VICTOR MEEDIJK SELECTING AS WE SAW LAST TIME. Part 2 there are a lot of fac­ tors you should consider in selecting re­ THE BEST sistors for your projects and designs. As you might expect, the same holds true for capaci tors . In capacitor selec tion, you should consider such things as operating RESISTOR/CAPACITOR temperature, humidity, AC ripple, and operating frequency. In addition, capaci­ tance, as well as other capacitor specifica­ tio ns such as curre nt rat ing , leakage current, voltage rating, and life expectan­ cy, should be cons idered so that the device There are a lot of factors to consider when selecting the proper chosen will be appropriate for the applica­ capacitor for your design or project. In this article we'll look at tion at hand. Materia ls used in manufacturing a ca­ those factors, and which of the many, many types of pacitor, as well as how those materials capacitors is right for your application. have been assembled , will effect capacitor spec ifications. As an exampl e, capaci­ tance is based upon electrode area and the type and thickness of the dielectric used. those devices are thin enough to mount compe nsate for temperature -cau sed Varying any or all of those things will, of beneath unsocketed IC's, thus reducing changes in resona nt frequency in tuned course, change the capacitance of the de­ the length of a trace for a bypass capacitor. circuits. When used in that second ap­ vice. But that is not the only parameter That is important in high-frequency cir­ plication, the ceram ic capacitors should that will change . cuitry since a PC trace can have an induc­ be mounted close the the tuned circuit, For instance, if the electrode surface tance of 10 nanohenries/inch. but be shielded from any heat generating area of an aluminum electrolyic capacitor Capaci tors come in a variety of styles components. is increased (to increase the unit's capaci­ including ceramic, mica, paper, plastic, The EIA has broken ceramic capacitors tance) through the use of finely etched aluminum, and tantalum types. into categories. Class I capaci tors are electrode foils, the device will have a Each type was desig ned for best perfor­ larger ESR (Equivalent Series Resistance) mance in a specific applica­ than similar smooth-metal foil units. That ti on or env ironme nt. is because the ESR depend s upon the vol­ Each type of capacitor is ume of the foil used . discussed below, and You can also increase capacitance by the important spec­ using dielectrics with high dielectric ifications a n d (high-K) constants . But capacitors that considerations use high-K dielectrics are not as stable that pertain to (they are more sensi tive to temperature the type of ca­ and voltage variations) and generally have pacitor are a higher dissipation factor than capacitors sum marized that use dielectrics with lower dielectric in Table 2.Ta­ constants. ble 3 is a glos­ Capacitor package styles also should be sary of capaci­ considered. High lead inductances, com­ tor terms and mon to tubul ar units, restrict high-fre­ specifications. quency performance . Tubul ar ceramic One note about capac itors however, are the most stable Table 2-the speci­ form of capacitor and, since there is no fications shown there opposing electrode to provide stray capac­ are only provided as itance pickup, almost the total capaci­ guidelin es. It is certainly tance is provided by the ceramic. possib le to find units with Dipped or molded radial-lead packages slightly, or even greatly different reduce interconnection impedances by al­ specifications. lowing the capac itor to be mounted close to a PC board surface . Ceramic capacitors Chip capacitors have contacts, rather Cera mic capac itors are used in many than leads, to even further reduce inter­ applications . For instance, they are used connection imp ed an ces . In add itio n, as bypass capacitors. They are also used to TABLE 2-CAPACITOR SELECTION GUIDELINES

