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simple metal detector on seven silicon transistors
The metal detector allows to detect any metal object at a distance of up to 20 cm. The detection range depends only on the area of the metal object. For those who do not have this distance, such as treasure hunters, you can recommend to increase the size of the frame. This should increase the depth of detection.
simple metal detector on seven silicon transistors

Detector concept
The circuit is assembled on transistors operating in a mode of microcurrents, and consists of HF generator (100 khz) on VT1 which is adjusted by the R1 resistor on maximal sensitivity to metal subjects.

The basic scheme of simple improvised metal detector on transistors.



Two frames are used as coils L1 and L2 (Fig. 2). Transistors VT2, tz are included as diodes and provide stabilization of modes of the Autogenerator-VT1 and active detector on VT4 at change of a supply voltage and temperature.

The R6 resistor sets the sensitivity of the detector. On transistors VT5 and VT7 the sound autogenerator which is switched on transistor VT6 is assembled. In order to provide loud sound hf1, parallel to it the coil L3 is included.

This increases the voltage by resonance between the internal capacity of the HF1 and the inductance L3. When entering the field of coils L1-L2 metal Object The frequency of the generator changes, which leads to a decrease in the voltage amplitude at the entrance of the detector (VT4). It locks, and the VT6 transistor opens, which allows the operation of the sound generator.

This scheme, compared to similar devices, using the principle of beating frequencies, provides greater sensitivity and easier to manufacture.

Details and Design


A battery of the type "corundum" or "krona" (9 V) is used as a power supply, but any stationary source with a voltage of 6 - 10 V can be applied. Current of consumption in the standby mode no more than 1.5 ma, at work of a sound signal - 7 MA.

Simple detector design on transistors design.



All elements of the circuit can be placed on a printed circuit board of one-sided. Case for a frame it is necessary to make from any dielectric materials, for example, to glue from Plexiglas.

The L1 and L2 coils should be identical and contain 40 + 40 turns of wire PEL diameter 0.25 mm (perimeter of coils 340 mm).

The L3 coil is wrapped on two rings of 400-1000 nm type, which are glued together, and contains 250 - 300 coils of the wire PEL diameter 0.1 mm.

The built-in resistors R1 and R6 should be of type SP 5-16, the rest can be any small-sized. Capacitors C7-Type to 50-35 on 16 in, others-type to 10-17.


Printed Circuit board homemade detector.



The VD1 diode can be replaced by any pulse. Microswitch SA1 type DD-9-2.

When setting up the device, if you can not get the generation on the VT1 by adjusting the R1 resistor (you need to control the oscilloscope voltage on this resistor), you need to change the connection phase of the output of the L1 coil.

When adjusting the circuit to the maximum sensitivity to metal objects may need to change the overlap distance of coils "a" , after which the frame of coils should be fixed with glue.
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