VLF Madera metal detector

Consider another homemade metal detector called “VLF Madera metal detector” that requires a minimum investment and not so much knowledge to assemble. The uniqueness of the metal detector is that it does not have a round coil, as in classic models, but an oval (or almost square) shape. The type of metal detector can be attributed to balancers, it has two coils, RX and TX.
Unfortunately, practically no information is indicated on the technical characteristics, including the presence of a discriminator on the source site. Hypothetically, such a metal detector, like its counterparts, should see the target at a depth of at least 1-1.5 meters (for large objects). Materials and tools for homemade products: – electronic elements for creating a board (can be seen in the diagram); – wire for the coil (PEV 0.35 mm);

  • – multi-colored tubes (cambric with multi-colored wires);
  • – carnations, plaque, paper, pencil to create a coil template (or other materials);
  • – foil;
  • – tinned wire (diameter 0.15-0.25 mm);
  • – insulating tape;
  • – soldering iron with solder;
  • -fum tape;
  • – materials for creating the body of the device and more.

VLF Madera metal detector

Metal detector manufacturing process:

Everything starts as usual – with assembling the circuit. In this regard, the author provided not very much information. First, you need to download and print the printed circuit board in LAY format:

Well, then a seal is created, all the details are carefully soldered and you can proceed to the next step.

Step two. Assembling the metal detector coil

First of all, you need to draw a coil template on paper. What it should be can be seen in the photo. The author also recommends drawing an arrow in which direction to wind the wire, since you can get confused in the process of creating a coil.
Among other things, you will need multi-colored tubes (you can remove the insulation from a thin wire). These tubes are put on the ends of the wire, this will allow you to remember where the beginning and where the end is. Also, the tubes protect the ends from breaking off.

 

The template is made from a board, for this you need carnations. Nails need to be driven into the board by biting off the caps from them. Further, cambric is put on these nails, they protect the insulation of the coil from damage during assembly.
In total, you need to make 80 turns with a 0.35 mm PEV wire. You need to try to wind the wire in the middle of the nails, this will allow you to crawl to the coil from all sides if necessary. Further, when the coil is wound, it must be wrapped, without removing it from the nails, with a thick thread (as the wire harnesses are wrapped around). Subsequently, the whole thing is covered with furniture varnish. You need to try not to varnish the places where the nails are, otherwise you will not remove the coil later. Well, when the varnish is dry, the coil can be removed and the remaining fragments can be varnished.

Step three. Coil tuning

Next, the coils need to be tuned, they are tuned into resonance at a frequency of 32768/4 = 8.192 kHz. For tuning, you need to select the capacitance of a capacitor of 0.1 microfarad, which is connected in parallel to the circuit. You need to start with a capacitance of 0.06 microfarads, and then gradually increase until the resonance becomes maximally the same on a digital variable voltmeter (parallel to the coil). The procedure must be carried out at the transmitting connector of the device.

A similar procedure should be carried out with the receiving circuit, for this it must be temporarily connected to the TX connector and configured.

Further, the coil is wrapped with insulation, the author used fum tape for such purposes. Then the RX coil can be wrapped with foil; for such purposes, you can remove the tape from electrolytic capacitors. In the middle of the upper part of the coil, you must not forget to leave a gap in the screen with a width of 10 mm, in the figure the place is marked in red.

Next, you need a tinned wire with a diameter of 0.15-0.25 mm, they need to wrap the foil. You need to start winding from the place where the screen breaks to the starting wire of the coil, this is done on both sides. Then they twist together and form the ground with the initial one. Finally, the coil is wrapped with electrical tape.

Two LEDs are connected to pin 7 of U2B, they work as indicator lights. They are connected in parallel-opposite, using a 470 ohm resistor. The rod must not be metal.
In the next step, you need to reduce two contours. The author fixes the transmitting coil statically, it is in plastic or textolite. The receiving room is superimposed on the first by 1 cm. At the first output of U1A, a squeak of 8 kHz will be heard, it can be controlled with an AC voltmeter, and it is best to use high-impedance headphones. The setting is that the receiving coil must be moved until this squeak subsides to a minimum, or the voltmeter reading decreases to several millivolts. When the spool is flattened, it can be locked.

Download PCB (Sprint Layout)

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