CERAMIC Notes : DC blocking, filter, bypass, coupling, and transient supres­ Values : 1 pF to 2.2 flF sion applications. Close tolerance, high frequency capability Tolerance: 10% or 20% (40--400 kHz) and high insulation resistance. Not suitable for sam­ Voltage rating: 3.3 volts to 6 kilovolts DC ple/hold circuits, fast settling amplifiers, or filters due to dielectric, Dissipation factor: to 5% absorption characteristics. Small size, medium stability, and long Temperature coefficient: to 200,000 PPMf C life expectancy under load. For NPO's- Tolerance: .25% to 10% Metalized polyester/polyester toi/­ Temperature coefficient: 0 :!:30 and 0 :'::60 PPMf C Values: .001 to 100 flF Notes: General purpose high insulation-resistance devices used Voltage rating: up to 1500 WVDC for transient decoupling of IC's and compensation of reactive Dissipation factor: 1% (at 25°C and 120 Hz) changes caused by temperature variations. Applications include Temperature range: - 55 to + 125°C (with 50% derating above filtering, bypass, and non-critical coupling in high frequency cir­ 85°C) cuits. Frequency sensitive (capacitance will vary with frequency) Notes: See polycarbonate for typical applications. Moisture resis­ so characteristics should be measured at intended operating fre­ tant and high insulation resistance. Small size, medium stability quency. Should be mounted next to components being compen­ and very good load life. Capacitance will however vary widely with sated, and shielded from sources of heat. Due to low voltage failure temp erature. Foil units are generally lower cost than metalized problems, should not be operated significantly under rated voltage types . Polyester film is commonly known as Mylar, which is a under humid conditions. In circuit design, considerations should DuPont trademark . be given to changes in the dielectric constant caused by tem­ Polystyrene toi/- perature, electric field intensity, and shelf aging. Values: to 10 fl F Voltage rating: up to 1000 WVDC CERAMIC CHIPS Dissipation factor: .03% (at 25°C and 120 Hz) Values : 10 pF to .18 fl F Temperature range: - 40 to 85°C without derating Tolerance: 5 to 20% + Notes: Used in timing, integrating, and tuned circuits. High insula­ Temperature range: - 55 to + 125°C Insulation resistance: greater than 100,000 megohms tion resistance, and small capacitance change with temperat ure. Has excellent dielectric absorption characteristics. Large size with excellent stability and very good load life. MICA Values: 1 pF to .1 f.lF Paperlmetalized paper/paper tol/- Voltage ratings: 100 to 2500 volts DC Values: to 100 f.lF Temperature range: - 55 to +150°C Voltage rating: to 5000 WVDC Temperature coefficient: - 20 to + 100 and 0 to + 70 PPMfC Temperature range: - 30°C to + 100'C (derated by 30% over Derating factor: 60% voltage (dipped case) and 40% voltage 75°C) (molded case) Temperature coefficient: greater than 4,500 PPMfC Mica chips- Notes: General purpose. Medium stability and very good load life. Values: 1 to 10,000 pF Large size: low cost. Metalized paper has paper coated with thin Voltage rating: to 500 volts layer of zinc or aluminum and are smaller than metal foil units. They Notes: Used in timing, oscillator, tuned circuits, and where precise are, however, prone to dielectric breakdown of insulation resis­ high frequency filtering is required. Capacitance and impedence tance and have poor surge handling capability. Paper foil units limits are very stable and capacitors perform very well at frequen­ used in high voltage/high current applications. Their dissipation cies of 10 kHz to 500 MHz. Devices using silver in their construction factor varies with temperature. Maximum temperature is + 125°C. are very susceptable to silver ion migration resulting in short cir­ cuits. Failures can occur in a few hours if capacitors are exposed to Polypropylene toi/lmetallzed polypropylene- DC voltage stresses, humidity, and high temperature. Values : to 10 fl F Voltage rating: to 400 volts DC and 270 volts AC (foil units: 200 to GLASS 1600 volts DC and 300 to 440 volts AC) Values: .5 to 10,000 pF Temperature range: - 55°C to + 105°C Tolerance: to 5% Notes: Foil units are used in tuned circuits, integrating circuits, Voltage rating: 100 to 500 volts DC timing circuits, and CRT deflection circuits. Metalized units are Temperature range: - 55°C to +125°C used in DC blocking circuits. Good high frequency capability, high Temperature coefficient: 0 to 140 PPMfC insulation resistance, close tolerance , high stability, and excellent Notes: High insulation resistance, low dielectric absorption and dielectric absorption characteristics. fixed temperature coefficient. Has much higher Q than mica de­ vices. Performs very well at high frequencies up to 500 MHz and Less common types- can operate in range of 100 kHz to 1 GHz. Capable of withstanding Polysulfone: Similar to polycarbonate and polyproplyene capaci­ severe environmental conditions but are susceptable to mild me­ tors. Small size, high temperature range (to 150°C), suitable for chanical shocks and should be mounted accordingly. high-frequency applications, and high insulation resistance. Excel­ lent in high current and military applications. Not for sample/hold, PAPER/PLASTIC DIELECTRICS fast settling amplifiers, or filters due to dielectric absoption charac­ Many dielectric and case configurations are available. Each type teristics. Poor history of availability. has its own characteristics. For example, metalized paper units Polyvinylidene fluoride: Considered experime ntal; Has high di­ have low insulation resistance and are prone to dielectric break­ electric constant (about four to twelve times that of polyester de­ down failures. Plastic types have superior moisture characteristics vices), which results in a very small sized capacitor. Those units en than paper units. Polycarbonate and Mylar types are used in suffer from significant capacitance change with temperature, par­ o applications that require minimum capacitance change with tem­ ticulary at low temperatures . Z perature, such as tuned or timing circuits. Polyethylene terph th alat e: For applications that require high re­ o a: Metallzed polycarbonate and polycarbonate fIIm­ liability ; high insulation resistance at high temperatures. I­o Values: up to 50 fl F Metalized paper polyester/paper polyester foil: The foil unit has W Voltage rating: to 1000 WVDC a slightly better dissipation factor than the metalized type. Operat­ ...J W Dissipation factor: .5%(at 25°C and 120 Hz) ing temperature of - 55°C to + 125°C with voltage ratings of 240 to o Temperature range: - 55 to + 125°C 600 (DC) available. (5 « Derating factors: 50% voltage; 80% of rated tempe rature Paper po lyproplyene: Available in voltage ratings of 400 to 800 a:

64 (AC). Operating temperature from - 40°C to + 80°C. tolerences. Large values available. Etched foil has 10 times the Teflon/Kapton: Has a temperature range of - SsoC to + 2S0°C capacitance per unit volume as plain foil types. Peak AC and with a temperature coefficient of .009%fC. Teflon's extremely low applied DC voltages should not exceed rated maximums. Usable dielectric absorption makes it good for critical sample and hold to 200 kHz. Non-polarized foil are used in tuned low-frequency circuitry. Those capacitors used in specialized applications such circuits, phasing low-voltage AC motors, and in servo systems. as oil well drilling equipment. Those capacitors are large in size Sintered slug units are used in low-voltage power supply filtering since the dielectric is not available in thin gauges. and in DC applications. Can not withstand any