Elenco Electronics MO-1251 Manual do Utilizador descarregar pdf (Página 10)

100

TALK IS

CHEAP.

Have

you

heard? For less than

$90

your

AT or XT- compatible

com-

puter can talk!

All it needs is the

-2000 Computer

Voice

Kit from

Heathkit.

Reading

letters, transcriptions

and

computerized

instruction can be

easier

and quicker than

you ever

thought

possible. Computer

games

gain

a new dimension.

Your com-

puter can even

entertain

children

with

stories

and

songs.

If you have

a modem,

the

-2000

Computer

Voice will

allow

your

computer to

recite reference and

research information

from time

sharing

services. Or, speak radio

transmitted ASCII information.

The HV

-2000

Computer

Voice

Card, containing

speech synthesizer

and audio amplifier, plugs

into any

XT- compatible

computer's

expansion slot. An external

speaker

is also included.

Versatile, Heath -

developed software gives

you

wide

variety of

voices

and easy

terface to

high and low level

languages.

The HV

-2000

Computer

Voice.

At less than

$90,

talk IS cheap.

order,

call toll

-free 1- 800

-253 -0570.

Use

your

Visa,

MasterCard, Ameri-

can

Express or Heath

Revolving

Charge

card.

Or call 616 -982 -3614

for

the nearest

store location.

'Heath Company

subsidiary

of Zenith Electronics Corporation

Prices, product

availability and

specifications

are

subject to change

without

notice.

CIRCLE 86

ON FREE

INFORMATION

CARD

Asi

R -E

RAM INCREASE

I have

Tandy

1000SX

computer

and would like

increase

the

amount

RAM in the

circuit.

don't

want

to use a

memory

expansion

board because I'd like

keep

many

slots available as possible. Is it

possible

to add

RAM by piggy-

backing

memory IC's

on top of the

existing ones and tying in chip -se-

lect,

address, and data

lines

at ap-

propriate

points

on the

bus ? -B.M.,

Oakhurst,

CA.

Judging by the mail, a lot of peo-

ple

seem to

interested in

doing

something like that. It's

become a

bit more expensive

to experiment

with RAM

since the price of mem-

ory

has

multiplied

by a

factor

five in the last

year or so, but I can't

argue with the fact

that more

memory is

a desirable thing.

any event, while what

you

want to

probably the-

oretically

possible,

from a practical

point

view you're letting

your-

self

for a lot of potential

brain

damage. Since I

don't

have sche-

matics

on the

Tandy1000SX,

it's im-

possible to

tell

how much

of a job

it is to add memory

to the mother-

board; but there

are undoubtedly

several major factors

that you're

overlooking.

First

of all,

it's

a safe guess that

you're talking

about dynamic RAM

and that brings up several

ugly

necessities,

the chief of which is

refresh. Dynamic

RAM has to be

refreshed

periodically (usually

every 2 milliseconds), or the stored

data will fade away into hyper -

space. A reliable refresh system is

one

of the

major

components in

the design of the

circuit and

there's

probably an upper

limit

the amount

RAM it

can handle.

Adding memory

to the board

with-

out

knowing

exactly how

refresh is

done

a risky business.

You

also aren't paying any atten-

tion to how the control lines are

handled.

Tying

the select

lines

the new memory without

paying

any attention to how the memory

is organized may lead

to a situa-

tion where

you're enabling two

memory cells

at the same bit

loca-

tion

of the same address. At best

that

would

a waste

memory

and

worst

you'll damage

some

very

expensive silicon.

The

bottom line here is

that

it's

not a good

idea to monkey

around

with

an existing

design unless you

understand

the

design;

and

that

means having

the paperwork. For

what it's worth, I'd

willing

guess that the

board

isn't

generat-

ing the

proper control signals to

deal

with

any additional memory.

You'll have

to check the circuit to

see if that's

true, and, if it is, your

first job is

to build decoding

cir-

cuitry to handle the extra memory

you want

to add.

Remember,

there's more on a

memory

expansion board than a

bunch of

RAM.

ADD A JACK

I'd like

to add an earphone jack to

television

set so that

can

listen

to it without

disturbing anyone

else.

What's the

easiest way to

that?

E. Juzumas,

Seaford,

NY.

Adding

an earphone

jack to a

set

a straightforward

operation,

but there

are a couple of twists that

can make it more

difficult. Let's

take a look

the

simplest case and

then talk

about the problems that

you might run

across.

You

can't deal with the audio

un-

til the TV's front

end has finished

demodulating the RF and

sepa-

rates it into

audio and baseband

video,

as shown in Fig. 1.

Once

those two signals

are available, the

audio signal can be picked

up and

routed

to an earphone jack. There

are two places where

you can do

that.

The first is

at the volume control

and

you

have

two options there as

well.

You can take it from the

ends

the

potentiometer,

in which

case the TV set's volume

control

won't have

any effect on the level

at the

earphones, or

you

can take

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 99 100

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