Sandbanks

"" *****PI POLONES - METAL DETECTOR - P.I. PULSE INDUCTION (Original build file details)***** ""

"" It is an impulse locator operating on the principle of rectangular wave emission
electromagnetic deep into the ground. Such a wave, if you come across
a metal object induces in it the electromotive force of self-induction (so-called
SEM).
This force deforms another electromagnetic field beam, thus in the system
electronic recording of such deformation. It stays
converted into an acoustic signal that is easily understood by the user.
An indicator of the presence of metal is the acoustic signal from
a voltage-tuned generator whose frequency in the speaker changes
proportionally to the size of the localized metal, its mass and
inversely proportional to the distance from the inductor (antennas
locator).
The PI locator has a number of properties that locators do not have
other types. This type of device is able to detect a coin with an average of 2.5
cm at a depth of 28 - 35 cm and its range is approx. 180 cm.
The device's sensitivity is a function of the power consumption. The method used for detection
very low frequencies are characterized by soil insensitivity even
very humid (e.g. sea beaches), is therefore resistant to so-called effect
ground. The pulse locator has one more positive
property. It is the lack of losses caused by land, for example losses in
ground in locators with discrimination (phase) are 10 to 20 λ and in
other types (BFO, IB) up to 50 λ.
From a technical point of view, one of the disadvantages of this type of locator would be
include relatively high power consumption of approx. 80-100 mA and inability to
distinguishing ferromagnetic metals (iron, nickel) from diamagnetic
(gold, silver, bronze).
When detecting, the only thing that matters is the alignment of the metal object
locator coils. Colored objects, e.g. coins, will be more easily detected at
parallel positioning, while iron objects, e.g. a nail while laying
centric
In general, non-ferrous metals have the best detectability
especially some of their feet like bronze and copper-nickel. Very well detected
there is silver and slightly less gold. It has the lowest detectability
aluminum.
It should also be noted that detection efficiency increases for these items
(especially iron) that survived hundreds of years in the earth.
The field of influence increases then due to the oxidation of the parts
metal that has reacted with the earth.

*****GENERAL OPERATING PRINCIPLE*****

Everyone can build this system without the need for refinement.
As with most detectors, the basic element
There is a detector (exploration) coil. If it reaches the coil
the power supply generates an electromagnetic field proportional to
current flowing through it. When the power is disconnected the voltage in
the coil first drops to zero, then when the magnetic field disappears, it increases
it in the reverse direction when feedback SEM is induced in the coil
exploration. When a metal object comes within range of this field,
it will be affected either by generating eddy currents or
will be magnetized depending on whether it is a diamagnetic or
ferromagnetic.
However, the result is the same, i.e. feedback SEM
it lasts longer before the voltage pulse disappears. This effect is visible
when the pulse passes through 0 V.
This signal zone is then processed by amplifying the sample
waveform. This sample is then given to the integrator who
produces an output voltage proportional to the SEM feedback decay time.
Then this voltage is given to control the VCO generator and
speaker.

*****DETAILED PRINCIPLE OF OPERATION*****

US1 integrated circuit (timer 555), resistors R1, R2 and capacitors C2 and C3
they create an astable generator of negative pulses. Frequency generated
pulses is about 100 Hz, it is determined by the resistor R2, while the width
pulses is approx. 70 μS and depends on the R2 resistor and on the capacity
capacitor C2. These pulses from output 3 (US1) are given through the resistor R3 on
the base of the T1 transistor, where they are inverted and then through
resistor R6 on the base of the power transistor T2. Pulses are supplied from the T2 collector
on the search coil Ls. Then the signal is given by μA709. Because
this amplifier has no internal protection of inputs 2 and 3 against
exceeding the allowable differential voltage ? 5 V, necessary
is to protect the inputs by switching on two diodes opposite
polarization directions D1, D2 and resistor R8.
To ensure yet
stable operation of this amplifier, several elements should be used
external as C5, C6 and R10. Resistor R12 sets the gain of the circuit and in
in this case it is about 1,400 times (ratio R12 to R9). To enable
sampling the waveform in the search coil as it passes
pulse through zero, it is necessary to generate a delayed pulse.
This was accomplished using US 4011, where to build a delay system
four NAND gates were used. Goals A and B form the first
generator generating positive impulses with a width of 30μS, triggered by the back
on the edge of transistor T1, the second generator (gates C and D) is triggered by
first and generates 50μS positive pulses. These pulses from output 10
(circuit 4011) are fed through the resistor R14 to the gate of the transistor T3 (BF
245), working like an electronic key, opening it for the duration of these
pulses.
This causes pulses to pass from the US4 system to the US5 integrator,
built on the operational amplifier 741. Resistor R16 located in
feedback loop sets the gain of the input signal
from the T3 transistor, while the C8 capacitor provides
forming a sawtooth with slow growth, the level of which
DC voltage at output 6 (US5) is proportional to the pulse width
coming from US4. The signal from output 6 is given to transistor T4,
which controls the voltage tuned generator (VCO). To build
VCO generator a field effect transistor with P channel and a 555 timer were used.
This transistor works in such a way that the resistance between the drain and the source
it changes in proportion to the voltage coming to the gate, in turn
causes the change of timer frequency and thus the altitude change
tone in the headphones (speaker).
US8 integrated circuit and associated components
they form a voltage converter, which increases the supply voltage to about 20V,
then it is given to a 12V voltage stabilizer (US 7). Obtained in this
way positive stabilized voltage from the US7 stabilizer and negative voltage
5V from the US2 stabilizer is used to supply US4 and operational amplifiers
US5.

