I71896 48783
`
`UA-1010.001
`
`UA-1010.001
`
`

`
`April1991
`
`BUILD THIS
`
`---- . -~_. -._.. _.
`
`.-'-'-l
`
`Vol. 62 No.4
`
`_.~ --"
`.,.. -- ,
`
`.
`
`_ :
`
`. .
`
`'
`I
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`~)'OW
`--......
`'*-"*
`.,.."""
`
`4D--n
`DC*AC
`~-'
`,......,...4C
`
`17 POOR MAN'S LASER PRINTER
`Build your own and save big bucks!
`Paul Renton
`
`33 MAGNETIC FIELD METER
`Use this easy-to-build gaussmeter to find out if you 're being exposed
`to potentially dangerous magnetic fields.
`Reinhard Metz
`
`43 LINE POWER FROM 12 VOLTS
`This 40-watt DC-to-AC inverter lets you run appl iances from you r
`car's cigarette lighter.
`David Cuthbert
`
`45 BUILD THIS VIDEO PHONE
`Send and receive video pictures over standard phone lines !
`Charles Colby
`
`63 THE STEPPER·MOTOR ROBOT
`Our friendly robot is a great teaching tool.
`Fred Eady
`
`TECHNOLOGY
`
`.
`
`I
`
`27 FCC APPROVES NO-CODE
`Now you can get a Technician-class Amateur Radio license without
`passing a Morse-code test!
`Mike Stone WBOQCD
`
`49 EXPERIEMENTS IN VOICE RECOGNITION
`Two simple projects let you use voice commands to control things.
`Daniel B. Cooper
`
`57 INSIDE SWITCHING POWER SUPPLIES
`Learn the basics of switching regulators.
`Harry L. Trietley
`
`PAGE 43
`
`PAGE 45
`
`DEPARTMENTS .
`
`.
`
`.
`
`I: AND MORE
`
`D~
`~ C
`
`_
`
`98 Advertising and Sales
`Offices
`98 Advertising Index
`12 Ask R-E
`13 Letters
`88 Market Center
`26 New Lit
`22 New Products
`4 What's News
`
`--1.
`
`6 VIDEO NEWS
`What's new in this fast-
`changing field.
`.
`David Lachenbruch
`18 EQUIPMENT REPORTS
`Hewlett Packard 5600A
`Portable Oscilloscope.
`71 HARDWARE HACKER
`New hackable project ideas,
`and more!
`Don Lancaster
`- - - - - -
`
`80 AUDIO UPDATE
`Audio amplifiers : Do they
`sound different?
`Larry Klein
`85 COMPUTER
`CONNECTIONS
`The evolution of standards.
`Jeff Holtzman
`
`UA-1010.002
`
`

`
`ON THE COVER
`
`If you've been worrying that just
`about everything in your life can
`cause cancer, at least you can stop
`worrying that you're paranoid. Be-
`sides smog,
`red meat, cigarettes,
`radon gas, etc., studies have shown
`an increase in cancer rates in those
`who are exposed to even low-level
`magnetic fields. Electro-magnetic
`fields (ELf) are created by the gen(cid:173)
`eration, distribution, and use ofelec(cid:173)
`tricity and electronic devices(cid:173)
`meaning that you're exposed to it at
`home from everything ranging from
`your blow dryer to your microwave,
`as well as at work. Those who live
`close.to .power-dlstributlon.substa- -- --(cid:173)
`tions and power lines are consid-
`ered to be particularly at risk. To find
`out if you and your family and co-
`workers are being exposed to po(cid:173)
`tentially hazardous ELF levels, build
`the portable ELF gaussmeter shown
`on page 33.
`
`.COMING NEXT MONTH
`THE MAY ISSUE
`GOES ON SALE
`APRIL 3.
`
`BUILD THIS RAM TESTER
`Verify that your memory is working properly and at the rated speed.
`
`BUILD THE PHON·COM
`Turn your telephones into a home intercom system.
`
`MICROCELL
`Is the "poor man's cellular network" the phone network of tomorrow?
`
`BUILD THE PULSE MATE
`A handheld pulse generator makes a handy troubleshooting tool.
`
`As a serv ice to readers. RADIO-ELECTRONICS publish es available plans or information relating to newsworthy produc ts ,
`techniques and scient ific and technological developm ents . Because of possible variances in the quality and conditi on of
`materials and workmanship used by readers. RADIO-ELECTRONICS disclaims any responsibility for the safe and proper
`function ing of reader-built projects based upon or from plans or information published in this magazine.
