Functions and capabilities
Simple compact metal detector used to detect the walls under a layer plaster a variety of metal objects (e.g., pipes, wiring, nails, fixtures). It is a fully Autonomous device, is powered by a 9 volt battery type "Krona", consuming her 4-5 mA.
The detector has sufficient sensitivity to detect:
- pipe at a distance of 10-15 cm;
- wiring and nails at a distance of 5-10 cm.
The sensitivity can be significantly increased by increasing the size of the device, but as shown for home use do not always advisable.
Schematic diagram
From circuit point of view, the device is an LC oscillator field-effect transistor is coupled to the audible indication device.
Readout device used sound, though it is more expensive light, but much more economical compared to battery power. As usual the led consumes about 10-15 mA (normal visibility in the daytime time), and buzzer intermittent sound with the piezo oscillator of about 2 mA. The device is quite simple, its schematic diagram is shown in Fig. 2.45, and.
Fig. 2.45. Compact metal detector on the field-effect transistor: a - schematic scheme; b - circuit Board; - appearance of the device
The device operates as follows: filing a diet, you need to install variable resistor R4 mode the generator on the verge of collapse. While the generator operates at frequency of the order of hundreds of kilohertz), the AC voltage from its output is rectified by diodes VD1, VD2, charges the capacitor C5 to the voltage V. 2-3
This voltage is sufficient to block the intermittent operation of the generator sound collected on the logic elements of the IC DD1 according to the standard scheme. It should appear next to the coil L1 metal object, like a generation breaks down, the capacitor C5 for 20 MS discharges through R5 and now permitted operation of the generator on DD1.1, DD1.2, and under his management starts to work intermittently generator on DD1.3, DD1.4.
System ZQ1 starts beeping intermittently. If the metal is removed from the coil, generation circuit L1C2 immediately restored and the sound emitter pauses.
Setting of the metal detector
Depending on the degree of battery discharge, air temperature, subjects, near detector requires frequent tuning resistor R4 in the process. The engine resistor is necessary to take first in the position of maximum resistance is generated in the LC circuit must be broken and the device must submit the audio signal.
Then slowly reduce the resistance R4 to the recovery of generation - device ready to work. In some cases, you may need a selection of the resistor R3. To achieve the maximum volume of the radiator it is desirable to select the value or R9 C7 so that there came the sound resonance in the system.
Element base
The device does not contain scarce or expensive parts. Field-effect transistor can be any of a series of CP, the IC can be applied cheaper, 176 series. The inductor frameless contains 50+50 turns of wire with a diameter of 0.1 mm, wound on a mandrel with a diameter of about 7 cm Can be wound on a glass the bottle, then slide the coil with it, bonding the coils slightly of thread and fluff whole hog glue type "Moment".
All fixed resistors - MLT-0,125, or similar. Capacitors - any compact, with a TKE and error, as you still have constantly adjust the generator manually. The system also any. Electrolytic capacitors should not have large leakage currents, especially C1. To correspond to this requirement most of the new capacitor type K50-35 or similar import.
Installation of the metal detector
All parts except the battery, variable resistor, a sound emitter and inductors are mounted on a printed circuit Board (Fig. 2.45 b). Fee further together with the battery, the radiator and a variable resistor is placed in the housing is of a suitable size.
The inductor is mounted on a dielectric stand a length of 15 cm, otherwise, the device will detect its own battery.
The use of interchangeable coils
You can even try to make a few replacement coils of different diameter, as this will depend on the distance at which the device can detect metal.
So, when the diameter of the coil form 12 mm, detection range is a few millimeters, but the metal detector responds to even the sawdust. With large coils it at large distances can detect only large objects.
Publication: www.qrz.ru