Choosing USB isolator, alternate option - Page 1
Forum section: electronics / beginners

author: sairfan1
author_rank: Frequent Contributor
timestamp: August 31, 2021, 04:06:43 pm
content: I bought a cheap USB isolator from Aliexpress.I was using Arduino Duo with Reprap RAMPS 1.6 module when i increase the voltage to 24v, the voltage regulator installed on Arduino Duo gave magic smoke, luckily everything else was safe including my computer.But after all this my USB isolator stopped working, when I plug it in the computer it start getting hot, any idea, what i can do to save it or its just gone?I attached the picture of my existing one, can somebody tell me what is the dip switch is for?I also want to know some well known USB isolator? (while staying on lower price)OR can i use some serial voltage level convertor like in thispost

author: Renate
author_rank: Super Contributor
timestamp: August 31, 2021, 06:14:12 pm
content: I'm not sure which regulator the arduino uses, but...The 78XX series has a limit of 35 V input, but that's really only for the higher output voltage units.Theoretically a 7805 should be able to tolerate 24 V, but why try.Do you really need USB isolation?Maybe you should isolate somewhere else at a lower data speed.For instance (yes, I know, not your use case) if you are using USB for a serial connection, isolate the serial, not the USB.For your multiaxis thing, some stepper drivers have isolated inputs.

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 01, 2021, 04:26:51 pm
content: What is that dip switch on if for??Does anyone know the reliable USB isolator

author: Gyro
author_rank: Super Contributor
timestamp: September 01, 2021, 06:06:45 pm
content: All of these isolators use Analog Devices ADUM3160 or ADUM4160 isolator ICs. It's worth downloading the datasheet to understand them, the pin functions are very simple. The switch will be there to select the slew rate to match USB low speed orhighfull speed (the opto is there to mirror the same setting on the other side).Each side of the isolator is separately powered to maintain isolation. You don't say what part of the isolator is getting hot, but it sounds as if it got back-driven with greater than 5V when your Duo smoked.As for which ones are reliable - they all use a variant of the ADUM datasheet app circuit, so there's probably little to choose between them (apart from maybe DC-DC converter wattage). Once you look at the datasheet, it is very easy to see what features are implemented on any particular isolator from the product photo. There's not really much that affects 'reliability' so, within reason, the cheaper the better if you're likely to fry one.On the up-side, the isolator almost certainly saved your PC USB port from damage. They are a good idea on the bench when it's possible to use them (anything that doesn't demand 480Mbps USB2 High speed).

author: magic
author_rank: Super Contributor
timestamp: September 01, 2021, 07:36:48 pm
content: Quote from: Gyro on September 01, 2021, 06:06:45 pmHmm, given the lack of markings on the chip I wonder if there is a chance that they don't.

author: Gyro
author_rank: Super Contributor
timestamp: September 01, 2021, 07:46:35 pm
content: I'm not sure if they've been successfully cloned yet - the inductive coupling would be tricky. Maybe ewaste salvage? I'd lay odds that the pinout is identical anyway.Maybe the widespread IC part number removal is such an ingrained practice that they don't realise that their competitors will know exactly what chip they're using.

author: thm_w
author_rank: Super Contributor
timestamp: September 01, 2021, 10:12:23 pm
content: If they actually cloned the ADUM's I don't see why they wouldn't mark their own company part number on it and sell it publicly.Its either lasered off by the person who made them, or lasered off by the e-waste salvage company, then when resold the buyer decided not to bother to blacktop and put new text on it. This is so you could put a custom or recent date code on it.

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 15, 2021, 05:12:07 pm
content: And an-other one has goneThat does not make sense, whenever it receive higher voltage like 12v/24v its just gone, i bought these for about $12 each and its too expensive in that sense that it will protect once only.I need 250,000 speed on serial, is it possible that rather than using USB to Serial with isolator, can I use some IC RS232 for voltage level conversion? for exampleUSB to Serial -> RS232 voltage level convertor -> Arduino -> RAMPSThis way, if higher voltage reach Arduino it will not destroy USBDid anyone use Adafruit USB isolator, does it works good or anybody have any different brand?Is there some other work around like using opto ICs to isolate?