`
`Since some of the equipmentand circuitry described in RADIO-ELECTRONICS may relate to or be covered by U.S. patents,
`RADIO-ELECTRONICS disclaims any liability for the infringement of such patents by the making, using. or selling of any such
`equipment or circuitry, and suggests that anyone int erested in such project s consult a paten t att orney.
`
`RADIO-ELECTRONICS. USSN 0033-7862) April 1991. Published monthly by Gemsback Publications. Inc.. 5oo·B Bi-County
`Boulevard. Farmingd ale. NY 11735 Second -Class Postage paid at Farmingdale, NY and additional maili ng office s. Second-Cl ass
`mail registr ation No . 9242 authorized at Toronto, Canada. On e-year subscript ion rate U.S.A. and possession s $17.97, Canada
`$23.97. all other countries $26 .97. All subscri pti on orders payable in U.S.A. funds only. via internation al postal mon ey order or
`check drawnon a U.S.A.bank. Singlecopies$2.95. @1991by GernsbackPublications. Inc.Allrights reserved. Printedin U.S.A.
`
`POSTMASTER: Please send address changes to RADIO·ELECTRONICS, Subscription Dept.. Box 55115, Boulder. CO
`80321 ·5115.
`
`A stamped self-add ressed envelope must accomp any all submitted manusc ripts andlor artw ork or photographs if their return is
`desired should th ey be rejected. We discl aim any responsibility for the loss or damage of manuscript s andlo r artwork or
`photographs while in our possession or otherwise.
`
`Hugo Gemsback 11884-1967) founder
`
`Larry Steckler, EHF. CET.
`editor-in-chief and publisher
`
`EDITORIAL DEPARTMENT
`Brian C. Fenton, editor
`Marc Spiwak, associate editor
`Kim Dunleavy,
`assistant technical editor
`Teri Scaduto, assi stant edi tor
`JeHrey K. Holtzman
`computer editor
`Robert GrossblaU, circuits editor
`Larry Klein, audio editor
`David Lachenbruch
`contributing editor
`Don Lancaster
`contributing editor
`
`Kathy Terenzi, editorial assistant
`
`ART DEPARTMENT
`Andre Duzant, art director
`Injae Lee, illustrator
`Russell C. Truelson, illustrator
`
`PRODUCTION DEPARTMENT
`Ruby M . Yee, production director
`Janice Box,
`editorial production
`Karen S. Brown
`advertising production
`Marcella Amoroso
`production assistant
`
`CIRCULATION DEPARTMENT
`Jacqueline P. Cheeseboro
`circulation director
`Wendy Alanko
`circulation analyst
`Theresa Lombardo
`circulation assistant
`Michele Torrillo,
`reprint bookstore
`
`Typography by Mates Graphics
`Cover photo by Jack McConnell and
`Diversified Photo
`Services
`
`Radio·Electronics is i ndexed in
`Applied Science & Technology Inde x
`and Readers Guide to Periodical Liter(cid:173)
`ature.
`Microfilm & Microfiche editions are
`available. Contact cir culation depart(cid:173)
`ment for deta ils.
`
`Advertising Sales OHices listed
`on page 98.
`Badio-Electronics Executive and
`Administrat ive Offices
`1·516·293·3000.
`Subscrib er Customer Service:
`1·800·288·0652.
`Order Entry for New Subscribers:
`1·800·999·7139.
`
`6 The
`
`Audit
`Bureau
`01 Circulation
`
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`UA-1010.003
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`

`
`Here are two simple
`projects that will allow you
`to control things using up to
`eight voice commands.
`
`SOME OF THE MOST FASCINATING
`things that electronics experi(cid:173)
`menters can do are those that
`seem impossible. Remote control
`and voice synthesis are two areas
`of experimentation that were
`once nearly impossible for hob(cid:173)
`byists and amateurs to work
`with, but integrated circuits
`have brought both within the
`reach of even novice tinkerers.
`Another area that has always
`been very difficult to work with is
`voice recognition. And now there
`is a new IC which brings simple
`speech-recognition technology
`within the reach of novice experi(cid:173)
`menters.
