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Chapter 11, Keyless Entry Welcome Home

Let’s now examine the conceptual diagram in Figure 11-1 in detail. The

actual, physical lock is referred to as the physical plant. You’ll make some

small modifications to provide a means to transmit events from the physical

plant onto a control medium. The devices that can transmit over the control

medium can either directly trigger the controlled devices to turn on or off,

or relay those events to an intelligent dispatcher. The dispatcher can process

the events and place commands back on the control medium to be received

by the controlled devices. It’s possible to eliminate the dispatcher and have

events managed by the interface alone, but this will severely limit the flex-

ibility of the system; this is explained in the section “The Control Medium.”

Once the modifications to the lock are complete, you can install it according

to the manufacturer’s instructions.

Control medium? Intelligent dispatcher? What the heck is this stuff? In English: the

control medium is nothing more than the electrical wires in your house’s walls,

and the intelligent dispatcher is your computer.

Linking the Physical Plant to the

Control Medium

The first thing you need is a means to relay the state of the lock to the other

parts of the system. In other words, when the door is locked, you want the

lock to be able to announce that it’s locked; you want ...