IoT & Hardware
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You're reading from  Building a Home Security System with BeagleBone

Product typeBook
Published inDec 2013
Reading LevelIntermediate
PublisherPackt
ISBN-139781783559602
Edition1st Edition
Languages
C++
Tools
BeagleBone
Concepts
Single Board Computers
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Author (1)
William Pretty
William Pretty
author image
William Pretty

Bill Pretty began his career in electronics in the early 80s with a small telecom start-up company that would eventually become a large multinational. He left this company to pursue a career in commercial aviation in northern Canada. Next, he joined the Ontario Center for Microelectronics, a provincially funded research and development center. Bill left this for a career in the military as a civilian contractor at what was then called Defense Research Establishment Ottawa. Thus began a career that was to span the next 25 years and continues until today. Over the years, Bill acquired extensive knowledge in the field of technical security and started his own company in 2010. This company is called William Pretty Security Inc. and provides support in the form of research and development to various law enforcement and private security agencies. Bill has published and presented a number of white papers on the subject of technical security. For a number of years, he was also a guest presenter at the Western Canada Technical Conference, a law enforcement-only conference held every year in western Canada. A selection of these papers is available for download from his website.
Read more about William Pretty

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The hardware

The alarm system, in this case the BeagleBone, must be able to monitor the world around it. It does this by using ICs called comparators. You can think of a comparator as an op-amp with extremely high gain. Like an op-amp, when the voltage on the positive (+) input is higher than the voltage on the negative (-) input, the output goes high. When the opposite is true, the output goes low.

The LM339 comparator

We will be using an LM339 comparator. I chose the LM339 comparator because it has been around forever, and still comes in through-hole DIP packages. It is cheap and easy to source. Best of all, it is hard to blow up! The device has an open collector output. What this means is, a resistor is required to pull the output high. By connecting the output pull-up resistor to 3.3V, we now have a level converter that can be safely connected to the BeagleBone.

In the following diagram of the single zone comparator circuit, a 4.7K ohm resistor—R5 is used as a pull-up. The LM339 comparator...

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Building a Home Security System with BeagleBone
Published in: Dec 2013Publisher: PacktISBN-13: 9781783559602
© 2013 Packt Publishing Limited All Rights Reserved

Author (1)

author image
William Pretty

Bill Pretty began his career in electronics in the early 80s with a small telecom start-up company that would eventually become a large multinational. He left this company to pursue a career in commercial aviation in northern Canada. Next, he joined the Ontario Center for Microelectronics, a provincially funded research and development center. Bill left this for a career in the military as a civilian contractor at what was then called Defense Research Establishment Ottawa. Thus began a career that was to span the next 25 years and continues until today. Over the years, Bill acquired extensive knowledge in the field of technical security and started his own company in 2010. This company is called William Pretty Security Inc. and provides support in the form of research and development to various law enforcement and private security agencies. Bill has published and presented a number of white papers on the subject of technical security. For a number of years, he was also a guest presenter at the Western Canada Technical Conference, a law enforcement-only conference held every year in western Canada. A selection of these papers is available for download from his website.
Read more about William Pretty

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