Isolated USB ports
Problem:
Multiple bench meters, scopes, etc. that connect to a workstation through a USB hub. Not all of the bench devices are optically isolated from the USB bus, so it is possible to get undesirable (and possibly damaging) ground loops through the equipment.
Solution:
While there are commercial USB hubs that provide isolation, they are rather expensive… typically starting around $350 for only a few ports. It seems that one should be able to build something like this for much less.
One might think that it’s just a matter of splicing a couple of opto-isolators into the data wires, it’s much more complex, as shown here.
There are some useful chips on the market with fairly simple application notes.
This design will be based on the Analog Devices iCoupler ADuM3160 that supports both high and low speed USB, it may also supply peripheral power using an ACuM5000 chip.
We’ll keep the initial version simple and skip the common-mode chokes, and leave out any diode networks for ESD protection.
Multiple bench meters, scopes, etc. that connect to a workstation through a USB hub. Not all of the bench devices are optically isolated from the USB bus, so it is possible to get undesirable (and possibly damaging) ground loops through the equipment.
Solution:
While there are commercial USB hubs that provide isolation, they are rather expensive… typically starting around $350 for only a few ports. It seems that one should be able to build something like this for much less.
One might think that it’s just a matter of splicing a couple of opto-isolators into the data wires, it’s much more complex, as shown here.
There are some useful chips on the market with fairly simple application notes.
This design will be based on the Analog Devices iCoupler ADuM3160 that supports both high and low speed USB, it may also supply peripheral power using an ACuM5000 chip.
We’ll keep the initial version simple and skip the common-mode chokes, and leave out any diode networks for ESD protection.
Based on this chipset, I should be able to provide isolated USB ports for $10 – $15 per port.
Digikey has shipped the parts, now to design the board!
more to follow…
Corgitronics 