Memorex CP8 TURBO UNIVERSAL REMOTE CONTROL Manual de usuario descargar pdf (Pagina 62)

100

They often

also have a built -in

cassette

player, bass

and

treble

controls,

and a power

output of

several watts

per

channel

or more. Finally,

car radios

are

very

rugged

and are

well

shielded,

thereby reducing

interference.

car radio can

form the basis

for a

very

good sound system.

All you

have to

is add a mains

power supply,

two

speakers,

and

a suitable

cabinet.

Choosing Your

Radio

The

old adage

that you get what

you

pay for holds

true

here. You

can

either take the low -cost

route with

a no- frills

$25

radio,

or you can

buy something with

a cassette player

and

a few other "bells

and whistles."

a matter of interest, we

took a quick

flick through

couple

catalogs.

Each

offered a

complete AM /FM

-stereo

radio

-cassette

player for around

$79.95, but

you can

also buy

fully synthesized

models with

electronic

tuning and AM

stereo with

prices starting

the $350 range.

Radio

Shack

carries

wide

range of

models, with

features

and prices

suit

every

budget. Of particular

interest

is a new synthesized

model

that sells for just

$250.

They also

have a $400

model

with

a "logic-

controlled"

cassette

deck, Dolby

B -C noise

reduction

and 15 -watts per

channel

of output

power.

Of course,

you don't

have to buy.

You may

already have a

surplus

car radio stashed

away in

the garage or

under the

workbench.

so, then

the price is right,

and it's

the ideal

candidate for

conversion

to mains power.

If you

don't already

have

radio,

but want

to save money,

try a local

auto

wrecker.

They often

have car radios

available

for

a few

bucks; but

make sure

that the model

you choose

still in working

order.

A radio that's

been pulled from

a wreck

may

have been

damaged

in some way.

We decided

"whole

hog" and

convert

a Pioneer

KE433AM

AM /FM

radio -cassette

player with

synthesized

tuning,

I8- station

memory,

AM stereo,

and 4 -watts per

chan-

nel power

output.

It is

an excellent radio,

although

unfor-

tunately no

longer part

of the Pioneer

lineup.

The Power

Supply

Figure

1 shows

the power supply

circuit that we'll

use in

2156

155404

117VAC

1114002

EARTH

TO CASE

OF RECEIVER

CAR RADIO 'CASSETTE

POWER

SUPPLY

4700

IN IDUT

GND

Fig. 1 -The

conversion

of the car radio for home

use requires

little

more than providing

suitable power supply, like that

shown here. T1,

a 15 -volt stepdown transformer, feeds

full

wave

bridge

rectifier,

consisting

of diodes D1 -04, with its

-volt output filtered by a

C2. and

regulated

by U1. The

ground

connection of the regulator is

jacked up by about 1.4

volts

by diodes D5 and D6. to

deliver a 13.4 -volt

output.

our

conversion.

As you

can see,

the circuit is very simple.

transformer with

a 15

-volt secondary

feeds

a conventional

full -wave

bridge

rectifier,

consisting

of diodes

D1 -D4. The

output of

the bridge is

then filtered

by a 4700 -µF

electrolytic

capacitor

to give

a smoothed

DC voltage

about 20

volts.

Voltage

regulation

is provided

a 3- terminal

12 -volt

regulator (the

7812). In

this case,

however, the

ground con-

nection

of the regulator

is jacked

up by

about 1.4 volts

series-

connected

diodes D5

and D6.

As a result,

the supply

delivers

a 13.4 -volt

output to the

radio.

The

inclusion

of D5

and D6 may

be seen as

"gilding

the

lily"

somewhat.

After all, the

radio will work

quite

happily at

12 volts,

why

bother'?

Our reasons

are

that the diodes

are

cheap (about 10

cents

each) and the

extra 1.4 -volts

improves

the

available power

output from

the built -in

audio amplifiers

Shown here is the

power

supply board prior

to installation

the

system

cabinet. Note

the orientation

and installation

the

U1, the three

-terminal regulator.

U1 is mounted

facing

(flat

side down) with

its leads

bent

right

angles,

and

secured to

a heat

sink.

of the car radio

and

also improves

its RF (radio

frequency)

sensitivity.

Diodes D5

and D6 also

reduce the

power dissipation

the

7812 by

lowering

the

voltage

between

the IN and

OUT

terminals.

A second

4700 -µF

electrolytic

capacitor

filters the output

from

the 7812

and provides

high short-term

current

capability

when

required.

Diode D7 is

included as

a safety measure

and

protects

the

output of

the 7812

against connection

to external

voltages

(e.g.,

charged capacitors).

Strictly

speaking, D7

is not required

here as the supply will

be permanently

connected

the radio. We've

included

it for

those

readers who

want

to build

the supply

as a free- standing

unit for

use in other

applications.

It is

necessary

to fit a small

heatsink

to the 7812

regulator

obtain

the

required

current rating,

because

the 7812 includes

internal

thermal

overload protection.

Our supply

delivers

about 1 ampere

a continuous

basis and 1.5

A on a short-

term basis, which

should

enough for just

about any

car

radio,

even high

- powered units.

PCB

Assembly

Figure

2 shows the printed

-circuit

board, foil pattern

for the

power

supply

used in the

conversion of

our car radio for

home

use. If you lack

the expertise

needed to reproduce

that board,

or simply

prefer to

use perfboard

(for

whatever

reason),

feel

free

to go that

route. Once the

board is etched (assuming

board construction),

and

you've obtained

all the parts,

you

are

ready

begin

the assembly

process.

Using Fig.

3 as a guide,

begin installing

the printed-

circuit

mounted

components.

All the

parts,

except for the power

1 2 ... 57 58 59 60 61 62 63 64 65 66 67 ... 99 100

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