Building a High-Tech Alarm System with Raspberry Pi (Second Edition)

Building a High-Tech Alarm System with Raspberry Pi

William Pretty

Copyright © 2024 by William Pretty

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All rights reserved. This book or any of its portion may not be reproduced or transmitted in any means, electronic or mechanical, including recording, photocopying, or by any information storage and retrieval system, without the prior written permission of the copyright holder except in the case of brief quotations embodied in critical reviews and other noncommercial uses permitted by copyright law.

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Created in the United States of America

Library of Congress Control Number: 2024923320

ISBN: Softcover 979-8-89518-441-7

e-Book 979-8-89518-442-4

Published by: WP Lighthouse

Publication Date: 10/25/2024

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Phone: +1-888-668-2459

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Contents

Chapter 1: Introduction to Alarm Systems 1

Motion Detectors: 3

Glass Break Sensor: 4

Fire Alarm Sensors: 5

Access Control: 11

Chapter 2: Hardware 14

Voice Output: 29

Chapter 4: Software 35

Chapter 5: Printed Circuit Board 57

Printed Circuit Board 62

Chapter 6: Alarm System Wiring 72

Testing the Harnesses 75

Wiring the Sensors 78

Chapter 7: Planning your Alarm System 87

Step 1 – The Walk-about 88

Typical Four Bedroom House 89

Commercial Office Space 96

Laboratory 98

Chapter 8: Future Enhancements 101

CAD Software: 110

Smoke Alarms, Solenoid Locks, Suppliers: 111

Chapter 9: Adding more Inputs and Outputs 112

Trouble Shooting the System: 115

Chapter 1:

Introduction to Alarm Systems:

In this chapter we will discuss the basic components of any alarm system. All alarm systems have two basic functions. First, they monitor their environment looking for a change such as a door or window opening or someone moving about in the room. The second function of the system is to alert the human to this change. Our alarm system uses a scanning type software to detect intruders. We will use the ‘standard’ guard dog as an analogy. In a scanned type of system, the guard dog paces back and forth at the fence looking out for either an intruder or someone that it recognizes. In our design, if you have an alarm key, you can disarm the system and enter. In an interrupt driven system, the dog is asleep until it hears an intruder (or you). It then wakes up and deals with the situation. I have chosen the scanning method because in my opinion the software is easier to write and explain. It can scan all eight zones in about one second.

You don’t have to be an electrical engineer to install an alarm system, just a good carpenter, painter, and plasterer! I’m not by the way so I’ll leave hiding wires up to you.

Also, because our alarm system runs on 12 volts, you don’t have to be a licensed electrician to install it. If you can plug in a wall adapter, you can build and test this alarm system.

Alarm System Sensors:

Door / Window Contact:

The simplest and one of the most common sensors is the door / window contact. This sensor consists of a magnet which is installed on the moving part of the door or window. This magnet holds a switch closed. The switch portion of the sensor is attached to the door or window frame. Figure 2 shows what is inside a typical sensor of this type.

Figure 1-1. Door / Window Contact Schematic

Figure 1-2. Door / Window Contact

Motion Detectors:

The next most common sensor is the PIR or Passive Infra-Red detector. This sensor measures the ambient temperature of the room and waits for a change in the ambient. Often called a ‘blip’.

Figure 1-3. How PIR Sensor works

Simple PIR sensors tend to be fooled by large pets (like your guard dog). For that reason, they have a pet setting which ignores any object less than 30 pounds, which is moving close to the floor. More modern (expensive) sensors also have a mmWave sensor built in which tends to reduce false alarms and makes the sensor harder to fool. The dual sensor is about three times the price of a simple PIR detector and communicates with the panel with the same contact switch arrangement.

Figure 1-4. PIR Motion Sensor

Glass Break Sensor:

Another type of sensor is the glass break sensor. This type of sensor is commonly used by shop owners to help detect vandalism. This sensor uses a microphone to ‘listen’ for the sound of breaking glass.

Figure 1-5. How Glass Break Sensor works

The system consists of a sensitive microphone, an amplifier, and a filter (usually digital signal processing). The output of this filter is connected to a detector circuit which activates the alarm system contacts when the sound of breaking glass is ‘heard’ by the microphone.

Figure 1-6. Typical Glass Break Sensor

Fire Alarm Sensors:

Heat Detectors:

There are two basic types of heat detectors, mechanical and electronic. The electronic type of detector uses a thermistor as the sense element. A thermistor is type of resistor that changes its value based on the ambient temperature. In practice two thermistors