`Most voice-recognition proj(cid:173)
`ects and experiments have used
`personal computers as the back(cid:173)
`bone of the recognition device. A
`number of voice-recognition ex(cid:173)
`pansion cards for both Apple and
`IBM-compatible computers are
`available, but they're relatively
`costly and require the computer
`in order to be usable. The voice(cid:173)
`recognition IC, the VCP200
`speaker-independent word rec(cid:173)
`ognizer,
`is a stand-alone device
`that provides all of the essential
`elements for speech recognition
`in a single 20-pin package.
`
`The project
`There are a number of applica(cid:173)
`tions, both serious and fun,
`useful and merely entertaining,
`
`for the VCP200. Rather than lim(cid:173)
`it this interesting device to a sin(cid:173)
`gle-purpose project, we are pres(cid:173)
`enting two separate projects: one
`is suitable for experimentation(cid:173)
`and also makes a nifty science(cid:173)
`fair project-and the other is less
`ideal for experimentation but
`better for actual use in an ap(cid:173)
`plication of one sort or another. A
`variety of adjustments and inter(cid:173)
`facing techniques will be dis(cid:173)
`cussed, and some flexible inter(cid:173)
`face and driver circuits will be
`presented. None of the parts,
`wi th the exception of the VCP200
`itself, are exotic or costly, and
`most are probably in your junk
`box or parts collection.
`The experimenter's version is a
`self-contained device with a mi (cid:173)
`crophone and eight indicator
`LED's. The addition of a power
`supply is all that's needed. The
`project will recognize eight words
`and short phrases from almost
`any speaker, and light the corre(cid:173)
`sponding LED in response. Out(cid:173)
`puts are provided for driving
`other circuits or devices.
`The "working" version of the
`circuit eliminates the indicator
`LED's and their driver IC's, and
`uses a much smaller PC board.
`However, it retains the eight out(cid:173)
`puts and all other circuitry, and
`is therefore more suitable for
`building into a motorized model
`or other project.
`
`DANIEL B. COOPER
`
`Voice recognition
`The basic elements of voice or
`speech recognition have been
`known for a number of years .
`Human speech consists of
`phonemes, which are the small(cid:173)
`est individual units of sound that
`make up words and sentences.
`The "ah" sound in "father," the
`"t" sound in "top," and the "rr"
`sound in "radio" are all examples
`of phonemes. Any word in a par(cid:173)
`ticular language can be created
`by stringing together the proper
`sequence of phonemes and
`spaces of silence. Not all lan(cid:173)
`guages use the same phoneme
`sets; English, for example, lacks
`a glottal stop and the click found
`in many African languages.
`Electronic voice recognition
`consists of analyzing the ar(cid:173)
`rangement of phonemes in a spo(cid:173)
`ken sequence and matching
`them against stored patterns or
`templates to determine the word
`or phrase. There are many varia(cid:173)
`tions in the actual processes
`used for each of the three steps:
`storing the patterns, analysis,
`and matching. However,
`the
`basic techniques used for voice
`recognition can be loosely
`grouped into four categories.
`In speaker-dependent voice
`recognition, the intended user of
`the recognition device "trains" it
`by carefully pronouncing the list
`of recognized words, several
`
`4
`
`UA-1010.004
`
`

`
`times each. The system creates
`detailed templates. or patterns of
`that speaker pronouncing those
`words, and stores them . The sys(cid:173)
`tem will have a very h igh success
`rate in recognizing that speaker
`pronouncing those words, but it
`will be less able (if at all) to recog(cid:173)
`nize another speaker saying the
`same words-and, of course, it
`will only recognize those specific
`words that it has been trained to
`recognize.
`A discrete-word speech recog(cid:173)
`nizer can only decode speech
`when it is a series of separately
`spoken words . It could not un(cid:173)
`derstand "Move the cursor to
`field one, " but the sequence
`"Goto" (pause) "Field" (pause)
`"One" would be understood.
`Speaker-dependent discrete(cid:173)
`word recognition systems are the
`most common types in use.
`A speaker-dependent con(cid:173)
`nected-word recognition device
`must be trained to recognize
`each different speaker's pronun(cid:173)
`ciation. However, more powerful
`analysis capabilities allow decod(cid:173)
`ing of words strung together in a
`long phrase or sentence. This
`type of recognizer could decode
`"Move the cursor to field one, "
`but is typically costly and com(cid:173)
`plex. The success rates are als o
`typically lower than for speaker(cid:173)
`dependent discrete-word recog(cid:173)
`nition systems.
