The Security System


I wanted the security system to be controllable and queryable from the central controller. This would preferable occur over the home control network, since the security system could be a long distance away. At the time of my search (fall 96) I could not find any system at an affordable price that precisely met my needs, so I decided to build one instead. This section will not be very detailed for obvious security reasons.

The system runs on a small commercial microcomputer board, with the program written in C. It has the following sensors, all hardwired:

  • Exterior Door Sensor
  • Windows
  • Motion Sensors
  • Glass Break Sensor
  • Smoke Detector interface
  • Garage Door Sensor
There were several features I implemented to increase reliability:
  • All sensors wired via twisted shielded cat 5 cables
  • High Current (5mA) loops for all zones
  • All inputs have individually customizable half second software filters to remove glitches
  • There is a hardware watchdog timer that the processor pings at a set rate. Should the processor die (due to glitch, brown out, programming error, or whatever reason) a hardwire security circuit takes over. This circuit simply trips the alarm horn and flashes lights when there is a security violation while the system is armed.
  • 12 Volt, 50Ahour battery for backup power

These are the features of the system:

  • Electronic bell pings a number of times depending on which door opened, allowing us to know where the entry occurred
  • Modes (perimeter, away, normal) etc. setable from the central controller
  • Status of all zones continuously available to central controller
  • Disarm and degree of Arm controllable by central controller
  • Central controller turns on a light if it is dark one exterior doors
  • Central controller turns on interior light if its is night time and a certain collection of lights is off
  • As in the case of the standard X-10 alarm system, all lights in the house flash when there is a security violation. A very loud horn mounted exterior to the house also sounds in this case
  • Central controller calls and speaks or pages in case of violation
  • Central controller speaks the zone of violation or entry (future enhancement)
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