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Fun Projects 25 Chapter

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     -          _


                     ALARM (E/P)
       OVER-TEMPERATURE
Thiscircuit produce
         will                 beeps a piezoelectric
                    intermittent    by                     when
                                                   transducer
the temperature overa
              rises      preadjusted                          in
                                          Youcan usethiscircuit
                                     value.
greenhouses,       etc.The
            heaters,             is
                          Sensor a common         diode an NTC
                                            silicon    but
canalsobe usedif youchange some  components'values.

Exchanging                                        to
          positions R1andPl withDl willcause device operate
                  of                       the
                     alarm.
as an under-temperature
Theintermittentsignal generated twooscillators. (pins1,2and3)
                     is           by              lGla
is aninverter controls b and
            that        lCl      lOlc (oscillators). c (pins 9 and10)
                                                 lOl       8,
is a very-low-frequencyoscillator provides modulation for the
                                that         the            rate
second  oscillator. second
                 The                  (pins5,6 and
                             oscillator            4) hasits frequency
determined R2andC1.The
           by               produced audio                   by
                                           tonecanbealtered adjust-
ingbothC1andR2within large
                         a      range values.
                                      of

Power comes                     power
              froma 3- to lS-volt    supply" portable a small
                                             For       use    9-
voltbattery recommended.
           is                      drainis verylow,about mAwhen
                             Current                    0.5
thetoneis otf.When toneis on,current
                   the                  drain rises about mA.
                                                   to    5

A schematic the Over-Temperature is shownin Figurc 1. lOl, a
          of                 Alarm
40ggB, twogatesoperating oscillators twoas butfer'inverters.
      has               as         and

Componentsplacement a homemade
                 on                        boardis shown
                               printed-circuit          in
Figure2.You made
           can                                 PC
                             using single-sided board.
                 yourprototype    a

Position thepolarized
       of                    especially
                    components,        diode (used sensor),
                                            D1      as
should observed. sensor be
      be         This    can                          by
                                placed fromthedevice using
                                      far
common  wiring. musttakesomecareto avoid
              You                         humidity water
                                                 or     falling
ontothesensor,which cause
                   will   adversely     the
                                   atfect alarm operation.

BZ is a piezoelectric      (Radio
                   transducer       27g-O7g equivalent) a
                                Shack     or         or
crystalearpiece.
Operation adjusted P1.Setthispotentiometergetsound the de-
          is      by                       to         at
siiedtemperature. get a moreprecise
                To                            you
                                   adiustment can replacethe
common                                 potentiometer.
              potentiometer a multi-turn
        trimmer           by


ltf
                                   Pfrfrcl25 M-Iomnnurulhm

                                                 vcc
                                               +3Vto +15V



         P1
        10M

         R1
        100K




                             Figure 1


               0V +Vcc   +




                             Figure2

Getthesensor       your
            between fingers seehowit works:
                            to              when tempera-
                                                the
turerisessomedegrees circuit produce serieof beeps.
                   the     will       a                 the
                                                  lsolate
sensor, aftersome
       and        secondssound         will
                                emission stop.
ftnPniloctsfi$e mdlffibl

            PartsList - Over-Temperature
                                      Alarm
      lC1 - 4093CMOSintegrated
                             circuit
      D1   - 1N914 1N4148
                  or             purpose
                           general             diode
                                         silicon
                                                                ;
      BZ   - Piezoelectric     or       earphone
                       transducer crystal                       j


             (Radio
                  Shack 273-073 equivalent)
                              or                                I
                                                                I
                                                                !



      R1   - 100,000           resistor
                    ohm,1l4W,5olo
      R2    - 33,000         resistor
                   ohm,114W,5%
      R3    - 2,200,000 114W,5%
                      ohm,    resistor
      Pl    - 10,000,000 trimmer
                      ohm      potentiomer

      Cl    - 0.047 metal or ceramic
                   uF   film       capacitor
      C2    - 0.47uF metal or ceramic
                         film       capacitor
      Cg    - 100uF,16WVDC          capacitor
                          electrolytic


                           ldeasto Explore
To learnmore                         performance:
            about circuit to getbetter
                the     or
                                  tonepitchor bothR3 andG2to
      o AlterbothR2 andC1 to change
                    rate.
      altermodulation
      o Replace witha 10,000 100,000 NTC, witha2,200
                 Dl             to    ohm    Rl
      ohmresistor, P1witha 100,000 1,000,000 potentiometer,
                 and               to      ohm
      to geta newkindof sensor.
      o Tryto adda power{ul
                         output   stage
                              audio                   such
                                       using transistor, as
                                            a
      a 8D135 a smallloudspeaker. other
              and                See     projects thisbookfor
                                                in
                     the
                about configuration.
      suggestions



r50
                                     Pnfocfl ow-lcmrunnnilnm
                                          25

Scienceprojects
              and otherapplications:
     o Chemical  processesthat involveheatchangescan be controlled
     usingthis alarm.The sensorshouldbe protectedagainstmoisture
                           involving
     and waterin experiments        liquids.
     o Replace by an LDRor photodiode. circuitwill operate a
                D1                          The                 as
     lightalarmor darkalarm,depending   upon sensorposition. Withan
     LDRit wouldbe betterto replace witha 1,000,000
                                   P1               ohm potentiom-
     eter and R1 with a 10,000            Lensesplacedin frontof the
                              ohm resistor.
     LDRor phototransistor be usedto increase
                           can                  sensitivity.
     o The circuitcan alsooperate a water-level
                                  as               alarmby usinga two-
     wire sensorto replaceDl. The sensoris madewith two barewires.
     The wires are separated a distanceof about2 or 3 inches.
                             by                                   The
     watercompletes circuitwhilethe wiresare immersed.
                     the                                     Whenthe
     waterlevelfallsbelowthe wires,the circuitis openedandthe alarmis
     triggered.
    . o Temperature greenhouses,
                     in            animalpens,incubators aquari-
                                                         and
      ums can be monitored                And if workingwith an LDR
                          usingthis device.
      as the sensor,
                   experiments        lightcan be conducted.
                              involving




                                                                  tut

				
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