I fried my laptop (a cautionary tale)

I was helping our intern build a test fixture, and had my laptop connected to the PCB to program through an unenclosed FTDI. Was showing the intern how to connect up an led to display when the 24v motor driver was on and one of the wires touched the FTDI.

Took out the PCB, FTDI, and laptop. Poof! At least is was a very old laptop I was planning on replacing.

Aside from enclosing the FTDI next time, is there any such animal as USB cable protection from over voltage?


There are USB isolators that would probably do the trick!

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USB-Isolator, standard oder mit integriertem 4-fach Hub (meilhaus.de)

i’ve been curious about USB Isolators for a while as I have yet to come across a need for them, hence this thread caught my eye.

I found a few interesting YouTube vids

and this EEVBlog episode

in the first, the isolation is shown for ground differentials causing issues, whereas dave seems to be talking about protecting from probing and wiring mistakes

One time we built a small product for a client in the industrial sector, which was specifically designed to connect by USB to a laptop. They had a list of various industrial equipment CE standards it had to pass, in hindsight a couple of them were inappropriate for this kind of gadget.

In one of the first rounds of compliance testing, with the product up and running connected to a test laptop, the test engineer induced the specified high current pulses into the cabling. The product under test kept right on working, but the pulse completely fried the laptop! Ironically the unit passed that test, but we couldn’t demonstrate that at the time because the test computer was dead.

We had to retest several more times for other issues. As I recall, we got an exception that allowed us to install a grounding wire from the USB shield to the local earth ground, despite the product not having any ordinary provision for chassis wiring. Everyone agreed that particular spec didn’t apply to a small plastic box with no earth connection, but the customer was too big to change the requirements.

Indeed I would go with an isolated USB adaptor these days.