Popular Electronics
`
`WORLD'S LARGEST- SELLING ELECTRONICS MAGAZINE AUGUST 1979 /$1.25
`
`n
`
`New, Exciting Low -Cost Projects
`For Joggers: Electronic Pedometer
`For Motorists: Low -Fuel Warning Buzzer
`For Boating: Portable Gas -Leak Meter
`For Basements: Sump Pump Switch /Alarm
`
`o
`
`11
`14024 14278
`Pop ddr -Ire vonlci
`
`in
`
`.1.01116
`
`ao
`qbç
`61730 CPO 66alli98
`www.americanradiohistory.com
`
`10 Speaker System
`HIE Phono Cartridge
`r II Model 4 Personal Computer
`
`IPR2017-01058
`Garmin EX1021 Page 1
`
`

`

`no loose ends
`
`All -In -One: computer, floppy, I /0,16K RAM. $1595*
`
`Oil 1N 2t1 eicroprocesfors
`Usti* 2.1488Nz
`MwM! 16K bytes RAM expendable to 48K
`Molly: 25 lines by 88 characters
`
`Characters: 5 x 7 dot matrix, upper 6 lower case
`
`6raphlcso 33 special graphics characters
`control (8 user -definable)
`Keyboard! 72 keys, 61 alphanuuric t 12 function
`control (8 user- definable)
`
`Nutria Mppadl 12 keys
`Curer Addressing' relative 6 direct for Lull cursor control
`pit Functions! Insert or delete character or lint
`M1Ael Moral and revers, by character for hilhlighttng -
`
`j-:.c',.-;1i,r,
`
`1,-= '!d! ,MIL
`
`,.111e,
`
`102K bytes storage
`New Heathkit® H89
`All -In -One Computer
`Built -in floppy disk system gives you fast
`access to programs and data. Each 5t/4-
`Heath takes the risk out of selecting a
`inch diskette has more than 102K bytes
`balanced computer system. Now, video
`of storage area, enough to hold entire
`terminal, floppy, keyboard and 8 -bit
`files. The All -In -One comes with 16K
`computer are brought together in one
`RAM, expandable to 48K.
`self- contained, compact unit. Nothing
`hangs out.
`Hundreds of uses at
`home or work
`Two Z80's
`The All -In -One Computer runs programs
`The personal computer has never been
`written in MICROSOFT" BASIC and
`simpler. Or smarter. Two Z80 microproc-
`ASSEMBLER Languages. And it accepts all
`essors mean terminal never shares pow-
`current software written for the popular
`er with computer, as do most desk -top
`units. So this terminal is capable of a
`Heathkit H8 computer. You can choose
`from scores of practical programs for
`multitude of high -speed functions, all
`home and business.
`controllable by keyboard or software.
`$1195 without floppy. Mail order kit price, F.O.B. Benton Harbor, MI. Also available at Heathkit Electronic Centers at slightly
`without notice.
`
`Learn by building
`What better way tc learn about comput-
`ers than to build one yourself? The All -
`In -One is available in easy -to -build kit
`form, as well as completely assembled.
`Like all Heath electronic kits, it comes to
`you with its own easy -to- follow assem-
`bly manual and a nationwide network of
`service centers to assure smooth sailing.
`FREE CATALOG
`For complete details on the
`Heathkit
`Heathkit H89 All -In -One
`Computer and nearly 400
`other electronic kits for your
`home, work or pleasure, send
`today for the latest Heathkit
`Catalog of values.
`higher prices. Prices subject to change
`CP-165
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`
`HEATH COMPANY, DEPT. 010 -560, BENTON HARBOR, MI 49022
`CIRCLE NO. 5 ON FREE INFORMATION CARD
`
`www.americanradiohistory.com
`
`IPR2017-01058
`Garmin EX1021 Page 2
`
`

