Big Picture
There are many good hubs on the market. For example:
https://www.dlink.com/de/de/products/dub-h7-7-port-usb-2-0-hub
positive: cheap, widely available
positive: USB2. No unneeded USB3 complexity.
negative: chipset not specified - may be changed by manufacturer
negative: Very low cost chip FE1.1S
negative: Voltage on the USBA connector may drop below 4.7V
negative: USB geometry asymmetrical: Internally 2 USB hubs. We might hit the 7 tiers limit of USB.
positive: cheap, widely available
positive: USB3. As we only require USB2, USB3 is unwanted complexity
negative: chipset not specified - may be changed by manufacturer
negative: Voltage on the USBA connector unknown
negative: USB geometry asymmetrical: Internally 5 USB 4-port-hubs. It would have been possible to have a top 4-port-hub with 4 downstreams hubs, thus requireing 2 usb tiers. But this is not the case: The internal hubs are assymetrical requiring 3 tiers!!!
The benefits of octohub4:
negative: Not out of the box. Needs to be ordered in china.
positive: Know and stable USB 2 chip USB2514B_Bi.
positive: USB geometry symmetrical: We hit the 7 tier limit later.
positive: Excellent 5V power management
Features
Recommended BOM
Order recommended parts to assemble your tentacles: Parts list
Fast and cheap manufacturing
The assembled PCB may be ordered at https://www.jclpcb.com. The production files are located here: kicad/octohub4_v0.x/production_v0.x.
The price of a assembled PCB is ~USD9 when ordering 20 pieces.
Power Management
TPS259474LRPWR chip
limit the current to 4.9A
Voltage slew rate: The Voltage will raise from 0 to 5V withing 12ms.
Overcurrent: I there is overcurrent during 500m: * The outputs will be unpowered * Red error led
Power input
The power may be provieded by ether
Standard 5V power displays with a 5.5mm Barrel Jack. Central plug is +5V.
Clamp terminal
Solder terminal
Stacking
Stacking using M3 standoff mounts. The standoff mounts connect the 5V power - only one hub requires to be powered!
Reduce number of tiers
This article explains usb tiers: https://community.crestron.com/s/article/3082
In octoprobe we experienced USB errors under high load. If these errors are debian internal or related to the usb hardware is not know.
However, it is always best to try not to reach the maximum level of 7 usb tears. With octohub4 we have control over the adding new tears by wireing usb upstream