Part 2: Arduino Home Security

Security sensors are usually wired with 22 gauge solid-conductor wire but the Home Depot near me didn’t have any in stock. I grabbed 50′ of Category 3 instead. Cat 3 wire is meant for phone installations, has twisted pairs, and is 24 gauge, so I figured that would be good enough to get me started and I could upgrade the wiring later.

My first test was to hook up the door sensor only and see if I could get a reading on the Arduino.

I hooked one lead of the door sensor to one of the Arduino’s analog inputs and the other lead to the board’s 5V output. The analog input produces a reading between 0 and 1023 depending on the voltage. When the door was closed, I got a reading of 1023 and, when it was opened, the reading dropped down into the 900 range. Success!

I chose to place the Arduino near my cable modem and router and plug it in to my UPS so that in the event of a power outage the security system would still work. To get all of the alarm leads over to where the Arduino would be placed, I used a breadboard and the Cat 3 cable to extend the wiring from the main security system panel. The sensors share a common wire that goes to the 5V output so that is also extended to the Arduino. Not the most elegant wiring job but I plan to make it more permanent later:

The different sensor leads go into the different analog inputs, and the Arduino’s USB port hooks to an old USB phone charger to provide power. The Ethernet cable is not shown in this picture:

Leave a Comment