(developer Petrucho – md4u forum)
Pinpointer- this is a special type of metal detector, which has a unique compactness and is designed to clarify the location of metal targets when searching. Such a detector does not have great sensitivity, it simply does not need it, but it very accurately “shows” the location of metal objects.
Thanks to this, it is used to accurately identify a find during a search, inspecting the walls of buildings for fittings, metal supporting structures, hidden wiring, hiding places, etc.
Pinpointer Minimax PP-2 is a simple, reliable and small-sized metal detector, developed by one of the md4u forum participants under the nickname Petrucho. It has been tested on land and in water, and works great in the salty waters of the Black Sea.
First, let's take a look at the technical characteristics of the device (TTX):
Supply voltage…………………….. 3-5 Volts;
Current consumption………………………….. 18 mA;
Indication………………………………….. sound (fixed tone);
Coin detection range…………. 5 cm (5 kopecks USSR).
See a short introductory video about the operation and performance characteristics of the pinpointer below.
So, let's take a look at the device diagram (picture below).
I provide a description of the operation of the Minimax PP-2 pinpointer from the author (part of the text used was taken from the author’s website, the md4 forum and personal correspondence with the author). So:
...It is based on the principle of measuring quality factor. The circuit is quite simple - only 1 microcircuit and 4 transistors. The circuit can be powered within 3-5.5 Volts (5.5 Volts is the maximum possible power supply for the MCP602 chip).
For the minimum size of the pinpointer, it is recommended to use either 2 AA or AAA cells, or one 3-volt lithium battery (or a 3.7-volt lithium battery). For example, LIR123 (photo below).
A self-oscillating LC generator with voltage resonance (series resonance) is assembled on elements Q1,Q2, D1,D2, R1,R2, C1,C2,C3 and L1. The oscillatory circuit is formed by the total capacitance of capacitors C1, C2, C3 and inductance L1.
Recharging of C1, C3 occurs relative to the power buses through the base-emitter junctions of the transistors and also through the protective diodes D1, D2. Due to this, transistors Q1, Q2 operate in switching mode (the bases of transistors Q1, Q2 “dangle” relative to the power buses within +- 0.7 Volts).
Of course, the generator has a rather long linear mode when switching from one state to another. The switching time is approximately 1/10 of the period. This is due to the fact that the switching of transistors occurs when the growth rate of the sine function is small.
Is this good or bad? It’s good in the sense that fewer harmonics are driven into the circuit - the result is a fairly clean sine wave. Bad from a consumption point of view. If it were possible to eliminate the linear section, then the current consumption would decrease by 2..3 mA.
Yellow - voltage at the collectors of the generator transistors.
Blue - voltage on the coil.
A power filter is implemented on C4 and L2 to eliminate false interference through the positive power bus.
The negative half-wave of the alternating voltage removed from the inductor is rectified by a half-wave rectifier at D3, R3, C5.
Additional signal filtering for low-frequency interference, for more stable operation - R4, C6.
Capacity C7 sets the “target tracking” speed of the dynamic mode. If the stability of the threshold is unsatisfactory (the device “poorly holds” the adjusted threshold), the capacitance C7 should be increased.
Also, for good and stable operation of the Minimax PP-2 pinpointer, film or polystyrene capacitors should be used in the circuit.
In the diagram these are the following parts: C1, C2, C3, C5, C6, C7. The remaining capacitors, resistors and other parts of the circuit can be used in SMD design.
The pinpointer search sensor can be made to operate at different frequencies. Coil L1 is wound with varnish insulated wire with a diameter of 0.25-0.3 mm and consists of 700-500 turns, respectively. Coil L1 is wound on ferrite with a diameter of 10 mm and a length of 5-7 cm. For maximum sensitivity, you can wind the coil closer to the edge of the rod.
If 1-1.5 cm of sensitivity is not critical, but you still want to make the dimensions (diameter) of the pinpointer smaller, then winding is done to the width of the entire ferrite rod.