`A much more difficult process
`is to decode the speech of a vari(cid:173)
`ety of speakers. No two people
`pronounce words in quite the
`same way. When analyzed elec(cid:173)
`tronically and graphically, varia(cid:173)
`tions, even with very similar(cid:173)
`sounding speakers, are quite
`
`FIG.1-THE PINOUT OF THE VCP200.The
`output pins 8, 9, and 10 respond to dif(cid:173)
`ferent words or phrases, depend ing on
`the operating mode selected.
`
`+5V
`
`T
`
`!viIC
`
`i"--
`i"--
`[1)-~p- vep
`
`200
`
`HIGH-GAIN
`AMP
`
`CLIPPING
`COMPARATOR
`
`LED
`I INDICATORSII
`IC\
`'-Y
`1--- - --
`1-- - - - - -
`- ----
`- ----
`LED --- --
`12\
`DRIVER
`~\
`
`-t>- 1------
`
`-
`
`-
`
`~
`
`~
`
`I
`
`FIG. 2-BLOCK DIAGRAM of the voice-recognition circuit. The VCP200 contains almost
`all of the required circu itry, and needs only a power supply, microphone, and high-gain
`amp lif ier with clipping comparator output for operat ion. The LED indicators and their
`drivers are optional.
`
`marked. That natural variation
`makes it very difficult for a sys(cid:173)
`tem to recognize, with a high suc(cid:173)
`cess rate, the same words spoken
`by different people.
`Speaker-independent voice
`recognition follows the principle
`that all speakers have certain
`similarities in their pronuncia(cid:173)
`tion . For ex a m p le, nearly all
`
`speakers pronoun ce the word
`"s top" with the following sim(cid:173)
`ilarities: an initial sibilant ('sss') ,
`a short plosive Ct'l. a soft vowel
`('ah'), and a final plosive ('p'). By
`m atching s el ected phonemes
`and allowing for variation in the
`matching algorithm, the same
`words can be identified and de(cid:173)
`coded from a variety of speakers.
`
`PARTS LIST
`
`All resistors are V4-watt, 5%
`R1-2200 ohms
`R2-1000 ohms
`R3-10,000 ohms
`R4, R7-470,000 ohms
`R5-11 ,000 ohms
`R6, R8-5600 ohms
`R9-4700 ohms
`R1G-10 megohms
`R11-100,000 ohms
`R12-19-470 ohms
`Capacitors
`C1-Q.22 fLF, 16-volts,tantalum
`C2, C3, C12-Q.01 fLF disc
`C3-39 pF disc
`C5-4.7 pF disc
`C6-C8-0.1 fLF disc
`cs, C1G-27 pF disc
`C11-10 fLF, 16-volt tantalum
`Semiconductors
`01-08-red light-emitting diode
`(optional, see text)
`IC1-LM324A quad op-arnp
`IC2-LM7805T 5-volt, 1.5-amp
`voltage regulator
`
`IC3-VCP200 speaker-independent
`word recognizer
`IC4, IC5-C04011B quad NAND gate
`(optional, see text)
`Other components
`JU1-switch or jumper (see text)
`MIC1-electret microphone
`XTAL:.1-10 MHz crystal
`Miscellaneous: PC boa rd (See
`text), bus wire, SPST power switch,
`SPOT mode switch, normallyopen
`pushbuttonreset switch, 9-voltbat(cid:173)
`tery or 8-15 volt DC power supply,
`9-volt battery clip, three 14-pin IC
`sockets, one 20-pin IC socket,
`mounting screws and standoffs,
`4-40 x %-inch screw and nut,
`hookup wire , solder, alum inum
`sheet for heatsink.
`Note: The VCP200 may be avail(cid:173)
`able from Radio Shack (it has
`been discontinued but many
`stores still stock them) as part
`number 276-1308, or from VCPI,
`1 Willings Place, Monterey, CA
`93940, for $14.95 postpaid.
`
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`

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`-
`
`ptns .S, 6, and I, and must pro-
`phoneme analysis and matching
`The drawbacks to speaker-in-
`vide about 15 milliamps. Its os-
`program using a proprietary al-
`dependent systems are that the
`cillator crystal connects to pins 4
`gorithm. The algorithm analyzes
`number of separately recogniz-
`able words is limited, the recog-
`and 5, each of which must also be
`a modified voice input signal and
`tied to ground via 27-pF capaci-
`nition success rate is generally matches it against a selection of
`lower than that ofspeaker-depen-
`tors to complete and stabilize the
`stored word-recognition te m-
`oscillator tank circuit.
