Elenco Electronics MO-1251 Manual de usuario descargar pdf (Pagina 62)

100

pins

facilitate an internal

carry look

ahead

feature that is useful

in fast

counting applications.

Synchronous

down counters

Synchronous up

/down counters

are

devices

that can

count in either direc-

tion. Counting

direction

controlled

by either

of two methods.

The first by

using

a single clock

in conjunction

with

UP DrTAWI control

pin. The

second by

using two

separate clock

signals,

with one

controlling

the up-

count

and

the

other controlling

the

down- count.

All CMOS

up /down counters

are

presettable

types that

output a

4 -bit

binary

word, or BCD

number,

with

either

synchronous or

asynchronous

clearing

functions.

Because the

up/

down

counters

are presettable,

the

outputs can

be forced to agree

with

the

4 -JAM pins, otherwise

called

PRESET

pins.

Figure 19 shows the

4029B counter.

That device

uses a

single clock

with

count direction

controlled

via

uP/

DowN pin. The

IC can act as either

decade (BCD

output) counter,

or as a

binary (4

-bit)

counter,

depending

the

logic setting of a

BINARY DES

pin. The actions of the CARRY

OUT pin

facilitate

fully synchronous

action in

multi- decade counting

applications,

shown in Fig.

20. Here, all IC's are

clocked

in parallel, and the CARRY

OUT

pin of each counter

is used to enable

the

following one.

Several 4029B's

can also be cas-

caded and

clocked in an asynch-

ronous ripple

mode but that's

subject for another

article. R -E

SECURITY

continued

from

page 46

You don't need

module

for each

door or

window:

you

can connect a

complete,

normally closed

loop to

each

transmitter module. (The

man-

ual for the system

makes no mention

of that potentially

valuable feature.)

Although

you might feel that

wiring

such loops defeat the

whole

purpose

of- a

wireless

system,

it really

doesn't -you

still

can get away

with-

out having to drill any holes to fish

wires through. If you really object to

having any

wires visible,

you

can in-

stall a transmitter at each

window

and

door.

Although the Dicon unit comes

with

reed -type sensors, you are free to

include any passive,

normally

closed

sensors within the loop.

Mounting the base unit and emer-

gency speaker /siren are two

important

considerations. The base unit,

course, must be mounted near a tele-

phone line. It doesn't have to be

mounted

near

an exit

door, and in-

deed,

it is preferable not to mount it

there for two reasons. First, since the

heart of the system is a telephone

dialer, the last thing you

want

a bur-

glar to do is to unplug the

9000 from

the telephone line. Since the

obvious

place for the control center to be

mounted is by the front door,

it's

the

first place the burglar

will look, and

therefore

the

worst

place to mount

it.

The second reason

that makes it un-

necessary to mount the unit by the exit

is that remote keypads are available.

The remote can

be mounted by any

exit door,

can

be left handheld.

burglar can do

very little

with

the

remote- unless

he knows your secur-

ity code.

The emergency speaker

/siren not

only is an attention -getter

times

emergencies,

it also is used to

give

information

to the user.

For

example,

when

you arm the system,

the base

unit

gives a report

troubles

with any

of the modules. If you arm

the alarm

using

the remote

keypad, you still

want to hear any of those reports.

And

you can, thanks to the

speaker. If an

intruder breaks in he

will hear the

report

of "Security emergency!"

fol-

lowed by your recorded

message. If

that doesn't chase him

off, he may use

the

speaker to guide

him to the base

unit and disconnect

it from the phone

line.

protect

against such

brazen

burglars,

it might be

wise

to conceal

the

speaker and base unit -or

perhaps

use a cellular telephone.

Anyone

who

has ever armed

alarm only to

find himself rushing

around

to get out before the

time

delay

expires

will like

the

9000's non -delay

feature. Instead of giving

you a spec-

ified time to get

out the door, the 9000

looks at the door's

status.

Once you

give your command to arm

the sys-

tem, it

waits for you to close the door

before actually arming

itself.

Some professional

alarm installers

insist that a

wireless system is not as

reliable or

secure

as a

wired system.

(What if the batteries die?

What about

false alarms? etc.)

honest,

had the same reservations.

However,

it doesn't have to be true about

wire-

less

system. In the Dicon

9000, bat-

tery status

is constantly

monitored.

All sensors report to the

base unit

regularly.

When a battery goes

low

(meaning that it has about a

month of

life remaining), the

TROUBLE LED

lights, and pressing

a special

key

gives

verbal report of the

trouble.

Every time

the alarm is set,

the trou-

ble report

is given again

so that it's

difficult to forget. (Any

modules that

FIG. 21 -THE

HEART

a Dicon

remote

transmitter

small, removable

module.

The module is programmed by

the

base

unit

with

a unique code.

Therefore any

emergency condition can

be tracked

down

to the

exact

module.

have

been

turned off are

also re-

ported.)

Signal strength

is always

monitored

for level.

The signal range

for the

system is 200 feet.

That in-

creases to 500 feet with

the addition of

a small

whip

antenna.

Since the RF

signals

are in the 300 -MHz range,

you

must be sure

not to mount

the

base

unit in, or too

close to, such

things as metal

file cabinets.

eliminate false

alarms, the

transmitter

modules send

a 16 -bit dig-

ital

message, which

is repeated

times within

2 seconds. Three

of four

consecutive messages

must be identi-

cal, or they will

be considered false.

Although

not a scientific

test, in six

months

of actual use, our

test system

never falsed.

Which

system

best?

Both

wired

and wireless

systems,

as you've seen,

have their advantages.

Neither one

can be considered the

best for all instances. But we hope

that this article has

given you an idea

what

features can be found in

home -alarm systems,

and has helped

you make

a decision as to

which

type

is best for

your home. R -E

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