reverse voltage. Parylene: Manufactured by Union Carbide, those capacitors are Leakage current lowest of all tantalum types: no appreciable leak­ equivalent to polystyrene types in performance but are rated to age below 8SoC . Usable to frequencies of 1 MHz. + 12SoC, versus + 8SoC for polystyrene. ALUMINUM ELECTROLYTIC TANTALUM ELECTROLYTIC Values: .68 to 220,000 f.l.F Solid type- Tolerance: - 10 to + 7S% Values: .001 to 1000 f.l.F Voltage rating: up to 3S0 volts Temperature range: - ss-c TO + 8SoC (if derated, to + 12S°C) Temperatu re range: - SsoC to + 8S0C (if derated, to + 12S°C) Voltage rating: 6 to 120 volts DC Dissipation factor: varies with temperature Tolerance: S% TO 20% Temperatu re coefficient: varies with temperature Leakage current: varies with temperature Notes: Used in filter, coupling, and bypass applications where Derating factor: SO% voltage large capacitance values are required and capacitances above Notes: Used in low-voltage DC applications such as bypass,coup­ nominal can be tolerated. Sum of the applied AC peak and DC ling, and blocking. Not for use in RC timing circuits, triggering voltages should never exceed the the rated DC voltage. Aluminum systems , or phase shift networks due to dielectric absorptio n electrolytics are larger than tantalum electrolytics but less expen­ characteristics. Also not recommended for applications subject to sive. Loss of capacitance, to as little as 10% of rated value, will voltage spikes or surges. High capacitance in a small volume with occur as the aluminum oxide electrode electrochemically com­ excellent shelf life. Solid types not temperature sensitive and have bines with the electrolyte. Oxide film deterioration also requires lowest capacitance-temperature characteristic of any electrolytic capacitors to be "re-formed" after storage to prevent dielectric unit. Dielectric absorption and high leakage currents make them failure. That involves application of rated voltage for a period of 30 unsuitable for timing circuits. Except for non-polarized units, these minutes, or more,to restoreinitial leakage current value. Overtime, devices should never be exposed to DC or peak AC voltages in dissipation factor can rise by as much as SO%. Four terminal excess of 2% of their rated DC voltage. To prevent failures due to devices are available (two leads for each connection) that offer low leakage or shorting when series connecting for higher voltages, ESR and inductance at high frequencies. Those units were de­ parallel each unit with a shunt resistor. signed for use in switching power supplies. Chip types- Values : .068 to 100 f.l. F TRIMMER CAPACITORS Tolerance: S% to 20% Values: range from .2S to 1 pF and 1 to 120 pF. Voltage rating: 3 to SOvolts DC Glass /Quartz: Low loss. high Q , and high stability for high tuning Temperature range: - SsoC to + 12SoC sensitivity applications. Frequency range up to 300 MHz. . Leakage current: varies with temperature. Sapphire: High level of performance between 1 and S GHz. Non-solid types­ Plastic: High grade units can be operated up to 2 GHz. Values: .S to 1200 f.l. F Ceramic: Smallest sized single turn units with maximum capaci­ Tolerance: - 1S to + 30, and 20% tance under 100 pF. Capacitance changes with temperature. Voltage rating : to 350 WVDC Air : High level of performance through UHF Band, from 300 MHz Temperature range: - SsoC to + 8SoC (if derated, to + 12S°C) to 1 GHz. Leakage current: varies with temperature Mica: Has wide capacitance range and relatively high current Notes: Polarized foil units are used for bypassing or filtering out handling capability. low-frequency pulsatmq DC. Allowance must be made for leakage Vacuum /Gas: Used for high voltage applications. Values from Sto current. Not suitable for timing or precision circuits due to wide 3000 pF, with voltage ratings from 2 to 30 kilovolts (DC).