*****CONSTRUCTION AND TUNING*****

As long as the system is correctly assembled according to the Schematic Diagram and Fig.
mounting plate the detector should work properly without the need
experimenting and using complicated measuring equipment (that's enough
ordinary digital meter), but with an oscilloscope and a frequency meter
you can check individual detector blocks at startup.
Voltage converters. Solder in US8, R31, R32, C17, C18, C19, C20, C21,
D3, D4, D5 and D6, connect the power supply. The output should get voltage
approx. 20V (? 3V). Solder in US7 and US2, US7 stabilizer output will be
12V, while the output of the US2 stabilizer will receive -5V,
(voltages measure against so-called artificial ground i.e. plus supply voltage).
Pulse transmitter. Solder in US1, R1, R2, C2 and C3. On output 3 US1
we will get a negative rectangular waveform.
Solder in R3, R4, R5, R6, T1 and T2, connect the search coil and switch on
power supply (the coil should purr quietly). To the collector of T2 transistor
connect the oscilloscope probe and check the waveform we should get
"Pin" with a voltage of approx. 80V.
Solder in R7, D1, D2, R8, R9, R10, R11, R12, R21, R24, potentiometer
mounting Pr1, C5, C6 and US4. Set the potentiometer Pr1 to output 6 US4 voltage approx. 0.8V. Approaching a metal object to the coil
this voltage will decrease by approx. 0.1 to 0.3V. Signal waveform.
Delayed pulse generator. Solder in US3, R27, R28, R29, R30, C12,
C13, C14, C15. Connect the oscilloscope to output 3 US3, we received a positive one
rectangular pulse about 30μs wide, then make an analogous one
measurement on output 10 US3, we should get a positive square wave pulse
width about 50μs.
Sampling gate and integrator. Solder T3, R13, R14, R15, R16, R17,
US5, R22, R23, P1, C7, C8, turn on the power. Connect to output 6 US5
DC voltage voltmeter when approaching a metal object near the coil
this voltage should change in the range from -3 to 12V.
Buffer and VCO (voltage tuned generator).
Solder T4, T5, US6, R20, R25, R26, R18, R19, C9, C10, C11, C16 and
connect the speaker. When setting potentiometer P1 in the leftmost
setting in the speaker will be silent, while when set to max
the speaker will hear sound at a frequency of approx. 10kHz. Now again
set potentiometer P1 so that the speaker can hear single pulses,
when approaching e.g. a coin, the pulse frequency will increase until
until a continuous tone occurs.
The detector should respond to the coin medium size from a distance of approx. 30cm. It should be noted that nearby
The detector should not have any devices causing interference including
they may therefore prevent proper alignment. Instead of potentiometer P1
two can be used, connecting them in series e.g. 47kΩ + 4.7kΩ, we get
then more precise tuning so-called coarse and accurate.
High quality components should be used to build the detector.
As US1, US6, and US8 the best would be ICM 7555, because of the lower
current consumption from NE 555 series systems. Other systems of any companies,
however, it is advisable to have them in excess, because they can hit
defective copies, especially the 709 series operational amplifiers.
Use BF 245 or BF 256 as T3. Any transistor can be used as T5
field with channel type p. T1 - any pnp transistor e.g. BC 178C, BC 308.
T4 with a high gain factor from group C e.g. BC 108C, BC 109C, BC
413C. As T2, use any NPN power transistor with a minimum power
30W and a minimum operating voltage of 80V, e.g. BD 285, BD901 or 2N6487.
Capacitors, except electrolytes, are only styroflex (stable in function
temperature). Capacitors C5 and C6 can be ceramic, while C4, C16 and
C22 may have smaller capacities, but it is desirable that they be of high quality.
Resistors with a power of 0.25W or 0.125W with the exception of R7, whose load capacity
should be at least 1W.

