Need some help interpreting reply from EBay seller of USB device - Page 1
Forum section: electronics / beginners

author: nzo
author_rank: Regular Contributor
timestamp: November 08, 2015, 09:00:06 am
content: Hi all,Some months ago I purchased a USB Isolator from EBay, so I can hook up my software/hardware oscilloscope to my PC, with the protection such an isolator offers.The EBay page that offers the device describes it as a:Low noise USB Isolator,short circuit protection, ADUM4160, Hifi, JTAG isolation.The sellers description is as follows:This module is designed based on ADUM4160, a Full/Low speed 5kV USB isolator. It's a good choice for appilcations that isolation is needed between PC and peripheral device. This module features a low noise power that is very suitble for Hifi devices. In additon, overcurrent protection circuit is included. When short circuit happens in your device, the power supply will be cut off to protect both your device and this module. A red LED will light when overcurrent condition occcurs.Features :USB 2.0 compatibleLow and full speed data rate: 1.5MBps and 12Mbps, selected by jumperBidirectional communicationOn-board LDO regulator for low noise applicationsWide power input range: +6V to +24VDownstream port overcurrent protection( This function is very useful for protecting your device from damage when short circuit happens)The USB 2 compatible was the clincher for me. However, when I tested the isolator, the PC display was slow and "jaggy" - not at all what I would expect from USB2. I queried the slow speed with the seller, and said:I'm sorry to give you this feedback. This item is *NOT* USB2 capable. This makes it useless when using this isolator with a USB oscilloscope. The PC screen is very slow to update because the isolator uses the old slow USB.The seller replied:Aha! I understand what you mean. Once a Russian guy also wanted to use an USB isolator for his PC based USB virtual oscilloscope.This module is based on Adum4160 device,it's definitely USB 2.0 compatible in fact.I'm not sure if you know that USB 2.0 standard includes (low speed/full speed/high speed) three speed modes.The oscilloscope must works in high speed mode to transfer high volume data to PC.This module only supports low speed and full speed. So the performance must be degraded when you connect your scope to this module. A device which is USB2.0 compatible doesn't mean it must support all the speed modes. l haven't seen a high speed isolator for USB that could supports 480Mbp. Maybe it's difficult to achieve this performance in technology.Thank you for your feedback. I hope my answer will helpful for you.Finally to my question. Does what the seller said make sense? I don't know enough to be able to make up my own mind, hence this post.Thank you!!!

author: wraper
author_rank: Unknown
timestamp: November 08, 2015, 09:26:36 am
content: QuoteThen what did you expect.12 mbps is indeed USB2.0full speed.480mbps ishigh speedwhich wasn't claimed to be supported.Also good luck finding 480mbps capable USB isolators.

author: ataradov
author_rank: Super Contributor
timestamp: November 08, 2015, 09:27:01 am
content: Yes, it makes sense and it is true. ADuM4160 only supports Low and full speed modes (1.5 Mbps and 12 Mbps). High speed (480 Mbps) is not supported by this device. It is very hard to galvanically isolate 480 Mbps link.Device still stays compliant to USB 2.0 spec.Correction: It is very easy to galvanically isolate 480 Mbps link using fiber optic cables. It is hard to do so cheaply and in one small IC.

author: Whales
author_rank: Super Contributor
timestamp: November 08, 2015, 09:34:35 am
content: Quote from: ataradov on November 08, 2015, 09:27:01 amPresumably then opto-isolators (+amplifiers) can do the job?

author: Ian.M
author_rank: Super Contributor
timestamp: November 08, 2015, 09:35:55 am
content: Quote from: nzo on November 08, 2015, 09:00:06 amUnfortunately, YES.http://www.usbmadesimple.co.uk/ums_1.htmIts an issue that's well known to those of us who regularly work with USB and high voltage circuits. If you need 'High' speed, and your bankroll's thinner than a Mafia Boss you end up floating a sacrificial laptop or netbook, running from batteries with a wireless keyboard and mouse for safety. If you need to keep OSHA/HSE happy, you have a perspex box to put it in! See the discussion here:https://www.eevblog.com/forum/chat/high-speed-usb-isolator/

author: ataradov
author_rank: Super Contributor
timestamp: November 08, 2015, 09:37:03 am
content: Quote from: Whales on November 08, 2015, 09:34:35 amYes, but not regular LED-based isolators. You will need lasers and other fiber-optic stuff.I believe there are actual High Speed isolators with physical optical cables separating two ends. But they cost some crazy money.

author: Gyro
author_rank: Super Contributor
timestamp: November 08, 2015, 10:08:24 am
content: I don't really think you have any sensible cause complain or give the seller bad feedback, his description looks very clear. He clearly states the device used and that it supports USB Low and Full speeds and the relevant bit rates. Nowhere does it claim 480Mbps.The listing states "USB2 Compatible", which is quite true - you can plug it into a USB2 Port, and you can plug a USB2 device into it. Both will default to the highest speed supported by all of the device in the chain...USB Full Speed in this case. It was you who introduced the term "USB2 Capable" in your contact with the seller, and the device clearly doesn't claim to be USB2 speed capable.You need to do basic homework before buying anything.

