Radio Shack SSM-1750 User Manual download pdf (Page 59)

One interesting side effect here is that

the

inherently

limited charge and dis-

charge

rates

of a double -layer capacitor

give automatic

short -circuit protection.

Some batteries, especially Ni -Cds, in-

stead tend to get

downright violent when

you short them.

Several manufacturing

options are

available that trade off maximum possi-

ble charge and discharge currents against

cost and size. The smallest and cheapest

versions

are intended for long -time, low -

current

memory

backup uses.

Let me know what

interesting uses

you

can come up

with

for this

exciting,

yet

imperfect, new

hacker component.

OK.

How

did you do it?

If there's one thing

can't

resist, it's

good

hack,

especially

if it lies well be-

yond the far side of

"disgustingly

ele-

gant." Check

the

capacitor

lettering in

Fig. 1. Note that

not only have isome-

tric

lettering, but the lettering is also cor-

rectly

wrapped

around a cylinder!

This

was

quickly

and easily "drawn"

with

the

stock and standard

Apple Writer word

processor, as

were

all

parts

of all

figures

in this column. Oh, yes, I did add a short

little

custom

text routing

own that

I'll be happy to share with you. The same

routine also lets you

set

text in a helix or

inwardly

closing spirial.

Write

or call

for you free

copy.

How

can

Control AC Power

With a Personal

Computer?

There

are two problems involved in

con-

trolling high -power

loads with

a per-

sonal computer or microprocessor paral-

lel port. The first is

that the weak port

signals must

somehow be amplified to

make

them

"strong

enough" to

control

high power load.

The second hassle is

that there is a very deadly

shock

hazard

involved with

ac power

control,

which

means that some

sort of safety isolation

an absolute must.

While you

could use a

relay

driver

and a relay,

the usual

way

to handle

110 -volt ac high -power interface

today

to connect a phototriac

optoisolator to a

triac power control

device. Figure 2

shows details.

+5V

PORT

MOC

3010

phototriac

optocoupler

3305

100 watt

light

bulb

220Q

2N6154

TRIAC

110 VAC

WARNING: Extreme

shock

hazard

right half of this circuit!

Fig. 2.

A 110 -volt ac power

control interface

for

a personal computer.

The triac optoisolator consists of a

light- emitting diode that drives a photo-

sensitive ac power control device called a

phototriac. When the LED lights, the

phototriac

turns and activates the

main

high -power triac to switch the

load.

Because only a light beam connects the

input to the output, you get total safety

isolation. The

"amplification"

you need

comes

from

both the

internal phototriac

and the main power triac.

There

are some important details

you

have

to be aware of

when you

use this cir-

cuit. First and foremost,

note

that there

is a deadly shock hazard anywhere to the

right

the triac

optoisolator; so

use

ex-

treme caution

when working

on any cir-

cuit of this type.

The

power

triac will switch

or off

most any ac

load,

such as

lamps, motors,

heaters,

whatever. A minimum load

must

always be provided

for proper oper-

ation, say 7 watts or so. The maximum

load depends on the triac and the size

the

heat sink you use.

One .classic

handbook for

triac power

control

the SCR

Manual from General

Electric. My issue is

sort

of dated, so it

may have a new name and a new

price

now. Cost should be around $5.

You also must use a phototriac optois-

olator,

rated at least 200 volts for

110

-volt ac operation, or 400

volts

for

220 -volt

ac operation. Note that the

other types

of optocouplers

will instantly

self- destruct

you try to use them for ac

power control.

The Motorola MOC

3010

is often a good choice and costs slightly

over a dollar.

I have

also shown the

inputs

to this cir-

cuit connected "backwards" from some

other circuits you may have seen. There is

very

important reason for this. Most

parallel

ports

on microprocessor systems

are much better

at sinking current

ground than they are at

sourcing

current

from

a positive

voltage.

With

this circuit, the output

port either

sinks current to ground, activiating the

phototriac optoisolator and powering

the load, or doing nothing and not deliv-

ering power to the load. Connected

"backwards," the

optoisolator

is much

better matched to the parallel computer

port and will work much more reliably.

One little gotcha with this "back-

wards"

connection:

Your port will

now

be active

low,

so a

zero

at the port

will

ac-

tivate the load. Your software must, of

course,

recognize

this

fact, and write

zeros to the port

locations when you want

power the

load.

Note

that a

machine

-language com-

mand of FOR #$FF

will

automatically

convert all of

the

ones

in a word to zeros

and

vice versa.

From BASIC, an XX =

Say

You

Saw

It In Modern Electronics

September

1986

/ MODERN ELECTRONICS /

1 2 ... 54 55 56 57 58 59 60 61 62 63 64 ... 83 84

Comments to this Manuals

No comments

Radio Shack SSM-1750 User Manual Page 59

Comments to this Manuals

Related products and manuals for Audio mixers Radio Shack SSM-1750