Author Topic: Crappy USB-RS485 interface rant  (Read 3858 times)

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Offline mikeselectricstuff

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Crappy USB-RS485 interface rant
« on: June 11, 2011, 11:46:01 am »
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Offline thmjpr

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Re: Crappy USB-RS485 interface rant
« Reply #1 on: June 12, 2011, 02:13:27 am »
Excellent video.

There is no channel to channel isolation right? Its just the four optocouplers.
 

Offline mikeselectricstuff

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Re: Crappy USB-RS485 interface rant
« Reply #2 on: June 12, 2011, 09:55:23 am »
Excellent video.

There is no channel to channel isolation right? Its just the four optocouplers.
Correct - it would be more accurate to say the PC is 'Isolated' (to the extent that a ~10mil track gap comprises isolation)  then the 232/485 ports, which all share the same ground.
How useful this would be (if it were done properly) depends a lot on your application, although it is a major cost-saver, and not unreasonable if it's clearly stated in the spec.
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Offline Bored@Work

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Re: Crappy USB-RS485 interface rant
« Reply #3 on: June 12, 2011, 12:40:35 pm »
Don't the modern FTDI ICs all come with a preprogrammed serial number? So there should be no problem to distinguish them.

As for the rest, ouch, what a heap of garbage that box is.

I think it gets worse every day. Yesterday I confiscated a USB hub and power supply from one of the kids. It smelled funny. Today I had a look at the hub, the GL850A had a hole in it, R.I.P. The USB bus power and the power via the external power supply were just connected in parallel. No diodes, no switch.

But the power supply, of course Made in China, took the cake. Two thin, barely isolated wires carrying mains run under the 5V part of the PCB. One already damaged, because it was sandwiched between a standoff and the PCB. The PCB has a cutout below the transformer, but to mitigate this, there is a heatsink straddling the cutout. And both pins of the Y cap are also just slightly away from a heat sink. A few random splashes of solder here and there, and something that looks like bad hand soldering at the main switching transistor.

But the screw holding the enclosure together took the cake. It was hidden behind the sticker on the outside of the enclosure, which was its entire isolation. And isolation it needs. Because it was going right through a tight hole on the PCB, through a track carrying mains with no clearance at all.

What the hell do these incredibly incompetent Chinese assholes who develop and produce this shit think? I don't call them engineers, I call them pieces of shit who either don't give a damm or intentionally try to kill people.

To the unknown scrupulous assholes developing, manufacturing, putting a CE mark on it, and selling a 100 - 240V to 5V, 3A power supply called Moder [sic] YD-4802, PCB marking XH-009 (followed by symbols that look like "fA"), please do the world a favor, do a career change. If you love dead people, why don't you just become an undertaker?
« Last Edit: June 12, 2011, 12:44:43 pm by BoredAtWork »
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Offline mikeselectricstuff

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Re: Crappy USB-RS485 interface rant
« Reply #4 on: June 12, 2011, 12:46:17 pm »
Don't the modern FTDI ICs all come with a preprogrammed serial number? So there should be no problem to distinguish them.
FT232R does, but the high-speed FTx232H ones don't - they need external eeproms. FTx232H also need an option set in eeprom to enable the TXEN funcitonality.
Youtube channel:Taking wierd stuff apart. Very apart.
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