author: Howardlong
author_rank: Super Contributor
timestamp: November 08, 2015, 10:22:14 am
content: Regrettably I concur with others here, in fact you'll probably find it's USB 3.0 compatible too.The biggest cock up is the USB nomenclature, believe me it takes a while to be confident in knowing the difference between USB high speed and USB full speed. It's a typical result of a standards body.Almost all of the PIC microcontroller range is USB 2.0 compatible, but only a few of the very latest PIC32MZs support high speed 480Mbps. There are other components to the USB 2.0 stack besides 480Mbps such as OTG.In short a USB 2.0 device doesn't have to support 480Mbps, but a USB 2.0 High speed device does.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 08, 2015, 05:30:24 pm
content: This is a case of being technically correct, but probably ethically wrong. Due to backwards compatibility elements of USB 2.0, the device is fully compliant. But just about everyone on earth expects USB 2.0 devices to be better than USB 1.x devices. This device is no better than USB 1.0. I suspect the seller understood the psychology and the degree of ignorance about the detail meaning of low, full and high speed USB and carefully worded his ad to exploit this. Almost all salesmen do this, and it is why the profession has little respect.

author: Gyro
author_rank: Super Contributor
timestamp: November 08, 2015, 07:19:13 pm
content: QuoteI think it's unfair to the seller to describe it as ethically wrong. The description is very clear, it explicitly states speeds supported and device used. Analog Devices themselves describe the ADUM4160 as "USB2.0 Compatible".

author: ataradov
author_rank: Super Contributor
timestamp: November 08, 2015, 07:50:20 pm
content: Quote from: ErikTheNorwegian on November 08, 2015, 10:28:29 amBoth products require to get a quote for the price. When this happens, you know you are not going to like what you hear in response

author: dadler
author_rank: Unknown
timestamp: November 08, 2015, 08:15:50 pm
content: ADUM4160 is explicitly only a low/full speed USB device:http://www.analog.com/en/products/interface-isolation/isolation/standard-digital-isolators/adum4160.htmlEven the Adafruit version is explicit about the supported speeds:https://www.adafruit.com/products/2107

author: DimitriP
author_rank: Super Contributor
timestamp: November 08, 2015, 09:08:56 pm
content: Quote from: wraper on November 08, 2015, 09:26:36 amJust a few thoughts:So far, three pieces of information have not been revealed:A) Was the isolator connected with the jumper to the correct speed?B) What is the speed the USB oscilloscope specifies as required?C) Has the OP tried a different cable from the isolator to the computer's USB port ?A) The OP hasn't mentioned setting the jumper to the correct position.B) The OP hasn't mentioned which USB 'scope he has.After a quick search for USB 'scopes I looked up a Hantek and it specifies 12Mbps but his may be different.C) Sometimes USB cables can drive you crazy by appearing to "work good" except they are not.

author: Whales
author_rank: Super Contributor
timestamp: November 09, 2015, 12:27:55 am
content: Alternative if latency is not an issue:Get and old/cheap computer that supports the USB speed you want. Get a pair of wifi dongles that will have a high enough data transfer rate and setup a (normal or adhoc) connection between the sacrificial computer and main computer. Use a USB over IP solution (like usbip, linux).

author: amyk
author_rank: Super Contributor
timestamp: November 09, 2015, 01:02:52 am
content: Quote from: ataradov on November 08, 2015, 07:50:20 pmI found a price for it, on what appears to be an "audiophile" site, and it's actually not all that extravagant if you consider it a piece of test equipment:http://www.thewelltemperedcomputer.com/HW/USB_Isolator.htm($230)

author: Howardlong
author_rank: Super Contributor
timestamp: November 09, 2015, 11:49:47 pm
content: Quote from: amyk on November 09, 2015, 01:02:52 amI'm sure they'll upsell you an oxygen free USB cable to go with that, hand braided on the thighs of virgin mermaids using the fibres made from unicorn nether regions.

author: ataradov
author_rank: Super Contributor
timestamp: November 09, 2015, 11:52:12 pm
content: Quote from: Howardlong on November 09, 2015, 11:49:47 pmIt has noting to do with audiophiles. $230 is a reasonable price for a functioning USB HS isolator. That's about how much I would have expected it to be anyway.

author: Howardlong
author_rank: Super Contributor
timestamp: November 09, 2015, 11:57:51 pm
content: Quote from: ataradov on November 09, 2015, 11:52:12 pmIndeed, I just went off what the poster had quoted (I bolded the "audiophile" deliberately in the quote). It would appear that the site quoted is indeed reputablehttp://www.thewelltemperedcomputer.com/HW/USB_cable.htm

author: Gyro
author_rank: Super Contributor
timestamp: November 10, 2015, 10:07:00 am
content: They don't appear to intend it specifically as an 'Audiophile' product. Applications listed are:Industrial automation systemsMeasurement devicesEnvironments requiring safety insulationMachine protectionBroadcast and Studio