Epson L90P - TM Two-color Thermal Line Printer Manual de usuario descargar pdf (Pagina 40)

M5

Fig. 18.

Author's prototype

may be

duplicated

or

used as

a guide.

Because

of

the

length

Fl

of M7, the Power Supply

mod-

ule, it is mounted

along

the

rear

apron of the

chassis. When

using

a different physical

lay-

out,

remember that the

Power

Supply

generates some

heat

and mount it out of the way

where it

will

not affect

the

heat -

sensitive components

that are

mounted

on

the other modules.

S2

display should

last only as

long

as the

COUNTING

light is dark.

The

counting

units

should start to count at

the same

instant

that

the COUNTING

light comes

back on.

Placing the SENS.

switch on

either the 1 or

10

position should stop

the

counting

operation.

If

the counter

passes all of these tests,

it is

probably

working

properly

and is

ready for use.

As

a

final

check, and to

gain some

experience

in

using the coun-

ter, use a bounceless pushbutton

circuit

( described in "Low -Cost Counting Unit,"

POPULAR ELECTRONICS, February 1968, or

ELECTRONIC EXPERIMENTER'S

HANDBOOK,

Winter 1969)

and a

low- frequency audio

oscillator. When

using

the

counter,

al-

ways start

with

the SENS.

switch down

to the

1 or .1 position as

required

to

get

a

stable reading. Also,

do

not

forget

that

an input lead (

whether

it is

coaxial

cable or

phono lead) that is too

long

will

attenuate

(and load) a

high- frequency

signal.

Key Waveforms. The following

infor-

mation can be used

if trouble

is

experi-

enced

in getting the counter to operate

properly. The waveforms at

various

points

in

the

circuit

vary

depending

on

switch

settings and the

nature

of

the in-

put.

However,

there

are some critical

points at which

the waveforms can be

checked

to

determine whether

the

count-

er is working

properly.

Comparator

(M1) When

sufficient

in-

put signal

is

applied,

the output at

the

square

-wave terminal of this

module

(connected to

DI

and

R7)

should be

either a square or

a

rectangular

wave

from

0 to 2.4 volts

positive. The output

goes

positive when the instantaneous

input signal

drops below

+10

mV

and

drops

to

zero

when the

input

exceeds

+30

mV. The

rise

and fall times

of this

wave-

form

should be about 60 nanoseconds.

The feedback

to pin 2 of IC1

should

show

a steep

leading

edge that reaches

+80

mV, followed

by a

rapid

decay

(about

90

ns)

to the +30 mV

level.

The

trailing edge of this waveform should

have a

rapid

transition

to

-40

mV and

a

rapid

decay back to

+10

mV. This

sig-

nal

is

present only when an input

sig-

nal is

applied

to

the

counter. Because

of

the

very fast switching

of this waveform,

you will

have to

use a

high -quality,

lab -

type

oscilloscope to make

exact

measure-

ments although the basic signal can be

seen

on

a

conventional service scope.

The synchronizing circuit in the

Com-

parator can be tested by using a bounce -

less pushbutton and observing the

DCU's

and the

COUNTING

indicator

light, in

the

0-

200

-Hz

range. The first

count after

the COUNTING

light comes on

should

not

be counted, and the

first DCU

should

display

starting at the

second

count.

The

first

count after

the COUNTING light

goes

off should

be

counted and

the

dis-

play should

remain

steady

after

that.

Correct

operation

of this circuit guaran-

tees

that

the

device will only count whole

input

cycles.

Scaler

(M2) The input to the

A scaler

should

be

identical to the

square

-wave

output

observed

on the Comparator.

Output

A /10 should

be a

rectangular

44

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