USB Cable Signal Integrity - Page 1
Forum section: electronics / beginners

author: AlwaysAbia
author_rank: Contributor
timestamp: September 05, 2024, 06:51:25 pm
content: I'm using a USB camera module for a project I'm working on. The project has to spinning parts on which this camera is mounted on, both of the spinning parts have slip rings installed.The camera has a 4 pin universal connector socket and a cable with one side USB and one side the connector that connects to the camera. Connected straight to the laptop, the camera works fine, but to keep my range of motion, I cut up the cable and fed it through the slip rings, and then resoldered the usb side on the bottom to connect to the laptop, which caused the laptop to not recognize the USB device anymore. Is it possible that by cutting and resoldering wires I damaged the signal integrity and so the USB device fails to interface? If so, what can I do to make this setup work.Note 1: I have triple checked that my cable connections are right, will quadruple check tomorrow.Note 2: the total length of the wire is less than a meter.Thanks in advance!

author: Andy Chee
author_rank: Super Contributor
timestamp: September 05, 2024, 06:56:26 pm
content: I cannot imagine slip rings will be good for USB signal integrity!Are you sure you cannot use a WiFi camera in your application?Another outside of the square solution, is a rotating mirror assembly above the fixed camera. You will need to re-orient the image in software processing.

author: AlwaysAbia
author_rank: Contributor
timestamp: September 05, 2024, 07:20:40 pm
content: I'd rather not use an extra ESP to get a wifi camera working, unless there's another way, maybe it's possible to twist the slip ring cables around e.o. and wrap them in a faraday cage like foil in an attempt to improve signal integrity.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 05, 2024, 07:51:41 pm
content: How about using more slip rings?I assume you only have four slip rings; V+, D+, D-, GND.If you use an eight ring connector; V+, V+, D+, D+, D-, D-, GND, GND.

author: magic
author_rank: Super Contributor
timestamp: September 05, 2024, 07:52:55 pm
content: I suppose it's not about noise, EMI or anything like that, but wave impedance is all screwed up at the slip rings. Maybe if they were very small and very close together... Or maybe still not.Are slower devices like keyboards working?

author: radiolistener
author_rank: Super Contributor
timestamp: September 05, 2024, 08:12:21 pm
content: Quote from: AlwaysAbia on September 05, 2024, 06:51:25 pmYes, high speed transmission lines are very sensitive to impedance, so even a large solder droplet may affect transfer speed. If you cut the cable in the middle and insert some circuit it will affect cable impedance at that point. But if soldering is accurate, it should works with slow USB2 devices.

author: gcewing
author_rank: Regular Contributor
timestamp: September 07, 2024, 10:23:06 am
content: It seems that slip rings designed for USB exist:https://www.rotarx.com/en/slip-rings/usb-slip-rings/

author: CaptDon
author_rank: Super Contributor
timestamp: September 07, 2024, 12:24:15 pm
content: Are your slip rings home made? Slip rings are incredibly noisy electrically. One 'brush' per slip ring will never work. You will need at least two brushes per slip ring and I would suggest a USB speed limit. USB 3.0 may not work reliably while the older slower standards may possibly work with this less than ideal setup. Slip rings have always been a trouble point for radar systems and some of them use 4 brushes per ring spaced 90 degrees apart for full coverage and impedance stabilization and on top of that may use 2 slip rings per signal path totalling 2 rings and 8 brushes per signal line. Less is less and cheap won't cut it.

author: AlwaysAbia
author_rank: Contributor
timestamp: September 07, 2024, 03:38:22 pm
content: Thanks for replying!I got it working.I got rid of the soldered connections and western union spliced those connections instead, and I wrapped the data+ and data- wires around each other spirally because I had heard that USB cables do that. Although it's working, I'm not sure how stable it is, I'm thinking of putting aluminum foil around it to act as a noise shield, and maybe a ferrite core, both of these steps could very well be overkill though.