`

`LEGAL DEFENSE
`
`No -Fault
`Radar
`
`If you've ever been caught by radar
`or if you own a radar detector, please
`read this important message.
`
`JS &A has never offered a radar detector.
`As our president put it, "A radar detector is a
`flagrant anti -police device that does nothing
`but permit abuse of our traffic laws."
`Although many devices were presented to
`JS &A, none were acceptable. Despite all of
`our efforts, our president stood firm, "Our
`company will not, under any circumstances,
`sell radar detectors."
`For three years we saw radar detectors -
`some good, some bad -but because of our
`president's policy, we were unable to offer a
`single unit. We saw the units go to both X and K
`bands; we saw the police develop radar jam-
`ming devices; and we saw the FCC prohibit
`jamming devices. We followed with
`these
`great envy as other companies sold thou-
`sands of them while JS &A stood firm on its
`decision not to sell them.
`In January of 1979, our president was travel-
`ling on an interstate highway at 55 miles per
`hour. Other cars were passing him.
`As he approached the top of a hill, he
`neglected to pay attention to his speedometer.
`As he rolled down the hill his speed increased
`to 63 MPH. At the bottom of the hill was a
`police radar trap.
`He was apprehended and charged with
`exceeding the speed limit by eight miles per
`hour. He was taken to a Justice of the Peace
`who was in the barber shop, so our president
`had to wait until he finished. Finally there was a
`quick trial and a fine was paid.
`Our president was four hours late. He felt
`that he was treated like a common criminal
`despite his good driving record and he lost
`very valuable time.
`ATTITUDE CHANGES
`This small incident created an entire change
`in his attitude. Our president saw for the first
`time that even law- abiding citizens are subject
`to the inequities of radar justice. He saw that
`the law- abiding citizen must also be protected
`from the abuses of radar power when unfairly
`used.
`And when he studied the entire situation,
`our president realized something very fright-
`ening for all motorists. Many police depart-
`ments have quotas imposed on them to realize
`either federal or state funds. They must issue a
`AUGUST 1979
`
`certain amount of tickets to qualify. With more
`and more motorists using radar detectors and
`CB's, police must strictly enforce speed limits
`to reach their quotas. Now, even law- abiding
`motorists, who might make a slight mistake,
`are more vulnerable to speeding violations.
`NEW MEMORANDUM
`In a recent memorandum our president
`stated, "Due to the changing nature of police
`radar, JS &A may offer radar detectors as part
`of its program if presented within the quality
`image of our company and if the product
`truly unique radar detector
`represents a
`product."
`With the green light to find a radar detector,
`our product selection group was prepared.
`They had brochures from practically every
`manufacturer in the world. And they eventually
`selected what even our president thought was
`the most professional and well- designed unit
`available.
`
`HIDDEN ANTENNA
`Manufactured by a company called Chicago
`Radar, the unit consists of two parts -one that
`is hidden behind your grill, and the other under
`your dash. There's nothing on top of your dash
`that you've got a radar
`board to indicate
`detector and the system is difficult for anybody
`to steal. The unit under your dash is attached
`with a self- adhesive Velcro material so there's
`no screws or installation to worry about.
`The control unit has two lights -one to indi -,
`cate that the unit is on, and the other to indicate
`that your car is under radar surveillance. There
`is also an audible alarm that will sound. But at
`night, when the light is all that you need, you
`can switch off the audible sound.
`The control unit plugs into your cigarette
`lighter. The radar antenna is placed behind
`your grill. Just pull into any service station and
`the mechanic can easily install the entire
`system. The Velcro material and mounting
`brackets are all provided.
`AMPLIFIED SENSING
`The antenna is one of the keys to the unit's
`Instead of the square -
`high performance.
`shaped dish antennas, the Chicago Radar
`version is a round cylinder. It tends to sense
`the radar signals sooner and around curves
`and hills because of its unique design.
`
`www.americanradiohistory.com
`
`The unit responds to both police radar
`bands X and K and uses all solid -state
`computer technology in its design.
`We urge you to test our selection of what we
`feel to be the nation's finest radar detector.
`Order one from JS &A. When you receive it,
`drive to your nearest service station or CB
`dealer and have them install your unit. The
`antenna installs with just a few brackets and
`the control unit attaches under your dash with
`the Velcro material.
`Then use it for 30 days. During that time,
`the number of radar traps you en-
`count
`counter. On the 30th day, turn off your unit as
`you travel. See how naked and unprotected
`you feel.
`
`40 DAYS PROOF
`If for any reason you are not completely
`satisfied, just return your unit within our 40 -day
`trial period and we'll gladly send you a prompt
`and courteous refund.
`To order your system, send $179.95 plus
`$3.00 for postage and handling to the address
`shown below. (Illinois residents, please add
`5% sales tax.) Credit card buyers may call our
`toll -free number below. By return mail, you'll
`the complete system, all cables,
`receive
`instructions and a 90 -day
`Velcro material,
`limited warranty.
`The patented unit is precision crafted by
`Chicago Radar -one of the most respected
`names in radar detection systems. JS &A is
`America's largest single source of space -age
`products- further assurance that your modest
`investment is well protected.
`We firmly support our police departments
`and their efforts, but if they are encouraged to
`use radar to maintain quotas, the law abiding
`consumer has no choice but to protect himself.
`today. Order your unit now at no
`Start
`obligation.
`o
`PRODUCTS
`O
`HAT
`T
`THINK
`g
`Dept. PE One JS &A Plaza
`(312) 564 -7000
`Northbrook, Ill. 60062
`800 323 -6400
`Call TOLL -FREE
`In Illinois Call
`(312) 564 -7000
`©JS &A Group, Inc.,1979
`
`1
`
`IPR2017-01058
`Garmin EX1021 Page 3
`
`

