Fun Projects 31 Chapter

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					lril Plolocts thsHDcilmomol
            lcr

                           (P/E)
                    REGISTER
            oNE-EVENT
               memory can be usedto storea simplebit of information,
Thisis a one-bit    that
                                       detector, a touchsensor.
suchas a remotepower-failure closed-trap
                           or                  or

                                                      the
                                               between alligator
                             When the resistance
The circuitoperatesas follows:
clipsfalls, SCRis triggered,
          the                powering the LED.
                                    ON

The SCR and LED stay in the ON stateevenafterthe appliedpulseto the
                                                                        i

                                                                        I
inputis gone.So the device"memorizes" event.
                                    the                                 1
                                                                        i
                          switch(reedswitch), microswitch, a touch
The sensorcan be a magnetic                   a            or
switch. simpletouchswitchis a metalplatewiredto G2.To get bestsensi-
       A
tivity, needsa goodground. can alsouse as sensortwo metalplates
      G1                   You
that are touched the sametimeto triggerthe circuitON.
                at

The circuitis powered fourAA cellsandcurrent
                    by                       drainis verylowwhenthe
LEDis off.Whenthe LEDis on, currentdrainis lessthan10 mA.

To resetthe deviceyou only haveto toggleS1. Anotherway to resetthe
circuitis to wire a momentary switchbetween anodeand cathode the
                                             the                  of
SCR.Sensors     can be wiredto the device                  wires.
                                         with longunshielded

Theschematic the One-Event shownin Figure l.ThoughR2and R3 are
              of              is
shownas fixed,you can use a 1,000,000  ohm potentiometer you prefer.
                                                       if          A
sensitivity        will get betterperformance
          adjustment                         fromthe register.

Figure 2 showsthe One-event Register, terminalstrip mounting. it is
                                     on                       As
an experimentalcircuityou can also use a solderless
                                                  board to installthe
components.

The circuitcan easilybe housedinto a smallplasticbox.Observe posi-
                                                            the
tionsof all the polarized         suchas
                        components,       the LED,SCRand powersup-
plv.
                        if      is            suchas the
                                     OtherSCRs,
Resistor is onlynecessary TlC106 used.
       R3
MCRl06 Cl06,
       and          require
                don't      R3.



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Figure I




Figure2


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                PartsList- One-Event
                                   Register
      SCR - TlC106 MCR106
                 or                    Rectifier
                              Controlled
                        Silicon

      LEDs - Red,yellow greencommon
                       or

      R1     - 470ohm,114W,5%
                            resistor

      R2     - 100,000         resistor
                     ohm,114W,5%

      R3     - 47,000ohm,1/4W,5%       -
                                resistor seetext

      S1     - SPSTslideor toggleswitch

      81     -6V-fourAAcells

      G1,2 - Alligator
                     clips




                         ldeasto Explore
Toget betterperformance to learnmoreaboutthe circuit:
                      or

      o Youcan replaceR1 and the LEDwith a buzzeror audiooscillator
      to get an alarm.But, remember therea voltage
                                   that            dropof about2
      voltswhencurrent  flowsthrough SCR.This
                                    the        voltagedropcan be
      compensated addingtwo or threevolts to the powersupply.
                     by                                        For
      instance, you use a 6-voltrelay, recommended
                if                   the            voltagefor the
      power  supply 8 or 9
                    is      volts.
                                                          on
                 drainis verylowwhenthe LEDis off,depending the
      o As current
             use,51 can be removed.
      intended
      .                           in
                 howthe SCRoperates thiscircuit.
           Explain




192
                                   FrFcr 8l holnillrffr

      and
Science uncommon
               applications:
    o Youcanconnect LDRbetween andG2fora light-operated
                   an           Gl
    one-eventmemory alarm. single
                  or     A       shortpulse lightcantrigger
                                           of
.   thecircuit.
    o Usethiscircuit knowwhensomeone
                      to               touches object
                                              an      when
    you leaveit unattended. canalsoknowif someone
                         You                          your
                                                entered
    room whenyouwereout.
    a By usingtwo barewireas sensors, havea water-level
                                    you              alarm.
    TheLEDwillglowwhenthewater          the
                                touches twobarewiresat the
    sametime.




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