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DESIGN IDEAS BILL TRAVIS ANNE WATSON SWAGER Scheme implement
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BILL TRAVIS ANNE WATSON SWAGER
Scheme implements multiple output ports
KURDTHONGMEE, NAKORN THAMMARAT, THAILAND
systems, sometimes need many output ports update ports simultaneously. instance, systems that multiplexing techniques, output ports require refreshing every scanning period. example system multiple dot-matrix LEDs. Suppose that N-column, matrix uses row-scanning technique. Every eight-dot column connects port (n=1.N) (m=0.7), which switching transistor controls LEDs. update each row, row's switching transistor turns off, ports receive update from display buffer. switching transistor that then turns method Listings Figure allows simultaneously update output ports. approaches available implementing parOUTPUT PORT DATA DB0.7 NOTES: DECODED ADDRESS=CHIP SELECTION. IC4=SN74HC574N. OUTPUT PORT
allel-output port. first approach, every output port address. address-enable lines output ports connect chip decoder. update output ports, application program needs directly refer port's address (Figure 1a). native MCS-51 assembly routine Listing simultaneously updates output ports configuration Figure Assume addresses these ports OUTPUT_PORT0, OUTPUT_PORT1, OUTPUT_ PORT1+1.OUTPUT_PORT(N-1). Alternatively, connect output ports configuration Figure this method, only address refers output ports. example, update ports, application program must refer ports' address then iterate following steps times: Read data from address from buffer, route data
OUTPUT PORT OUTPUT PORT
NOTES: DECODED ADDRESS=CHIP SELECTION. IC4=SN74HC574N.
update output ports address every port (a); another method address them simultaneously (b).
referred port, N=N-1. Note that, above example, data from location buffer updates port, where between N-1. Listing MCS-51 native routine simultaneously update output ports. Assume that single address ports OUTPUT_PORT. using this sin-
gle-address configuration, need refer output ports' addresses every time need update them. thus eliminate instruction update loop, making routine shorter faster. This routine suitable implementation interrupt-service routine. #2151) Vote This Design, Circle
LISTING 1-MCS-51 ROUTINE
UPDATE OUTPUT PORTS
LISTING 2-MCS-51 ROUTINE
plots pixels sans controller
DARYL CHRISTOPHER, JUNIATA COLLEGE,
FISHER, INEXPENSIVE SYSTEMS, HUNTINGDON,
5-MHz cycle frequency. Because sometimes desirable display needs 8192 pixels approxioutput graphically, rather FIGURE mate 70-MHz refresh rate, than numerically. However, operathe time issue only approximately tion increases system complexity nine commands each pixel. Moreexpense. addition itself, over, this time must include timing usually need graphics controller pulses (Figure well data. least kbyte RAM. However, matching PIC's capayou obtain satisfactory plot (Figbilities task recognizing that without controller graph specialized display. plot RAM. first glance, parameis single-valued function ters seem daunting. least expensive display points graphics LCDs (for example, time. majority pixels carry Optrex DMF696, $39.51 from information whatsoever. Inasmuch Digikey (Thief River Falls, MN)) have maximum resolution possible resolution (width height) vertical axis only part pixels, which equates 1024 bytes. This simulated plot shows blinking byte (1-in-256 resolution) more midrange such cursor X=74 measuring Y=177. than adequate contain datum, 16C37A, only bytes available, including whatever need program vari- bytes more than enough plot. allow borders, graph Figure actually ables. Furthermore, must frequently refresh LCD: plottable area only pixels.) Another problem write code that terse enough Optrex recommends 70-Hz rate. PIC's cycle time (the time takes execute command) nsec. maintain required refresh rate. fastest move divides 20-MHz oscillator input produce (pixel) rotate through carry flag
into output port. This operation would normally mean wasting entire output port, because remainder port's pins would always contain "stale" shifted pixels. However, allows input through pins designated digital input, pins usable. Figure shows 16C73 port assignments. Listing shows code fragment that displays single pixel screen. Note that routine requires only cycles. However, include start-of-line pulse (CP1, cycles), subroutine calls (two cycles), other overhead, worst case requires cycles. This time budget results unacceptable refresh rate approximately screen areas that require unchanging information, such borders, tick marks, labels, stored program ROM. Because would take many cycles recover this data from lookup tables (which cumbersome PIC), code each byte explicitly clock them time using routine Listing need approximately lines repetitious coding large, binary shape table specify static information; good editor simplifies this chore. implement blinking x-axis cursor periodically replacing datum appropriate location with decimal. This operation effect drawing flashing vertical line above pointed-to datum. setting screen scans with without 255, obtain blink rate approximately sec. control cursor's position rotating potentiometer that feeds PIC's converter through RA2. cursor moves, coordinates position display numerically bottom graph. updatable, three-digit positions (requiring total bytes RAM) make classic character generator, with each numeral's shape stored bytes RAM.
