Features of the metal detector
This design may well be able to make even hobbyists-novice. In this case the metal detector is sensitive enough.
Using the proposed device can be used to detect copper coin with a diameter of 20 mm and thickness 1.5 mm up to a depth of 0.9 m.
The principle of operation
The principle of operation of the metal detector is simple, it is based on the comparison of the two frequencies. One reference (reference oscillator) and the other variable (from search generator). Moreover, the deviations depend on her appearance in the field a highly sensitive search coil metal objects.
Modern metal detectors that can reasonably be attributed consider the design, the reference oscillator operates at a frequency on the order different from the one that arises in the field of the search coil.
Schematic and PCB
Schematic diagram of the detector and the printed circuit Board is presented in Fig. 2.35.
Fig. 2.35. A simple metal detector: (a) schematic diagram; b - printed circuit Board
The reference oscillator is based on two logical components 3I-NOT chip DD2. Its frequency is stable and is determined by the quartz resonator ZQ1 (1 MHz). Search generator made on the first two elements DD1 chip. The oscillating circuit is formed here by the search coil L1, capacitors C2 and C3 and the varicap VD1. For tune to a frequency of 100 kHz is used, the potentiometer R2, which sets the required the varicap voltage VD1.
As buffer amplifiers are used logic elements DD1.3 and DD2.3, the mixer running on DD1.4. The indicator is a high-impedance a Cup BF1, the capacitor C10 is used as a shunt for high frequency component coming from the mixer.
Food
The metal detector is powered by a DC source voltage of 9 V, used battery type "Crown". As a filter successfully employed capacitors C8 and C9.
The manufacture of the search coil
The search coil requires great precision and attention during manufacture. Wind the coil preferably a vinyl tube with an outer diameter of 15 mm and internal - 10 mm, bent in the shape of a circle with a diameter of 200 mm. The coil has 100 turns of wire sew-0,27. When the winding is completed, coil curl with aluminum foil to create an electrostatic screen (reduce the influence of the capacitance between the coil and ground).
When winding and the entanglement foil it is important to prevent electrical contact between wire winding and sharp edges of the foil. In particular, will help here "obviuse obliquely". To protect the aluminum coating from mechanical damage the coil additionally, one has to twist the insulation binding tape.
The diameter of the coil may be different. But the following applies. Than the diameter of the search coil is smaller, the sensitivity of the entire device becomes higher, but the size of hidden metal objects narrows. If you increase the diameter of the coil opposite effect is observed.
Work with a metal detector
To work with a metal detector as follows. Placing search engine the coil in the vicinity of the surface of the earth, to set up a generator potentiometer R2, and so that in a telephone earpiece sound is not auditioned.
When moving the coil over the surface of the earth (close to last) and found metal object - the advent of sound in the telephone earpiece.
Author: Kochetov N.