USB control of equipment - Page 1
Forum section: electronics / testgear

author: FuzzyOnion
author_rank: Contributor
timestamp: August 05, 2016, 04:38:48 pm
content: This is about USB instrument control - not USB-based instrumentation, such as Pico, Signal Hound, etc.This is just a high-level question - nothing specific.I've been considering taking some time and fiddling with instrument control via USB. Most of my equipment has either a GPIB, RS232 or USB connection. I'm not even looking at the GPIB as the Fluke meter also has an RS232 port and came with USB/UART cable. But I'm getting specific and that's not my intent.My primary question is do you guys use USB hubs when/if you do control? I'm planning to use a laptop to tinker with this (i7/12GB RAM, W7pro) and of course, it has a limited number of USB ports.Do you use isolated USB hubs? I have a BlackBox branded isolated hub I inherited some time back. It seems that all isolated hubs are bandwidth limited to 12Mbs/sec. This doesn't seem to be a huge limitation as far as a reference to RS232 control. I like this hub and have used in other situations since I've had it. It allows for an external power supply via a terminal block. That's come in handy with a couple ham radio projects in the past when using a linear supply for the hub.So, any general dos/don'ts? Your experience has confirmed what? Whatever I do, don't do .......Thanks in advance for any words of wisdom you may have.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 05, 2016, 05:14:27 pm
content: That hub looks really similar tothe one I haveto save my costly USB 3.0 ports.I'm really happy with it. It already went into current overload a few times when I shorted stuff on the breadboard. Really happy with it.Bandwidth is not an issue when you're not hooking up mass storage stuff or logic analyzers.Somehow it'sreallydifficult to isolate USB 2.0, and they (analog devices) are still stuck at USB 1.1.If you'd want a faster isolated port. Look at USB-Over-IP. Ethernet is isolated up to 1500V, and would theoretically be able to at least approach USB 2.0.

author: free_electron
author_rank: Super Contributor
timestamp: August 05, 2016, 05:20:42 pm
content: the isolated hubs are indeed limited because theyare all based on the same analog devices usb isolator...for what you do : i would make a small usb to rs232 board with an ftdi4232. put digital isolators between the ftdi4232 and the max232 ( or whatever your fancy of transceiver is)now you have a quad isolated rs232 box.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 05, 2016, 07:04:35 pm
content: That is indeed cheaper. I made that alreadyhttp://jeroen3.nl/isoftdiQuestion is, do you really need anisolatedlink? You most likely do not. Try continuity on rs-232 chassis/usb chassis to mains-earth and see if it's beeps. Then you do not need an isolated link.Isolating two mains-earth references appliances would be a waste of money.Unless you're doing something off-spec of course. Such as not having mains earth or using an isolation transformer.

author: ebclr
author_rank: Super Contributor
timestamp: August 06, 2016, 12:11:19 am
content: http://www.coolgear.com/product/usb-isolator-high-speedhttp://intona.eu/en/products