`dent systems, and the system can
`plates to identify twelve different
`Pins 2, 16, 17, and 18 of the
`be easily fooled by similar words.
`words and short phrases : Yes,
`VCP200 are not used in a stan-
`For example, "swap," "stat,"
`No, On, Off, Lights, Left Turn, Re-
`dard application. They are spe-
`"spat," "spot," and "spit" all have
`set, Stop, Slow Reverse, Turn
`cial-purpose control pins that are
`phoneme patterns that are sim-
`Right, and Go.
`usually tied to +V or ground, and
`ilar to "stop." Most speaker-inde-
`The chip is switchable between
`are connected that way on our PC
`pendent word recognition sys-
`On/Off and Command modes. In
`board. Generally, these pins may
`terns will be unable to dis-
`the On/Off mode, it recognizes
`be ignored, as they are normally
`tinguish between those words.
`only the two word pairs On/Off
`used to set the VCP200 into vart-
`Most dedicated voice- or word-
`and Yes/No. In the Command
`ous test and special-application
`recognition systems are speaker-
`mode, it recognizes the other
`modes that are not useful to the
`independen t discrete-word
`eight words and phrases. A sepa-
`experimenter.
`types. Although they have some
`rate output for each word is pro-
`severe limitations, they excel at
`The reset input, pin 20, is held
`vided, which is latched low when
`high for normal operation and
`simple voice-control tasks tnvolv-
`the word is successfully recog-
`~g a few carefully chosen wor:.ds_' _ n ized ._ILth :v.:CE200_cannoLfind_brought low-for. a -reset.-Asimple-
`and phrases. The VCP200 is a
`a close match among its word
`resistor-capacitor pair connected
`speaker-independent discrete-
`templates, all eight outputs are
`to this pin will cause a power-on
`word recognizer.
`left high.
`reset. The VCP200 can be man-
`The dream of designers; con-
`The VCP200 is Virtually a
`ually reset by strobing the pin low
`trol engineers, and science-ftc-
`stand-alone device, requiring
`at any time, by holding itlow, you
`tion writers is a system that can
`only a lO-MHz crystal and four
`can safely disable the chip's oper-
`recognize normal, connected
`passive components for opera-
`ation.
`speech from a wide variety of
`tion. The only outside circuitry
`Pin 19 is the operation-mode
`speakers. Despite much effort,
`that is required is a special input
`select input. When this pin is
`no such system yet exists. The
`amplifier, built from a common
`high, the chip is set to the YeslNo
`first successful "natural speech"
`op-amp, that delivers a sharply
`mode, and only Yes/Off (pin 9),
`recognizer will almost certainly
`clipped and amplified voice sig-
`No/On (pin 8), and Not Sure (pin
`demand the resources of a dedi-
`nal. That quasi-digital signal can
`10), which indicates a recogni-
`cated supercomputer to handle
`be easily analyzed by the micro-
`tion failure, are active. When pin
`the massive analysis and com-
`processor.
`19 is low, the VCP200 is placed in
`putational steps required. How-
`The VCP200's biggest disad-
`the Command mode, and all
`ever, keep in mind that speech
`vantage is the limited and non-
`eight outputs are active, with
`syn thesis, now achieved with
`expandable word list. However,
`each corresponding to a different
`single dedicated IC's, also once
`considering that the chip is inex-
`recognized word or phrase.
`required a full-sized computer.
`pensive and easy to use, that lim-
`The VCP200's audio input, pin
`itation shouldn't bother .anyone
`7, requires an input signal that is
`who is interested in exploring
`either quiescent, or swings past
`voice-recognition technology
`the digital logic thresholds. That
`without making a heavy invest-
`requirement translates into a
`ment of time or money.
`highly amplified, sharply clipped
`Unfortunately for experimen-
`signal that is "shut off'when it is
`ters, VCPI regards the VCP200's
`not of sufficient amplitude. Such
`program and word-recognition
`a signal is easy to achieve with a
`algorithm as proprietary infor-
`standard op-amp, as we'll see.