`

`ANNOUNCING
`AMERICA'S ONLY
`LAND, SEA AND AIR
`SCANNER.
`
`Only the incredible, new,
`no- crystal Bearcat 220 Scanner
`tunes in all the real excitement of
`the entire AM aircraft band-plus
`every FM public service
`frequency -with pu button
`ease.
`
`Now.
`Tune in all the
`real excitement of
`the wild blue yonder, at
`the touch of a button.
`The new, no- crystal Bearcat 220
`Scanner searches and tunes in the entire air-
`craft band. Jets at 30,000 feet. All the tense tower
`talk. Everything is pre -programmed in space -age
`memory banks.
`Only the 7 -band Bearcat 220 Scanner also
`brings home every public service frequency, too.
`Pre -programmed Marine frequencies. Police ac-
`tion. Fire calls. Weather warnings. You name it.
`The new Bearcat 220 has all the features and
`quality Bearcat Scanners are famous for. Track
`tuning. Decimal display readout. Automatic Search.
`Selective Scan Display. Automatic squelch and
`lockout. Priority. And much, much more.
`After all, Bearcat invented Scanning. And we'll
`of land, sea. and air.
`Ele
`
`stop at nothing to bring you all the excitement -
`
`EARCAT
`Y20 SCANNER
`Follow the leader to real excitement.
`Copyright 1979 Electra Company Division of Masco Corp of Indiana 300 East County _me Road. Cumberland. Indiana 46229
`CIRCLE NO. 20 ON FREE INFORMATION CARD
`POPULAR ELECTRONICS
`
`2
`
`www.americanradiohistory.com
`
`IPR2017-01058
`Garmin EX1021 Page 4
`
`