tho se that have very predi ct able tem­ various desig nations mean. A s an exam­ capacitor short circuiting. perature vs. capaci tance characteri stics. ple , an X7R capacitor wi ll vary in capaci­ To keep internal inductance small for One type of Class I ceramic capacitor is tance by no more than a factor of ± 15% hi gh-frequency use, button-style silver­ the NPO (Negative-Positive-Zero) capac­ over the temperature range of - 55°C to mi ca capaci tors have the anode connected it or. That designation means th at the + 125°C. throu gh the center of the stack of mic a negative and positive temperature coeffi­ sheets. The other terminal is formed by cient s of the device are zero and that they Mica capacitors the case, which is connected to all points suffer almost (nothing is ever absolute) no There are two type s of mica capacitors. around the outer edge of the electrode. change in capacitance vs . temperature. One type is a stacked foil unit consisting That design permits the current to fan out Other Class I capaci tors have very predic­ of alternate layers ofmetal foil (or deposit­ in a 360° pattern from the center term inal table changes in capacitance w ith tem­ ed metal film) and sheet mica in sulators. thus providing the shortest RF curre nt perat ure . For i ns ta nce, a ceramic The metal foil layers are connected to­ path from the center terminal to the chas­ capacitor that is speci fi ed as N 750 has a gether w ith tin-lead foi l str ips with termi­ sis. negative temperature coefficient of 750 nal s attached by using solder coated One of the more common micas used parts-per-million, per-degree -centigrade. pressure clips. for capacitors is Muscovite mica , wh ich Th at is, for each degree centigrade the The second type ofmica capacitor is the comes from India. Th at substance has a temperature rises, the capacitance of the silver-mica capacit or. Those have a silver dielectri c constant between 6.5 and 8.5. unit w ill drop 750 parts-per-million . electrode material screened on the mica can be split into thin sheets, is non-por­ Class 2 capacitors are those that are stampings, which are then assembl ed as ou s, and does not readily abs o r b non-linear. Their temperature coefficients described above. The silver-mica capaci­ moisture. ~ are specifi ed by a three letter code that tors are very susceptible to sil ver-ion mi­ Mica capacitors are temperature and » gration, whic h can occur within a few :n specifi es the low and hi gh temperature frequency stable. have a low dissipation o ranges and the maxi mum change in ca­ hours, when exposed to hi gh DC -voltage factor, and perform well at frequencies up I ...... pacitance from that at 25 °C. Tabl e 4 stress, high humi dity, and hig h tem ­ to 500 MHz. Th ose high precision unit s (0 shows the EIA Class 2 code, and what the perature. The io n migration result s in the are used in a variety of appli cations, in- enCD

65 eluding tuning circuits, oscillators, fil­ ters, a ~d RF power circu its. TABLE 4

Glass capacitors Number Letter Maximum Capacitance Letter Low Temp, High Temp. Glass capac itors are used in app lica­ Symbol Symbol Symbol Change tion s that require high stabi lity in a hostile A + 1.0% environme nt. Th ose devices ca n with­ B :t 1.5% stand vibra tio n, accele ration , ex tre me Z + 10°C 2 + 45°C C + 2.2% moisture , vacuum, and high ope ra ting D + 3.3% temperatures; they are , however, suscepti­ 4 + 65°C E :t 4.7% ble to dam age fro m mild mech ani cal Y - 30°C 5 + 85c C P + 10.0% shocks. They have a life expectancy of R + 15.0% 30 ,000 hours or greater. 