`mation. Few details are available,
`Finally, pins 8 through 15 are
`and VCPI's literature and docu-
`the VCP200's outputs. During or
`mentation discusses the tech-
`after a reset (pin 20 brought or
`nology only in general terms. An
`held low), all eight outputs are
`interesting exercise for the ad-
`held high. When the chip sue-
`vanced experimenter would be
`cessfully recognizes a word or
`attempting to work out the es-
`phrase in Command mode, the
`sen tial elements of the al-
`corresponding output will be
`gorithm, using standard refer-
`latched low until the next recog-
`nition attempt ,occurs. If the
`ence information on voice recog-
`nition, digital analysis of analog
`VCP200 fails to find a match to
`signals, and pattern matching.
`an input signal, all eight outputs
`The pinout of the VCP200 is
`will remain high. In the Yes/No
`shown in Fig. 1. The chip is
`mode, during or after a reset,
`powered from a single-ended 5-
`pins 8, 9, and 10 (as well as the
`volt supply, which connects to
`five unused outputs, pins 11-15)
`
`TheVCP200
`The VCP200 speaker-indepen(cid:173)
`dent word recognizer, from Voice
`Control Products, Inc . (VCPI), is a
`mask-programmed Motorola
`6804 microprocessor. The 6804
`is a 20-pin device that imple(cid:173)
`ments most of the standard
`6800-series instruction set and
`capabilities, and contains , one
`kilobyte of onboard ROM . Al(cid:173)
`though an EPROM version is
`available for user development,
`production devices such as the
`VCP200 use a ROM that is mask(cid:173)
`programmed at the time of man-
`g ufacture with the appropriate
`z data and control information.
`oc:: That approach, used for many
`t; computationally-based special(cid:173)
`UJ
`...J purpose devices, is a viable alter(cid:173)
`UJ6 native to designing a costly sin-
`o gle -purpose chip from scratch.
`~
`The VCP200's ROM contains a
`
`52
`
`UA-1010.007
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`

`
`will be high. Some recognition
`failures in the YeslNo mode can
`also cause all three active outputs
`to go high.
`
`The circuit
`there are two
`As said earlier,
`versions of the circuit. A block
`diagram of the experimenter's
`version is shown in Fig. 2. The
`circuit contains a power supply.
`an input amplifier and com (cid:173)
`parator, the VCP200, and output
`drivers. The power supply is
`qutte conventional, using IC2,
`an LM7805T 5-volt regulator.
`The input amplifier is not a
`conventional design; the output
`signal, if it were connected to a
`speaker, would be quite distorted
`and unlistenable. The purpose of
`the two-stage amplifier, with its
`overall gain of about 800,
`is to
`increase the microphone signal
`to a useful level. The output is
`then passed to a comparator that
`keeps the final output signal ei-
`
`ther quiescent (flat-line) .o r
`switching between the supply
`limits-a quasi-digital signal.
`The output of the amplifier is
`passed to the VCP200's audio in(cid:173)
`put, where the signal can then be
`analyzed.
`The VCP200's eight outputs
`are made available, via current(cid:173)
`limiting resistors, so that exter(cid:173)
`nal interface circuits maybe add(cid:173)
`ed to control motors, solenoids,
`and other active elements. Eight
`LED's are added to give a quick
`and easy indication of the cir(cid:173)
`cuit's response. The LED's are
`driven by CMOS buffers, which
`isolate the LED's from the out(cid:173)
`puts, preventing either the in(cid:173)
`dicators or any outlying circuits
`from interfering with each other.
`Figure 3 shows the complete
`schematic for the experimenter's
`version of the voice-recognition
`project. Note that the schematic
`of the working version would be
`exactly the same, except for the
`
`omission of LED's 1-8 and IC4
`and IC5.
`Power for the voltage regulator,
`IC2, can be from 7.5 to 15 volts.
`Since the circuit draws only
`about 22 milliamps peak, a 9-volt
`battery is a good choice. Capaci(cid:173)
`tors ClO and Cll filter and sta(cid:173)
`bilize the regulator's output.
`The signal from the electret mi(cid:173)
`crophone, MICl, is coupled to the
`LM324A op-amp, ICI, through
`Cl. The amplifier uses ICl-a and
`ICl-b to form a two-stage device
`that amplifies the microphone
`signals with a gain of 500-800.
`That transforms the weak input
`signal (under 5 mV) to a signal
`that swings from one output lim(cid:173)
`it to the other, often with consid(cid:173)
`erable clipping.
