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Fun Projects 42 Chapter

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Fun Projects 42 Chapter Powered By Docstoc
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                          (E/P)
                 PHOTOMETER
Some themost
     of       commonapplications LDRs assensing
                              for     are               in
                                                 elements
      photo-relays,
alarms,         counters, meters
                       light      forphotography alsoexperi-
                                              and
     in
ments optics.
Theprojectdescribed is a simple meter
                  here        light    made froman LDR(Light
DependentResistor Photoresistor),
                 or           a 0-200uA             and
                                        microammeter, a 3V
      formed twoAA cells.
battery     by
                                                    ratio.
                                           resistance
Useanygeneral-purpose witha highdark-to-light
                   LDR
     the                               you        an
Since circuit operating shortdurations don'tneed ON-OFF
            is          for                                      j
switch. putthecellsin the battery
      Just                                    the
                                     whenusing unit.
                                holder                           i
                                                                 I




         sensitivity the range yourworking intensity.
Pl adjusts        to         of          light
                                                 is
FigureI shows schematic thePhotometer. ammeter notcritical.
             the         of            The
Anytypewithfullscale      from100uAto 1 mAcanbe used.
                    ranging
            a mounting using
 Figure2shows        view,                as          device
                              aterminalstrip chassis.The
            in     plastic Themeter LDRareplaced the
canbe housed a small     box.        and              on
frontpanel.
lf theammeter                         you
             usedis outof specification, need adjust Tryvalues
                                             to    P1.
between 10,000 and 100,000  ohms.                    in
                                  The LDRcan be housed a small
opaque     depending theapplication.
       tube,         on




250
           tnmfl   rtmmu




Figure I




Figure2


                      2tl
IunPlolects tfielrneilmGntGl
         fol

                       PartsList - Photometer
      LDR - AnycommonLDR(LightDependent
                                      Resistor)

      M1      - 0-200uA - meter- see text

      P1      - 100,000         potentiometer
                      ohm trimmer

      R1      - 10,000         resistor
                     ohm,114W,5%

      81      - 3V - two AA cells



                                 to
                            ldeas Explore
To get betterperformance to learnmoreaboutthe circuit:
                       or

      .    Try to use a phototransistor placeof the LDR.
                                     in

      o Replace ammeter a common
              the     by        multimeter.

      o Youcan replace LDRby an NTCand convert deviceintoa
                     the                     the
                meter.
      temperature
      projects
Science           the
             using device:
      o Anyexperiment involves measurement be conducted
                    that     light      can
           this
      using device.
      o Youcan calibrate meterscaleusinga common
                       the                      photography
      photometer reference.
               as




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