From almost improvised materials. Despite all its simplicity, the metal detector works, it can find a coin at a depth of up to 10 cm, a pan at a depth of 30 cm, and the device sees a sewer hatch at a depth of 60 cm. This is of course not much, but for such a simple device it’s pretty good. However, if you work with it on the beach or just build it for informational purposes, then you won’t waste your time.
Materials and tools for homemade:
- a complete list of board parts can be seen in the diagram, it includes the K176LA7 microcircuit;
- wire for the coil (PEV-2 0.08…0.09 mm);
- armored magnetic circuit;
- epoxy;
- headphones;
- soldering iron with solder;
- materials for creating a bar, body, and so on.
Metal detector manufacturing process:
Step one. A few words about the scheme
L1 needs to be wound on a frame with three sections with a tuning core and placed in an armored magnetic core with a diameter of 8.8 mm, made of 600NN ferrite. In total, the coil has 200 turns of PEV-2 wire 0.08...0.09 mm.
Coil L2 is made from a piece of aluminum tube with a diameter of 6-9 mm and a length of 950 mm. You need to thread 18 pieces of wire with good insulation through it. Next, the tube needs to be bent using a mandrel; it should be approximately 15 cm in diameter. The wire sections are connected in series. The inductance of this kind of coil should be within 350 μH.
There is no need to short-circuit the ends of the tube, but one of them must be connected with a common wire.
For the circuit described above, the author used a rubber hose with a metal base inside, as well as a solid wire coated with varnish. To avoid damaging the insulation, tweezers with rubber tubes at the ends were used. The winding must be fixed as carefully as possible, otherwise the device will give false alarms.
It is important to note the fact that the cable running from the board to the coil must be shielded.
Step two. Further assembly and configuration
To adjust, the capacitor knob must be turned to the middle position, and then by rotating the tuning core L1, you need to ensure that there is no beat in the headphones. The setting will be correct if, when turning the variable capacitor knob to a small angle, a hum is heard in the headphones.
The adjustment is carried out at a distance of at least one meter from massive metal objects.
The author was able to increase the sensitivity of the device if he screwed in the core of the tuning coil all the way, and by adjusting the setting using a variable capacitor, achieved almost complete absence of sound in the headphones. However, if you turn on the headphones at full power, the sound will be quiet.
If it turns out that the sound in the headphones is not audible at all, you need to check the presence of a U-shaped signal at pins 4 of DD1 and DD2; for such purposes you will need an oscilloscope. There should be a mixture of signals at pin 11 and 8 of DD3.
It should also be noted that the original circuit indicates a resistance of R3 of 300 kOhm, but the headphones will not work with this resistance. It needs to be replaced with 3 kOhm. Instead of 5600 pF capacitors, the author also used 4700 pF capacitors, since the former could not be found.
The disadvantages of the circuit include the fact that the chamber is sensitive to ambient temperature; therefore, the device must be constantly adjusted with a variable capacitor, achieving zero beats.
Step three. The final stage of assembly
The author recommends filling the coil with epoxy, this will allow the wires to be securely fixed. Otherwise, there will inevitably be false positives, since during the search you have to hit rocks, sticks and other obstacles, and the coil can be easily damaged. Instead of epoxy, wax or plasticine is suitable, which needs to be melted and poured. Paraffin should not be used, as it becomes brittle after hardening and has no elasticity. If the choice fell on plasticine, then you need to take care that it does not leak out when heated in the sun.
Among other things, gently replace resistor R3 in the circuit; its value should be 300 kOhm. You also need to adjust the frequency of the reference generator so that confident and clear clicks are heard in the headphones. The sensitivity of the device is determined by the frequency of clicks; the lower it is, the better. With these settings, the author finds a USSR penny coin at a depth of 10 cm, which lies horizontally.
If you make the click frequency high, the presence of metal under the search coil can be determined by a change in sound.
The author also assembled another such device and discovered a problem - no sound in the headphones. The solution was to remove capacitor C7 from the circuit. The author also removed the volume control, since the sound itself became quieter. With this modification, the device did not lose sensitivity.
The plastic housing for the device can be bought at a radio store; it cost the author 31 rubles. To shield the circuit, you need to cut out a “shirt” from cardboard and wrap it in foil. The edges of the foil are attached to the cardboard with tape, then the wire is attached using a stapler and connected to the minus.
You also need to install an electrolytic capacitor of 47-100 uF in the circuit after turning on the power with a voltage of at least 10V.
Some digital CMOS logic microcircuits, such as K176LA7, K176LE5, K561LA7, K561LE5, as well as foreign analogues 4001, 4011, can also operate in linear amplification mode.
To do this, the input and output of the logical element must be connected with a resistor or a negative feedback RC circuit, which will apply voltage from the output of the element to its input and, as a result, the same voltage will be established at the input and output of the element, somewhere between the value of logical zero and logical unit. For direct current, the element will be in amplifier stage mode.
