We describe the detector in its capabilities somewhat inferior similar devices, but it is easier according to the scheme. They can, for example, to detect in the soil nickels on a depth of about 2 cm and larger objects at a depth of several tens of centimeters.
The detector consists of two RF generators, collected on the transistors T2 and T3, and the detector - amplifier transistor T1, serve as an Indicator head phones. As the oscillating circuit L1C3 you can use any of a commercially available inverter circuits (465 kHz) with a branch from the part turns (for example, from radiograms "Ural-57"). You can use the whole filter Assembly with screen or to remove only armored core with a coil and attach it directly to the circuit Board of the detector. Screening is optional.
The winding of the inductance coil L2 is wound a wire of PEL on a wooden or 0,38 a plastic ring with a diameter of 250 mm and contains 31 round (removal from the 10 loop on top of the scheme).
The capacitor C6 - ceramic PDA-3. You can take a small capacitor, but then when establishing parallel to it will have to connect the capacitor is constant capacity. Capacitors C5 and C9 paper (e.g., MBM, BM). The rest capacitors ceramic or mica. The resistors can be any, including and ULM. The primary power source battery flashlight (SWС-L-0,5) Instead of transistors P13 can be applied P14-p with In about 30.
When the coil of the metal detector approaches a metal object, the frequency generator on the transistor T3 is changed. The frequency of another oscillator (T2) remains the same. As a result, the beat frequency that can be produced by phone, changes.
The annular coil L2 is attached to a wooden block of width 40 mm, with a thickness of 15 mm. its Length is selected such that it is not stooping to examination of the surface of the soil. The lower part of the bar has a trapezoidal neckline, in which is placed the frame of the metal detector with a wound on her coil L2. In the neck is tightly fitted wooden wedge, pre-lubricated carpentry glue. You need to pay special attention to the fact that the frame was fixed on the block-holder. Otherwise, a small displacement of the frame relative to the bar will lead to additional (false) changes the tone of beats.
At a distance of 200-300 mm from the frame on the narrow side of the bar holder is attached the capacitor C6. The mounting plate is attached to the other side, here is and the power switch. The battery is placed on lower broad the side of the holder. The current consumed from the battery, does not exceed 4 mA.
Conclusions connecting with a metal detector circuit Board made of the the same wire, which is wound frame. To shield the detector is not necessary.
If after Assembly of the detector and switching it on, the rotation of the rotor of the capacitor C6 cannot ensure that the phones were tapped beats, frequency which would change as the rotation of the rotor, it is possible to increase the capacity capacitor C7 to 200 PF. If you still can't hear the tone of the beats, should short-circuiting the capacitor C7. Hearing the tone of the beats, it is necessary to ensure that the appearance of the tones corresponded to the middle of the range of the capacitance of the capacitor C6, this is achieved by a careful selection of the capacitance of the capacitor C7.
A metal detector should be used: to wear head phones and turn food. The rotating axis of the capacitor C6, bringing a metal detector to the ground surface to achieve the possible occurrence lower tones of the beats. After that, the frame is moved parallel to the surface. At higher frequencies, the frame slowly moved over the place where there is an increase frequency to more accurately determine the location of the metal. In this case a transient increase in the frequency clearly stands out against the monotonous sound.
When searching for small items it is better to drive frame is not parallel to the surface, and positioned lateral surface close to the ground.
Moist soil, unlike metal, lowers the tone of the beats, so when changing soil moisture may need to be adjusted the capacity of the capacitor C6 in the search process.
Author: B. Salivary