Memorex CP8 TURBO UNIVERSAL REMOTE CONTROL Instrukcja Użytkownika Pobierz pdf (Strona 84)

100

Charles D.

Rakes

Get

your

shopping

list

ready

for

this

month's

supermarket of

electronics

circuits

GET READY FOR

A WORKOUT,

CAUSE

this month

the Circus is going to

run an

electronic marathon

to see

just how

many "user

friendly"

circuits can

crammed

into the allotted

space.

Capacitance

Checker

The

circuit, in Fig. 1,

came about

at a

time

when

I couldn't locate

my old Eico

capacitor

checker to test the leakage

a tattered

electrolytic

capacitor that was

needed for

a project under construction.

Granted that

this simple capacitor

tester

won't

give you a digital

readout, but

with

a little practice

you can tell a good

deal about what's

tied to its input, and

in the

process learn a little

more about

capacitors in general.

The

capacitor tester,

using the com-

ponent

values

shown,

can indicate

UNDER

TEST

+9V

Fig.

1 -The

capacitance checker, using

the component values

shown, can

indicate a

leakage resistance

100

megohms. and

more.

When

checking

electrolytic capacitors

be sure to get

the polarity right

or the unit is

sure

leak like

a sieve.

PARTS LIST FOR THE

CAPACITANCE CHECKER

LED1

-Jumbo

light-

emitting diode

01, Q2- 2N2222 general

-purpose

NPN

silicon transistor

R1, R2- 1000

-ohm

1/2-watt,

re-

sistor

Sl-

Normally -open,

single -pole,

sin-

gle

-throw pushbutton switch

Printed circuit

perfboard materials,

enclosure,

sockets,

battery, wire,

solder,

hardware,

etc .

leakage

resistance ut IOU megohms,

and more. That's a bunch of ohms. But

number

of good- quality Tantalum ca-

pacitors,

most all non -electrolytic, and

number

of good- quality electrolytic

capacitors test

well

above that leakage

resistance

value.

When

checking electrolytic capaci-

tors be sure

to get the polarity

right or

the unit is sure

leak like

sieve. Most

electrolytic capacitors take a long time

to charge

unless SI

is pressed for

few

seconds, speeding up the charging pro-

cess.

As soon

as a good capacitor

charged, the leakage current should be

very

low or almost non

-existent, and the

LED should remain dark. After a long

period of time, depending on the size

and quality of the capacitor, the LED

may begin to glow dimly as a small

charging

current

flows

to replace the

capacitor's

voltage

loss due

the slight

internal leakage current and Q1's min-

ute base current.

A good 1- microfarad non -electrolytic

capacitor connected to the tester

causes

the LED to light and remain on for

about one minute

as the capacitor

charges. A 0.1- microfarad unit takes

about

seconds,

and a .0I- microfarad

unit takes

about

1 second to

charge.

the LED does not go

out after a suffi-

cient charging time, it's a good indica-

tion that an

internal

leakage resistance

is lurking somewhere between

the ca-

pacitor's leads. So, not only does our

simple

checker test

for

internal

leakage

resistance, but also gives a clue to the

capacitance

value.

If you are only inter-

ested in checking for leakage resistance

press S1 to speed up the testing pro-

cedure.

Simple

Voltmeter

Ube circuit in Fig. 2 is

almost

too

simple to

share.

But

it's so darn handy

to use that I

couldn't resist. No matter

how you

connect

the circuit to a

voltage

source, the meter always reads

up scale.

Diodes Dl -D4 can be any good-

quality

METER'S

TEST

LEADS

ANY

POLARITY

VOLTAGE

'01 -D4

SEE

TEXT

02-

03'

VOLT

METER

Fig. 2 -Any

voltage

applied to this

voltmeter

circuit is fed

to the meter,

with the

correct polarity. For

in-

stance, assume that

a DC source is

fed

across the input

to the

circuit, and

that the

upper terminal is

positive

with respect to

the lower terminal.

The

positive

potential at the

cathode

of D2

reverse

biases that

diode so that it

does

not

conduct.

At the

same time that

positive potential

is applied

to the

anode

D1, forward

biasing that

unit

and causing it to

conduct. While

that

action is

going on at the

upper ter-

minal,

a similar (but

opposite)

event

is taking place

at the lower

terminal.

PARTS LIST

FOR THE

SIMPLE VOLTMETER

Dl -D4-

Silicon

rectifier

diode (see

text)

M1- Voltmeter

Perfboard

materials,

enclosure, wire,

solder,

hardware,

etc

silicon

diode

with

a voltage

rating that's

greater than

the full -scale voltage

range

the meter used. Don't

forget to add

about I.2 -volts

to the meter

reading on

the low voltage

ranges,

to compensate

for the forward- voltage

drop of the di-

odes when

conducting.

The

circuit's operation is simple.

Any

voltage

applied

to the circuit is fed

the meter,

with

the correct polarity.

Let's assume

that a DC source is fed

across

the input to

the circuit, and that

the upper

terminal is positive

with

re-

spect

to the lower terminal. The

positive

potential at the

cathode of D2 reverse

biases

that diode so that it does not

conduct.

At the same time that

positive

1 2 ... 79 80 81 82 83 84 85 86 87 88 89 ... 99 100

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