author: magic
author_rank: Super Contributor
timestamp: September 15, 2021, 06:46:36 pm
content: Low voltage UART can be isolated with optocouplers quite easily if not too fast (standard speeds up to 115200 should be OK).No need for RS232 unless it's conveniently already available on existing hardware.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 15, 2021, 09:59:09 pm
content: usb over cat5/6 is cheap(er) and isolated to an extent some units are rated for 4Kv and more many are not. How much isolation do you need. Funtional or safety application, or both?have you looked at, egwww.amazon.ca/USB-Extender-Extension-Adapter-Cat5e/dp/B07C2MCJFY/ref=dp_prsubs_2?pd_rd_i=B07C2MCJFY&psc=1

author: thm_w
author_rank: Super Contributor
timestamp: September 15, 2021, 10:32:15 pm
content: Quote from: sairfan1 on September 15, 2021, 05:12:07 pmDon't blame the isolator yet. You originally said the RAMPS/Arduino board is failing in the first place. That could be passing 24V into the 5V line and feeding into the USB isolator no?Due is rated for 12V maximum and RAMPS is rated for 12V, MAYBE 18V according to here:https://reprap.org/forum/read.php?219,114272Get a proper 3D printer board rated for 24V+. Or regulate the voltage down from 24 to 5V yourself with a suitable converter. Then disconnect the 5V connection on the USB isolator.

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 16, 2021, 02:08:18 am
content: QuoteWe can remove power supply to Arduino Duo by removing D1 on RAMPS board that's how we can use it with 24v with RAMPS and arduino will be getting power from USB,QuoteThat's what happening, as its happened twice, once when I increased the voltage to 24vand it also happened once again while I was using 12v, so for sure its not the 24v and also i have been using this setup for about a month a it was working all good.Am I misunderstanding the USB isolator? like i expect when circuit got short and 12v made path to USB isolator, I expect that USB isolator will protect this higher voltage? though at some level it does as nothing happened to my computer's USB port but isolator itself was gone

author: magic
author_rank: Super Contributor
timestamp: September 16, 2021, 06:04:14 am
content: Quote from: Terry Bites on September 15, 2021, 09:59:09 pmWaste of time. The problem is not isolation, but the isolator IC failing from supply overvoltage on one side.Optocouplers may also fail like that, but they are cheaper to replace at least.And it goes without saying, OP, fix your circuit so it stops blowing up the isolator in the first placeQuote from: sairfan1 on September 16, 2021, 02:08:18 amWell, it works as expected. The point of isolation is to prevent current flow from one side to another (device / host). That's why your computer is still alive. The chip cannot withstand unlimited voltage on its supply or data pins on either side. Genuine ADuM3160 is rated 6.5V maximum.

author: Gyro
author_rank: Super Contributor
timestamp: September 16, 2021, 08:20:41 am
content: Quote from: sairfan1 on September 15, 2021, 05:12:07 pmYes, the isolator again worked perfectly. It sacrificed itself to prevent you from blowing up your PC for the second time. Even at the rate you are destroying them, $12 for each PC rescue is excellent value!You are clearly not understanding the isolator's purpose. As others have said, you need to ensure that your RAMPS/Arduino stops pumping 12-24V into it.Did you download and study the ADUM3160 datasheet as I originally suggested? Conform to the datasheet specifications and you will not blow up the isolator.

author: magic
author_rank: Super Contributor
timestamp: September 16, 2021, 08:44:32 am
content: Quote from: Gyro on September 16, 2021, 08:20:41 amBTW, aren't those poor Arduinos getting blown as well? Or are they saved by some on-board regulator?

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 16, 2021, 04:38:28 pm
content: QuoteOn first accident my Arduino was safe, as by mistake i put 24v on RAMPS but later i removed D1 (Diode) on RAMPS that directs main power to ArduinoBut 2nd time it was a true accident, RAMPS was setup on 12v because of some unknown reason stepper motor driver DRV8825 installed for X Axis gave magic smoke that caused the short circuit and current passed to Arduino, so Aduino gone as well.

