-adum3160-and-adum4160.

The isolator chip is limited to 12Mbps speeds, which are fine for development boards like Arduino etc.

PCB design is at https://github.com/vhs/vhs-pcbs/tree/ma ... b-isolator

I've put some on Tindie at https://www.tindie.com/products/TomKeddie/usb-isolator-pcb-only/
Last edited by TomKeddie on Mon Dec 05, 2016 2:02 pm, edited 1 time in total.
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Re: Simple USB Isolator

Postby rsim » Fri Mar 21, 2014 4:47 pm

Good call on putting them up on Tindie!

I haven't needed to pull the backup battery from my MBP when I've soft-killed my USB ports though; it just requires resetting the SMC and/or PRAM (sorry, I can't post actual links - boo! URL fixups should be obvious):
support.apple_domain/kb/ht3964
support.apple_domain/kb/ht1379

Of course, that's hoping that it's only soft-killed (and that isn't applicable to PC's)... so this is definitely an awesome tool for VHS members to have in their toolkit!
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Re: Simple USB Isolator

Postby Sjaak » Sun Mar 23, 2014 2:06 pm

I would not use the same pc/laptop to power the device, as that will kill the optoisolation you carefully build. Prolly you gonna use a charger os such, but I would replace it with a screwterminal or a barrel jack. Also add a polyfuse rated max 500mA for extra protection.
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Re: Simple USB Isolator

Postby ryemac3 » Mon Mar 24, 2014 10:34 am

So both USB connections have to be made for the board to work? Maybe I'm having trouble getting my head around the reason for this, but if the power/ground/data is isolated from the PC, what is the point of plugging it into the PC?

I often power my breadboard off my Arduino, which is connected to my computer. If I short some jumpers on my breadboard, I get that dreaded "A USB device is drawing too much current and will be shutdown" message. I'm amazed I haven't killed my computer yet.

I though the purpose of isolation was so that if you short something out on the connected device, you don't damage the computer. Is that what this does? If so, what's the purpose of 2 USB connections?

Thanks
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Re: Simple USB Isolator

Postby sparkybg » Mon Mar 24, 2014 1:08 pm

I think the better way to do this is to put an isolated DC-DC on the PCB and remove the third USB connector. For example, Murata MEV1S0505DC is a good choice, and I've used it on many projects. For example, I have USB-CAN project that uses it. And it only needs the twisted pair and the ground on the CAN side - all the power is from the USB port.

This way, you can build universal isolated USB cable that will work on almost any device. Eventually, speed selecting jumpers or microswitches are to be added on the PCB and that's all. It will be excellent solution for a programmer or debugger like PicKit3 for example.

In all other cases, I think it is a better practice to put isolation inside any device where different/damaging ground potentials are present/possible or ground loops are to be avoided. The cost of the device will rise of course, but I think this is the right way to do it. For example, my new universal soldering controler (which will be published here when I have a working prototype) uses this chip insde it, in order to have absolute freedom how to connect different soldeting irons/tips. Several commercial soldering controllers do have some sort of isolation inside them, either by using this chip, or, in the vast majority of cases, by using plain USB-RS232 chip, and optical isolation on the RX and TX buses after it. The price of both solutions is more or less comparable, so it is almost pure engineering choice.


This is not a criticism. Just sharing my thoughts.
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Simple USB Isolator

Postby TomKeddie » Mon Mar 24, 2014 5:33 pm

Thanks for the tips.

The second usb is most definitely for a wall wart. I hate barrel connectors because they never match properly for me. i could have used micro usb for one connector i suppose. This board is meant to be cheap and useful to those who know how to use it. I might update the silkscreen to improve the doco.

The eval board I based this on has an isolated p/s. I wanted people to be able to get a good 500ma out the back end, here you get out what you put in.


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Simple USB Isolator

Postby TomKeddie » Mon Mar 24, 2014 5:33 pm

BTW I did suggest to Ian this would make a nice update for the smoke tester.


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Re: Simple USB Isolator

Postby sparkybg » Tue Mar 25, 2014 3:37 am

TomKeddie wrote:Thanks for the tips.

The second usb is most definitely for a wall wart. I hate barrel connectors because they never match properly for me. i could have used micro usb for one connector i suppose. This board is meant to be cheap and useful to those who know how to use it. I might update the silkscreen to improve the doco.

The eval board I based this on has an isolated p/s. I wanted people to be able to get a good 500ma out the back end, here you get out what you put in.


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There's plenty of space on the PCB, enough for both the 3-rd connector and isolated p/s. The PCB will be more universal this way, and will still be cheap if someone wants it to be cheap. The users will decide if they need the isolated p/s or not.
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Re: Simple USB Isolator

Postby ryemac3 » Tue Mar 25, 2014 8:51 am

I downloaded the PCB/SCH from Github, but they don't open with my version of Eagle. Are they Eagle 6 files?
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Re: Simple USB Isolator

Postby TomKeddie » Wed Mar 26, 2014 8:58 am

ryemac3 wrote:I downloaded the PCB/SCH from Github, but they don't open with my version of Eagle. Are they Eagle 6 files?


Yes they open fine in Eagle 6.5 for me.
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Re: Simple USB Isolator

Postby Tachyon » Wed Jun 04, 2014 9:54 am

Thank you for an awesome project Tom :)

I'm having the same problem as ryemac3 - neither the board nor schematic will open in Eagle 6.4 or 6.6. The message I get is as follows:

Error:
line 7, column 18: This is not an EAGLE file.

Any ideas?

EDIT: Okay, I figured it out. Downloading the individual files was somehow creating issues. Going up one level and downloading the full zip solved things :)
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Re: Simple USB Isolator

Postby viya0414 » Thu Aug 31, 2017 10:22 pm

I would not use the same pc/laptop to power the device, as that will kill the optoisolation you carefully build.
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