Elenco Electronics MO-1251 Instrukcja Użytkownika Pobierz pdf (Strona 41)

J

WIRELESS

SECüRITY

SYSTEM

L

-LF

DAN

BECKER

Build a

wireless

security system

that

monitors

an

area casing an

invisible infrared beam

and

beeps a

hand

-held

buzzer unit

when a problem

is

detected.

EACH

YLAK

'UIL NUT) FUR A SECUREIY

alarm in the home increases. For-

tunately,

security-

system technology

increases,

too, as does the ease of

installation.

Our

system is

a good ex-

ample-it uses an unseen infrared

beam which, when interrupted,

acti-

vates

an RF transmitter that broad-

casts a signal to a hand

-held

beeper -

like device. By making

the system

wireless,

installation is simplified

and

one or more remote locations can be

monitored.

How

it works

Figure

1

shows

a block diagram of

the system, which

contains an IR

transmitter, an IR receiver /RF

trans-

mitter,

and an RF receiver /alert

beeper.

Two IR -LED's

in the transmitter

transmit a pulsed

beam of invisible

infrared light

to the receiver, which

contains an IR phototransistor.

The

phototransistor

detects and amplifies

the pulse

-modulated IR beam. If

the

receiver

section senses

that the IR

beam is momentarily

interrupted by

an object blocking the

beam's path, it

triggers the

transmitter whose output

is a 49.890 -MHz

carrier that is ampli-

tude modulated

by a 490 -Hz tone.

Upon receiving

the 490 -Hz ampli-

tude- modulated

carrier, the RF re-

ceiver /beeper unit sounds an alarm

that alerts the user to the

intrusion.

The system is not limited to just

one RF

transmitter.

A single RF re-

ceiver /beeper can be used to monitor

any number of RF transmitters

(or

locations).

However, the receiver/

beeper unit can not discriminate be-

tween different transmitter

sites in

multiple-

transmitter

systems.

IR

TRANSMITTER

PULSED IR BEAM

\

7

ANT

a9.890MHi

ANT

T7/ß

IR RE CEIVER R, TRANSMITTER RF

RECEIVER

ALERT BEEPER

FIG. 1 -BLOCK

DIAGRAM

of

the wireless infrared security system.

47

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 99 100

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