Fun Projects 13 Chapter by MohamedSheba

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               AUDrO         (E)
                    OSCILLATOR
Thislow-power           oscillator generate
              experimental       can                    in
                                                  signals the
                                            audible
range  between100and2,000Hz,driving smallloudspeaker a low-im-
                                   a                 or
pedance  earphone. circuit be powered 2 twoor fourAAcells a
                 The     can          by                  or
fixed6 voltpowersupply.                for         depend
                            requirements thiscircuit
                      Current                            upon
the power supplyvoltage the loudspeaker
                      and              impedance range
                                                 and      typi-
callyfrom10to 300mA.
Potentiometer adjusts operating
             P1      the         frequency can be set within
                                         and                a
largerange values.
          of                                ohmscan be used,
                  Potentiometers to 1,000,000
                               up
        the
changing frequency range lower to about10Hz.
                             limit
                  and                       are
                         between andO.22uF suitable
C1canalsobealtered, values     0.01                    for
experimentation. C1values produce
              Large      will              in        part
                                  frequencies thelower
of therange.
                                  games,
Thecircuit be usedas partof alarms,
         can                           toysandto learnmore
                oscillators.
    transistorized
about
FigureI shows schematic
              the        diagram the Audio-Oscillator.andQ2
                                 of                 Q1
                   amplifier Rl/Cl is theclosed thattakes
forma directed-coupled     and                 loop      the
     back
signal    fromtheoutput theinput.
                      to                     .      ,
Figure2shows layout thecomponents, a terminal aschas-
               the    of          using      strip
                           supply be housed a smallplastic
sis.All the components power
                    and         can       in
box.
Thekeyis atelegraph homemade-type     butyou alsouseanSPST
                                switch,      can
toggle slide
        or  switch continuous
                   for        operation. keyis recommended
                                       A                   if you
want usetheoscillator a
      to               as Morse
                              Code        in
                                   sender demonstrations or prac-
                                                      to
    Youcanwirethe points and B to the contacts a relay usethe
tice.                     A                   of
circuit partof an alarm.
       as




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                        B1
  cl                  3TO6V
0.047pF




    Figure I




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    Figure2

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                                                                      :
                  PartsList - AudioOscillator                         1



                                                                  I
     Q1     - 8C548      purpose
                   general     NPNtransistor
                                                                  l
                                                                  I



     Q2     - 8C558      purpose
                   general     PNPtransistor
         -              loudspeaker
     SPKR 4 or 8 ohmsmall
     K      - Telegraphic - See
                       key     text
     81     - 3 to 6 volts- twoor fourAAcells

     Ri     - 10,000         resistor
                   ohm,114w,5%
     R2     - 1,000         resistor
                  ohm,114W,5%
     Cl     - 0.047 metal or ceramic
                   uF   film       capacitor


                         ldeasto Explore
Tolearnmore                         performance:
           about circuit to getbetter
               the     or
     o Change fora capacitor therange
                C1             in         between and0.22uF.
                                                0.01
     Thefrequency  range the produced willbe altered.
                        of             tone           With0.01
     uF or lowervalues Cl, the circuit produce
                      for            will                Use
                                               ultrasounds. a
     tweeter a piezoelectric
             or            transducer thiscase.
                                     in
     . Replace witha TlP32orTlP42 poqerthecircuit a 12
               Q1               and             with
                  getmuchmorepower theoutput.
     voltsupply.You'll           in
     .          why
          Explain oscillators
                            needa closedloopto the signal work.
                                                        to
      projects other
Science      and   applications:
     o Experimentsacoustics bemade thisdevice. circuit
                in        can     with      The
     canproduce tonebetween and20,000 andeven
              any           10        Hz,     higher.



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o A telegraph
            station be simulated thiscircuit. canfind
                  can          with        You
MorseCodein anybookabouttelegraphy.
o Byreplacing witha reed
             K              wired points andB,thecircuit
                        swich   to     A
willoperate an alarm.
          as
o Experiments
            involving
                    conductivity materials be made
                              of         can      with
probes
     plugged points andB.
           to      A
o Connect           transducers LDRs NTCs points and
            resistive         as     and    at      A
B to geta light-dependent
                        or temperature-dependent
                                            oscillator.
a Using metalrodsas sensors, circuit be useas a lie
        two                       the     can
       or
detector bio-feedbackdevice. Replace witha 0.22or 0.47uF
                                      Cl
capacitor adjust to getseparated
        and      Pl                  pulses the speaker.
                                          at             The
pulse willbealtered
    rate                  the
                    when skinconductivitytheinterrogated
                                            of
personchangeswhilein a stateof strain to a lieor stress.
                                    due
o A 117V+V x 250mAtransformer replace
                               can      SPKR produce
                                              to
          pulses nerve
high-voltage    in               experiments. generated
                       stimulation        The
pulses reach
      can     voltages highas 400Vpp.
                     as
o Experimentsanimal
              in     physiology beconducted
                             can                sounds
                                            using
or highvoltage described other
             as        in     projects.
                                      Growth plants
                                           of     sub-
mitted high-power
       to         sounds high-voltage can be observed
                       or           fields
using circuit practical
      this    with      experiments.
o ACfields begenerated replacing speaker a 2O-turn
           can         by        the        with
coil.Theplants animals be positioned
              or     can           within coil's
                                         the     electric
field.Seethesameexperiment the DCDimmer coilandex-
                         using             for
periment details.




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