And the gain will depend on the parameters of this OOS circuit. In this mode, the logic elements of the above mentioned microcircuits can be used as analog amplifiers.
Principle diagram of low-power ULF
Figure 1 shows a low-power ULF circuit based on the K561LA7 (4011) microcircuit. The amplifier turns out to be a two-stage one, if at all it is appropriate to talk about stages here. The first stage is made on logic element D1.1, its input and output are interconnected by an OOS circuit consisting of resistors R2, R3 and capacitor C4.
In practice, the gain here depends on the ratio of the resistances of resistors R2 and R3.
Fig.1. Schematic diagram of a low-frequency power amplifier based on the K176LA7 microcircuit.
The AF input signal through the volume control on resistor R1 is supplied through the separating capacitor C1 to the input of element D1.1. The signal is amplified by it and sent to the output power amplifier on the remaining three elements of the microcircuit, connected in parallel to increase their output power.
The output stage is loaded onto miniature speaker B1 through isolation capacitor C3. The output power has not been rated, but subjectively the ULF is about as loud as the ULF of a pocket radio with an output power of about 0.1W.
I tried a variety of speakers, from 4 Ohms to 120 Ohms. Works with anyone. Of course the volume varies. Almost no setup is required.
When the supply voltage is more than 5-6V, significant distortion appears.
Direct amplification broadcast receiver circuit
The second figure shows the circuit of a direct amplification broadcast receiver for receiving radio stations in the long or medium wave range.
The ULF circuit is almost the same as in Figure 1, but differs in that one element of the microcircuit is excluded from the output stage and a radio frequency amplifier is made on it, while, naturally, the power of the output stage, in theory, has decreased, but practically nothing is heard no difference was noticed.
And so, on element D1.4 the URCH is made. To transfer it to amplification mode, an OOS circuit is connected between its output and input, consisting of resistor R4 and an input circuit formed by coil L1 and variable capacitor C6.
Fig.2. Schematic diagram of the receiver on the K176LA7, K176LE5, CD4001 microcircuit.
The circuit is connected to the input of the RF amplifier directly, this became possible due to the high input impedance of the CMOS logic IC elements.
Coil L1 is a magnetic antenna. It is wound on a ferrite rod with a diameter of 8 mm and a length of 12 mm (any length can be used, but the longer, the better the sensitivity of the receiver). For reception on medium waves, the winding must contain 80-90 turns.
For reception on long waves - about 250. Wire, almost any winding. Wind the medium-wave coil turn to turn, and the long-wave coil in 5-6 sections.
Variable capacitor C6 - from the “legendary” receiver assembly kit “Yunost KP-101” of the 80s of the last century. But, of course, some other one is also possible. It should be noted that using the KPI from a pocket superheterodyne receiver, connecting its sections in parallel (there will be a maximum capacitance of 440-550 pF depending on the type of KPI), it will be possible to reduce the number of turns of the L1 coil by two or more times.
From the RF output to D1.4, the amplified RF voltage is supplied through the isolation capacitor C8 to a diode detector on germanium diodes VD1 and VD2. Diodes must be germanium. These can be D9 with other letter indices, as well as diodes D18, D20, GD507 or foreign production.
The detected signal is isolated on capacitor C9 and, through the volume control on R1, goes to the ULF, made on the remaining elements of this microcircuit.
Application of logic elements in other circuits
Fig.3. Scheme of a magnetic sensor on a logic element.
Logic elements in amplification mode can be used in other circuits, for example, Figure 3 shows a circuit of a magnetic sensor, the output of which appears an alternating voltage pulse when the magnet moves in front of the coil, or the coil core moves.
The coil parameters depend on the specific device in which this sensor will operate. It is also possible to include a dynamic microphone or dynamic loudspeaker as a coil, so that this circuit works as a signal amplifier from it. For example, in a circuit where you need to react to noise or impacts on the surface on which this sensor is mounted.
Tulgin Yu. M. RK-2015-12.
Some digital CMOS logic microcircuits, such as K176LA7, K176LE5, K561LA7, K561LE5, as well as foreign analogues 4001, 4011, can also operate in linear amplification mode.
To do this, the input and output of the logical element must be connected with a resistor or a negative feedback RC circuit, which will apply voltage from the output of the element to its input and, as a result, the same voltage will be established at the input and output of the element, somewhere between the value of logical zero and logical unit. For direct current, the element will be in amplifier stage mode.
And the gain will depend on the parameters of this OOS circuit. In this mode, the logic elements of the above mentioned microcircuits can be used as analog amplifiers.
Principle diagram of low-power ULF
Figure 1 shows a low-power ULF circuit based on the K561LA7 (4011) microcircuit. The amplifier turns out to be a two-stage one, if at all it is appropriate to talk about stages here. The first stage is made on logic element D1.1, its input and output are interconnected by an OOS circuit consisting of resistors R2, R3 and capacitor C4.
In practice, the gain here depends on the ratio of the resistances of resistors R2 and R3.
