Ed Grochowski's Website

Home Security System



This is the alarm system I have in my house. I designed and built this project in 2002. It is the fourth alarm system I have created. This is a traditional wired alarm with an entrance and exit delay, shut-off timer, 6 digit combination lock, and rise-fall siren. The alarm has 3 sensor loops: one delayed, one instantaneous, and one that is always on.

Commercial alarm systems are invariably based on microcontrollers. This project is built with low power Schottky TTL. A board full of TTL chips would not be cost-competitive today. But TTL was easiest for me to design!

The alarm's design is practically a textbook example of finite state machines. The main FSM has 7 states: off, door open, exit delay, armed, entrance delay, intrusion, and shut-off. It clocks at a leisurely 1.5KHz.