`The amplifier has a restricted
`bandwidth, with a more or less
`flat response from about 500 Hz
`to 9 kHz. Signals under 300 Hz
`and over 15 kHz are sharply at(cid:173)
`tenuated. That covers the
`
`a
`
`b
`
`FIG. 4-AMPLIFIER (a) AND COMPARATOR (b) output waveforms. The comparator con(cid:173)
`verts the amplifier signal
`into a clipped, quasi-digital 4-volt pop signal only when the
`amplitude of the amplifier's signal exceeds the comparator threshold.
`
`l,
`Jr
`
`5:
`
`UA-1010.008
`
`

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`
`FIG. 6-THE VOICE-RECOGNITION CIRCUIT offers eight voice-activated outpu ts for
`expe rimenting with voice cont rol.
`
`19, is controlled by setting JUI.
`On the PC board, JUI is actually
`three pads which may b e con (cid:173)
`nected to an SPOT s witch , or
`simply jumpered. However, jum(cid:173)
`pering is not recommended; a
`switch will make it eas ier to ex(cid:173)
`p eriment with both operation
`modes.
`The eight ou t p u ts, pins 8
`through 15, are left open for the
`experime n ter to u se as n eces sary.
`Since the outputs are act ive-low,
`they can sink about 10 rnA and
`source somewhat less. Tha t is
`sufficient enough to drive logic
`devices and transistor drivers. If
`high-current devi ces such as re(cid:173)
`lays or motors are to be driven, a
`buffer/driver must b e u s ed. To
`prevent damage to the VCP2 00
`from a n acc idental overl oad of an
`output, 470-ohm cu r re nt-lim it(cid:173)
`ing resis tors (RI2-RI 9) a re pro(cid:173)
`vided . Th ey lim it
`t he o u t p u t
`cu r re n t to a b ou t 9. 5 mA, even
`under worst-case con ditio ns.
`The ei ght LED indi cators ,
`LEOI-LE08, are driven from
`C MOS drivers IC4 a n d IC5 ,
`which are C04011B quad NAND
`g a tes . However, s everal other
`
`common chips could be sub(cid:173)
`stituted h ere, a m on g them the
`C0400lB quad N OR gate and the
`C0409 3B quad NAND Schmitt
`trigger.
`
`Construction
`Foil patterns are provided for
`both versions . Although a PC
`board is recommended, perfo(cid:173)
`rated con s t ruc t ion board and
`point-to-point wiring could also
`be used. Ifyou use point-to-point
`construction, be s u re and keep
`all wiring, especially in the area
`of the input amplifier, short. The
`very high gain of the amp will
`cause it to pi ck up and amplify
`electrical noise if excessively long
`connecting wires are u sed. You
`should u se socke ts for all the IC's
`to m ake them easier to replace if
`necessary.
`If you a re going to build the
`experi menter's ve rs io n of the
`proj ect, follow t h e parts-place(cid:173)
`m ent diagram s hown in Fig . 5 . If
`you are going to build the smaller
`"wor k ing" version, simply use
`the s m a ller foil pattern; parts
`placement is the same as the
`larger version , except that the
`
`VCP200's input range of 300 to
`5500 Hz , with some additional
`headroom for the easily-los t
`higher fre q uencies . The ampli(cid:173)
`fier's chara cteristics are impor(cid:173)
`tant, because the quality of the
`input s ig nal large ly de termin es
`how well the voice recognizer will
`work.
`To k eep t h e VCP200's in p ut
`quiet , unless a signal of suffi(cid:173)
`cient s trength is present, and to
`ensure a sharply clipped signal,
`the output of the amplifier is
`passed to a comparator, ICI-c.
`(Th e fourth op-amp on the
`LM324A, ICl-d is not used , and
`its pins are left unconnected .)
`The comparator's output re(cid:173)
`mains steady unless the input
`signal swings past its threshold.
`__ . Input signals of less than 2 .5
`volts peak-to-peak will be ig(cid:173)
`nored. How ever, all signals s tron (cid:173)
`g e r than that will cause th e
`comparator's output to swing
`from limit to limit, or about 4
`volts peak -to -peak , which is
`within one-half volt of each su p(cid:173)
`ply rail. A comparison of the am(cid:173)
`plifier a n d comparator output
`s ign als is shown in Fig . 4 .