16C73A sends these signals DMF697. startof-scan, start-of-line, data latch, driver-voltage polarity, data. FIGURE
LISTING 1-CODE FRAGMENT
This minimal circuit displays graph permits cursor movement; makes provision acquiring data.
essential frequently update screen continuously reverse polarity LCD's electrodes thus prevent destruction display. line takes care this operation switching polarity beginning each screen scan. Although possible invoke short routines between scans, must perform lengthy routines, necessary blank screen using call Erase_Screen. program requires approximately kbytes program memory Page ROM) bytes data RAM. download program MPASM 1.40-compatible source file from EDN's site, www. ednmag.com. registered-user area, into Software Center download file from DI-SIG, #2153. Although using controller/video imposes severe restraints what display, this approach reduces complexity cost simple graphs. #2153) Vote This Design, Circle
LISTING 2-CODE OBTAINING
Antenna extension provides open-door policy
RICHARD PANOSH, VISTA, BOLINGBROOK,
Metal garage doors solid secure, they transparent FIGURE radio waves. your garage aluminum siding, experience frustration with operation your garage-door opener. must drive door nearly touch TWIN-LEAD drive near window activate CABLE door opener, this Design Idea you. antenna extension Figure NOTCH BREAK LEAD moves receiving antenna beyond SIDE door system respond your command. Construction simple. antenna GROUND completely passive uses J-pole design. antenna uses readily availHOOKUP RG-174 able flat twin-lead RG-174 WIRE miniature coaxial cable. length suits opener that operates MHz. Most popular openers, such Stanley, Genie, Chamberlain, operate this frequency. However, some units operate MHz, some SHORTED replacement controls operate TOGETHER MHz, some automobile manufacturers offer 380-MHz designs. usually find operating frequency sensitivity treatment your garage-door opener uses readily available coaxial user's manual, obtain cable twin-lead simple configuration. directly from manufacturer. J-pole antenna consists half-wave antenna matched shield RG-174 coaxial cable frame impedance coaxial cable means door opener effectively ground locate quarter-wave matching stub. Figure half-wave antenna above garage door wood trim. antenna comprises piece wire above notch into staple across twin-lead. side flat twin-lead cable. solder Mount twin-lead door using adhesive pads lower ends stub together. Experiments show that nylon cable ties means single small nail screw optimum location coaxial above short- each through center twin-lead. end. RG-174 coaxial cable lead-in. attach coaxial cable garage rafters ceiling with Route this lead above garage door through same nylon cable ties adhesive keep weather stripping without drilling holes. sure that moving parts. Route cable above door allow center conductor coaxial cable connects half- normal operation door below garage-door wave side twin-lead that ground braid con- header beam that door's weather stripping seals when nects notched side twin-lead. Solder both these door closes. addition this antenna extension garage-door connections cover them with clear silicone rubber opener markedly increases operating range. Measurements protect them from weather conditions. Prepare coaxial cable that connects show improvement approximately equivalent existing garage-door antenna exposing center con- increase range. improvement espeductor soldering 6-in. length hookup wire. cially noticeable installations which garage effeccan insulate connection with heat-shrink tubing tape. tively shielded metal doors, metal siding, lack Twist hookup wire tightly around existing antenna windows. #2152) wire full length form gimmick capacitor suitable coupling signal into receiver without unduly Vote This Design, Circle loading receiver altering characteristics. Secure
Dual comparators stabilize proximity detector
ARTHUR HARRISON, ARMY RESEARCH LABORATORY, ADELPHI, JOSEPH STERN, MAXIM INTEGRATED PRODUCTS, SUNNYVALE,
proximity detector Figure 4-in.-sq piece copper-plated board serves antenna that forms plate capacitor. approaching (grounded) person serves other plate, producing capacitance value that increases person approaches. from copper plate, example, person produces capacitance value approximately simplified circuit illustrates circuit transforms distance/capacitance into proportional voltage (Figure Transitions input square wave apply directly lower input exclusive-OR (XOR) gate delayed 0.693 before comparator reconstructs transitions applies them upper input. filter resulting output produce voltage proportional distance. output's duty cycle proportional R1-C1 network's delay comparator's propagation delay, small variation comparator delay mask small changes antenna capacitance. circuit Figure overcomes this limitation using dual comparator (IC1). Passing inputs through nearly identical comparators largely nullifies effect offset voltage, drift, propagation delay through comparators.
ANTENNA PLATE RG316/U 6-IN. LENGTH 4530 FOSC=1 4990 TURNS 10.0 1000
Exclusive-ORing inputs, delayed R1-C1 network, subsequent filtering implements capacitance-to-voltage conversion.
