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pulse metal detector PI polonese

 Pulse metal detector PI polonese

 We present one more (in addition to the numerous ones available on the site ) construction of an impulse metal detector. The details here are inexpensive, widespread, and the scheme itself is taken from the bourgeoisie, where, judging by the reviews, it passed all the tests and was highly appreciated.

 As for the circuit, its main advantage over other home-made detectors is that there is no programmable microcontroller, that is, solder the parts without errors and everything will work. The current consumption is within the range of 100-200 mA, which depends on the frequency, it is regulated by PR2. Handle this with care as it is easy to burn the transistor T1. The PR1 knob controls the frequency of the audio signal.

You should also remember about pairing resistors on the CD4011 (4093) microcircuit, as this affects the stability of the metal detector. Using a 12V 1.3 Ah battery will give up to 8 hours of battery life.  


Pulse metal detector coil 

The coil can be of different diameters, most preferably somewhere between 22 and 30 cm, and the wire has a thickness of about 0.5 mm. Large coils can see large objects deeply, but not small ones. The little ones see small things, but not deeply. 


In this case, the simplest search coil is made - in the shape of a circle. The coil resistance should be about 1.5-2 ohms for about 17 turns. With a lower impedance, there is a risk of T1 flying out, it would be nice for it to install a heatsink.

The next step was to make the coil. Two circles were cut out of a piece of thin film-faced plywood and 5 blocks of chipboard 10 mm thick were glued to one of them (of such length and in such a place that both coils rest on them).

Then the frame holder is made of thin fiberglass. In one of the circles, two oblong holes are cut to accommodate the handle, which are then glued with a poxypol and a hole for the wire in the inner spool. 

The next step was to lay and glue the coils, and connect and place the shielded cables. It's time to glue the second disc across 5 visible blocks. After the glue dried, the gaps on the sides were covered with fiberglass putty. Irregularities were smoothed out with ordinary machine putty, then painted black. 

  Although shielding the coils is not really necessary. The cable can even be from a TV, it is important that the wires are thicker than the coil wire. A shielded cable is simply less convenient to install. Probes have a negative effect if the diameter difference is too small. As for the duration of the metal detector's operation, the device worked for the longest time for 3 hours without turning off. The speaker is needed for at least 8 ohms, here it is used from an old mobile, plus a headphone jack is added.

There are 4 potentiometers on the front panel, one for the sound level, the other for the frequency of the sound signal and 2 more for fine tuning the frequency, as shown in the diagram. To make the operation more convenient, install the charging terminals and switch: power supply - off - charging, as well as a fuse and LED.

A well-assembled detector should pick up a coin from about 30 centimeters (with a 30 cm coil). Of course, this is a chuyka in the laboratory. In the field, with the span of the coil, there is practically no chance of finding a trifle 30 cm deep - the pulse frequency is too low. The detector will not be able to process information about the found object.

Download files:

PCB file (Sprint Layout)

Reference post: radioskot

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