6 + 105°C Glass capac itors perform very well at S + 22.0% high frequenc ies up to 500 M Hz, and have X - 55°C 7 + 125°C T :t 22%- 33% a frequency range of 100 kHz to I G Hz . U + 220/0-56% Because of their characteristics, those de­ V :t 220/0-82% vices are co mmo nly used in missile and spacecraft electro nics . paper units, which have low insulation suitable for are in RC timing circuits , trig­ Paper/plastic capacitors res istance a nd ar e prone to di electric geri ng systems, or phase-shift network s. Paper and plastic cap acitor s are used in breakd own .)Plas tic types are less af­ That' s because they have high " dielectric app licat ion s that require high and stable fected by humid co nditions tha n paper ab sorptio n" charac teristics . Th at is, in su lation res istance a t hi gh te m ­ unit s since they are non -ab sorb ent. Plastic when a capac itor is discharge d , the di­ peratures, and good ca pacitance over a capacitors, suc h as po lycarbonate and electric retai ns a res idual charge , Thus , wide temperature range. (However, an ex­ po lyester (Mylar) types, are ge nera lly in­ even if a capacitor that has a high di­ ception to that are the metalized- we'll tended for app lications where minimum electric absorption characteristic has been' talk abo ut metalization in a mom ent- capacitance cha nge wi th temper ature is discharged to "zero ," it may still be hold­ requ ired . TIley are especially suited for ing a co nsiderable charge . That , as you tuned and precision-timing circuits. might imagine, ca n cause con siderable TABLE 3- GLOSSARY In metalized capac itors, a thin film of problems in timing circui ts and the like . D.C leakage-Small curren t that flows metal is dep osited directly on the paper or Tantalum capacitors also are not rec ­ through or across the s urface of the di­ plastic die lectric . Doing that gives the ca ­ o m me nde d for circu it s th at p rod uce electric or ins ulation of the capacitor. pacito r a " se lf-hea ling" charact eri stic spikes, surges, or pul ses. If their voltage Dielect ric-Insulating material between ca lled " clearing ." If there is a hole or rati ng is exceeded by even a few volts, the the plates of a capacitor. contaminent in the dielectri c of the capac­ device is likely to fail. Dielectric absorption-A property of a itor, a sho rt may occ ur, resulting fro m the Tantalums may be polarized or non­ capacitor's dielectric suc h that even when heavy curre nt flow in the fault area. In a po larize d . Polarized capacitors sho uld the capacitor is discharged to zero, a re­ me talize d capacitor, that heavy curre nt never be exposed to a reverse DC or peak sidual charge remains stored in the di­ electric. flow will melt away a very sma ll part ofthe AC' voltage greater than 2% of its rated Dissipation Factor- Important inACap­ thin metal film , thus disconnecting the DC voltage . No n-polar ized unit s, as their plications, it is the ratio of effective series fault from the ca pac itor. These capac itors name would apply, do not suffer from that resistance (ESR) to capacitive reactance are best for analog circuits because the lim itation . No n-po lar ized units are made Xc, and is usu ally expressed as a percen­ momentary current flow during the clear­ up of two pola rized unit s in seri es with tage. The dissipation factor factor varies ing action may result in a spur ious signal their catho des connected together. with temperature, humidity, and frequen­ and cause false triggering in digital logic cy. circuits. Aluminum electrolytics Electrolyte-Current conducting so lution Metalized plastic devices work well in Aluminum electrolytic capacitors are (li quid or so lid) between two electrodes or plates of a capacitor. swi tchi ng power-supply output filters be­ ge nerally larger than tantalums, and are Equivalent se ries resistanc e (ESR)­ cause they have a co mparatively low ES R, less expe nsive . On e prob lem with alumi­ Energy losses in the ca pacitor due to lead as we ll as stable temperature c ha rac­ num s is that they will change ca pacitance resistance, termination losses, and dis­ teristics. Whe n using those capac ito rs in (drift) over time . Th at is caused by the sipation in the dielectric. such an applicatio n, however, be sure that alum inum oxide e lectrodes che mica lly Insulation res ist ance (IR)-Measure of the unit selec ted is rated to hand le the com bining with the electro lyte. Because a capacitor's insulation quality expresse d voltage surges produ ced by the circ uit. of that , ca pacita nce ca n drop subs ta n­ either in megohms or as a time