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CIRCUIT CELLAR F)b&?h o

THE COMPUTER

APPLICATIONS

JOURNAL

FOUNDER/EDITORIAL

DIRECTOR

PUBLISHER

Steve Ciarcia

Daniel Rodrigues

EDITOR-IN-CHIEF

Ken Davidson

PUBLISHER’S ASSISTANT

Susan McGill

you’re supposed to fill out and mail back to “register your

warranty.” What the number of people living in your house or the brand of

underwear you prefer has to do with toaster warranties, I’ll never know.

The tax man wants to know how much you earned last year. The credit

card companies want to know how much your mortgage payment is while

the mortgage company wants to know how much is on your credit card. The

federal government wants to know how many people live in your house (for

the census) and the local government wants to know how many rooms live in

your house (for property assessments).

Just when you thought you could escape data collection by withdraw-

ing into your own home, along comes version 2 of the HCS II and its data

logging capabilities. Now you can even keep track of how long you spend in

the bathroom!

On a somewhat smaller scale is our first project this month. Using the

infrared communications capabilities of the popular HP-48SX calculator, the

ADCM-48 I/O interface provides a very portable means of doing data

acquisition and control in even the most inaccessible areas. John Wettroth

gives a full accounting of his design process, so you can decide for yourself

if he’s met his goals.

Next, we look at data collection of a different sort: digitized speech.

While most people are familiar with the more popular methods of speech

storage and playback (such as PCM, ADPCM, or LPC), many haven’t yet

heard of CVSD. Let Jeff Schmoyer be your guide into the inner workings of

CVSD, while Jim Hubert presents some practical hardware.

Our final feature is a continuation of William Von Novak’s computer-

controlled light dimming system from last month. This time, he discusses

some of the more common dimmer circuits and describes the hardware and

software of a complete, working system.

Kicking off our columns, Ed explores the timing of the ISA bus in detail

and begins to piece together his Firmware Development board. For all you

RISC junkies who haven’t been able to use your favorite processor in your

latest embedded project, Tom has some good news for you. The new

AMD29205 looks to have a promising future in those embedded designs

where 8 bits just won’t do.

Jeff and John both build sample applications based around the

displays they presented last month (LEDs for Jeff and vacuum fluorescent

for John). Finally, Russ looks at several patent abstracts that look nearly

identical, and among the inventions he highlights is a “device for transmitting

sonic vibrations, such as music, to a fetus [through]...an abdominal

belt...worn by the mother.” Not to be missed!

CIRCULATION COORDINATOR

Rose Mansella

TECHNICAL EDITOR

Michael Swartzendruber

CIRCULATION ASSISTANT

Barbara Maleski

ASSOCIATE EDITOR

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Gregory Spitzfaden

ENGINEERING STAFF

Jeff Bachiochi & Ed Nisley

BUSINESS MANAGER

Jeannette Walters

WEST COAST EDITOR

Tom Cantrell

ADVERTISING COORDINATOR

Dan Gorsky

CONTRIBUTING EDITORS

John Dybowski & Russ Reiss

NEW PRODUCTS EDITOR

Harv Weiner

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TIONS JOURNAL (ISSN 0696-6965) IS published

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q /‘

Issue #33 April 1993

The Computer Applications Journal

Data Acquisition and Control

with the HP-48SX

by John Wettroth

What Makes CVSD Tick{

by Jeff Schmoyer

Generate Digital Speech Using CVSD

by J. Conrad Hubert

Computer-controlled LIGHT DIMMERS

Part 2: Filters, Snubbers, and Design Issues

by William Von Novak

Silicon UpdateiTom Cantrell

RISC Faces Reality-And Reality Blinks

Editor’s INK/Ken Davidson

Take Up a Collection

Embedded Techniques/John Dybowski

Bring Your Vacuum Fluorescent Display to Life

Reader’s INK

Letters to the Editor

Patent Talk/Russ Reiss

New Product News

edited by Harv Weiner

ConnecTime-Excerpts from the Circuit Cellar BBS

conducted by Ken Davidson

Firmware Furnace/Ed Nisley

Barnacles on the ISA Bus:

Starting the ‘386SX Development Card

Steve’s Own INK/Steve Ciarcia

Voice Recognition and Professional Reinvestment

From the Bench/Jeff Bachiochi

Advertiser’s Index

You Can Count On It

Issue #33 April 1993

The Computer Applications Journal

3nB~$~INK

OMISSION?

better class of folks. While I can empathize with some of

In reading your article “Temperature Monitoring” in

your frustration, I can also make some recommendations.

the February 1993 issue, I noticed an omission which

My company is basically a one-man show. While I

many readers may want to be aware of. I have used the

have some very good subcontractors, most of the real

LM34 for many jobs, however the output is not uncondi-

work that gets done falls on me. While involved on a

tionally stable when driving a capacitive load, such as a

project recently, I had to reengineer about 10 hours of

shielded twisted pair cable. This type of cable is often

work my so-called “engineer” had already done. Lacking

used to allow the LM34 to be placed far from receiving

both knowledge and information of some particular parts,

electronics. The capacitance of these cables can be up to

I started making calls.

100 pF/ft between conductors.