`

`VOLUME 16, NUMBER 2 ',
`
`AUGUST 1979
`
`About the cover:
`A soldering iron
`and a few
`inexpensive parts
`can be used
`to make some
`especially useful
`devices to add
`safety and convenience
`to your lives.
`
`Cover Art by George Kelvin
`
`JOSEPH E. MESICS
`Publixher
`P. SALSBERG
`Editorial Dinetnr
`LESLIE SOLOMON
`Terh, ,,
`l ()tree tor
`JOHN J. MCVEIGH
`ce hnrrol Editor
`JOHN R. RIGGS
`Managing, Editor
`HAROLD A. RODGERS
`Senn, Falttor
`ALEXANDER W. BURAWA
`Features P;ditnr
`EDWARD I. BUXBAUM
`Art I),rer'tor
`ANDRE DUZANT
`Te<hntr rd Illustrator
`CARMEN VELAZGUEZ
`Product ,on Editor
`Contributing Editor.,
`Hal Chamberlin, Lou Gamer, Glenn Hauser
`Julian Hirsch, Ralph Hodges, Forrest Mims
`JEFF NEWMAN
`,sixtant to the Editor
`LINDA BLUM
`-4rll ert i.,'fig Service A1artoger
`MARIE MAESTRI
`Exer'utire Assi.strtnt
`EDGAR W. HOPPER
`Pub! fishing Director
`
`AUGUST 1979
`
`Popular Electronics®
`
`WORLD'S LARGEST -SELLING ELECTRONICS MAGAZINE
`
`Feature Articles
`
`SCANNER BEAM PINPOINTS THE ACTION!! Robert Grove
`Make -it- yourself antenna for improved reception of public service bands.
`SIMPLE TRS -80 PROGRAMS SOLVE ELECTRONICS CALCULATIONS/ Roy Babylon
`BASIC program for Ohm's law. resonance and inductive formulas.
`THE ART OF EQUALIZATION/ Ethan Winer
`An expert tells how to achieve that special recorded
`
`'sound."
`
`Construction Articles
`
`FOUR LOW -COST PROJECTS FOR YOUR FAMILY'S CONVENIENCE & SAFETY
`SOLID -STATE LEVEL -SENSING SWITCH FOR SUMP PUMPS/ Phillip Windolph
`VEHICLE LOW -FUEL INDICATOR/ BradleyAlbing
`PORTABLE GAS LEAK METER/ Cass Lewart
`ELECTRONIC PEDOMETER FOR JOGGERS/ Andrew A. Modla
`BUILD A SPEAKER PROTECTION CIRCUIT/ Mike Rogalski
`SPACE -AGE ELECTRONIC PROJECTS FOR BOATS, Part 2/ Harold Wright
`How to build bilge alarms. a tachometer. and protection circuits.
`
`Columns
`
`STEREO SCENE/ Ralph Hodges
`Recording as Nature Intended.
`EXPERIMENTER'S CORNER/ Forrest M. Mims
`IC Interval Timers.
`HOBBY SCENE/ John J. McVeigh
`DX LISTENING/ Glenn Hauser
`WARC -79
`SOFTWARE SOURCES/ Leslie Solomon
`COMPUTER BITS/ Leslie Solomon
`Windows in the CRT.
`PROJECT OF THE MONTH/ Forrest M. Mims
`A "Matchbox" LED Oscilloscope.
`
`Julian Hirsch Audio Reports
`
`FISHER MODEL ST460 SPEAKER SYSTEM
`SHURE M95HE STEREO PHONO CARTRIDGE
`LECTROTECH MODEL PPI -400
`
`Electronic Product Test Report
`
`COMPUCOLOR II MODEL 4 PERSONAL COMPUTER SYSTEM
`Departments
`
`44
`47
`49
`
`31
`34
`41
`42
`54
`55
`
`20
`60
`66
`70
`73
`74
`78
`
`23
`24
`25
`
`67
`
`4
`EDITORIAL/ Art Salsberg
`The Ti! Piggybacking Furor.
`6
`LETTERS
`8
`NEW PRODUCTS
`15
`NEW LITERATURE
`94
`OPERATION ASSIST
`97
`ADVERTISERS INDEX
`98
`PERSONAL ELECTRONICS NEWS
`POPULAR ELECTRONICS (ISSN 0032 -4485). Published monthly by Ziff -Davis Publishing Company. al One Park Avenue, New
`York. NY 10016, Philip B. Korsant. President, Selwyn Taubman. Treasurer, Philip Sine. Secretary One year subscription. U.S.
`and Possessions. $13.00: Canada. $16.00. all other countries, $18.00, cash orders only. payable in U.S. currency. COPYRIGHT'S
`BY ZIFF -DAVIS PUBLISHING COMPANY. ALL RIGHTS RESERVED.
`
`www.americanradiohistory.com
`
`3
`
`IPR2017-01058
`Garmin EX1021 Page 5
`
`