Also, after manufacturing the search element and checking the functionality of the circuit, it is necessary to impregnate (fill) the turns of the L1 coil with epoxy resin or varnish. This will give the search element rigidity and stability in operation.
Pinpointer indicates a found metal target with a sound signal. This sound is produced by a buzzer (piezoelectric element with a built-in audio frequency generator) with an operating voltage of 5-6 Volts.
Now the nuances.
At the output of the diode assembly D3, there may be a signal of decent amplitude.
Therefore, D3 must have a reverse voltage of more than 100 Volts and at the same time it must be high frequency.
Possible replacements for the DMN2075U field effect transistor
In the SOT-23 package:
IRLML2502 NTR4501N Si2302ADS BSS138
In TO-92 housing:
BS108 BSN254 BSN304 ZVNL110 ZVNL120 ZVNL535 ZVN4424
Well, there are many more options...
Replacing transistors Q1 and Q2
MMBT4403 on KT361, KT3107, BC327, BC328...
MMBT4401 on KT315, KT3102, VS337, VS338…
The pinpointer's power supply is not stabilized, so it is recommended not to be greedy and use good alkaline batteries. They have very little internal resistance right up to the discharge!
Possible modernization of the pinpointer.
Instead of a buzzer, the device can use an LED or a vibration motor at the user’s request.
If you use the device according to the principle of plug and play all day, the batteries will not fail quickly, but they will not last long.
Well, if you work in the “press-check-release” power button mode, then alkaline batteries will last for a season or more!!!
…
And finally, a pinpointer board developed by one of the MD4U forum members.
Good luck with the making, it's awesome!
Alexander Serbin (Kharkov)
We present to you one of our new developments - a sensitive pinpointer. This device is designed to search for small metal objects. Used in conjunction with a metal detector during excavations - it is convenient to check the excavated ground for the presence of small coins, as well as to search for metal fittings in the walls. Among the advantages, I note the simplicity and repeatability of the circuit, dynamic mode combined with static mode, auto-tuning, high sensitivity, the presence of a VCO - (VCO).Schematic diagram of a homemade pinpointer:
The circuit was tested with a ferite rod with a diameter of 8 mm, length 50 mm, 320 turns of 0.3 wire. Ring with a diameter of 40 mm wire 0.14 - 150 turns. The test on the ground was carried out with a ring coil. With sudden movements or rotation of the coil around its axis, it reacts to the magnetic field of the earth, but this is not particularly annoying since the search is carried out with smooth movements and without rotational movements.
A flat coil can be made from a fiberglass plate cleared of copper.
The 78L05 integrated stabilizer can be replaced with a similar one with an output voltage of 5 volts. If a VCO (voltage controlled generator) is not needed, then resistor R16 needs to be reconnected to pin 12 of U1B - shown with a dashed line.
You can replace the transistors of the KT3102 pinpointer with any low-power silicon ones, you can use another sound emitter with a voice coil resistance of at least 100 Ohms, but it’s better to use a piezo one - it will be economical and loud enough. LED - any super-bright one.
This pinpointer is powered by a 9-volt KRONA battery. There are spaces left on the pinpointer printed circuit board for soldering current collector springs for connection to the battery. There is also space left on the board for a flat coil. The coils in this case can be of any design.
Capacitors C2 and C3 must be film or others but with zero TKE, the remaining capacitors can be of any type.
The “threshold” regulator does not have to be installed, but with its help you can increase the sensitivity and also reduce it when necessary. So I recommend not removing it. The sensitivity of the pinpointer is very high, the small gold ring begins to feel with manual adjustment from 7 cm.
Here is an archive in LAY format; when you hover the cursor over an element, the position of the element is displayed. Material sent by Slavake.