`Since the LM324A is op erated
`fro m a s ingle -e n d ed supply, a
`"false grou n d " or offset voltage
`mus t b e provided . The offset,
`along wi th the comp arator
`threshold voltage, is provided by
`the volt age divider string R5-R8(cid:173)
`R9 . The a mplifier offset is pro(cid:173)
`vided by the upper junction, and
`the compa rator threshold by the
`lower; C6 an d C7 stabilize those
`voltages . That design forces the
`cen te r voltage of the op-arnp's
`output signal to be separated by a
`volt or s o from the comparator's
`threshold, and is the key to cor(cid:173)
`rect operat ion. Adjusting the di(cid:173)
`vide r str ing is one of the ways
`t hat t he c ircu it's p erformance
`can be m odified.
`.
`Th e outpu t of the comparator
`.is then routed to p in 7 of the
`VCP20 0. The IO-MHz crys tal,
`XTALl, provides the ch ip's mas(cid:173)
`te r clock fre q uencies , with t he
`oscillator tank circ u it completed
`a n d s tab ilize d by C9 an d CIO. To
`provide a power-on reset, the RC
`p air Rll a n d C 8 hold t he
`VCP200's res et input low for a few
`milliseconds after power come s
`o n . As C8 charg es through Rl l ,
`the reset pin is brought hi gh, re(cid:173)
`s etting the VCP200.
`The VCP200 's mode input, pin
`
`W6o-
`
`c
`a:
`
`54
`
`(J)
`
`~zoa
`
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`f(cid:173)u
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`
`UA-1010.009
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`

`
`LED's and their drtvers, IC4 and
`Ie5, are left out. On both, keep
`the wire jumpers and resistors
`close to the board. Insert the disc
`capacitors so that their bodies
`are seated against the board, but
`don't chip the dielectric material.
`Be careful to observe the polarity
`on the two electrolytic capaci(cid:173)
`tors, Cl and Cll.
`The voltage regulator, IC2, re(cid:173)
`quires special mounting. The
`middle lead should be bent about
`0 .1 inch farther from the body
`than the two side leads, and all
`three bends should be made so
`that the regulator's mounting
`hole lines up with the hole in the
`board (see the photo in Fig. 6 for
`details.) If you are going to be
`using the project by itself, with
`no outlying devices powered from
`the board, no heatsink is needed
`for the regulator. If you are going
`to be powering other devices
`. from the regulator that will in(cid:173)
`crease the load to more than 100
`milliamps, a heatsink should be
`added to the regulator. A flat alu(cid:173)
`minum stock heatsink can be
`bent into a shallow "U" shape and
`installed under the regulator. Be(cid:173)
`cause there is no space for a large
`heatsink, the current drawn
`from the regulator should be lim(cid:173)
`ited to no more than 250 rnA even
`when using as large a heatsink as
`possible.
`For most experimenters,
`mounting MICI directly to the
`board will be adequate. In some
`cases, though, it may be better to
`mount the microphone remotely.
`In that case, light-gauge shielded
`cable.should be used to connect
`the microphone to the board .
`Electret microphones are polar(cid:173)
`ized, so be sure the positive ter(cid:173)
`minal is connected to the pad
`that leads to Cl and RI.
`If you like, the eight LED in(cid:173)
`dicators can be mounted re(cid:173)
`motely with a length of ribbon
`cable. If you mount them on the
`board, be sure to position them
`all at an even height. How you
`finish the remaining steps de(cid:173)
`pends on how you want to use the
`board . For display and experi(cid:173)
`mentation, you'll want the input
`and outputs of the circuit easily
`accessible with test points. Oth(cid:173)
`erwise you can hardwire driver
`circuits and the like directly to
`the board.
`In the prototype, the PC board
`and power switch are mounted to
`
`Command
`
`Pronunciation
`
`Yes
`Off
`
`No
`On
`Go
`
`yeSSS
`awFFF
`
`no
`on
`go
`
`Lights
`Left Turn
`
`LytSSS
`LeFFFT Turn
`
`Reset
`
`rESSSeTT
`
`Stop
`
`SSSTawPP
`
`Slow
`Reverse
`
`SSSloh
`rEverSSS
`
`Turn Right
`
`Turn-ryT
`
`a thick plastic base using spacers
`and screws, and the battery clip
`is secured by smaller screws. Al(cid:173)
`though the prototype has no re(cid:173)
`set switch and is strapped into
`the Command mode, you can
`easily add the controls. Just use
`a slightly larger mounting base
`and mount the switches in the
`same manner. If you are using
`the working version, and will be
`using it as a part of a complete
`