I’ve started building my own SensorGnomes this year with Raspberry 3B+ but have some stations coming up where I’ll need more than the 4 embedded USBs. Can anyone share any links for vetted/compatible USB hubs that can plug into one of the ports (assuming this is possible)? I believe I’ve seen D-link hubs used for this in the past (that seem out of stock everywhere), but wasn’t sure what else is possible. I’m new to the DIY thing (rather than buying premade), so any info is appreciated!
I know we’ve used the D-link ones in the past. The hub that we’re thinking of switching to using is made by Sabrent and can be purchased for about $38 on Amazon. It seems to work well in the lab, but it’s worth noting that we haven’t yet deployed one in the field and it requires 12 volts rather that D-link’s 5 volts.
We’ve also started to put together a short list of other USB hubs on Amazon that might work well for sensorgnomes, but none of these have been purchased and tested if you’re interested.
If your list of other USB hubs on Amazon include any 5V I would be interested in potential testing. You can send them to: mack.w.frantz@wv.gov. Thanks!
In general the key is to get Multi-TT hubs, which are harder and harder to come by… A recent D-Link 7-port hub I purchased wasn’t (it looked the same as the previously good model and it was pricey).
If you use a 3B (plus or not) you get a Multi-TT root hub. I would recommend to get USB splitters that are short (~6”) cables with two USB ports and then to plug one FCD and one other device (like a CTT radio or cell modem, or GPS) into the other port. You can also plug as many FCDs into the 3B’s ports as you have space, e.g. 3 into 3 ports and then the other devices into a hub on the 4th port. If you buy the splitters be sure to buy the ones that support 2 USB devices (thus contain a hub chip) and are not just “power splitters” to provide power to two devices.
If you use a 4B the splitters work as well, the “plug 3 FCDs into the ports and everything else on a hub” doesn’t work ‘cause the 4B’s hub is not Multi-TT.
Hi Mack
This is the USB hub I’ve been using to run my vocoders for digitial voice transcoding, It does very well running on a Raspberry Pi 4 or 5, I’ve found that the Pi 3 B+ is lacking in the processing speeds to handle multiple USB’s devices. Amazon.com
Rick
That’s a nice USB3 hub, but none of the Sensorgnome devices are USB3, and it’s unknown whether the USB1 support in this hub is Multi-TT or not… Maybe you can check that?
Most of the hubs are usb 2.0 backward compatible., I have an earlier version 6 channel Vocoder that uses USB 2.0 that’s connected and it works as well, There are several hubs that claim backward compatability, DLink, Sabrent , Adafruit , It’s usually noted in the specification if it is or isn’t,always check before purchasing..
The Pi 3 B+ should however negotiate the bandwidth at the USB 2.0 speeds with a backward compatible hub.
In case the hub doesn’t support Mult-TT as TvE mentioned,
You will need to use an older USB 2.0 hub or upgrade to a pi 4 or Pi 5?
This is my understanding of how it works.
In USB 3.x specifications, electrically the USB 2.0 interface is completely independent from SuperSpeed path, it runs in parallel, on dedicated old-style D+/D- wires. Unlike USB 2.0, USB 3.x doesn’t introduce “TT” (Transaction Translator), the USB 3.x super-speed transactions cannot be “translated” into HS USB 2.0 transactions.
However, internal pipes of the controller and system interfaces (internal fabric) have limited bandwidth, so the system must manage it. The xHCI specifications define the concept of “BI”, “bus instance”. BIs can be of SS type, or HS type, or LS/FS type. System can assign several BIs to a port, and allocate certain bandwidth for each port, so it is possible that too many USB2 devices may encroach into SS bandwidth. This will depend on xHCI implementation and on software driver stack. It is unclear to what extent modern USB stack is intelligent to manage all this flexibility. This write-up is an example of general confusion in the area of USB bandwidth allocation.