Figure delay capacitance consists 33-pF capacitor, parallel with coaxial cable foot) 4-in.-sq antenna plate. This capacitance charges through during each positive half cycle input square wave. When near detector, this capacitance equals produces delay 16.5 nsec upper input. With hand from detector, capacitance rises produces delay
IC1A MAX912 GND1 IC1B 0.22 GND2
30.1k 0.22 IC2B 1N4148 2N3904 HLMP3762
This proximity detector lights when person approaches antenna plate within threshold distance potentiometer
17.3 nsec, yielding time difference only nsec. detect such small time differences-over temperature with accuracy-the comparators must stable offset voltage propagation delay. (Changes offset voltage well propagation delay affect delay time.) 10nsec comparator generally stable within nsec. resolve subnanosecond intervals, dual-comparator approach Figure which increases useful resolution factor four five. IC2A offsets amplifies voltage TP1, which corresponds distance between hand antenna plate. hand movement toward antenna causes voltages rise. IC2B serve com-
parator with hysteresis, which compares voltage with 2.5V. Thus, voltage above 2.5V (which corresponds proximity in.) turns LED. adjust potentiometer threshold other than in., connect read proximity inches. adds hysteresis ensure well-defined transition. ensure frequency stability high-speed dual comparator Figure copper-clad board should have ground layer addition circuit layer. Power-supply bypassing should include 0.1- ceramic capacitors that very close comparators' supply terminals. #2150) Vote This Design, Circle
Low-cost switcher converts
PAUL FLORIAN, PLANO,
low-cost, three-transistor boost switching regulator Figure modified astable multivibrator comprising which substitutes load full output power oscillation frequency approximately kHz. efficiency with VOUT equal sourcing When base high, energy stores L1's magnetic field. When circuit drives base low, induced voltage from L1's magnetic field collapses with supply voltage. This voltage spike charges through When accumulated charge results voltage equal zener voltage plus 0.6V, pulls Q2's base ground, decreasing amount time subsequent oscillations thereby decreasing energy transferred This feedback through regulates output voltage 24.6V±the tolerance change output voltage circuit, simply change zener voltage Many VCOs require tuning voltages high 20V, this switching regulator generate tuning voltage from control voltage (Figure 1b). circuit configures one-half LM358N noninverting amplifier with gain eliminates gain noise generated supply. manually adjust tuning voltage using control voltage using feedback from PLL. #2159) Vote This Design, Circle
DCR2 ISAT200 CONTROL VOLTAGE ELECTROLYTIC
1N4933 ZENER 1N5252B
100k NOTES: 2N3904. RESITORS ±5%.
simple three-transistor switching regulator supplies circuit help provide tuning voltage from control voltage (b).
60-Hz modulator records process variables
WARREN JOCHEM, RESEARCH TRIANGLE INSTITUTE, RESEARCH TRIANGLE PARK,
circuit Figure allows record process variables three-phase power monitor designed record only waveforms. Many these recorders have seventh channel, normally used recording neutral current, which process-variable input. circuit operates generating 1V-rms output sine wave whose amplitude function 10Vdc input signal. rail-to-rail quad rated power supplies. Input stage IC1A buffers inputvoltage divider R1-R2 drives two-quadrant multiplier, IC1B. IC1B acts multiplier using switch gain from When off, IC1B gain Switching chops signal applied input into 60-Hz square wave whose amplitude proportional input signal. chopping signal comes from Schmitt trigger IC1C. portion power signal goes IC1C through voltage divider R8-R7. provide small amount hysteresis prevent oscillation ensure fast switching. output IC1C 60-Hz square wave that controls chopped signal from IC1B connects switched-capacitor filter, IC2. This eight-pole lowpass filter converts square wave from IC1B sine wave. Capacitor sets filter's 71-Hz cutoff frequency. form 16-Hz highpass filter that removes offset from output switched-capacitor filter. IC1D buffers filter provides 1V-rms, 60-Hz output. Calibration involves applying 10V-dc signal input adjusting until output reads voltmeter. Measurements show linearity within over entire input range. recorder, connect input process variable under measurement, connect output voltage-input channel 1V-rms power recorder. also circuit current-input channels designed low-voltage, 1V-rms current clamps. record 20-mA signals, shunt input with resistor. #2157) Vote This Design, Circle
OPOUT OPIN 0.0047 2N7000 fC=71 MAX292
INPUT 390k 100k
IC1C 79L05 1N4001 78L05
Chopper techniques convert input signal from process variable 60-Hz signal measurement three-phase power monitor.
Design Idea Entry Blank
Entry blank must accompany entries. $100 Cash Award published Design Ideas. additional $100 Cash Award winning design each issue, determined vote readers. Additional $1500 Cash Award annual Grand Prize Design, selected among biweekly winners vote editors. Design Ideas Editor, Magazine Washington Newton, 02158 hereby submit Design Ideas entry. Name Title Phone E-mail e-mail address published Company
Country Design Idea Title
Social Security Number authors only) Entry blank must accompany entries. separate entry blank each author must accompany every entry.) Design entered must submitted exclusively EDN, must patented, must have patent pending. Design must original with author(s), must have been previously published (limited-distribution house organs excepted), must have been constructed tested. Fully annotate circuit diagrams. Please submit software listings other computer-readable documentation disk plain ASCII. Exclusive publishing rights remain with Cahners Publishing unless entry returned author, editor gives written permission publication elsewhere. submitting entry, agree abide rules Design Ideas Program. Signed Date Your vote determines this issue's winner. Vote now, circling appropriate number reader inquiry card. winning Design Idea September 1997, issue entitled "Transistor trio makes vector anemometer," submitted Stephen Woodward University North Carolina (Chapel Hill, NC).
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