Memorex CP8 TURBO UNIVERSAL REMOTE CONTROL Instrukcja Użytkownika Pobierz pdf (Strona 67)

100

Fig. 1-

Battery

voltage is monitored by U1.

When the

voltage

drops

to below the threshold

value,

U2 begins

to oscillate,

turning

buzzer BZ1.

on and

remain on in spite of

small variations in the battery

voltage.

Note that

the circuit as shown

in Fig. 1 is powered by a

volt battery (obtained by

using four 1.5 -volt cells).

If you

wish

you can substitute a

9 -volt battery.

Buzzer Control

conserve

power (and your

hearing) the buzzer gives

short

warning

beeps

instead of

sounding continuously. The

buzzer

controlled

by U2, a CMOS

low

-power version of the

555

timer.

When turned on by UI,

pin 3 of U2 oscillates

high for

about .7

second followed by a .0I-

second low. The frequency

and duty cycle of the

oscillations are set by R4,

R5, and Cl.

Each time pin 3 of U2

goes low, the

voltage

across

the

buzzer causes

it to turn on briefly. The timer

continues to

oscillate and turn the

buzzer on and off until

the battery

voltage has

dropped

to about 2

volts.

Normally,

that

won't

happen for several days, giving

you plenty of time to notice

the alarm and

take action.

Customizing

the Circuit

You

can

adapt the circuit to sound an alarm

at any

voltage

level

from 3

volts on up to 16

volts.

All you

need

do is

calculate the correct

values for Rl, R2, and

R3.

Table

I gives

resistor

values

to use

for monitoring other

voltages.

One

caution:

Because the maximum supply

voltage rating for U2

is 18

volts,

the

batteries being monitored

should not exceed

that

voltage.

Cl BZ1

Parts

layout isn't

critical

for the lcw-battery alarm

circuit. Both 8 -pin ICs can be

mounted

a single 16 -pin

socket, and

either use wire wrap or

point -to

-point

soldering.

TABLE

1- RESISTOR

VALUES

Trip

Point

volts

kilohms

13 300

15 300

12 16

300

18 270

10 18 270

270

24 270

7 27

270

240 56

5 36

220

43 200 82

3 56

160

110

To custom -design

your own

battery

monitor, choose

a trip

point -the

voltage at

which you

want the alarm to

sound -

and the amount

of hysteresis

desired.

Plug those

values

into

this

equation.

R3 =

333,000

I.15/(TP

+ HYS)

Using

the resistor

values calculated,

solve these equations:

R2 =

x (TP-

1.25)/1.15

RI = 333,000

R3 R2

When

you've computed

the ideal

values

for

Rl, R2, and R3,

select

actual

values

close as possible,

using

available

components.

If you have another application

in mind, or if you just

know the

why

and

how behind

the numbers,

here is an

example to

help you design

with

the 8211:

If TP =5 and

HYS = .5, then:

R3 = 69,600

R2 = 227,000

R1= 36,300

Which

are

ideal

values.

Some actual

values,

using

available

resistors

to suit the application

would

be:

R3 = 68,000

R2 = 220,000

RI = 36,000

Construction

You can easily

assemble the circuit

on a

small piece of

perfboard

just 3 square

inches in area.

Or, if you

wish, the

circuit can

be built on a printed

circuit

board of your

own

design.

Regardless

which

construction

technique

you use,

the layout

of the circuit

is not critical.

For the enclosure,

use a

small plastic case

at least 1

inch

deep and cut

the circuit

board to fit it.

A plastic box

that has

been recycled

from another

use

will

fine -most en-

closures sold

for hobbyists' projects

are larger

than needed to

accomodate

the circuit.

Sockets

for the two

ICs are recommended.

save space

and

cost, both ICs can

be mounted

end -to -end

on one

I6 -pin

IC socket as shown

in the photo.

build the circuit,

mount the resistors,

capacitor,

socket, and buzzer

on the

board. Then use

Fig. I as a guide

wire

the

circuit, using

point -to -point

soldering

wire wrap-

ping. Be sure to

orient the buzzer

correctly -its

two legs

are

marked "

+ " and " " and

connect them

to the rest

of the

circuit

as shown

in Fig. I.

1 2 ... 62 63 64 65 66 67 68 69 70 71 72 ... 99 100

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