Elenco Electronics MO-1251 Manual do Utilizador descarregar pdf (Página 48)

100

meditate, or for self -hypnosis train-

ing.

You'll

find that the alpha

waves

occur

while

you're in a state of relax-

ed awareness,

which

is often called an

alpha state.

Circuit description

As Fig. 1 shows, a 555 astable os-

cillator (ICI), and transistor driver

(Q2) are used to flash the series

-con-

nected LED's over an adjustable

range of about 6.5 pps to 14.5 pps

(pulses per second), or, optionally,

3.5 pps to 7 pps.

ICI is configured as a conventional

astable oscillator

having an output

pulse that goes

low for 10 ms at the

rate set by potentiometer

R1. Re-

sistors R4, R5, and R6 allow

the os-

cillator to be

fine

tuned

to correct for

±20%

tolerance error in C2 and

RI.

You

can

use a frequency counter

pin 3 of ICI to

set RI's range, so that

has about the same overlap at each

end

of the 7- to I4

-Hz

band.

Note: Resistors

R4 -R6

can

omitted from the project, because

may

not

necessary to trim the flash

rate of your

instrument so precisely. If

you like, R5 can be a panel-

mounted

potentiometer for fine -adjusting

RI.

Transistor QI is normally

kept off

by R8; QI, in turn, keeps Q3 off.

low

-going pulse from ICI turns on Q1

for

10 ms, and pulses Q2 to momen-

tarily

flash the LED's. Resistor RIO

will

develop 650 mV across

it at

mA. That 650 mV

will

turn on Q3 and

limit

Q2's current to 54

mA. Having

that limiter, a constant current passes

through the

LED's with each pulse,

independent of the supply

voltage.

Most LED's are

rated for about 20

mA of continuous current,

but

at a

15% duty- cycle, they can

handle over

50 mA without harm.

The LED

brightness

is significantly increased,

yet

the battery drain is

still

kept quite

low. If you find that

the LED's are

uncomfortably

bright, increase

RIO to

between 15 and

27 ohms.

The specified LED's

are high -effi-

ciency

versions that emit a sur-

prisingly

intense beam of 30

-mcd

(millicandles are a

measure of light

intensity) at

20 mA. Standard

LED's

frequently have an

intensity of

to 5

mcd, and a

scattered, diffused

beam.

For the best effect, use

the specified

LED's because they

have lightly tin-

ted

lenses, higher output, and

a nar-

row

beam.

Commonly,

red

LED's have a

for -

cc ward

voltage

drop (VF) of about

1.7

FLASHRATE

10K

Cl G

tOµF

4.7K

15K#

SW2

0 P .

A/T J

r. C2

10µF

ICI

TLC555

10K

1N914

MINI PHONE -JACK

10K

2N3906

10K

CALIBRATE

4.7K

RED

33K

2N3904

NOTE.

SW2

AND C4

ARE

OPTIONAL

2N3904

BLK

GOGGLES

H D

R10

MINI PHONE -PLUG

12K

,,//,,//

,,/r

RED ,+/LEDI

0 LED2

DIODE-

CONNECTED J

TRANSISTOR

AS A

OPTION

- AC

ADAPTER

GOGGLE LEDs

BLK

FIG.

1 -THE

HEART OF THE

ALPHA MEDITATION

circuit

a simple 555

timer whose

pulse frequency is

controlled

by potentiometer R1. The pulse rate sets the visual flashing

rate of the LED's

in the

goggles.

volts

at 20 mA,

whereas

the brighter

ones typically have a

of over 2

volts.

Therefore,

up to

four standard

LED's

can be used

the circuit.

However, the

of the brighter LED's

prevents using four of them

with

a 9-

volt

supply.

Diode DI and capacitor Cl provide

better power -supply filtering

and

iso-

lation for ICI than a conventional R/C

filter. However,

100 -ohm resistor

can be substituted for Dl if you desire.

For a

very-low voltage

loss across Dl,

you could try using a Schottky diode

or a diode -connected transistor,

such

as a 2N2222 or 2N3904 (see Fig 1.).

That isn't really necessary, but it may

keep some purists happier.

Without

the filter, the high- current pulses

through the LED's can

adversely

af-

fect the 555's operation, particularly

with

weakening

battery.

A mini phone -jack, JI, provides a

convenient

way

to disconnect the gog-

gles

from

the control

box for storage.

Another jack, J2, allows

you to power

the A/MG from an

AC adapter having

12 -volt DC output. Make

sure

that the adapter

has the proper

polarity

(a DC output, not

AC), and a rating of

50 mA or

more. Remember

that

12-

volt adapter

will not make the LED's

any brighter than

a 9 -volt battery

be-

cause

of the current

limiting.

PC -board assembly

The control circuitry

does not

need

special care in

assembly

or layout, so

perfboard

should work just

well

the

author's PC- board;

the Parts

Placement

is shown in Fig.

2. For ease

of discussion, we'll

assume you're

using the PC

board. Note that

the PC

board supplied by the

author is silk

screened with

all parts labeled,

and

solder

-pads A through

K are identi-

fied. All the

holes have been

drilled to

their proper size.

The inside of the

control box is shown

in Fig. 3, while

the control

box exterior assembly

shown in

Fig. 4.

keep the board

oriented prop-

erly,

lay

the board on your work

sur-

face

with

the

copper side down and

SI's mounting

holes

your right.

Identify the locations

of all the com-

ponent mounting

holes,

and the

mounting pads. Keep

ICI in its anti-

static foam until you're

ready to in-

stall it.

2. Insert the switch into its mounting

holes and

solder

the three

leads. The

mounting tabs can be soldered to the

board, too, but you will have to scrape

the black finish from those tabs in

order to do that.

Install

Cl,

C2, and Dl.

Those

parts

are polarized and

must be installed as

indicated. (C4 should also be

in-

stalled

going to be used.)

4. Install all resistors except

Rl, and

also

install

C3.

There

are two ground

pads for C3 to accommodate

variety

of capacitor

styles and sizes.

5. Use a piece of capacitor

or resistor

lead

jumper the two pads on the 555

(pins

and

8). Install the

jumper

flat

1 2 ... 43 44 45 46 47 48 49 50 51 52 53 ... 99 100

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