Hardware Reference
In-Depth Information
frustrating. If a computer lying a plane malfunctions, it may lead to death or serious damage.
his is a
safety-critical system,
in which computers can cause harm if they do not function correctly.
here are particular tools, techniques and standards that apply to try to safeguard the public. his
is relevant to the project at hand because you should make sure that you have a manual override
for the door lock - because you don't want to be locked in a room by your Raspberry Pi. Typically,
most electric door lock systems can also be opened with a mechanical key.
Furthermore, just as a mechanical lock can be picked, computers can be hacked, so it's impor-
tant to be aware of how secure your system and code are. You don't want someone opening
your door because you didn't design your program properly.
Don't rely on your Raspberry Pi keeping your house secure unless you know what you're
doing. Also, have a manual override, so you don't get locked in, or out!
How Are Computers Hacked?
Most hacking incidents work by sending the computer data it is not expecting - too much
or the wrong format perhaps. In the C language, if the programmer is not careful, the pro-
gram will continue to accept input, which will overlow from the area of memory that had
been put aside for it. Think of this like illing in a form and going off the end of one line and
continuing onto the next. Sometimes the extra input data can overwrite something else in
the program. Programs are just a series of instructions the computer obeys that are held in
memory, and these instructions can be overwritten. If the attacker sends the right data, it's
possible to change the instructions to make the program do something else.
This particular type of attack is called a
buffer overlow
- the
buffer
being the area reserved for
input data. Luckily, Python manages the size of its buffers for you, so this shouldn't happen.
You should still be careful, and whenever you take input from a user expect the unexpected!
The Door Lock Hardware
You need a door lock that the Raspberry Pi can control through an electric signal. here are
two main types:
❍
Electromagnetic locks - Use an electric current to create a magnetic ield to hold the
door shut. When the current is switched of the ield collapses, and there is nothing to
hold the door shut. Typically, a lat metal plate is attached to the door that is held by
the electromagnet attached to the frame.
