Memorex CP8 TURBO UNIVERSAL REMOTE CONTROL Manuel d'utilisateur télécharger pdf (Page 93)

100

BOOKSHELF

ment. Now,

with

the help of

Radio Elec-

tronics' editors, you can have expert,

hands

-on help in urderstanding

solid

state

technology

and its applications.

Each topic

includes an introductory ex-

planation. Example circuits are

used to

illustrate how the

various solid state de-

vices

work, and there's plenty of infor-

mation on the applications

and special

uses of these circuits.

You'll cover op amps,

analog IC's,

and digital

ICs. For the

novice, there

STATE

SOLID STATE

CIRCLE 98 ON

FREE INFORMATION CARD

are numerous simple circuits to get you

started as you cover diodes, bipolar tran-

sistors, FETs,

MOSFETs, and

other pn

junction devices. You'll find out about

circuits that beep, blink, and

buzz,

cover

sensors,

power supplies, amplifiers, and

oscillators, and

build projects that range

from an audio preamp and dc

voltage

controlled switch to metal

sensing

de-

vices,

IC telephone ringer, an elec-

tronic lock, and a light dimmer.

The book contains

160 pages, sell-

ing for $9.95 from Tab Books Inc., Blue

Ridge Summit,

PA 17214.

Using Comparators

Detect and

Measure

(Continued from page 64)

the output of the top comparator goes high and lights LEDI

(green)

when

the temperature is too low. In that

circuit,

when

the temperature

falls within

the

window,

both

light

emitting diodes are off.

Bar -graph Display

The final

examile (Fig. 10) is a light meter

with

bar -graph

output.

Circuit design

made easy by using an LM3915

bar

-graph-

driver IC,

which

contains a series of 10 compara-

tors. The - input

each comparator connects to

the buffered

input voltage,

and the

inputs connect along a nine -resistor

voltage

-divider

network.

To use the LM3915,

you need only add a sensing circuit

and connect the comparator outputs to a bar -graph display

or succession of 10 light-

emitting

diodes.

In Fig. 10,

the

input at

pin 5 of U I is taken from a

voltage

divider made up of R 1 (a cadmium -sulfide photoresistor)

and

R2.

Each comparator inside U I compares the buffered

input voltage

to its reference

and

turns its light-

emitting

+9V

20K

10K

NTC

THERVISTOR

10K

AT 25

+9V

10K#

10K

It-

20K

LM339

10K

390n

LEDI

(GREEN)

2N2222

39052

LED2

(RED)

2N2222

Fig. 9-This

cut

-of- window

comparator detector

warns the

experi-

menter

too high,

well

as too

low, temperatures levels.

+9V

1.2K

LM3915

REGULATED

VOLTAGE

SOURCE

1.2V

CdS =

PHOTO

RESISTOR

10052

20K

+9V

Fig. 10-The number

of LEDs progressively lit in

the bar

-graph

display varies with the light level

sensed by photoresistor

R1.

diode on or off, as appropriate. The number of

light- emitting

diodes lit thus

varies with

the light level

at RI.

Resistor R3 sets the current in

each of the light- emitting

diodes

10 milliamperes,

and potentiometer R4 selects the

full -scale (all light- emitting diodes

on) input

voltage

be-

tween 1.2 and 7

volts.

Leaving pin 9 of

unconnected

will

change the display

from a bar graph to

single

-dot display. In that mode, only

one LED is lit

at a time (which saves on battery power!)

and

the position of the LED indicates

the signal level

and thus

the light intensity.

Now It's Your Turn

Comparators are circuit building -blocks that are both

easy

to use and adaptable to many circuit situations.

With

the

collection of circuits presented in

this article, you should

be able to begin to adapt the circuits provide here and design

your own comparator circuits to meet specialized

voltage

detecting

needs.

103

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