USB Hub - Page 1
Forum section: electronics / projects

author: MacAttak
author_rank: Unknown
timestamp: May 18, 2013, 05:22:44 pm
content: I'm interested in building out my own USB hub, partially out of curiosity but also because I haven't found ideal hardware for what I want.At a minimum, it needs six or seven ports (eight or nine would be ideal). USB3 speed is highly preferred because one of the devices is an external SSD used to run virtual machines. Some of the devices have a relatively large current draw - most notably my Superdrive DVD unit that I haven't been able to make work using any hubs yet (so far it only seems to work when plugged directly into my macbook). So I figure it might as well be powered, and capable of supplying .5A to each port.I'm looking for any pointers on where I should start doing research. I understand that there are some fairly stringent signal routing requirements at the very least.I realize this might be well beyond the reach of my current skills, but even if I fail or give up before fabrication, then I will at least have learned a little bit in the process.Might as well also just go ahead and ask if anyone is familiar with a decent-quality commercial hub that I might be interested in? - in case this project turns out in fact to be too difficult for me right now.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 18, 2013, 05:26:08 pm
content: USB 3.0 is going to be very difficult. USB 2.0 is much easier, but not much point when there are plenty of cheap but good hubs that you can modify.So buy a cheap but good USB hub, then put the circuit board in a bigger enclosure, complete with improved heatsinking, more or better bypass caps, a good PSU (old PC PSU works great), etc.

author: ivan747
author_rank: Super Contributor
timestamp: May 18, 2013, 06:52:09 pm
content: Quote from: MacAttak on May 18, 2013, 05:22:44 pmThe Superdrive might draw 1A. Macs have a special mode where a device such as an iPhone or iPad can request extra current, up to 1A. This allows the devices to be charged. Maybe the Superdrive can only work in this mode or expects to get the 1A when connected to the Mac, but for some reason it fails to figure out it is connected to a hub.Just a guess, though.http://forums.macrumors.com/showthread.php?t=420281

author: MacAttak
author_rank: Unknown
timestamp: May 18, 2013, 08:18:40 pm
content: Hmm that's pretty much what I suspected about the Superdrive (high current requirement), but from that forum link it also sounds like simply supporting a full amp on an external hub port probably won't work either. In that case, I guess the Superdrive would have to remain directly attached to a dedicated USB3 port, and everything else would need to be together on a hub attached to the other port (Macbook has only two usb ports).

author: elgonzo
author_rank: Unknown
timestamp: May 18, 2013, 08:35:09 pm
content: If the motivation is mostly about getting an Apple Superdrive DVD to work while connected to a hub, then forget it. There have been numerous reports and complaints (amongst them customer complaints on the AppleStore and Amazon) that the Superdrive does not work on hubs, but must be connected directly to the Mac (presumably due to a crippled drive firmware; a result of attempted vendor lock-in and/or planned obsolescence).

author: ivan747
author_rank: Super Contributor
timestamp: May 18, 2013, 09:41:14 pm
content: I believe the reason they only give you 2 ports is because they expect you to use Bluetooth mice and keyboards. A USB 3 hub is not a trivial thing at all and needs things like controlled impedance PCBs and such.If I were you, I would make a USB hub with enought ports for all my devices. One 4 port chip with 2 connectors supplying 500mA each, and a 3rd and 4th ones connecting to other hub chips only capable of 100mA. On the 100mA goes you test gear, programmers, mouse and keyboards.

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: May 19, 2013, 12:14:14 am
content: I have done a bit reasearch on this issue before and the best circuit i could find was thishttp://www.analog.com/static/imported-files/images/verified_circuits/CN0158_00_1024.gifSource sitehttp://www.analog.com/en/circuits-from-the-lab/cn0158/vc.html

author: ivan747
author_rank: Super Contributor
timestamp: May 19, 2013, 12:43:32 am
content: I think it is more or less obvious the hardest part of designing this properly is designing the voltage regulation with current cutoff (or limiting, I haven't read the spec.) properly and giving each port the amount of current it is going to be rated at and no more. That and also laying out the PCB in a way so that signal integrity is preserved and at the same time keeping everything small, cheap and simple.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 19, 2013, 03:39:07 am
content: Just use a bunch of PTCs or even disposable fuses as it's very rare to get a fault that blows the fuse. (At least for finished products - you probably want self reset and an ammeter on the ports for experimental hardware.) I suggest having at least one port at 2A for charging tablets and then using 2A PTCs for the remaining groups of 4 ports. (And, of course, a dedicated port for experimental hardware, with overvoltage protection on all lines.)

author: Bored@Work
author_rank: Super Contributor
timestamp: May 19, 2013, 06:17:29 am
content: Quote from: MacAttak on May 18, 2013, 05:22:44 pmDownload and read the USB specificationshttp://www.usb.org/developers/docs/

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: May 19, 2013, 09:34:10 am
content: Quote from: Bored@Work on May 19, 2013, 06:17:29 amI am sorry but i think that this is imposible for everyone!!! its over 600 pages(all docs combined)

author: amyk
author_rank: Super Contributor
timestamp: May 19, 2013, 11:00:04 am
content: By "building your own" do you mean using off-the-shelf hub controllers or designing your own hub ASIC?I'll assume the former...There are no single-chip USB 3.0 hub controllers that I could find with more than 7 downstream ports so if you want more you will need to chain them. You can look at the USB5537 if you want 7 ports (of which only 4 are 3.0).Hereare some rather large commercial hubs.Do read the USB standards...

author: Bored@Work
author_rank: Super Contributor
timestamp: May 19, 2013, 11:29:53 am
content: Quote from: ChrisGreece52 on May 19, 2013, 09:34:10 amNo, it is not. Reading standards like this is normal engineering work.

author: amyk
author_rank: Super Contributor
timestamp: May 19, 2013, 11:40:21 am
content: Quote from: Bored@Work on May 19, 2013, 11:29:53 amAnd I find the USB one is already far more readable than something like e.g. 802.11...

author: ivan747
author_rank: Super Contributor
timestamp: May 19, 2013, 11:54:01 am
content: Quote from: amyk on May 19, 2013, 11:40:21 amThe day I have to read this on a 3 day deadline to get something ready, I'm gonna shoot myself.

author: SeanB
author_rank: Super Contributor
timestamp: May 19, 2013, 04:03:28 pm
content: Quote from: ivan747 on May 19, 2013, 11:54:01 amThat is the time you get 4 cases of Red Bull, a portapotty and a case of Jacobs Extra strong to mix with the red bull as a kicker. A few little purple tabs might help as well.The next week you will be sleeping.

author: Monkeh
author_rank: Super Contributor
timestamp: May 19, 2013, 07:38:35 pm
content: Quote from: ChrisGreece52 on May 19, 2013, 09:34:10 amSorry kid, but reading specifications and documentation is not optional.

author: abyrvalg
author_rank: Frequent Contributor
timestamp: May 19, 2013, 10:51:06 pm
content: If you care about 3.0 drive's speed, better don't use it on a hub (bandwidth is shared between all devices plugged into same hub, while 2.0/1.1 devices create additional load on a hub - transaction translation between different speeds). Leave the drive in dedicated 3.0 port and use a 2.0 hub for the rest.

author: Neilm
author_rank: Super Contributor
timestamp: May 20, 2013, 05:59:53 pm
content: Also at these speeds you will have to start looking at the black art of signal integrity.Neil