Discuss the article PINPOINTER
Introduction
I’ve been struggling for a long time with clarifying what I found in the ground, since my metal detector has a large coil, and when I find a small object I spend a lot of time finding it. Finds such as buttons, small crosses and flake coins are small in size, and sometimes you had to sift through dozens of handfuls of earth to catch them. And if you go to the cops at night, the situation becomes even more complicated. Anyone who deals with antiquity will understand me perfectly. To reduce the time it takes to detect an already found object, diggers use additional devices - point metal detectors (pinpointers). The name comes from the bourgeois word - point-point. When the Great USSR suffered its collapse, our domestic manufacturer was no longer interested in developing point metal detectors, although domestically produced industrial metal detectors already existed by that time.
What is a pinpointer? The same metal detector but with a narrowly directed coil wound on a rod.
Commercially available pinpointers are quite expensive.
Minelab PRO-FIND pinpointer 25 - 6500p
Pinpointer Garrett Pro Pointer
- 6200p
Also on the Aliexpress website there is a Chinese uplift Garrett for 2000 rub. Judging by the reviews, people are unhappy.
The circuit is very simple, only 3 transistors, the most important thing is that it does not require any settings and starts working immediately after assembly. The power supply is 2 AA 1.5 V batteries, in my case a 3.7 V li-ion battery. Signet.
The diagram shows a number of transistors for the master oscillator, I personally used KT3107 and KT3102, they are available in almost all radio stores, finding them is not difficult. Film capacitors are recommended; I did not experiment and installed them as recommended by the author. C1 and C3 2 consecutive 1n 100 volts or more. If you take them with a lower voltage, a breakdown is possible, since the voltage on them can increase close to 100 volts. You can install any diodes; standard red glass ones can be pulled from old boards. Field worker, I personally installed bs108, it showed better results than 2n7000 (they love it on the forum). You can experiment and find an even better one, it is important that the gate opening voltage is 0.8-1.5 V)
Coil
The reel is winding on a ferrite rod, 5-6 cm long, 8-10 mm in diameter, 500-600 turns with 0.4 mm wire, it is advisable to concentrate more turns at the end of the rod; the feel will be higher. I took ferite from an antenna with a conductivity of 800; perhaps ferrite with higher conductivity will show better results. According to the plan, the frequency on the coil should be within 15 kHz, I measured it with a cartoon and it turned out to be 14.5 kHz. The frequency increases with a decrease in the number of turns on the coil, also with a decrease in the value of c1 and c3. It is not recommended to increase the frequency by reducing the number of turns; the sensitivity will be worse. At the end of winding, I filled the coil with epoxy, under a vacuum in the housing of a 10 cc syringe, which will allow it to work in unfavorable weather conditions.
Indication
As an indication, the author proposed using an active buzzer, an element that you have seen more than once on old motherboards or electronic alarm clocks. An active buzzer differs from a passive one in that it already contains an audio frequency generator and when the power is connected, observing the polarity, it begins to squeak. The passive one just clicks like a regular speaker. If you come across a passive buzzer, you can assemble the diagram below, and you will have an active one =)
You can also use an LED, a 1.5V vibration motor from a mobile phone, or an unknown device as an indicator.
setting
After collection, it should work immediately, the setting is carried out with a variable (you can adjust the sensitivity) or a tuning resistor, setting the threshold for the field switch (maximum sensitivity without causing interference. At C4 there should be at least 50V. (see diagram) With a well-assembled and configured device, the sensitivity should be about 5 cm per coin of 5 kopecks of the USSR. If the sensitivity is lower, check your coil, 500-600 turns of C1 C3 should be carefully wound - with a voltage of at least 100 V. Also, a large accumulation of rosin or flux in the frequency is not allowed. - the driving part. The frequency on the coil is about 15 kHz.
Features of the scheme.
When turned on, it goes into interference, after being brought up and sharply removed from a metal object, it stabilizes. (The reason in my case is the location of the elements, in particular the unknown one, too close to the coil.)
After warming up for 10 seconds, you can set the sensitivity higher; if you set it earlier, it will interfere. (In my case, the reason is probably the same)
Unstable operation - sensitivity drops (participants of the forum where this device is discussed have problems)
The frequency and soldering are normal, but the sensitivity is low - problems with the field worker are possible. Opening parameters 0.8-1.5v.
The coil squeaks very weakly and subtly.
