The detector operates by the method of beats. He has two interchangeable search coils of different diameter 250 mm and 500 mm. by means of a first coil can be searched small shallow located metal object like a nail in the brick wall under the plaster or Wallpaper) and using the second, more deep-lying objects such as drill bit 10 mm device with notices a distance of about 30 cm, and detects the hatch cover under a 1-meter layer of snow. Coin 5 rubles (modern "penny") the device detects with 12-15 see
In the diagram of the detector has two generators, a stable and search engine. A stable oscillator is made on the chip D1, the frequency is 100 kHz stable quartz resonator Q1. Search engine generator made in the chip D2, its oscillation frequency is about 100 kHz and is determined the parameters of the circuit L1C2C3C4. The frequency of this circuit is strongly influenced by the change the bulk inductance coil L1 when the location is not near metal items. Since the metallic parts of the apparatus that they had no influence on his work coil is mounted on one end of the dielectric (wood) rod length 80 cm, and the device at its other end.
Summed signals in the element D3.1 and its output signals are formed total and the difference frequency. The sum-frequency signal is suppressed by the circuit R7C8R8. Signal difference frequency (beat signal) is supplied to the Schmitt trigger on the elements D3.2-D3.3, which changes its state during each half cycle of the input signal. At the output of the Schmitt trigger enabled pulse shaper on a chain C9-R10 and the transistor VT1. As a result of operation of the Schmitt trigger and the shaper pulses we can hear the heartbeat frequency, not only from a few kilohertz up to hundreds Hz, and low frequency beats a frequency of 1-10 Hz, which are reproduced speaker B1 as crackles (reminiscent of the sound of the crackling radiation dosimeter). This allows you to hear a very slight deviation in the frequency of search generator.
As already mentioned, the device works with two replaceable coils. Both coils have the same design, but different diameter and number of turns. Coil 250 mm in diameter is wound on a mandrel of the same diameter. Only 30 turns of PEV-0,61. Then the coil is removed from the mandrel and the resulting ring harness tightly wrapped with rope coil to a coil (a rope, stack as wound ferrite ring). Then the coil is wrapped with a tape made of a thin foil, but not on all surface, and so that the opposite terminals of the coil part left unshielded portion of the length of about 10 mm. and Then tightly wrapped several layers of PVC electrical tape. In the mounting of the coil cannot be used the metal parts.
The second coil has a similar structure, but its diameter of 500 mm, and the number turns 21.
For rigidity of the coil is fixed to the associated strips, using taped epoxy glue the rope, the frogs.
The capacitor C2 is three-section air-dielectric 6-360 pF, all sections connected in parallel. B1 - any speaker.
The establishment is to adjust the contour L1C3C4C2 (by means of selection and C3 C4) so that when, about the middle, the position C2 can be achieved very low pitch sound, when further adjustment C2, rare rolling in crackling.
Author: V. Korotkov