`

`Popular Electronics:
`
`ZIFF -DAVIS PUBLISHING COMPANY
`Editorial and Executive Offices
`One Park Avenue. New York New York 10016
`212 -725 -3500
`Joseph E. Mesics (725 -3568)
`John J. Corton (725 -3578)
`Bonnie B Kaiser (725 -3580)
`Midwestern Office
`Sude 1400, 180 N Michiian Ave..
`Chicago. IL 60601(312- 346 -2600)
`Western Office
`9025 Wilshire Boulevard, Beverly Hills. CA 90211
`213 -273 -8050:
`Western Representative. Norm Schmdle,
`7050 OwensmouthAve.. #209
`Canoga Park, CA 91303 (813-999-1414:
`Japan: James Yagi, Op Palace Aoyama.
`6 -25, Minami Aoyama, 6 Chome, Minalo -Ki:
`Tokyo, 407- 1930/6821.582 -2851
`
`ZIFF -DAVIS PUBLISHING COMPANY
`Philip B Korsant. President
`Furman Hebb. Executive Vice President
`Phillip T. Heffernan. Sr Vice President
`Edward D Muhlfeld. Sr Vice President
`Philip Sine, Sr Vice President, Secretary
`Lawrence Sporn. Sr Vice President. Circulation and Marketing
`Baird Davis, Vice President. Production
`George Morrissey. Vice President
`Sydney H Rogers, Vice President
`Sidney Holtz, Vice President
`Albert S Trama. Vice President
`Paul H Chook, Vice President
`Edgar W Hopper. Vice President
`Robert N Bavier. Jr . Vice President
`Selwyn Taubman, Treasurer
`
`W Bradford Briggs, Vice Chairman
`
`ZIFF CORPORATION
`WNiam Zrff, Chairman
`I Martin Pompadur. President
`Hershel B Sarbin. Executive Vice President
`
`POPULAR ELECTRONICS. August 1979, Volume 16.Num-
`ber 2 Published monthly at One Park Avenue. New York NY
`10016 One year subscription rate for U S and Possessions.
`$13 00. Canada. $16 00, all other countries. $18 00 (cash
`orders only. payable in U S currency) Second Class post-
`age paid at New York, NY and at additional mailing .offices
`Authorized as second class mail by the Post Office Depart-
`ment, Ottawa, Canada. and for payment of postage in cash
`POPULAR
`including
`ELECTRONICS
`ELECTRONICS
`WORLD. Trade Mark Registered
`Indexed in the Reader's
`Guide to Periodical Literature
`COPYRIGHT
`n, 1979 BY ZIFF -DAVIS PUBLISHING COM-
`PANY ALL RIGHTS RESERVED
`Ziff-Davis also publishes Boating, Car and Driver, Cycle.
`Flying, Popular Photography, Skiing. Stereo Review. Elec-
`tronic Experimenters Handbook, Tape Recording 8 Buying
`Guide, Stereo Directory 8 Buying Guide. and Communica-
`tions Handbook
`Material in this publication may not be reproduced in any
`form without permission Requests for permission should be
`directed to Jerry Schneider, Rights and Permissions, Ziff -
`Davis Publishing Co.. One Park Ave., New York, NY 10016
`Editorial correspondence: POPULAR ELECTRONICS, 1
`Park Ave . New York. NY 10016 Editorial contributions must
`be accompanied by return pottage and will be handled with
`reasonable care: however. publisher assumes no responsi-
`bility for return or safety of manuscripts. art work, or mod-
`els
`Forms 3579 and all subscription correspondence: POP-
`ULAR ELECTRONICS, Circulation Dept , P 0 Box 2774,
`Boulder. CO 80302. Please allow at least eight weeks for
`change of address
`Include your old address. enclosing. d
`possible, an address label from a recent issue
`The publisher has no knowledge of any proprietary rights
`which will be violated by
`the making or using of any items
`disclosed in this issue.
`
`(ABC
`
`Member Au,lir Bureau
`or irrulatio,s
`
`4
`
`Editorial
`
`THE TV PIGGYBACKING FUROR
`
`In what appears to be a David vs. Goliath contest, Texas Instruments, with inspira-
`tional support from RCA, is attempting to have rules on Class I devices for TV
`amended to include a Class II category. This would permit legal sale of stand-
`alone r -f modulators to be used for computers and peripherals. Such a change in
`the present interface rule that requires r -f modulators to be FCC type approved
`together with signal- source equipment is vociferously opposed by Radio Shack,
`Apple, Commodore, and Interact, among personal computer makers.
`TI says, essentially, that its unfair to make a buyer purchase a video monitor
`when he could just as easily use an existing TV receiver if only the FCC would OK
`the use of separate r -f modulators. Other computer makers, who are already mar-
`keting personal computers, cry "foul," saying, in a nutshell, that such approval
`would give TI an unfair marketing advantage. Moreover, they point out that this
`would also cause increased interference with radio and TV reception.
`TI also requested a temporary permit to go ahead with the separate r -f modula-
`tor concept while the FCC's bureaucratic wheels turn ever so slowly to reply to the
`company's initial request for changing the rules. (Note: the FCC has yet to act on a
`similar request by RCA made about two years ago.) The National Association of
`Broadcasters (NAB) observes that this second request amounts to trying to solve a
`private marketplace problem by changing the rules.
`With the foregoing as background, let's examine the pro's and con's of the rules
`change proposal. [I'll ignore the waiver request entirely because (1) it indeed gives
`a company not yet in the field an unfair advantage and (2) since the Part 15 radia-
`tion standards are under active review, it's possible that the "temporary" r -f modu-
`lators will not be in line with new standards.]
`From a typical consumer's viewpoint, using a separate modulator to connect a
`computer to one's own TV receiver would likely appear to be an ideal opportunity
`to save substantial monies. Given the fact that computers are great noise genera-
`tors, however, it is possible that interference within the household and on nearby
`neighbors' receivers would be objectionable. Furthermore, using a home TV re-
`ceiver as information display equipment results in lowered video quality under the
`best of circumstances when compared to video monitors.
`Nevertheless, the possibility of employing a legalized separate r -f modulator is
`an appealing one, and should be pursued. I firmly believe, though, that the FCC
`should not rush into making a positive decision on this without setting signal radia-
`tion standards that we can live with in the future. On the other hand, it's unfair to
`penalize manufacturers by the foot -dragging procedures practiced by the FCC.
`RCA, by the way, has pointed out that the TI request for an r -f modulator physi-
`cally separated from computers is not the same as its petition for a rules change
`that relates to all -in- one -package video disk and tape machines. So the company
`suggests three classifications: the present Class I TV devices that require type ap-
`proval, a second classification for built -in r -f modulators, and a third for stand -alone
`modulators. (How come RCA and other TV makers don't incorporate video jacks in
`their TV receivers, which would make these rules change requests moot ?)
`Since this is written in May, I hopefully will learn more about all this at the Con-
`sumer Electronics Show in Chicago in June.
`
`www.americanradiohistory.com
`
`POPULAR ELECTRONICS
`
`IPR2017-01058
`Garmin EX1021 Page 6
`
`

