Practical Arduino Cool Projects for Open Source Hardware- P13: A schematic or circuit diagram is a diagram that describes the interconnections in an electrical or electronic device. In the projects presented in Practical Arduino, we’ve taken the approach of providing both a photograph and/or line drawing of the completed device along with a schematic. While learning to read schematics takes a modest investment of your time, it will prove useful time and time again as you develop your projects. With that in mind, we present a quick how-to in this section | CHAPTER 6 SECURITY AUTOMATION SENSORS Home Security System We have presented this system as simply a way to read security sensors but it could be extended to build a complete home alarm system controlled by an Arduino. Alarm systems consist of several subsystems including the alarm panel which is the cental control system that runs the show. The alarm panel needs to be securely locked away inside the house and innaccessible. It is often fitted inside a metal case that is mounted inside a cupboard or inside the ceiling. To build your own alarm panel you could mount the Arduino inside a box and hide it. An alarm system also needs a mechanism for arming and disarming it. This is often done using a numeric keypad mounted in an easily accessible location and containing no critical functionality that could disable the alarm panel. Intruders should be able to smash or tamper with the keypad without preventing the alarm panel from being activated. Another mechanism to arm or disarm the system could be the RFID reader project in Chapter 14. Rather than trigger a strike plate you could have the RFID reader deactivate the security system. Of course an alarm system also needs a way to get attention so you could wire up a relay using the transistor circuit used in the RFID Access Control System project so that it activates a siren and a flashing light. You could even use your Arduino to control a phone dialler or send an backup is also an important part of a security system. By combining a sealed lead acid battery a plugpack and a battery charger you can ensure your security system will run for many hours or days even if the power to your house is cut. Multiple Buttons on One Input Using an analog input to read the value on a multistate voltage divider is a very handy trick that can also let you connect multiple buttons to a single analog input. If you re running low on digital I O lines and want to connect more buttons to an Arduino you can set them up as a .
