USB Isolation

[Oleg] over at Circuits@Home has made a USB isolator for his hacking needs. This isolator separates the signal, ground, and power lines of a USB host device, such as a PC, from a USB device like a USB oscilloscope or logic analyzer. This might be useful for Keyboard sniffing, ECG, EEG or diagnosing the control system on the positive ground of your autonomous Ford 8N. What other applications can you come up with for this tool?


  1. Richard says:

    USB audio adapters to get around ground loop issues would be my first idea.

    Does this count as a hub when it comes to the USB extension limits?

  2. quadrapod says:

    looks very impressive like most things from circuits@home.

  3. Oleg Mazurov says:

    According to Analog Devices, ADuM4160 does count as a hub.

  4. hpux735 says:

    I want to install one of these permanently at my workstation to plug into all my custom USB stuff. I’m always worried about frying my computer with my negligence :)

  5. Adam says:

    Seems like a great way to protect your computer from mishaps, too — say, accidentally shorting mains voltage on a project board to the USB lines. I’d imagine that would fry any PC USB port, and could potentially take out the whole machine.

    Looking at the data sheet for the ADuM4160 part used on the isolator, the isolating insulation is rated to withstand 5000 Vrms for 1 minute. So it should do a good job of protecting your PC.

  6. svofski says:

    on my computer shorting out usb power to ground may cause a reset condition. i wonder if this device protects from such events.

  7. cantido says:


    Most host controllers disconnect the port if they sense a short or similar. I’ve created shorts on my Macbook’s(Running debian) ports a few times and there’s a nice message in dmesg saying that the host controller detected a short and disconnected the device.


    W(hy)TF would you have mains around your USB projects? I wouldn’t worry about blowing a port up, I’d worry about blowing yourself up! :P

  8. Buzzkill says:


    Home automation
    Lighting controls
    Relay or dimmer packs
    etc, etc, etc.

    There are lots of projects for using USB around mains voltage. And if you are rolling your own, then there is always the opportunity to cross a whire someplace, bridge a solder joint, or just plain user error that could drop mains voltage onto the logic side of board.

  9. strider_mt2k says:

    Nice! (And nice work there too!)

    Isolation lends itself to not blowing up all KINDS of cool stuff! ;)

  10. Awesomenesser says:

    My friend fried a $350 mother board and a atmel programmer when he was programming his 12 channel 120v dimming xmas light controller. Then I unfortunantly let his borrow my spare motherboard and the next night he took it out along with a another borrowed programmer.

    This was because he forgot to unplug the programmer and I guess the USB doesn’t like 120V. Oh and right after this he found the mistake on his PCB. But didn’t have a computer to reprogram it.

    Luckily asus didn’t know and replaced both motherboards.

    So yes this would be a great gift for him.

  11. Odin84gk says:

    This is a great reference design, but it does NOT provide mains isolation. The PCB layout clearance is only 1.63 mm, which means it can only isolate 150 volts DC at less than 1 watt of current.

    The board should be redone with at least a 5.5mm between the primary and secondary side of the isolation to provide the isolation specified in the datasheet.

    Here is a rule of thumb: If you are working with a component that provides isolation, do not create copper traces that are closer together than the footprints for the part.

  12. Odin84gk says:

    @Oleg Mazurov

    The device inserts the same timing delay as a USB hub, but it does not react like a hub. The high/low speed settings on the device takes care of the wait states between signals and the artificial delays required to keep the proper timing requirements. This is why both sides have a separate jumper to set the speeds.

  13. James says:

    This would probably be good for making a control circuit to turn my woot lights on and off via software.

  14. Nick H says:

    This seems like it could be useful for DIY “medical”/monitoring projects which require safe coupling with a human body, eg OpenEEG and the like. IIRC, they usually use an RS-232 serial port because it’s easier to use optoisolators on the lower speed signals.

  15. Wwhat says:

    Certainly useful for something, but I’m not sure it’s quite up to stopping mains from doing damage, I don’t think that’s quite the idea, just because something isolates signals and 5v doesn’t mean it’ll stop everything you know.

  16. Wwhat says:

    Hey I suddenly see hackaday accepts caps now, no more stripping? I wonder what else it accepts now.

  17. Wwhat says:

    Oh one more thing (last one I promise), if you have issues with shorts you could simply use some diodes at the USB connector, cheap and quick, no need to go through lengths like this project does.

  18. Stackbit says:

    THis is also very useful with connecting with PBX with usb ports for programming. Siemens HiRise 1100 series only allows a USB conection with a proprietary insulating dongle ( a ps/2 connector on the PBX side).

    With this you can just make a connector change-over, and use the insulator in the middle! Thx for the great hack!!!

  19. esdk says:

    Could you add a link to the other USB-adaptor:

  20. Buts says:

    Nice, but only full speed (=12 Mbps). Does anyone has a high speed (=480 Mbps) solution ?

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