Many radio amateurs who are interested in this topic, know the name and the scheme itself, too. However, in an attempt to replicate the scheme often may arise questions and some of the difficulties.
Often (and mostly) this is due to the fact that the original scheme was developed and is being done on domestic chips, which have long discontinued the issue and not everyone has the opportunity to find like.
general description
This article provides an alternative detector circuit on modern imported chips and methods of its adjustment after assembly.
As can be seen, the circuit is fundamentally no different from the original, published on the website once radioskot.ru (on which scheme and developed by the users of the site). The difference here is only in the type used operational amplifiers.
After practical "experience" and trial the various options, it was found that very good results are obtained by the use of chips from the TL series. In this series have a dual op-amp type TL072, which comprises two elements in one housing and thus has a small size (8-pin enclosure). That is such an option, and has been applied in the "modified" scheme.
But it should be borne in mind that pinout (pinout) this chip is not the same as in domestic chips K157UD2 type, namely it can sometimes cause issues and some difficulties in the PCB layout board.
The figure here given pinout diagram, the standard for all (almost) like chips imported. Therefore, instead of TL072 can be used, such - LM2904, LM358, LA6458, BA4558 and others like.
Instead of the transistor T1 can be put KT361 or any import analogue low-power transistor, this does not affect the quality of the instrument. If you want to use the dynamic head, the transistor T3 can be replaced as a sound emitter, for example, KT602, KT605, KT608, KT805, KT815 and the like.
If we will only use the headphones, it is quite suitable and low-power (KT315 type or similar imported). The field effect transistor T2 is also possible to put either on voltage "drain-source path" 50 volts or more (e.g. IRF48N, IRF1010, NDP603, RFP50N06 and others).
All electrolytic capacitors in the scheme should be put on the operating voltage of 16 volts or more. Capacitors C8 and C9, it is desirable to deliver a capacity of as much as possible.
They are not intended for "smoothing" voltage ripple, and energy storage and return it to the "pulse" with the greatest possible stability. From this depends heavily on the quality of the unit of work, his "sensitivity" and therefore "the range" detection of objects.
Methodology and recommendations for assembly
The search coil wound on the insulating frame, its diameter may be of the order of 15-30 cm. The diameter of the coil depends on the number of its coils. Wire for winding the coil is better to take the largest possible diameter (0.6... 1.2 mm²), its resistance to a minimum. coil winding technology and the selection of the desired number of turns, see below.
After soldering parts should verify correct installation and apply to a circuit supply voltage from the battery or regulated power supply. circuit current consumption in the "rest" must be in the range of 50 mA.
Instead of the coil is necessary for a time to connect the dynamic head of small capacity (0.5... 1W). When power is applied to hear sound dynamics - buzz operation with frequency oscillator (120... 180 Hz).
This shows the generator efficiency. Then connect the search coil. To start the bobbin need reel 30 - 40 of wire turns (the larger the diameter of the coil, the less need to wind coils).
Connecting coil and a resistor device R13 to the minimum possible frequency of the sound at the circuit output (headphones or speaker must be short clicks or "crackling").
Trays to the coil, e.g., a coin and determine the distance to respond to it. Then a couple of turns unwound from the reel and again check the reaction distance. We perform this operation as long until we find the greatest possible distance response. Cut off excess wire and reel ready.
It can "fill" sealant, epoxy, or simply wrap duct tape tightly. The wire from the device to the coil may be any stranded, e.g. SHVVP or PVA.
adjustment
When you set up it is important to comply with a condition: next should be no metal objects! The sensitivity of the device is high, so the distance to the closest objects of metal should be at least 1.5 m.
The housing can be taken out of metal or plastic. If the casing is metal, it is better to be connected to the "common" wire circuit. In the manufacture of coils and attaching it to the rod can not be used any metal elements- bolts, screws, wire and so on.
Rod itself must also be metal. When all these conditions, and proper assembly and configuration, the unit will operate stably and show good results. The "ideal" of such a metal reacts to the coin 5 rubles at a distance of 25 cm, while larger items up to 2 meters.