PSA: many USB UART adapter boards and cables tend to fail because they're literally just an FT2232 (legit or clone) or CH340 chip under the hood with the pins broken out to a header. this is true of the cheap AliExpress ones and most branded options too.
they have almost no protection against ESD, overcurrent (e.g. TX short to GND), overvoltage, or ground loop issues. they're non-isolated so ground voltage deltas can mess them up too.
look for an isolated model for higher reliability:
@gsuberland my issue with CH340 and FT2232 is less the lack of ESD protection on most devices, but the bad tolerance of level shifts/lack of load driving and/or missing pull up on inputs. resulting lost characters or even totally garbled results.
my experience with CP2102 based adapters has been better during the last decade. (yes, they are not as cheap as most CH340, PL2303 and FTs)
@adorfer the isolated option largely solves those deficiencies. in fact if you leave it in 3.3V mode it ends up being tolerant of 5V and 3.3V devices at the same time because Vgs(max) on the logic level conversion FETs inherently must exceed 5V anyway, and I've yet to meet a device with a TTL UART that won't register 3.3V as logic high.
@gsuberland I've generally found that genuine FTDI parts fare much better in the longer term (and with less careful hands) than most of the other / cheaper options.
I worked with someone a while ago who had problem-after-problem, until I encouraged them not to just buy a random cheap widget and get a "real" FTDI one instead.
If I had the choice and budget, I'd pick an FTDI over others. Optos are a bonus.
@attie yup, but unfortunately the only way to know you're getting genuine FTDI is if you're buying one from some major test equipment brand, at which point why bother? just get the isolated one for £20.
@attie in fact I'd argue that a cheap isolated one with a knock-off FTDI clone is better than a genuine non-isolated one with real FTDI, because if you accidentally shove 48V into it the cheaper isolated one will save your laptop.
the one I bought, pictured above, is sold on Amazon as "DSD TECH SH-U09C3" for just under £20. but that's just one example - you can find them on eBay and AliExpress for even cheaper.
one of the neat things about this design, which is shared by almost every isolated USB UART dongle I've seen, is that the IOs on the front are connected to the four jellybean SOT23 package MOSFETs used for logic level conversion, which then connects upstream to the optoisolator. as such, despite the lack of any discrete protection features (TVS diodes, zener clamp, current limiting resistor arrays, etc.), the MOSFETs can handle a enough abuse that it's very hard to kill the board.
and, even if you do somehow kill one of the logic level conversion FETs, they're jellybean SOT23s so it's trivial to replace them if you have any experience with SMD soldering.
(note: "trivial" seems to be a matter of debate here; I may be biased to thinking it's easy due to experience doing this kind of soldering work, YMMV)
@whitequark hmm, really? I've never had trouble with them. desoldering braid to remove the solder from the 2-pin side, then heat the other side and lift.
genuine FTDI chips can take a reasonable amount of abuse. most of these use fake FTDI chips or clones like the CH340 or CP2102, which tend to be more fragile, and it's impossible to tell from a photo which one you're getting.
however, I'd argue that this is mostly irrelevant in practice. a real FTDI chip in a non-isolated design offers less protection than a fake FTDI chip in an isolated design, and the isolated one is still likely to be cheaper!
case in point: if you accidentally connect a 24V power rail to the board, the non-isolated design with the genuine FTDI chip is unlikely to protect your USB port from getting fried, whereas the isolated design most likely will save you.
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