Epson L90P - TM Two-color Thermal Line Printer Manual de usuario descargar pdf (Pagina 45)

particular

amplifier in your project.

In

most

cases, this will

be a common

type

of high- impedance

microphone.

The

au-

thor used

a

low

-cost

lapel -type

crystal

mike.

This type of microphone

is mis-

matched

to the amplifier

and produces

low fidelity

;

however,

all the mike

does

is

pick up room noise

so fidelity

is not

important. For more

sensitive

operation

( such as might

be required in

using the

Riot Restrainer

as an intruder

alarm),

a cheap low- impedance

dynamic micro-

phone

will

be best.

Any

type

of

low-

power,

two -pole, dou-

ble -throw relay

can

be used for K1

as

long

as it

can be energized by

the collec-

tor

current of Q1. The transistor

can

be

almost any npn

audio type.

There

are many

types of alarms

avail-

able

-the

author used a conventional

electric bicycle horn having its

own in-

ternal batteries.

Be

sure that the

cur-

rent required

by the alarm does not

ex-

ceed the contact rating of

relay

K1.

The

normally open contacts

on

the

relay

sub-

stitute for the pushbutton

on

the bicycle

horn. For

any

other

type

of

alarm,

make

up

a

series circuit with the alarm, pow-

er source, and the

normally open

con-

tacts of the

relay. If you want to use

the

Riot Restrainer to

turn on a

117

-volt

light

or a

high

-power alarm, you

will

April, 1969

have

to

add another relay

with heavy -

duty contacts. Energize

the

second

re-

lay's

coil through

the

normally

open con-

tacts

of

K1.

Testing

and Adjusting.

Once

the project

is

built, check it carefully

for

any wiring

errors. Connect

the microphone

to

J1.

Connect a loudspeaker

to

the audio out-

put leads

(loudspeaker

common to

am-

plifier

common and

the other

speaker

lead to the

8- or 16 -ohm output,

depend-

ing

on the speaker)

and place

SZ in the

AUDIO

position.

Speak

into

the

micro-

phone

and adjust

R1

until the amplified

voice

can be heard. Audio quality

may

be poor,

but this system is designed

for

noise

pickup, not high fidelity.

Reset R1

for minimum volume.

Plug the

alarm

selected

into

SO/

and

place

SI in

the

RELAY

position.

While

talking near

the

microphone,

advance R1

until

the alarm sounds. The amount

of

time that

the

alarm stays on is

deter-

mined

by the setting of R5. If

desired,

this potentiometer

can be replaced

by

a

fixed resistor

whose value is

selected

to

keep

the alarm on for the

desired

period.

If the system

does

not

work,

first

check

to

make sure

that the SCR

is

firing.

To

do

this, place

a

short

between

the

emitter

and collector of transistor Q1,

Layout of the author's version.

Since layout is

not critical,

any

physical arrange-

ment will

do. Though battery

power is

called for,

you can use

a 6 -volt power

supply.

If you

want

a

high -power

alarm, use K1 to drive

a

heavy -duty

relay.

R5

RI

CI

R6

C OF

QI

R4

D2

DI

R2

R3

49

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