The first was to Digi-Key, and they were invaluable

Under this sort of load, the LM34 output begins to

in helping me locate parts that would run at the speeds

“lope” or “motorboat,” usually manifested as a triangle

needed. Next, they were honest in that some of the

wave added to the normal DC offset. It’s hard to detect

questions were beyond the realm of what they could

except as “noise” in the data or strange, cyclic variations

handle, but they gave me phone numbers of some

of temperature at some frequency related to the sam-

manufacturers that might be able to help.

pling interval of the monitoring system.

I called manufacturers “H,” “T,” and “S,” all to no

The cure is to place a 1-5 kfi resistor in series with

avail. Then I called National Semiconductor. When you

the LM34 output as shown in the National Semiconduc-

are a multibillion dollar, multinational firm, it’s reason-

tor application notes. This decouples the LM34 output

able to expect companies to be ecstatic when you conde-

from the load capacitance. For example, using a 2.2-ka,

scend to call them. When you are “Micro Ventures” you

5% resistor, I have been able to use a 25foot cable

usually are not treated the same. This concept holds true

without oscillations. The only caveat is that there will

at National Semiconductor. They treat you better. I

be a voltage-divider formed by the decoupling resistor

needed one of their reference books that five different

and the input impedance of the monitoring system.

vendors told me was out of print. The lady with whom I

Depending on the input impedance and bit resolution of

spoke assured me they were not, and I could get one free

the monitoring system, the effect may be negligible.

of charge in about a week from their California office.

Thanks for another fine issue. I’ve been reading

When I told her that time was of the essence, she Fed-

Circuit Cellar articles now for over ten years; each one’s

Ex’d a copy she had on her desk that very day, telling me

been a treat! Keep up the good work.

she fully understood that sometimes you just can’t wait.

Since then I have been trying to find her name so that I

H. Ward Silver

Vashon Island, WA

could write the president of National with my compli-

ments.

As if that wasn’t enough, once I had the reference

We don’t presume that Circuit Cellar readers take

book and solved one problem, another arose. I called

everything they read verbatim and jump off cliffs.

National’s tech support and was given more help and

Before applying a new technology or using a new device,

information than I could use. While I was still in a daze

we expect that successful application includes consult-

about the high level of service that had been afforded, the

ing a data book for additional facts.

engineer in tech support actually followed up with a

Editorial policy aside, the cables on all of the LM34

phone call to see how things were going. I told him that

probes I used were under 6 feet long and the outputs did

his parts were working fine, but I had an interface

not exhibit “motorboating,” so I overlooked the poten-

problem. Although the specific problem did not involve

tial eccentricity in alternative operation, The facts you

anything that National made, he had me describe the

point out are better defined as professional experience.

circuit and the problem. The next day he phoned me

We try to include as much wisdom as possible in our

again and gave me not one, but two solutions, both of

presentations. Thanks for adding more.-Steve

which he had checked on his circuit design/emulation

software! If I were Bill Gates or Ross Perot, I wouldn’t

expect this level of help and dedication, but to be MGC

SAMPLE GAME

Data Services, a “Micro Ventures” type firm, is beyond

I recently read your editorial “The Sample Game”

belief.

from issue #3 1. To paraphrase a punch line from one of

Since then, I have called Digi-Key numerous times

our southern jokes, maybe you need to be dealing with a

and not once been asked how much I was spending

Issue #33 April 1993

The Computer Applications Journal

Embedded PC

whenever I have needed their support department.

Also, National Semiconductor has shipped numerous

reference books from their literature department and I

didn’t have to pay freight. A commitment to customer

relations at these two firms is not dead. It does not

need to sink in at the top, but rather seems to emanate

from there. Guess who’s parts I will be buying and

from where, whenever possible regardless of price?

Gerald J. Nagy

West Columbia, SC

IN THE EYE OF THE BEHOLDER

I am writing in response to the letter in the March

1993 issue of the Computer Applications Journal from

Ronald Brown. I think many of us toy with the idea of

mixing art with controller technology to form some

kind of fantastic kinetic art object.

It occurs to me that this type of design experience

becomes an exercise in packaging. I am not certain

what Mr. Brown had in mind, but using a controller to

move motors, blink lights, or even talk is pretty much

a commonplace thing for controllers to do.

The trick is to decide what to move with these

motors (for instance, do you motorize a mannequin?],

how to use computer-controlled lights for theatric or

artistic effects, or even using controller-based sensors

so the artwork can sense when it is being viewed?

It seems that merging technology and art could

create some very dynamic and enjoyable objects.

These objects, should they become accepted, could

certainly enhance the public and private spaces on our

world. But I think the question really becomes one for

the critics to decide: what applications of controller

technology can be called art and which ones cannot be

called art? I have seen many objects-de-engineering

that gave me an impression that the engineer and the

artist are one, but that is just my opinion. Still, I

would urge Mr. Brown to follow his inspiration and

mix these two worlds together. Only after the critics

have something physical to talk about can they begin

to argue the artistic merits of it.

le 8OC88@ 8Mhz CPU Module

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#103

‘b-bit, 4_f

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unction

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The Computer Applications Journal

Issue #33 April 1993

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