`

`Don't take our word for it.
`
`"We can heartily recommend the Superboard II computer system for the beginner who
`wants to get into microcomputers with a minimum of cost. Moreover, this is a `real' com-
`puter with full expandability."
`Popular Electronics March, 1979
`"(Their) new Challenger 1P weighs in at $279 and provides a remarkable amount of com-
`puting for this incredible price."
`Kilobaud Microcomputing February, 1979
`"Over the past four years we have taken delivery on over 25 computer systems. Only two
`have worked totally glitch free and without adjustment as they came out of the carton:
`The Tektronic 4051 (at $7,000 the most expensive computer we tested) and the Ohio
`Scientific Superboard II (at $279 the least expensive) ... The Superboard Il and com-
`panion C1P deserve your serious consideration."
`Creative Computing January, 1979
`"The Superboard II and its fully dressed companion the Challenger 1P series incorporate
`all the fundamental necessities of a personal computer at a very attractive price. With
`the expansion capabilities provided, this series becomes a very formidable competitor
`in the home computer area."
`Interface Age April, 1979
`"The graphics available permit some really dramatic effects and are relatively simple to
`program ... The fact that the system can be easily expanded to include a floppy means
`that while you are starting out with a low -cost minimal system, you don't have to throw it
`away when you are ready to go on to more complex computer functions. Everything is
`there that you need; you simply build on to what you already have. You don't have to
`worry about trading off existing equipment to get the system that will really do what you
`want it to do. At $279, Superboard II is a tough act to follow."
`Radio Electronics June, 1979
`"The Superboard II is an excellent choice for the personal computer enthusiast on a
`budget."
`Byte May, 1979
`
`SUPERBOARD
`The world's first
`complete computer
`system on a board
`including full
`keyboard, video
`display, audio
`cassette interface, 8K
`BASIC -in -ROM and
`4K RAM. Expandable.
`Requires + 5V at 3
`amp power supply.
`
`-
`
`1.L-- 61111
`
`IP
`
`C1P $349.00
`Complete with enclosure and power
`supply. All features of Superboard II. Easy to expand
`to more memory and floppy disk.
`
`C1 P MF $995.00
`The first floppy disk based computer
`system the world has ever seen for under $1.000.
`8K BASIC -in -ROM, 12K RAM. Expandable to 32K RAM.
`
`OHIO
`
`SCIEN TIFIC
`
`See your Ohio Scientific dealer for full details.
`1333 S. CHILLICOTHE RD., AURORA. OHIO 44202 (216) 562 -3101
`CIRCLE NO. 41 ON FREE INFORMATION CARD
`
`AUGUST 1979
`
`5
`
`www.americanradiohistory.com
`
`IPR2017-01058
`Garmin EX1021 Page 7
`
`