In cold weather the sensitivity drops a little, but when using a variable resistor it is easily adjusted.
In field conditions, the device performed well. Stable detection of scales - 3 cm, coin 5-6 cm, cross 6 cm. When digging at night, it is simply irreplaceable; it saves a lot of time in uncoupling a find. At the end, as expected, a video test)
A pinpointer is a device that is part of the family of metal detectors. Used to search for metal objects in a variety of conditions, including underwater. The name of the device comes from English pin pointer, which translates as "dot pointer". The simplest pinpointer is small in size, similar to a flashlight. It may be quite useful for finding hidden electrical wiring in the wall.
Purpose of the device
A pinpointer is a metal detection detector. It determines the exact location of the metal at a fairly shallow depth, approximately about 5 cm. People who search for coins or other valuables made of metal, including archaeological ones, are called treasure hunters. They operate pinpointers in a variety of locations, from official excavations to waste dumps. Factory models of metal detectors are not always convenient for such purposes, and besides, they cost a lot of money. Therefore, it makes sense to assemble your own pinpointer according to the diagram. The device is most effective for use in a newly formed hole or dump soil. The soil may be scattered over a dense volume of grass or a large amount of foliage, which obviously makes routine searching difficult for treasure hunters. Knowledgeable and experienced people say that in this situation, a pinpointer is the best choice.
Parts for assembly
To assemble a pinpointer with your own hands, you will need certain tools. The main elements will be:
- Soldering kit: a certain amount of tin, solder and the soldering iron itself.
- A diverse set of screwdrivers or a set of attachments for a screwdriver base handle.
- Clamping tools: pliers, pliers. Cutting: wire cutters or similar object.
- To assemble a printed circuit board, you need to stock up on profile material.
It is worth noting that for different models, the list of necessary materials and tools may change during the assembly process. Basic skills in the manufacture of such boards will also be useful; knowledge in the field of electrical engineering and experience in it are welcome.
Schematic diagram of a pinpointer
The fundamental provisions of the device model are the following parameters:
When assembling a pinpointer with your own hands, you must take into account the basic principle of its operation - the level of quality of measuring the oscillatory circuit. When a metal object approaches it, a loss of energy power occurs. As a result of this process, the amplitude of the signal on the circuit decreases.
To increase the sensitivity of the device in the assembly, it is better to use film capacitors C2 and C3. The radiating element ZP-1 must be piezoceramic.
Assembly technology
The process of making a pinpointer with your own hands is not difficult, but it still requires certain skills in working with SMD components. Another option would be a DIP output element. A ferrite rod, which can be removed from an unnecessary transistor receiver, will become a sensor. The rod should be about 110 cm in length and 10 mm in diameter. Winding in coils occurs on the principle of superimposing one on top of the other. The material for it should be a wire in an insulating winding. The wire must be copper with a diameter of 0.3 mm. The required number of turns should be 200 pieces.
Particular attention should be paid to the polarity of the connection in a homemade pinpointer. If there is no generation at a frequency of 15 kHz, you need to change the extreme points of any winding. The characteristics of the coil (such as length, wire, rod diameter) can be changed. But it is worth remembering that it will directly affect the sensitivity of the device.
The pinpointer is configured by selecting the voltage in the area of the second pin of the microcontroller itself. This must be done using trimming resistor R2. At the time of adjustment, there should be no metal objects around the device. This will allow you to achieve the most effective sensitivity. A voltmeter will help in the measurement. To do this, you will need a device with a high resistance level, such as an oscilloscope.
Electronic frequency pinpointer
The operating principle of the frequency meter will tell you how to make a pinpointer in this version. The assembly diagram will not cause any particular difficulties. The operation is based on the operation of an electronic FM frequency meter. There is discrimination against ferrous metals, the search depth for objects is limited to 60 cm, the operating frequency is at 19 kHz.
All required details are simple and accessible. A little attention should be paid to capacitors, which must have thermally stable characteristics. These could be the K71 models from the old Soviet multimeter. It is not recommended to use ceramic ones, they will not work.
