Mitsubishi Electric MUX-25TV - E1 User Manual download pdf (Page 44)

Construction

Project

A

Versatile

Printer

Stand

This

build -it- yourself printer stand provides three

paper "trays "and features optional "smart "power

and printer- selector switches

By Bill Green

There are a

host

of convenience

features that one can add

to

personal computer

systems to

make

use

of these

machines more

ef-

ficient. A good example

is modifying

the typical

printer /stand setup.

At

the grass -roots

level, having to

indi-

vidually turn on and off power

for

each

item in your computing system

can

be frustrating. So can

juggling

cables to switch

from one printer to

another.

Finally,

if you routinely use

different

papers and

forms,

changing

from one to another

can be an aggra-

vating

chore.

The projects

to be discussed

here

can overcome

these problems.

The

"Versatile Printer Stand"

described

solves

the paper- changing

hassle.

Furthermore,

it can be equipped

with

a "smart"

switch

that automatically

turns on /off

power

with the flip of

the power switch

on just your com-

puter.

Finally, you can

add either a

parallel

or

serial

switch

that will al-

low you to select either

of two print-

ers

without

having to unplug and

plug in cables.

Naturally, the last two

devices

can be used alone.

Smart

Power

Switch

Shown in Fig. 1

is

the complete sche-

matic diagram of the Smart Power

Switch. This power controller can be

used

with

any system containing two

or more components that are usually

switched

on

and

off

simultaneously.

This

might

be a computer

/printer/

modem

combination

or a stereo re-

ceiver /tape

recorder /VCR combina-

tion or whatever.

(It

can also

be

used

as an add -on accessory

to the "Com-

puter System

Power Controller"

featured

in Modern

Electronics,

Nov. 1985.)

The Smart Switch

is designed

to

control ac

line power to a

slave ac

outlet when the equipment

plugged

into the master outlet

is

turned

on

and

off.

It

does so

automatically,

re-

lieving you of the

need to individually

turn on and

off each device

in your

system.

Pushbutton switch

SI can

be

used

to select between the Smart

and

Bypass functions.

In the latter

func-

tion,

the

Smart

Switch

is bypassed,

requiring that you

individually turn

on and off any

items plugged

into

the

SOI and

SO2 ac

receptacles.

Note in Fig. 1 that

there

are

four di-

odes (DI through

D4) connected

in

series with

master receptacle SOI.

When the computer

or

other

device

plugged

into

SOI

is off, little or

no

voltage is

dropped

by these diodes

and,

hence,

the

rectified

voltage

at

the

base

of QI

is not of sufficient

magnitude to

turn on the transistor.

When the device plugged

into SOI

is

turned

on,

however,

enough

volt-

age

is

dropped

by

DI

through

D4 to

turn on Ql.

This returns the

low

end

50

/ MODERN ELECTRONICS

/ April 1986 Say

You Saw

It In Modern

Electronics

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