USB isolation from mani earth for bench scoping? - Page 1
Forum section: electronics / testgear

author: Chriss
author_rank: Frequent Contributor
timestamp: July 22, 2019, 04:53:53 pm
content: Hi!I'm not sure does I'm in the right section of this forum, but hope yes.I always worry about when I connect my scope to mine development board for AVR which is connected/powered from my desktop PC USB port.My scope is a Siglent SDS1052DL+ scope, the PC usb GND is connected to mains GND earth, together with my scope of course.somehow I always have some strange feeling when I try to connect my scope probe to the dev board to check for signals.Is there any/cheap way to make the usb port complete isolated from the dev board but still to use it for powering and programming the board?For now I never experienced any problem but I'm afraid, one day sht will happen...Thank you.

author: Cosmic Osmo
author_rank: Newbie
timestamp: July 22, 2019, 05:05:36 pm
content: Itprobablyisn't really an issue, because the scope ground and the PC's ground are probably both tied to mains earth. That said, an overabundance of caution can't be a bad thing.USB wall warts are generally isolated, so use one of those to power your project while probing, or a USB battery bank.For programming, either get a USB isolator ($30 from Adafruit or wherever) or just don't probe while programming.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 22, 2019, 05:05:57 pm
content: you have many usb isolators on Ebay under 20$ usd 1.5 k and 3 kv isolation depending on the choosen modelsI had no problems with them

author: Chriss
author_rank: Frequent Contributor
timestamp: July 22, 2019, 07:17:59 pm
content: Assume something like this will do the job:https://www.ebay.com/itm/USB-1500v-Isolator-Isolator-ADUM4160-USB-To-USB-ADUM4160-ADUM3160-Module/263558200420?hash=item3d5d4afc64:g:VVYAAOSwmMNcRWGS

author: 0culus
author_rank: Super Contributor
timestamp: July 22, 2019, 07:40:54 pm
content: Quote from: Cosmic Osmo on July 22, 2019, 05:05:36 pmI probe circuits connected to USB a lot (FPGA boards mostly), both with o-scope and logic analyzer with no issues. HOWEVER, if you want to take precautions, I'd recommend instead powering your DUT with a quality DC supply that has floating outputs and solid current limiting. If you short something out, a battery bank will probably happily deliver a ton of current.

author: Chriss
author_rank: Frequent Contributor
timestamp: July 23, 2019, 04:56:54 pm
content: Ok, I bought one of these USB isolator from the link above.I will report here when it arrive.I hope this little gadget will give me more peace while scoping...

author: Zucca
author_rank: Unknown
timestamp: July 25, 2019, 02:16:09 pm
content: I bought it too... since in my german apartment the PE is just the N wire.Unfortunately it is just not a high speed but only 12Mbps.

author: Chriss
author_rank: Frequent Contributor
timestamp: July 25, 2019, 02:56:02 pm
content: 12Mbps should also do the r/w of the uC but it will isolate the gnd prom the pc... I hope ao. :-)Sent from my SM-J500F using Tapatalk

author: David Hess
author_rank: Super Contributor
timestamp: July 25, 2019, 09:37:52 pm
content: I would worry also.USB isolators are available which also supply isolated power.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 25, 2019, 11:47:05 pm
content: If you want a true isolation, use an isolation transformer on the main equipment you need to be connected withAn ADUM4160 normaly is safe for most app, sure you dont always get the full usb speedsome claiming a full isolated speed up to 100$ usd ??https://www.mouser.com/datasheet/2/214/kxusb150ds-179743.pdfhttps://www.mouser.ca/new/keterex/keterex-usb-150-isolator/https://hifimediy.com/high-speed-usb-isolator-480Mbpshttps://www.virtins.com/USB2ISO.shtml