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:
Scheme modification option. 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:
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.
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.
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 a 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)
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
They differ quite a lot. It should also be taken into account that devices of this type have their own sensitivity. The main element of a pinpointer can be safely called a coil. It is most often installed in an orthogonal type. However, in this situation, much depends on the accuracy class of the device. In order to assemble a simple pinpointer with your own hands, you need to familiarize yourself with the known configurations.
To make this type of pinpointer with your own hands, you must first prepare a housing for the device. To do this, many experts recommend using a regular flashlight. The main problem at this stage is finding a good modulator. As a rule, a nonlinear analogue is selected for a two-wire capacitor. The coil itself must be located in the front of the device. Batteries should be installed behind the modulator. You can also remove them from a flashlight. The minimum battery capacity must be 200 mAh. This is enough for 25 minutes of continuous operation.
Making a pinpointer with three-wire capacitors with your own hands is quite difficult. The modulator in this case is only suitable for the linear type. Nowadays it is not easy to find it in radio electronics stores. It should also be taken into account that the coil must be installed under the amplifier. Some additionally equip devices with zener diodes. They are ideal for increasing the sensitivity of the model. In this situation, batteries can be used as standard from a flashlight.
To assemble this type of pinpointer with your own hands, you must first take the body of the flashlight. The modulator must maintain a minimum threshold frequency of 200 Hz. All this will allow the sensitivity of the device to be maintained at a high level. This device is used quite often as a tester. To activate the interrupt mode, a regulator must be installed in the design.
Most often it is used of the push-button type. In this case, it is necessary to pay attention to the features of the body that belonged to the flashlight. It is better to choose a simple coil for this purpose. However, it must withstand the maximum input voltage at 15 V. All this will improve the accuracy of the readings.
Assembling the Malysh-FM2 pinpointer with your own hands is quite simple. This device differs in that its sensitivity is low. However, the cost of the model is extremely low, and this device is ideal for home use. The modulator in this case is used of a nonlinear type. It is mounted directly next to the regulator.
Most often you can find rotary analogues on the market. The inductor can withstand a maximum input threshold voltage of 10 V. It should also be noted that this device has a high current conductivity. This was achieved by installing a zener diode. Next, to assemble the Malysh-FM pinpointer with your own hands, you need to solder the capacitors. Only after this are the contacts connected to the zener diode. At the end of the work, all that remains is to secure the batteries in the case.
You can make a low-sensitivity pinpointer with your own hands using transistors thanks to a device such as a beeper. It is installed in the housing immediately behind the modulator. The amplifier for this device is suitable only for the pulse type. In this case, you can select different capacitors for the device. However, they must withstand a minimum input threshold voltage of 5 V.
It should also be noted that zener diodes are installed in devices quite often. Their maximum frequency is welcome at 200 Hz. It is important to consider that the accuracy of the readings depends on the transmission width of a given element most often does not exceed 3 microns. Batteries for the model are selected with a capacity of no more than 600 mAh. This is enough for the device to work continuously for 30 minutes.
How to make a high sensitivity pinpointer with your own hands? To understand this issue, you should understand that the coil you will need for assembly is quite powerful. It must withstand a minimum threshold voltage of 20 V. It should also be noted that modulators in this case are suitable only for the linear type. The accuracy of the readings also depends on the type of condensate.
In this situation, many experts advise using open-type models. On average, the capacitance parameter of these elements fluctuates around 5 pF. However, in this situation, much depends on the capacitor manufacturer. If we talk about a zener diode, then it is used with increased resistance. This is necessary to increase the sensitivity of the device. Batteries for this model should be selected with a capacity of at least 900 mAh.
To assemble a Minimax-PP pinpointer with your own hands, you need to select a beeper of the PP20 series. It should also be noted that vibration mechanisms are installed in devices of this type. In this case, a wide variety of indicators are used. If we talk about the coil, then in this case it is used of the orthogonal type. This component must withstand a threshold input voltage of at least 15 V. In this case, the resistance in the circuit should not exceed 4 Ohms.
The sensitivity of this device largely depends on the capacitors. There are two of them in the standard scheme. One of them must be installed near the coil. In this case, the second one is attached to the output of the modulator. The main problem of these devices can be considered the low bandwidth at the level of 2 microns. Due to this, amplifiers are used quite rarely in devices of this type.
Assembling this type of pinpointer with your own hands (the diagram is shown below) is quite simple. First of all, you need to choose a good case for the device. At the same time, the integral type controller does not take up much space. If desired, it can be purchased at any store with radio equipment, and it costs extremely little. A distinctive feature of this element can be safely called good conductivity. The capacitors in this case are installed of a two-electrode type. Their resistance value on average fluctuates around 2 ohms.
It should also be noted that the coil must be installed first. To do this you will have to use a blowtorch. Next, the modulator is attached directly. In this case, there should be batteries in the back. It is not advisable to use an amplifier in this case. This is due to the fact that the sensitivity of the device is significantly reduced due to an increase in the limiting frequency of the device.
A do-it-yourself pinpointer with multilayer capacitors is assembled with multilayer capacitors (the diagram is shown below) only if there are orthogonal coils. Modulators in this case are suitable for linear and nonlinear types. It should also be taken into account that vibration mechanisms are often installed in devices of this type. However, beepers can be found quite often.
Zener diodes are often used to increase the sensitivity of the device. At the same time, cardiode analogues are especially popular these days. To install them you will have to use In general, it should be noted that models with multilayer capacitors are universal and are ideal for home use. With their help, a person can quickly find out the exact location of the wiring in the wall.
Assembling this type of pinpointer with your own hands is quite simple. These devices are distinguished not only by increased accuracy of readings, but also by good sensitivity. This model is suitable for professionals. The device must be assembled by fixing the modulator. In this case, many experts recommend using linear analogues.
However, nonlinear modifications are also common. Beepers in this case are installed behind the coil. The input threshold voltage of the device should not exceed 20 V. For this purpose, zener diodes must be installed. In this case, the regulators are soldered as desired. At the end of the work, all that remains is to secure the batteries.
To assemble a device with a resonant regulator, you must prepare a blowtorch in advance. First of all, a high-quality modulator is selected for the device. In this situation, many experts still recommend using linear analogues. It is quite difficult to find them in the store, but they should cost little. On average, their conductivity parameter is 3 microns. Due to this, the input threshold voltage can be expected to be at a level of 15 V. A wide variety of zener diodes are suitable for the device. They must keep the maximum resistance at 5 ohms. It should also be noted that the device with regulators does not need beepers.
In this case, it is advisable to install the coil last. In this case, special attention must be paid to the insulation of the wiring. It should also be remembered that the device housing must be completely sealed. For this purpose, as an option, you can use a rubber seal. The regulator must be directly soldered to the modulator. Capacitors in this situation are mainly used of the field type. The minimum battery capacity must be 800 mAh.
The circuit of a fairly simple analog pinpointer is for people who search for coins, but cannot afford to buy a professional pinpointer. I collected this sample personally and confirm its full functionality. I designed a printed circuit board specifically for it, which can be found at the end of the article. In terms of characteristics, the pinpointer is quite good, perfect for target designation of a find....
MINIMAX-PP-2 pinpointer circuit
And finally, a few photos of the assembled board.
