Hardware Reference
In-Depth Information
Chapter 5
Security Monitoring Device
The Raspberry Pi can be used for a lot of different projects, two of which you have seen so far. There was one
application for the Raspberry Pi that I overlooked because I originally assumed it may be too complicated. This would
be how handy the Raspberry Pi would be to use to make a small home security system. This idea was given to me
by a close friend and the first thing I did was question him on the fact that I thought security systems were complex.
However, the devices used inside the systems at a very basic level are quite simple. A good example of this is when
I prompted my friend about pressure sensor pads and the lack of documentation I could find on them. He then
explained to me that the pad is just two contact points that touch when pressure is applied; simply put, the pad is a
normally open circuit. The idea of using the Raspberry Pi as a security monitoring device was then born.
I spent several hours thinking about how and what devices I could attach to the Raspberry Pi. In most common
security systems you may have come across, you may have noticed that they use more than one type of sensor for
monitoring. For example, a lot of motion sensors are a combination of a passive infrared sensor and an ultrasonic
motion detector. After all you don't want a false alarm resulting from something like your window curtain gently
moving.
The Raspberry Pi makes a wonderful little security device: you can place it anywhere in your home and it's easy
to keep out of sight. If you have Model B you can also take advantage of the Ethernet port to send remote alerts when
someone has tripped one of your alarms. You could also use the LCD screen (discussed in Chapter 4) to display alerts
if a zone has been breached. Or you may want to trigger another GPIO on the Raspberry Pi to do something when
a zone is breached. The fact that the Raspberry Pi is running Linux gives you so many opportunities for this project
compared to Arduino or a similar microcontroller. After all it's quite simple to add an Internet connection to the
Raspberry Pi so it can keep you up to date about the sensors. Or you may want to log how many people walk past your
house every day. Whatever your reasons are to use the Raspberry Pi as a security device, it's a very good choice.
In this chapter I will explore two of the most common devices you may come across in a security system:
•
A pressure mat
•
A passive infrared sensor
These two devices are easy to use and indicate a breached zone very well. By using the pressure mat you will see
how easy it is to use and it will also provide knowledge on how to use some other basic devices like tilt switches. I am
sure you are all waiting on the edges of your seats to find out how to use these two devices.
First up, you need to understand how these devices work. Only then will you see how simple they are in fact
to use. This also brings me to another point. Modern security systems have a lot of extra circuits and a lot of extra
components to ensure that they cannot be altered or tampered with. For the sake of showing you how the basic
devices can be interfaced I have left this side of the security devices alone. It would be very simple to tamper
with the way I have configured the devices in this chapter so by no means is the Raspberry Pi a full replacement for
your security system but it could make a good zone-watching device and would be perfect for all your home data
center needs.
