README: add project description

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King Kévin 2022-01-28 18:46:39 +01:00
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these are the hardware design files for **insert project name here**.
the CuVoodoo USB hub is a 7-port USB 2.0 hub meant for device testing.
most USB hub are super cheap and crappy, leading the poor connection connection and data transfer.
there are industrial USB hubs, but they are bulky and very expensive.
to solve this issue I decided to design my own USB hub, tailored to my needs.
when developing and testing hardware, you often end with a lot of USB devices connected.
USB allows to have up to 128 devices, but only with a maximum depth of 7.
thus you are only allowed to have a maximum of 5 USB hubs between computer and devices, and I often have to plan my setup to not reach this limit.
most 7-port USB hubs use two 4-port USB hub, the seconds being connected to the first.
there are some exception to that, but they are rare, old, and often not advertised as such.
this heavily limits the number of end devices.
this device is a 7-port flat USB hub, preventing reaching this limit too often.
the incoming and outgoing USB ports are individually ESD protected.
this safety becomes important when developing, testing, and handling bare electronic devices.
this also comes in handy against when connecting circuit with different ground potentials.
ESD protections already saved my day twice.
the issue is that they can blow without you noticing, but at least they protected the device once.
each output port is current limited to 500 mA.
no device should draw more that this specified limit.
it if does, there is very probably an issue with the device.
this protection allows to isolate the faulty device and not have it affect all other connected devices, or the hub itself.
the fault is also detected and reported by the hub to the host computer.
each output port is power controlled.
this allows to remotely switch on an off individual devices.
this is an important requirement when developing and testing devices, which require a power cycle.
additionally, a switch next to the power can force the power off state.
the USB hub can be self-powered (through the USB input port), externally powered by 5V, or externally powered by anything between 6 and 40V.
this allows to use higher voltage power supplies to provide enough current to all power.
the 5V are not feed back to the host.
each output port comes with a high voltage output power port, connected to the high voltage input port.
this allows to power devices which require more than 5V (e.g. 12V externally powered devices).
each of these power output is controllable.
as with the 5V USB power output, this allows to remotely switch on an off individual devices.
each port has status LEDs, indicating the speed and power of the connected device.
the board uses proper impedance and differential signal routing to provide clean USB transfer.
design choice
USB 3.0
this hub is only for USB 2.0 devices.
by far this are most of the devices I develop.
is makes it simpler and keeps the cost reasonable.
I often even disable USB 3.0 because of the 13-device limitation of the Intel xHCI.
when I need USB 3.0 for the very few devices, I connected them to the computer directly.
I wanted to use the FE2.1 7-port USB hub chip.
it does not need an external voltage regulator or crystal.
and it is easier to solder thanks to its TQFP package, and provides all required functionalities.
sadly I could not find a source for the 64-pin packages, and the 48-pin variant does not provide all required functionalities.
thus I had to fall back to the Microchip USB2517, which uses a harder to solder QFN package.
current limitation
the few USB hubs that have current limitation on the output, use a MIC2026.
this does limit the current to 500 mA, but only in constant current mode.
the fault is reported (e.g. to the hub, back to the computer), but it is up to the user to power off the faulty device.
instead I use poly-fuses, which automatically cut the power once the limit of 500 mA is reached.
this is faster, and removes user-based actions.
the fault is still reported.
this is very useful when testing devices.
LED color
the USB specification, LEDs are used as port indicator (section 11.5.3)
- off: powered off/disconnected
- amber: current limitation reached
- green: enabled or transmitting
instead the following color scheme is used:
- green off: power off or over-current
- green on: power on
- red: low speed device connected
- blue: full speed device connected
- purple (red+blue): high speed device connected
- red and blue off: disconnected