Hardware Reference
In-Depth Information
Power
Early models of the Raspberry Pi limited each USB port to 100 mA because of the polyfuses
included. Revision 2.0 models did away with these, leaving you with more options.
Even with the polyfuses removed, the end user should remember that the USB ports
are powered by the input to the Raspberry Pi PCB. This is supplied through fuse F3
(see Figure 4-3, shown previously in Chapter 2). This limits the maximum USB current to
500 mA for the Model A (which is the limit for one USB port anyway) and 300 mA for the
Model B. Exceeding these limits could cause fuse F3 to blow.
■
Note
Wireless USB adapters consume between 350 ma and 500 ma.
Powered Hubs
Whether you have a Model A or Model B Raspberry Pi, you'll want to use a powered USB
hub for high-current peripherals. This is particularly true for wireless network adapters,
since they often require up to 500 mA.
A USB hub requires coordination with the Linux kernel and thus requires Raspbian
Linux driver support. A number of hubs have been reported not to work. The following
web page is a good resource listing hubs that are known work with Raspbian Linux:
With the powered USB hub plugged in, you can list the USB devices that have
registered with the kernel by using the
lsusb
command:
# lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp.
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.
Bus 001 Device 004: ID 0451:2077 Texas Instruments, Inc. TUSB2077 Hub
The first three listed are the usual suspects from the Pi's own hardware. The last line
shows that a TUSB2077 Hub has been registered. Figure
6-2
shows my Belkin USB hub on
a busy workbench. If your hub fails to appear in this report, it likely means that there is no
driver support for it.