`

`McIntosh
`
`"A Technological
`Masterpiece..."
`
`Lao /
`Letters
`
`VcC
`
`'No
`
`INPUT
`
`R4
`
`I0k NPUT
`
`RS
`
`HIGH
`INPUT
`
`+
`
`SOLENOID THAT ISN'T
`We at Eumig thank POPULAR ELECTONICS
`for the fine review regarding our Metropolitan
`CCD cassette deck in the May 1979 issue.
`We did, however, note an error regarding the
`deck's transport in the "User Comment" sec-
`tion: "The solenoid- operated
`transport
`is
`astonishingly silent. We heard none of the
`thumps or clunks usually associated with
`solenoid operation." You then go on to state
`that there is a "motor" sound instead of a
`solenoid sound.
`As a point of information, the reason sole-
`noids are not heard is that there are no sole-
`noids. The motor sound is heard because the
`head mounting assembly is step -motor en-
`gaged, using the same motor that governs
`fast forward and rewind. -Tom Bensen, Eu-
`mig (U.S.A.) Inc., Great Neck, NY
`
`MAKING A BETTER WINDOW?
`The window comparator circuit shown
`above has fewer parts and has better input
`protection than that shown in Fig. 5 of the May
`
`MOPED TURN INDICATORS
`Many thanks for "Solid -State Turn Indica-
`tors for Mopeds" (May 1979). The article was
`clearly written. The project will almost certain-
`ly prevent accidents because blinking lights
`are easier to see and interpret. Also, the pro-
`ject is small enough to easily mount on all
`mopeds. -Bill Saehler, Minnesota City, MN.
`While looking over the moped turn- indica-
`tor article, I noticed that D4 and C3 are not
`switched out of the power circuit by S1. While
`this is not particularly important when the de-
`SIA ..ß+6V
`
`W40
`
`FI
`IA
`
`VOTES:
`EL /MIA/ATE
`SHADED AREAS.
`BOLD AREAS
`/ND/CNrE
`ADDtr/ONS
`
`RI
`IK
`
`D4
`6V
`
`rPF
`
`1979 "Experimenter's Corner." Resistors R1,
`R2, and R3
`the reference voltage
`form
`source with the upper limit defined by Vcc(R2
`+ R3) /(R1 + R2 + R3) and the lower limit
`defined by VccR3 /(R1 + R2 + R3). For small
`windows, R2 determines the window open-
`ing. For very small windows, on the order of 0
`to 15 mV, R2 can be eliminated and the
`opening can be adjusted via R7. Resistors
`R4 and R5 protect the inputs from excessive
`current during accidental inputs exceeding
`Vcc or ground. Diode limiting can be added
`from the inputs to Vcc and ground, using Dl
`and D2.
`System stability is a function of Vcc stabil-
`ity and op -amp drifts. For 741 s and 747s, Vcc
`should be between 8 and 30 volts. FET -input
`op -amps lend themselves well to this applica-
`tion. Resistors R4, R5, and R6 limit LED cur-
`rent and should be chosen to allow about 10
`mA. -Glenn Fasnacht, Lakewood, OH.
`
`vice is connected to a moped generator, if a
`battery is used, as suggested in the article, it
`would quickly discharge to the zener voltage.
`To obviate this, I would rewire the circuit as
`shown below.
`Note, too, that by substituting a dpdt (cen-
`ter -off) switch for S1 several advantages
`arise. Diodes D3 and D4 are eliminated, light
`assemblies do not have to be insulated from
`the frame, and return wiring from the lamps to
`the switch is not required. -Roy F. Gordon,
`Hampton, VA.
`
`T SIB
`
`2k% 2 T Z2Z2i12 + +2i2
`22.
`- -- FRONT - - --
`
`II
`
`12
`
`RIGHT
`
`13
`
`4
`
`R2
`I00K
`
`ICI 555
`
`01
`IN4001
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`10yF
`
`C2
`.OIyF
`
`www.americanradiohistory.com
`
`FRAME
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`CIRCLE NO. 35 ON FREE INFORMATION CARD
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`6
`
`IPR2017-01058
`Garmin EX1021 Page 8
`
`

`

`Introducing
`the Troubleshooter.
`
`Six functions and 24 ranges for $129* make the jump
`from Analog to Digital more affordable than ever.
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`oC,
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`There's a lot more to building a
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`Take the next step. Contact
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`Please send 8022A'IYoubleshooter data.
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`IPR2017-01058
`Garmin EX1021 Page 9
`
`

`

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