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Externally powered USB hub

Why

A 3D printer has a Raspberry Pi embedded computer, running from a standby 5V rail of an ATX power supply. The computer can control the power supply on/off state.

Several peripherals are attached via USB, and these have to be depowered when the power supply is shut down. But they are powered from the board's USB ports.

How

USB hub to the rescue.

A cheap 4-port USB 2.0 hub was obtained. The 5V power line from the upstream connector was cut off.


Hub to modify

Hub board

Hub board

Hub board

A switch was attached, with its middle contact connected to the hub's 5V input.

One end of the switch was connected to the original USB upstream power, the other was attached to a wire to connect to an externally switched power supply.

The switch allows selection between USB and external power. In the application the device was developed for, this allows powering the peripherals without having to energize the high-current parts of the machine, to facilitate easier software development. No need to power motor drivers and heaters when only a webcam is being hacked on.


Modified power wiring

Modified power wiring

A 0.9-amp Polyswitch fuse was attached between the switch and the hub to protect the wiring against shorts on the output ports.


Switch with a Polyswitch fuse

Switch with a Polyswitch fuse

Switch with a Polyswitch fuse

Final assembly

Hub specifications

The hub is a cheap Akasa AK-HB-07BK model. Its construction is somewhat flimsy and it runs on a FE1.1s, with a single-transaction-translator. This may cause some bottlenecks when multiple USB1.1. devices are attached.

The bus reports as 1a40:0101 Terminus Technology Inc. 4-Port HUB.

The lsusb -v report is

Bus 001 Device 013: ID 1a40:0101 Terminus Technology Inc. 4-Port HUB
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            9 Hub
  bDeviceSubClass         0 Unused
  bDeviceProtocol         1 Single TT
  bMaxPacketSize0        64
  idVendor           0x1a40 Terminus Technology Inc.
  idProduct          0x0101 4-Port HUB
  bcdDevice            1.11
  iManufacturer           0
  iProduct                1 USB 2.0 Hub
  iSerial                 0
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           25
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0
    bmAttributes         0xe0
      Self Powered
      Remote Wakeup
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         9 Hub
      bInterfaceSubClass      0 Unused
      bInterfaceProtocol      0 Full speed (or root) hub
      iInterface              0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0001  1x 1 bytes
        bInterval              12
Hub Descriptor:
  bLength               9
  bDescriptorType      41
  nNbrPorts             4
  wHubCharacteristic 0x0000
    Ganged power switching
    Ganged overcurrent protection
    TT think time 8 FS bits
  bPwrOn2PwrGood       50 * 2 milli seconds
  bHubContrCurrent    100 milli Ampere
  DeviceRemovable    0x00
  PortPwrCtrlMask    0xff
 Hub Port Status:
   Port 1: 0000.0100 power
   Port 2: 0000.0100 power
   Port 3: 0000.0503 highspeed power enable connect
   Port 4: 0000.0103 power enable connect
Device Qualifier (for other device speed):
  bLength                10
  bDescriptorType         6
  bcdUSB               2.00
  bDeviceClass            9 Hub
  bDeviceSubClass         0 Unused
  bDeviceProtocol         0 Full speed (or root) hub
  bMaxPacketSize0        64
  bNumConfigurations      1
Device Status:     0x0001
  Self Powered


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