author: magic
author_rank: Super Contributor
timestamp: September 16, 2021, 06:31:42 pm
content: I'm not familiar with that 3D printer stuff so not sure what failed and why.In general, it's good to have few-kΩ resistors between MCUs and high voltage ICs like motor drivers. Then, even if the driver fails short, resistors limit the current into protection diodes of the MCU to a few mA and give it a chance to survive. Also, some 5.1V or 5.6V zener from VCC to ground to absorb that current in the event it exceeds normal power consumption of the MCU and causes VCC to raise uncontrollably.I see you asked for an optocoupler capable fo dealing with 250kbaud UART. That's probably beyond the reach of the cheapest stuff, but there are some fancy ones that could do it, I have personally tried H11L1 and it was OK up to hundreds kbaud. Not very expensive, $1 a piece it seems. Will tolerate up to 16V on the output side without any extra protection effort.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 16, 2021, 06:54:18 pm
content: The standard fast Optocouplers are 6N137. They are supposed to be good for 10 MBit/s. So good enough for the AVRs UART.They are a bit large (typical DIP8) though. Essentially the same is also available under different names. For 100 kBaud the 6N138/9 may also be fast enough. If in doubt add some transsil to avoid excessiver voltage for the supplies.If the signal goes to an UART an the Arduino, there is no need to use an USB isolator. A standard USB to UART module and than isolated CMOS level UART is the logical way.

author: magic
author_rank: Super Contributor
timestamp: September 16, 2021, 07:09:52 pm
content: Nice stuff and inexpensive, I like itBut also more sensitive to output supply overvoltage and still the annoying open drain output.

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 16, 2021, 09:41:47 pm
content: QuoteSounds good, do you think if i use RS232 to interface Arduino serial port to communicate at 250,000 baud rate, it will be good enough to handle accidents at 24v 4Am

author: magic
author_rank: Super Contributor
timestamp: September 17, 2021, 05:26:09 pm
content: Kinda depends on how dodgy the USB/RS232 dongle is and how dodgy the 24V PSU is and whether the 24V could become 48V or 240V one day...Isolation is safer.

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 24, 2021, 09:53:58 pm
content: I have a PSU HP 6543A bought it as hobby but never used it, its in very great shape, I wanted to know can it help to avoid such situations like when stepper driver got short circuit at that point it quickly cut off the power automatically and reduce the loss? Just sharing thoughts on it, have no idea of its capabilitiesI have ordered different types of modules, I will keep posting how they behave.

author: thm_w
author_rank: Super Contributor
timestamp: September 25, 2021, 01:03:11 am
content: Quote from: sairfan1 on September 24, 2021, 09:53:58 pmhttps://www.keysight.com/ca/en/assets/7018-03196/data-sheets/5990-9298.pdfDon't think it has any overcurrent trip, so best you can do is set the current limit to reasonable level for first power up (~1A?) and keep an eye on it. Once you print you'll have to raise the current up higher.Most stepper modules should handle output short circuits, but, best to keep all the wiring clean, verify crimps/connections/etc before powering up.

author: sairfan1
author_rank: Frequent Contributor
timestamp: September 25, 2021, 01:43:20 am
content: I attached the picture, it has buttons Protect, OCP (over current protection), OV (over voltage) i have no experience using such PSU just bought for hobby. I was thinking may be its the best time to take advantage of it, (if its helpful in such scenarios) i hope this may reduce the possibility of damaged down to other connected devices like arduino.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: September 25, 2021, 11:47:56 am
content: 6N137 or 6N135 are my default choice for USART isolation. If you use a USB->Serial module, there are no additional components needed

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 25, 2021, 12:16:00 pm
content: Quote from: sairfan1 on September 15, 2021, 05:12:07 pmThese things can tolerate a reasonably high voltage (1kV or more) between the primary and secondary side but the power supply voltage on either side can just be 5.5V maximum when measured from it's own GND pin. Just as your microcontroller chip. Same applies for optocouplers. If you put 12V over the LED of an optocoupler, then it releases the magic smoke and it stops working.High speed optocouplers also have built-in electronics for signal conditioning. For example, the 6n137 mentioned earlier can also only go to a maximum of 7V on the "output side" and will also get fried when you apply 12V to it.So the real solution is to find out why you keep putting high voltages on low voltage IC's and then stop doing that.A common fault is if you have clipped off wires lying on your desk and you lay a bare PCB over it. This easily generates shorts at random places in your circuit.The cheap USB isolators are also just breakout boards, and part of a bigger project.