*****EXECUTION OF SEARCHING COIL*****

To wind the coil, use enamelled copper wire (DNE) with a diameter
cross section 0.5 to 0.65mm. Length of measured wire for winding 16 meters
(regardless of the diameter of the coil).
E.g. a 20cm diameter coil contains 24 turns, 30cm diameter - 17 turns and
diameter 40cm - 11 turns.
For the construction of the coil, use a PVC tube with a length of about 1.2m (for the coil
standard diameter 30cm) and diameter 15 to 22mm.
Prepare, e.g. a 30 cm pot, then carefully heat the tube
over the flame, try to bend it on a pan so that it forms a circle.
Excess tube (formed circle) should be cut to between the ends of the circle
a gap of about 0.5 to 1 cm was created. An easier method is to prime the tube
boiling water: after clogging with one stopper (preferably rubber) at one end
tubes pour boiling water inside the tube and the flexible tube is easily bent into
circle (we also plug the other end after filling with water). I recommend this method
make a coil from a thinner tube (no gaps are formed) - I advise on the bathtub
or a bowl (with gloves of course).
At this stage, leave the coil structure and proceed to articulation.
To make the articulation, prepare an approx. 10 cm section of the tube
made of PVC, diameter approx. 32mm. In one end, drill a section of tube on
outlet with the diameter of the hole as it has in a round tube. In second
drill a hole with a diameter of approx. 5mm for the cable outlet
(this is the easiest way to set up the joint, the disadvantage is that there is no way
coil slope changes. The hinge can be made movable, the coil is
much more convenient to use, but I leave it to the designer
<Joint must not contain metal materials>).
The next stage is sliding the joint over the previously created circle.
Measure out a 16-meter section of DNE wire and try to wind it by pulling
through the inside of the tube a roll after a roll (leave a 10 cm section
beginning of the wire), taking care, however, that loops do not form in the winding process.
After winding all turns, leave approx. 10 cm of wire end.
Then turn the hinge back to where the ends connect
circle and connect the sections of wires protruding from the coil, introduced into
joint with a two-core cable (solder and insulate). Adjust the joint
relative to the circle at an appropriate angle of about 120 degrees. Then pour it
interior of the joint with quick-drying resin, putty or cable mass and
leave to dry. Equip the other end of the cable with a plug, e.g. mono
Big jack type. The probe made in this way has several advantages because it is
easy to make, light and waterproof.
The frame should be made by adjusting the length of the detector to your own height.
The frame can be made complete or folded. We use to make the frame
tubes of the same diameter as the joint structure (optimally 32mm). At
a folding frame, the PVC pipe should be cut into appropriate compositions, then
by turning one of its ends over the fire we extend it with a second tube (preferably
composition).

*****EXPLOITATION*****

The best search results will be obtained if the user
the detector has experience with this type of apparatus, possibly after some
during tests in various field conditions and with different objects. In front of
the device should be switched on for approx. 2 before commencing field searches
minutes (this is to stabilize the temperature of some components
working in the pulse transmitter under excessive load).
As you know, the effectiveness of metal detection (apart from the skill of a person
operating the device and assuming full efficiency of the device) depends above all
everything from the size of the item and the position in which it lies in the ground.
Practical tests with a set of coils with diameters
20, 30 and 40 cm respectively showed the highest sensitivity for small
objects like coins, wedding rings for coils with a diameter of 30 and 20cm.
While
a 40 cm diameter coil is recommended for larger searches
items over 1dm. E.g. pipelines. A standard coil is assumed
most often a probe with a diameter of 30cm.
The device made according to the above documentation has the following
ranges in the ground (they assume parallel arrangement of items for consideration
search coil. With oblique arrangement depending on the position angle
object, detectability will be less):
- coin with a diameter of 2.5 cm -------------------- 30-32cm
- item with a diameter of 5 cm ------------------- 44-48cm
- item with a diameter of 10 cm ------------------ 65-70cm
- item with a diameter of 15 cm ------------------ 75-80cm
- item 20 x 20 cm ------------------------- 100-110cm
- item 30 x 40 cm ------------------------- 130-140cm
- object 60 x60 cm -------------------------- 170-180cm
--max. item 1 x 1m ------------------------ approx. 2m

