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the CuVoodoo USB hub is a 7-port USB 2.0 hub meant for device testing.
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purpose
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=======
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most USB hub are super cheap and crappy, leading to poor connection and data transfer.
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there are industrial USB hubs, but they are bulky and very expensive.
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to solve this issue I decided to design my own USB hub, tailored to my needs.
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when developing and testing hardware, you often end with a lot of USB devices connected.
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USB allows to have up to 128 devices, but only with a maximum depth of 7.
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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.
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most 7-port USB hubs use two 4-port USB hub, the seconds being connected to the first.
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there are some exception to that, but they are rare, old, and often not advertised as such.
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this heavily limits the number of end devices.
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this device is a 7-port flat USB hub, preventing reaching this limit too often.
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the incoming and outgoing USB ports are individually ESD protected.
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this safety becomes important when developing, testing, and handling bare electronic devices.
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this also comes in handy against when connecting circuit with different ground potentials.
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ESD protections already saved my day twice this way.
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the issue is that they can blow without you noticing, but at least they protected the device once.
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each output port is current limited to 500 mA.
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no device should draw more that this specified limit.
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it if does, there is very probably an issue with the device.
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this protection allows to isolate the faulty device and not have it affect all other connected devices, or the hub itself.
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the fault is also detected and reported by the hub to the host computer.
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each output port is power controlled.
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this allows to remotely switch on an off individual devices.
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this is an important requirement when developing and testing devices, which require a power cycle.
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additionally, a switch next to the power can force the power off state.
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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.
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this allows to use higher voltage power supplies to provide enough current to all ports.
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the 5V are not feed back to the host.
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each USB port comes with a high voltage output power port, connected to the high voltage input port.
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this allows to power devices which require more than 5V (e.g. 12V externally powered devices).
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these power outputs are controllable.
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as with the 5V USB power output, this allows to remotely switch on an off individual devices.
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each port has status LEDs, indicating the speed and power status of the connected device.
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the board uses proper impedance and differential signal routing to provide clean USB signal transfer.
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design choice
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=============
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USB 2.0
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-------
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this hub is only for USB 2.0 devices.
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by far this are most of the devices I develop.
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is makes it simpler and keeps the cost reasonable.
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I often even disable USB 3.0 because of the 13-device limitation of the Intel xHCI.
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when I need USB 3.0 for the very few devices, I connected them to the computer directly.
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USB2517
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-------
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I wanted to use the FE2.1 7-port USB hub chip.
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it does not need an external voltage regulator or crystal.
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and it is easier to solder thanks to its TQFP package, and provides all required functionalities.
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sadly I could not find a source for the 64-pin packages, and the 48-pin variant does not provide all required functionalities.
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thus I had to fall back to the Microchip USB2517, which uses a harder to solder QFN package.
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power control
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-------------
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some USB hub chips allow to remotely control the power output on individual ports.
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this capability is here also used to control the power on the higher voltage output.
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thus you can completely power off even larger target devices.
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current limitation
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------------------
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very few USB hubs that have current limitation on the output.
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this does limit the current to 500 mA, but only in constant current mode.
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if well designed, the fault is also reported to the computer.
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sometimes the hub also turns off the power, or it is up to the user to power off the faulty port.
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on this hub, the fault is reported, and the power is automatically disabled, preventing damages on the device due to prolonged shorts.
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this is very useful when testing devices.
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the power is restored once the current limit is cleared.
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LED color
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---------
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the USB specification, LEDs are used as port indicator (section 11.5.3)
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- off: powered off/disconnected
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- amber: current limitation reached
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- green: enabled or transmitting
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instead the following color scheme is used:
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- green off: power off or over-current
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- green on: power on
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- red: low speed device connected
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- blue: full speed device connected
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- purple (red+blue): high speed device connected
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- red and blue off: disconnected
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usage
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=====
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it mainly works like a regular USB hub, at least when it comes to the data transfer.
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just plug the device in a port.
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power on the Downstream Facing Ports (DFPs) is only available when the Upstream Facing Port (UFP) is connected.
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the hub can operate as bus powered (power coming from the UFP), but it would not be able to provide more than 500 mA across all DFPs.
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it is preferable to connect an external 5V power supply to be able to provide 500 mA on all DFPs.
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this will also turn the hub into self powered, not using any power from the UFP.
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alternatively, you can connect a 6 to 40V power supply on the other power input.
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the power for the hub and the 5V for the DFP will be derivate from this higher voltage supply.
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the same higher voltage will be available on the power output next to the individual DFPs.
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a switch next to each DFP allows to turn off the power output on the USB and power ports.
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the green LED is on when power output is available.
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the power output on the USB and power ports can also be turned on/off remotely using standard USB commands.
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this power output control is implemented in [uhubctl](https://github.com/mvp/uhubctl):
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~~~
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# list controllable USB hub ports
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sudo uhubctl
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# switch of port
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uhubctl --action off --location 1-1.4 --ports 5
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~~~
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when too much current is drawn on the USB port, the error is reported to the host and the power output is automatically disabled.
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