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Fun Projects 26 Chapter

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Fun Projects 26 Chapter Powered By Docstoc
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                     TESTER(P)
              GAPACTTOR
Thiscircuit beused testmetal ceramic
          can       to       film                    types
                                      capacitors other
                                              and
                    of     between pFto 10 uF.
of capacitors a range values
            in                    470
Thedevice formed anaudio-oscillator produces tonedetermined
          is      by              that      a
bythecapacitor under                                    The
                             connect capacitor thecircuit.
                   test.Probes      the      to
frequency theproduced is higher lower-value
         of           tone      for        capacitors.falling
                                                     A
toneindicates badcapacitor.
             a
      capacitors the range
Testing        in         between and10 uF,the oscillator pro-
                                  1                     will
            audio
duceseparated     pulses,working a metronome.
                               like
Thecircuit powered twoor fourAA cells, current
          is        by                 and     drainis verylow.
              to
P1 is adjusted setan audible               according value
                           toneat thespeaker,      the       of   I
thecapacitor     tested.
             being
                       to                    Two
                                       values. capacitors
                               capacitor
Youcan alsousethisdevice compare
withthesamevalue givethesame
                will        tone.
Theschematic         of          Tester shown Figute 1.The
             diagram the Capacitor     is      in
                                                   as
                                             working a direct-
                                   transistors
circuit as its hearttwo complementary
      has
coupled        Feedback provided resistor andthecapacitor
       amplifier.       is      by        R1              un-
dertest.
Gomponents                    stripis shown Figure2. Usethis
           placement a terminal
                    on                     in
partsplacement a guidewhenassembling terminal
              as                      the      stripandwhen
               into
housing circuit a box.
       the
Termination      should shortas possible avoid
         components   be               to     instability.

Position thepolarized
        of                                               and
                                                 capacitor
                     components, as theelectrolytic
                                such
power       should observed
      supply,     be                    The
                             whenmounting. capacitor     test
                                                     under
is placed thecircuit twoalligator as shown Figure
         in        by           clips     in      2.
         can       in      plastic
Thecircuit be housed a small     box.




r0!
                                        ?nhcrfi ffiffiFnr




P1
1M
     .-l
                                         Q2        S1 \
                                        BC558
           R2                                         I
           4K7                Q1
                             AnA/iA
                                          cl
                                        'l00pF
                                                      I
                                                      I
                 *l(
                                                     -L
                                                  81 ._
                     :t-
                                   R1            3/6V T
                 CAPACITOR         1K
                  UNDER
                   TEST



                                          4/8n




                       Figure I




                        Figure2

                                                            til
HiFilIOEEI*IhHruffiUT                                                  j




                 PartsList - GapacitorTester
      Q1   - 8C548general-purpose transistor
                               NPN
      Q2   - 8C558general-purpose transistor
                               PNP
      R1   - 1,000         resistor
                 ohm,114W,5%
      R2   - 4,700         resistor
                 ohm,114W,5%
      P1    - 1,000,000 114W,5%
                     ohm,     resistor
      Cl    - 100uF,6 WVDC          capacitor
                          electrolytic
      Cx    - capacitor test
                      in
      S1   - SPSTtoggle slideswitch
                      or
      81   -3orOV-2or4M-cells
          -          -
      SPKR 4 to 8 ohms 2to4 in.loudspeaker




                        ldeasto Explore
To get betterperformance to learnmoreaboutthe clrcuit:
                       or
      o Replace with 10,000,000
                P1                                      under470pF.
                                    ohmsto testcapacitors
                            clipsor probes
      Don'ttouchthe alligator             whentestingsmallcapacitors
      bellow1,000pF.

      o Explainhowcapacitors       in           Whatis feedback?
                           function this circuit.




It2
                                       Frohc|28 Grrrcllrlffi

      projects uncommon
Science      and      uses:
    o Mount experimentalcapacitor aluminum andpaper
             an                  using     foil     as
             Test          using device compare value
    dielectric. thecapacitor   this    and      the
    withknown  capacitors.
    o Experiments    involving                   can
                                       transducers be conducted
                              capacitive
    withthiscircuit. circuit be usedas an analog-to-digital
                   The        can                           (A/D)
    converter. These         can
                      circuits convert            (an
                                       capacitances analog quan-
    tity)                 (a
         intofrequencies digital  quantity). an appropriate
                                          With           conver-
    sionscaleit will be possible usea frequency
                                to                    to
                                                counter measure
    capacitances.




                                                               r03