Hardware Reference
In-Depth Information
SOMETIMES, THINGS DON'T
go entirely smoothly. he more complex the device, the
more complex the problems that can occur—and the Pi is an extremely complex device
indeed.
hankfully, many of the most common problems are straightforward to diagnose and ix. In
this chapter, we'll look at some of the most common reasons for the Pi to misbehave and
how to ix them.
Keyboard and Mouse Diagnostics
Perhaps the most common problem that users experience with the Raspberry Pi is when the
keyboard repeats certain characters. For example, if the command
startx
appears onscreen
as
sttttttttttartxxxxxxxxxxxx
, it will, understandably, fail to work when the Enter
key is pressed.
here are typically two reasons why a USB keyboard fails to operate correctly when con-
nected to the Raspberry Pi: it's drawing too much power, or its internal chipset is conlicting
with the USB circuitry on the Pi.
Check the documentation for your keyboard, or the label on its underside, to see if it has a
power rating given in
milliamps (mA)
. his is how much power the keyboard attempts to draw
from the USB port when it's in use.
he Pi's USB ports have a component called a
polyfuse
connected to them, which protects the
Pi in the event that a device attempts to draw too much power. When this polyfuse is tripped,
it causes the USB port to shut of, at around 150 mA. If your keyboard draws anywhere
around that much power, it may operate strangely—or not at all. his can be a problem for
keyboards that have built-in LED lighting, which require far more power to operate than a
standard keyboard.
If you ind that your USB keyboard may be drawing too much power, try connecting it to a
powered USB hub instead of directly to the Pi. his will allow the keyboard to draw its power
from the hub's power supply unit, instead of from the Pi itself. Alternatively, swap the key-
board out for a model with lower power demands. he repeating-letter problem may also be
traced to an inadequate power supply for the Pi itself, which is addressed in the next section,
“Power Diagnostics”.
he issue of compatibility, sadly, is harder to diagnose. While the overwhelming majority of
keyboards work just ine with the Pi, a small number exhibit strange symptoms. hese range
from intermittent response, the repeating-letter syndrome or even crashes that prevent the
