Docstoc

Fun Projects 45 Chapter

Document Sample
Fun Projects 45 Chapter Powered By Docstoc
					        for
HnProlcct$ thcHloilmcnbr

                  METAL       (E)
                       DETECTOR
Youcan use this simplemetaldetector locateplumbing
                                      to                 pipes,electrical
wiringinsidewalls,find a lostwatchor coin at the beachor evena treasure
with goldcoinsburiedyearsago by pirates.

Youcanalsousethe circuitin experimentswhereyoucan showthe magnetic
properties materials.The
         of                        between
                         ditferences       paramagnetic,
                                                       diamagnetic,
and nonmagnetic materials                                  can
                                                 experiments be
                          can be shown.Interesting
conducted usingthe metaldetector         here.
                                 described

This circuitwill detectthe presence metallic
                                   of        objects throughany noncon-
ductivematerial   suchas dirt, wood,stone,plasteror plastic.

With a littlepractice, will be able to detectmetallic
                     you                              objectsto depthsof
overseveral   inchesand will giveyou a fairlygoodideaof theirsize.
                                method detectan object.
Our circuitusesthe beat-frequency     to

Thefrequency the searchcoiloscillator
                of                            whenthe conductance
                                        changes                   in
                                            when metalscomewithina
                                   Therefore,
the field of the searchcoil changes.
shortdistance thecoil,thefrequency changed,
                of                   is                         the
                                              whichin turnchanges
pitchof the audible sound.
                                                 that
The soundis produced the speaker a common receiver tunes
                    by         of        AM
the coiloscillator.

A schematic  diagramof the MetalDetector shownin Figure 1. Observe
                                           is
                                             oscillator. can also use a
that the circuitis a very simpleone-transistor        You
general-purpose silicontransistor,
                  PNP                  inverting powersupplypolarity.
                                               the

The physical         of             components,
            arrangment the electronic            usinga terminalstrip
          is                          partof this project the search
as chassis, shownin Figure2.Thecritical                 is
coil.

The searchcoil is woundin a large6-inchplasticFrisbee.
                                                     Beginby securing
one end of the enameled  magnetwire form  (18 to 22 AWG)with masking
tape.On thetenthwrap(haltway)                        wireforthe center
                               forma loopin the magnet
tap,thencontinue  untilyou complete 20 turnsof wire.
                                   the
                    rcbct l5 tcfirl !0bcbr




 c1
22AOpF




         Figure 1




         Figure2


                                       ttE
        lor
lunPnlec$ lltcHlcrlmcntor

It is veryimportant secure coilwirefirmly, one looseloopin the coil
                  to      the            as
                     to
willcausethe detector be unstable.

To use:

Fix a smallportableradiocloseto the oscillator shownin Figure 3.
                                             as

Tunethe radioto a freepointof the rangebetween and 1,600kHz.Adjust
                                             550
CV in thesearch oscillatorto thissignal a whistle. youcan'tfind
                coil            tune        as       lf
             signalin theAM band,reduce enlarge search by a few
the oscillator                          or     the      coil
turns.

Passing searchcoil over a metallicobjectwill changethe pitchof the
        the
       Whenthe mostpronounced
whistle.                     changeoccurs,    you shouldbe directly
overthe metalobject.




                              Figure3


2t6
                                                PnFGr ftfiilromau
                                                    t5

                  PartsList - MetalDetector
     Q1- 8C548
             general-purpose silicon
                          NPN      transistor
     Ll - Search - seetext
               coil
     CV- 365pF - anyvariable       (from
                           capacitor    nonworking radio)
                                                 AM
     C1 - 2,200 ceramic
               pF     capacitor
     C2- 0.1uFceramic
                    capacitor
     Rl - 10,000
               ohm,114W,5%
                         resistor
     51 - SPSTslide toggle
                   or    switch
     81 - 6 or 9V - fourAA cellsor 9V baftery




                        ldeasto Explore
          performance to learnmoreabout circuit:
Togetbetter        or                 the
     o Make  experiments ditferent
                       with      kinds materials seehowthe
                                     of       to
            works
     detector    witheachone.
     o Explain  whathappens
                          when metalobject introduced a mag-
                                a         is         in
     neticfield. thereanywayto identify metal
               ls                     the   beingdetected?
     o Thecircuit alsobe usedas an RFsignal
                  can                        generator. getthe
                                                      To
     signalfromthisoscillator,
                            connect
                                  a probe thecollector thetran-
                                        to           of
     sistor           pF
          witha 1,000 capacitor an alligator to theemitter.
                                and         clip




                                                               m
Iun      for
   Proiecls hc trncilmcmcl

Scienceprojects          applications:
              and uncommon
      o Several             involving
                  experiments                     can be conducted
                                     metaldetection
      usingthissimplemetaldetector. example
                                    An       wouldbe a workto show
                    between
      the differences      paramagnetic,diamagnetic non-magnetic
                                                   and
      materials, suggested
                 as         earlier.

      o The searchcoil can be modified applyRF signals plantsor
                                     to                to
             Experiments find the effectsof RF (RadioFrequency)
      animals.           to                                   on
      seedgermination plantgrowthcan be madewiththis circuit.
                    or




218