*****LIST OF COMPONENTS*****

*****RESISTORS*****
R1 1kΩ
R12 680kΩ
R23 220kΩ mounting potentiometer
R2 68kΩ
R13 330Ω
R24 100kΩ
R3 1kΩ
R14 68kΩ
R25 10kΩ
R4 270Ω
R15 100Ω
R26 10kΩ
R5 100Ω
R16 820kΩ
R27 22kΩ
R6 330Ω
R17 10kΩ
R28 22kΩ
R7 150Ω <1W>
R18 100Ω
R29 33kΩ
R8 1kΩ
R19 2.4kΩ
R30 33kΩ
R9 470Ω
R20 1mΩ
R31 33kΩ
R10 1kΩ
R21 1mΩ
R32 22kΩ
R11 220kΩ
R22 47kΩ
R33 10kΩ

*****CAPACITORS******
C1 2200μF
C13 1nF
C2 220nF
C14 1nF
C3 100nF
C15 1nF
C4 220μF / 16V
C16 220μF / 16V
C5 10pF
C17 10nF
C6 4,7pF
C18 47μF / 25V
C7 100nF
C19 47μF / 25V
C8 220nF
C20 47μF / 25V
C9 100nF
C21 47μF / 25V
C10 100nF
C22 220μF / 16V
C11 100μF / 16V
C23 100μF / 25V
C12 1nF

*****DIODES / TRANSISTORS / IC'S*****

D1 1N4148
T1 BC178
US1 NE555
D2 1N4148
T2 BD285
US2 uA 7905
D3 1N4001
T3 BF245
US3 CD 4011
D4 1N4001
T4 BC108C
US4 uA 709
D5 1N4001
T5 2N3820
US5 ua 741
D6 1N4001
T6 BC107
US6 NE555N
Dioda Zenera 9,1 V
T7 BC177
US7 uA 7812

*****MISC*****

others:
1 big jack plug + socket
2 two-core cable
3 speaker 8-40Ω
4 power switch
5 P1- rotary potentiometer <linear> 22 ? 47kΩ
6 Pr - mounting potentiometer 100kΩ ? 470kΩ
7 Headphones input can be built-in
8 Housing

*****EXECUTION OF THE DETECTOR PLATE******

Making the tile itself is quite a laborious activity. It will be necessary
laminate (dimensions 7 x 13.5 cm), pickling acid (e.g. popular trichloride
iron), track marker, drill with small drill bit
Cut out the path diagram, stick it on the laminate (copper side), drill it
holes for the elements, draw the appropriate paths and etch in accordance with
description on the etching agent packaging.

*****MY TIPS*****

1. Select components carefully.
2. Mount in order and check according to documentation.
3. Carefully check the paths on the circuit board several times before starting it up
somewhere short circuits.
4. Check if the components have been soldered correctly, ie they are on their own
places.
5. It is best to use bases for integrated circuits.
6. Replacement circuits or transistors can be used.
7. The detector can be built without the help of an oscilloscope (as someone can have
check individual waveforms).
8. The detector's coil should quietly purr (hold it to the ear).
9. The detector will not work properly in the rooms (electricity,
wall reinforcements, other disturbances), perform tuning outdoors.
10. It is not always possible to tune the detector as described (you just have to do it)
by eye potentiometers, i.e. find the range in which the device is best
detects metal).
11. T6 and T7 transistors and a Zener diode can not be used (this increases the consumption
current, and in the system it was only for indicating the battery status).
12. Personally, I use a 12V / 1.3 Ah gel battery instead of a battery
13. The weaker the supply voltage, the lower the detection (the detector starts
get out of tune).
14. Slower penetration of the area promotes better detection of the device !!!
15. The description of the mechanical construction of the coil and the frame is provided in the documentation
the easiest way, but here the designer imagination has a lot to show off. I
I made my frame similarly, but I introduced many modifications to it
(movable joint, fastening the housing to the tube with tube holders,
elbow rest, handle etc.)
16. REMEMBER POLARITY +, - !!! ""

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