constant, tially, to 10% of rated values . Those un its RC. in seconds. That value determines a Tantalum electrolytics also have a limited shelf life due to ox ide capacitor's leakage curre nt for a continu­ ously app lied DC voltage whe n a capaci­ Tantalum cap acit ors offer high capaci­ fi lm de te rio ra tion a nd mu st be "re­ tor is fully charged. tance in a sm all package size and have an formed" after lon g periods of storage . Re­ Temperature co efficien t- A ca pacitor's exce llent shelf life . Various types of tan­ formi ng consists of applying the capaci­ change in capacitance per °C. May be talum electrolytic capacitors are availab le tor 's rated voltage to the unit for a period

(f) positive, negative, or ze ro and is usually incl udi ng solid, sintered slug , plain foil, of 30 minutes. Re-forming also prevents oz expressed in part s pe r million per °C etched foil , wet slug , and chip. Applica­ dielectric breakdown or shorting . In addi­ o (PPMf C). tion s inelude low-frequency filteri ng , by­ tion, the dissipation factor o{these de­ a: Working voltage (WVDC)-The recom­ passing, co upling , and blocking . The vices can rise as mu ch as 50 % . ~ mended maximum voltage at which a ca­ solid types are not temper atu re sens itive To prevent electro lyte evaporation and &1 pacitor s hould be operated -l and have a lower capacit ance-temperature co mponent cleaning probl em s, aluminum W Quality factor (Q)-Afigure of merit use d 0­ mostly in tuned circuit applications. It is characteristic than any other electro lytic electrolytics sometimes have an epoxy o capacitor. end sea l. However, without a vent, such « defined as a 1/DF or Xci ESR. a: App lications that tantalums are not continued Oil page 109

66 NEW IDEAS mounted at t he door so that it RESISTOR/CAPACITOR makes contact when the door is continued from page 97 opened and visa versa when the 'continued f rom page 66 door is closed. 52 and 53 are no r­ capacitors may explode if exposed to re­ mally-open momentary switches, verse or overvoltage conditions. lights, someone has tripped the and 54 is a 5P5T. circuit. The remaining LED Aluminum electrolytics are used in fil­ With switch 54 engaged, the cir­ tering , coupling. and bypass applications provides a visua l indication of the cuit draws 10-11 milliamps of cur­ were large capacitances. and capacitance delay time. rent , and w hen ope n, it d raws only that are higher than the nominal value, W hen the circ uit is untrip ped, a 5-6 milliamps. If you include the can be tolerated. low is applied to the input of IC3­ aud io portion of the circu it, it can Trimmer capacitors b. Therefore, a hi gh is output at be used to test the operatio n of the pi n 10. Pressin g sw itch 53, TEST, circuit. LE D's 2 and 3 should be red Trimmer capacit ors fall into three cate­ provides a path to ground through and green , respectively, to make it gories: multi-turn, single turn , and com­ pression types. Multi-turn capacitors have LED2 and causes it to light, ind icat­ easier to check the status of the ing that the circ uit has not been either glass, quartz , sapphire, plastic, or circuit. LED1, the de lay t ime in ­ air dielectrics, while single-turn devices t ripped. dicator, can be either co lo r. (It's use ceramic, plastic, or air dielectrics. However, pressin g the RESET swi­ your cho ice.) Compress ion types use a mica dielectric . tc h (52) causes t he f lip-f lop to To test the project simply trip Glass, quartz, or air dielectric devices change states, which means that the circuit several times and check are selected for applications requiring low pin 10 goes low and pi n 11 of 1C3-d its status, as shown by watc hing loss, high Q. stability, and tuning sen­ goes high . Now a press on 53 the LED's, and listening for t he sitivity. Glass and quartz devices are used causes LE D3 to light and LED2 re­ buzze r (if it's included). The un it at frequencies up to 300 MHz . Air di­ electrics are usable to about I GHz . For ma ins dark . A lso , a d e l ay is may also be used atwindows alo ng frequencies of I GHz , sapphire dielectrics provided so that you can ente r or w it h a lou d bell or siren to scare off leave your apartment w it ho ut trig­ offer the best performance. unwant ed visitors. There are ot her Ceramic and plastic styles are less ex­ gering the circuit. possibi liti es as we ll, li ke triggering pensive, with high grade plastic dielectric If switch 51 is closed when the a hidden video monitor and -re­ devices being usable at frequencie s up to delay times out, o r the circuit is corder, etc.