After years of our home alarm not quite working, and an abundance of newly found time on my hands I have decided to design and build a new home alarm system, with some slightly new features that didn’t exist when we bought our house.
There was nothing truely wrong with the alarm, it did go off randomly when we weren’t home, and it didn’t dial our phones (although that is an option), I just didn’t feel like paying an alarm installer to reprogram it. Now with home automation and arduino’s and things it’s the perfect time to update it a little.
First Attempt:
* Spoiler: I didn’t notice I had flipped some pins on the schematic, so only 2 of the channels worked 🙂 *
I decided the alarm should have battery backup functionality, I decided that I wasn’t going to bother with battery charging – I could use an off the shelf charger. I used an LM324 opamp as a window comparator to ensure that the wire going to the sensor isn’t susceptible to being cut or shorted together.
See attempt #1’s schematic
I spun the first board and here is the 1st board, when testing for fit when it arrived.
Off to solder the components
Stay Tuned for the next version.
Paul Rickard 
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