Important! The stability of the device directly depends on the quality of the capacitor!
The power source for the pinpointer can be batteries or other rechargeable elements with a voltage of 9-12 V. The printed circuit board itself will only need 10 mA, the rest will be “pulled” by the speaker, an alternative to which can be headphones.
Analog pinpointer
Do-it-yourself analog pinpointer is quite easy to assemble. Its effectiveness lies in finding small objects, such as coins.
Capacitors for this type of metal detector for the generator are selected as film type. The voltage must be 100 V or higher. The contour coil can be mounted on a ferrite rod, the diameter of which should be 10 mm. You can also use the rod from the magnetic antenna built into old radios. The nominal length of the rod should be 10 cm. For winding in a coil, an enameled wire is taken and wound in 4 layers. After completing this process, it is necessary to treat the coil with a special varnish in a homemade pinpointer. Finally, the coil will need to be crimped with heat shrink tubing.
Simple, reliable pinpointer
January 17, 2017
This diagram shows a simple metal detector, such as a pinpointer. The circuit is not complicated, after assembly it works almost immediately. Requires minimal adjustment: resistor R1 sets a voltage of about 2.5V on leg 7 of the LM324; this voltage must be adjusted after each sensor change.
After detecting a target, auto-tuning reduces the sensitivity of the detector and after a while the sound and light signaling stops. If the target approaches again, the alarm is resumed, this will continue until the automatic control fails, after which the alarm will not turn off until the target is at such a distance from the coil at which the auto-tuning resumes its operation again.
When the temperature changes, and in connection with this, the parameters of the circuit elements change, the feedback compensates for the change in voltage on the generator and the operation of the circuit is not disrupted and does not require any manual adjustment.
If you put elements R14, R15 indicated in the diagram with a dashed line, then you can additionally adjust the sensitivity threshold in manual mode.
In the diagram in the generator, the resistance rating - R3" (680 Ohm) is given for a coil on a ferrite rod of 50 mm, diameter 8 mm, which contains 320 turns of 0.3 wire. If there is another coil, the generator will not start. Therefore, it will have to be reduced until stable generation, or use the following modification option:
Option for improving the scheme. To reduce sensitivity, as well as make it easier to start the master oscillator (oscillator circled in red) with different coils, you can change the following:
- Replace R3" in the generator with a jumper
- R3 use 430 ohm
The sensitivity will noticeably decrease - the influence of the earth's magnetic field will decrease; with sudden movements of the coil around its axis, the signal will not be triggered. During the tests, many noted that this solution was the most successful.
In the version with a jumper instead of R" and R3 = 430 Ohm, the device works with any coils if they ensure operation of the generator at frequencies from 15 kHz to 20 kHz. One of the sensor options for this scheme is 60 turns 0.5 on a 7 cm mandrel. With a coil 19 cm is definitely not for coins - with such a coil for coins, its sensitivity is weak (frequencies up to 20 kHz were tested).
One of the design options for the coil connector is shown in the figure below:
Instead of KP303A in this circuit you can use - BF245, 2N4416, 2N5457. BF245 recommended. Transistors 303E, 303D, 303G are not recommended.
The value of R1 may not be enough to set zero on U1D.
As a speaker, you need to use a high-resistance piezo emitter; the volume and brightness are selected by resistor R9. You can also use a regular tweeter, but the consumption of the entire circuit will increase.
If the sensor reacts to touching the ground on the coil, it is recommended to make a screen.
By setting: If it reacts only to pieces of iron and does not see non-ferrous metal at point-blank range, then the generator may not have started. Check to see if there is a sine wave on the generator coil? If not, then an EMF is simply induced in the coil from magnetized pieces of iron moving in front of it. In this case, there should be no reaction to non-ferrous metal at all.
If you do not install the LED, there will be no K-E current and the transistor will not work.
If it does not work at low temperatures, you can add a 470 nF capacitor between R2 and the second pin U1A, remove R10 (disconnect), use 300 kOhm for R14.