-Ronald I. Goers 2 GHz . R-E tr ipped by someone entering the apa rt me nt, IC2 o utputs a high . That high is de live red to the input of the flip-f lop via diode 0 1 and resistor RS . That, in turn, causes ~5~~~foRE the flip-flop to change states. Now ladill-lllIlIlranilill. o Build Your Own Satellite TV Receiver $7.00 0 Special Projects (Spring 1981) $4.50 a high is at the anode of LED3, o 8-Ball SatelliteTV Antenna $5.00 0 Special Projects #4 (Summer 1982) S4 .50 w hich means itwililightwhen 53 is o Build Your Own Robot S12.00 0 Special Projects # 5 (Winter 1983) S4.00 o TV Descrambler (January. February 1981) $3.00 0 Special Projects # 6 (Spring 1983) $4.00 p ressed , showing that someone o Radio -Electronics back issues (1984) $3.00 0 Special Projects # 7 (Summer 83) NOT AVAILABLE has been in your apartment. o Radio-Electronics backissues (1983) S3 .50 0 Special Pro!ects i.Il(Fa ll 83) $4.00 The delay ti me is dependent on (January. February1983 notavailable) 0 Special Projects #10(Spring 84) $4.00 Writein issues desired 0 Radlo-Elecfronlcs Annual 1983 $3.50 the sett ing of potent io me ter R1 o Radio -Electro nicsback issues (1982) $3.50 0 Radi o-Electron ics An nual 1984 S2 .50 and the value of capac itor C1. Write in issues desired 0 How to Make PCBoards S2 .oo Make sure that the de lay provides o Rad io-Electronics back issues (1981) $4.00 0 AllAbout Kits . : $2.00 (Jan.. Feb.. March . Dec. 1981 not available) 0 Modern Electronics (Vol. 1. #1 $2.25 amp le time for you to enter and Writein issuesdesired April 1908) check the status of the watc hdog o Etch your own PC boards $3.00 0 Electro ImportingCo . Catalog $4.95 o Hands On El ectronics #1 $3.00 (1918) (176 pp) circuit, or to leave the apartment. o RE Annual '85 $2.50 0 Low Freq uency ReceivingTechniq ues $6.00 The delay t ime may be varied to Toorder anyofthe i1 ems indicafed above. check off theones Buildingand usingVLF Ante nnas you wa nt. Complete theorder form below. includeyour pay- 0 Newideas - 42 circuits for experimenters . . $4.00 suite your needs using R1 . ment,checkormoney order (DO NOTSENDCASH), and mail When switch 51 is t ripped, ca­ 10 Radio-Eleclron ics, Reprint De partm ent. 200 Park Ave. pacitor C1 begins charging South, New York, NY 10003. Please allow 4-6 weeks for delivery. ARTIC LE through R1 and the voltage at pin 3 IIyou need acopy ofan article that isinan issue we indicateis of IC2 begins to rise. When that unavailableyou can order it direcfly from us. We charge 50¢ • PAGES MON TH YEAR vo ltage reaches the leve l of that at per page. indicate the issue (month & year), pacesand article desired. Includepayment infull, plusshippingand handling @ 50¢ each --,-~ pin 2 (set by the R2/R3 series com ­ charge TOTAL PAG ES TOTAL PRICE bination), IC2 outputs a hig h at pin --- -- ~ ------~ ------MAIL TO : Radio-Electronics 6, w hich tr iggers the flip-flop. That ReprintDepartment, 200 Park Ave. South, New York.NY10003 All payments must be In U.S. funds turns LED2 off and LED3 on . Totalprice oforder ...... $ _ The method of construction is Sales Tax (New YorkState Residents only) ""''-' " $ _ Sh ipping & Handling (U.S & Canada only) (Includes FIRS~ CLASS POSTAG E) $1 .00 per Item ...$ _ not critical; wirewrap, po int-to­ Aliother countries (S2 .00peritem. sea mail) $ _ point wiring, or a PC board of your ($4.00peritem. airmail) S _ :!:: own desig n works fi ne . Housing Total Enclosed . . » ...... $ -- - - :0o for the circuit is again a matter of Name _ :r choice. 51 is a normally-open mag­ Address netic, security-type switc h, and is City State Zip _

L ....:....------.....J109