This metal detector was developed by Evgeniy based on the “Terminator Pro”. The device has shown itself to be the best, high-level discrimination, low current consumption of the device, cheapness and availability of parts, as well as the ability to work on heavy soils. The device board has been tested and works great.

Technical specifications:

• The operating principle is inductively balanced
• Working frequency, kHz 8-15 kHz
• Dynamic operating mode
• Precise detection mode (Pin-Point) no
• Discrimination mode, two-tone sound (low — iron, high — non-ferrous metal)
• Supply, 9-12
• There is a sensitivity level regulator
• Ground balance is available (manual)

Air detection depth with DD-250mm sensor

• coins 25mm – about 35cm
• gold ring – 30cm
• helmet 100-120cm
• maximum depth 150cm
• Current consumption:
• Without sound approximately 35 m

Metal detector diagram:

Soldering must be neat – there should be no clamps or sticking, after assembly the board must be washed with alcohol.

The printed circuit board was provided by a user nicknamed DeD, for which I thank him very much.

We begin to make the metal detector block.

The board was etched.

We drill holes)) drill 0.8.

We start the assembly by soldering the jumpers, then carefully solder the sockets for the microcircuits and everything else.

Another recommendation, it is highly desirable to have a tester that can measure the capacity of capacitors. The thing is that the device has two identical amplification channels, so the amplification on them should be as equal as possible, and for this it is desirable to select those parts that are repeated on each amplification stage so that they have the most identical parameters as measured by the tester (that is, what readings in a specific stage on one channel are the same readings on the same stage and in the other channel)

Here is the finished board from the parts side.

In my assembly I did not solder the battery discharge unit.

From the soldering side.

Correct assembly of the board begins with checking the correct power supply to all nodes. Take the diagram and the tester, turn on the power on the board, and checking with the diagram, go through all the points of the nodes where the power should be supplied with the tester. Where there should be 4 volts – then there should be 4 volts (well, plus or minus a few millivolts), and so on through all the points.

Next, to get the correct response to the threshold handle, you need to select the MC7 and MC8 microcircuits. No current should flow through resistors R27 and R28, for this, the voltage at the MC8 output should exactly match the voltage at the MC7 output. To do this, pull MC8 out of the socket and put MC6 in its place. Check the voltage at pin 6 of MC6-MC7 and at pin 8 of MC6-MC7, if they are equal in pairs, pull the microcircuit out of the MC6 socket and put it in place of MC8. In fact, the output voltage of MC7 is equal to the input voltage of MC8, then no current flows through R27 and R28 and the circuit is thermally stable. The output voltage of MC8, when it is selected as needed, is regulated using R60 within 0…+1V. Usually, at a supply voltage of +4.040V, the output voltage of MC6, MC7 is about +1.950…+2.002V. If the output voltage is strongly from these levels

if it differs, then either the microcircuits are crap.

In my case, this was the most difficult stage in the setup. Since not all the chips were suitable. I bought 14 pieces of HEF4069 chips. 8 pieces were HCF4069. And it worked only with CD4069 chips.

Making a coil

The DD sensor is manufactured according to the same principle as for all balancers, so I will only dwell on the required parameters.

TX – transmitting coil and RX – receiving coil. Number of turns: 30 turns with wire folded in half Wire diameter: 0.4 enameled winding Both the transmitting and receiving coils are wound with double wire (that is, there should be 4 ends of the wire), we determine the arms of the windings with a tester and connect the beginning of one arm with the end of the other, we get the middle terminal of the coil. After winding, the coils are tightly wound with threads, impregnated with varnish. After drying, they are tightly wound with electrical tape around the entire circumference. Shielded with foil on top, there should be an uncovered gap of 1 cm between the end and the beginning of the foil, in order to avoid a short-circuited turn. The middle terminal TX is connected to the minus of the board (without this, the generator will not start), the middle terminal RX is needed only for frequency tuning, after frequency tuning (resonance) it is isolated and the receiving coil turns into a regular one (without a terminal). The receiving coil is connected for tuning instead of the transmitting one and is tuned to 100 Hz – 150 Hz below the transmitting one. Each of the coils is tuned by frequency separately, there should be no metal objects nearby!!! The coils can be shielded with graphite, for this 1: 1 mix graphite with nitro varnish and cover it with an even layer on top of the tinned copper wire 0.4 wound on the coil (without gaps), connect the wire to the case. Balance is achieved by shifting the coils (like on wedding rings) relative to each other. The balance should be within 20-30 mV but not higher than 100 mV.

The device can operate from 7 kHz to 20 kHz. The lower the frequency, the deeper it will take the target, but at the same time the discrimination on some targets will be worse, and vice versa, the higher the frequency, the less depth but better discrimination on some targets (such as gold, for example). Therefore, I think it is better to choose, as they say, the “golden mean” – this is approximately 10 kHz – 14 kHz.

The cable has 4 cores in a common screen, two wires to the transmitting coil and two to the receiving coil, the screen to the body.

Next, we installed C5 for the start 4n7, passed the ferrite over the coil (if a double beep was heard, then everything is fine, if a single beep, then the ends on the TX were switched around), connected the oscilloscope probe to the output of C5 and moved the coils to achieve a minimum amplitude.

So the device works, to which coil TX or RX should additional capacitors be soldered when setting up the reaction to metals!

Chocolate foil is on one end of the scale, copper is on the other end. That’s what you should be guided by.

Here is the entire VDI scale for reference, with the discrimination knob at minimum, the device should see all non-ferrous metals, when the discrimination is screwed up, all metals should be cut out in order up to copper, copper should not be cut out, if the device works like this, it means it is set up correctly.

A few words about the work of BG.

The BG 100k resistor should have a resistance of 100k at the 7 o’clock position and 0k at the 17 o’clock position. When rotating clockwise, the resistance decreases.

Soil is a weakly mineralized thing, so it is balanced at BG=100…80k, i.e. almost to the left stop. Ferrite is a highly mineralized thing, so it should be balanced at BG=15…10k, i.e. at 15 o’clock. In this case, the sounding should be as follows: if BG is adjusted from 7 to (approximately) 15 o’clock, then the sounding on ferrite should be high, this indicates that ferrite is undercompensated. if BG is adjusted from 15 to 17 o’clock, then the sounding should be low, this indicates that ferrite is overcompensated (in fact, we moved it to the iron area). During normal operation ON REAL weakly mineralized soil, ferrite is ALWAYS undercompensated and is sounded in a high tone, although the tone is blurred and unclear. When setting the VDI scale, check the sounding of ferrite.

Setting up ALLMET mode

Resistor R8 type 3296W adjustable. Turn on the device in ALLMET mode, take a nickel and a piece of ferrite and wind R8 so that the nickel has a high tone, and the ferrite has a low tone.

For the site http://www.radioingener.ru/ the assembly was repeated by a user under the nickname smertnuj .