Fig.1. Schematic diagram of a low-frequency power amplifier based on the K176LA7 microcircuit.
The AF input signal through the volume control on resistor R1 is supplied through the separating capacitor C1 to the input of element D1.1. The signal is amplified by it and sent to the output power amplifier on the remaining three elements of the microcircuit, connected in parallel to increase their output power.
The output stage is loaded onto miniature speaker B1 through isolation capacitor C3. The output power has not been rated, but subjectively the ULF is about as loud as the ULF of a pocket radio with an output power of about 0.1W.
I tried a variety of speakers, from 4 Ohms to 120 Ohms. Works with anyone. Of course the volume varies. Almost no setup is required.
When the supply voltage is more than 5-6V, significant distortion appears.
Direct amplification broadcast receiver circuit
The second figure shows the circuit of a direct amplification broadcast receiver for receiving radio stations in the long or medium wave range.
The ULF circuit is almost the same as in Figure 1, but differs in that one element of the microcircuit is excluded from the output stage and a radio frequency amplifier is made on it, while, naturally, the power of the output stage, in theory, has decreased, but practically nothing is heard no difference was noticed.
And so, on element D1.4 the URCH is made. To transfer it to amplification mode, an OOS circuit is connected between its output and input, consisting of resistor R4 and an input circuit formed by coil L1 and variable capacitor C6.
Fig.2. Schematic diagram of the receiver on the K176LA7, K176LE5, CD4001 microcircuit.
The circuit is connected to the input of the RF amplifier directly, this became possible due to the high input impedance of the CMOS logic IC elements.
Coil L1 is a magnetic antenna. It is wound on a ferrite rod with a diameter of 8 mm and a length of 12 mm (any length can be used, but the longer, the better the sensitivity of the receiver). For reception on medium waves, the winding must contain 80-90 turns.
For reception on long waves - about 250. Wire, almost any winding. Wind the medium-wave coil turn to turn, and the long-wave coil in 5-6 sections.
Variable capacitor C6 - from the “legendary” receiver assembly kit “Yunost KP-101” of the 80s of the last century. But, of course, some other one is also possible. It should be noted that using the KPI from a pocket superheterodyne receiver, connecting its sections in parallel (there will be a maximum capacitance of 440-550 pF depending on the type of KPI), it will be possible to reduce the number of turns of the L1 coil by two or more times.
From the RF output to D1.4, the amplified RF voltage is supplied through the isolation capacitor C8 to a diode detector on germanium diodes VD1 and VD2. Diodes must be germanium. These can be D9 with other letter indices, as well as diodes D18, D20, GD507 or foreign production.
The detected signal is isolated on capacitor C9 and, through the volume control on R1, goes to the ULF, made on the remaining elements of this microcircuit.
Application of logic elements in other circuits
Fig.3. Scheme of a magnetic sensor on a logic element.
Logic elements in amplification mode can be used in other circuits, for example, Figure 3 shows a circuit of a magnetic sensor, the output of which appears an alternating voltage pulse when the magnet moves in front of the coil, or the coil core moves.
The coil parameters depend on the specific device in which this sensor will operate. It is also possible to include a dynamic microphone or dynamic loudspeaker as a coil, so that this circuit works as a signal amplifier from it. For example, in a circuit where you need to react to noise or impacts on the surface on which this sensor is mounted.
Tulgin Yu. M. RK-2015-12.
Measurement techniqueGenerator based on K561LA7 with frequency control
Digital chips can implement more than just mathematical logic. One example of alternative functionality is clock generators.
In its simplest form, a generator is nothing more than an oscillating circuit assembled on the basis of a capacitor and resistance (the so-called RC circuit). However, such circuits are characterized by low quality of the output signal and nonlinearity of the generated pulses.
Microcircuits that implement simple “AND-NOT” logic, such as K561LA7 or analogs, can give them the correct “square” shape. But more about everything.
Description K561LA7
The microcircuit implements the logic of four independent “AND-NOT” elements (circuit with pinout below).
Rice. 1. K561LA7
The rated voltage for power supply is 10 V, the maximum is no more than 15 V.
It can operate at almost any temperature (from -45 to +85°C), consumes very little current (up to 0.3 μA) and has a short delay time (80 ns).
Direct analogues include the CD4011A microcircuit. However, in the described task the following can also be used:
- K176LE5 (direct replacement is acceptable without changing the circuit);
- Chips from the K561 series;
- K176PU2/or PU1;
- As well as other microcircuits that implement the logic of four or more independent inverters.
Just in case, here is a truth table.
Rice. 2. Truth table
Simple frequency generator
The circuit indicated below will generate a square wave (rectangular pulses).
Rice. 3. Scheme that will form a meander
In fact, you can do without the last block D1.4.
The oscillations are set by the C1R1 circuit, and the logic elements convert the sinusoidal signal into a rectangular one, cutting off the falling and rising edges according to the inversion logic (there is an input signal exceeding the threshold value - it is output at 0, if there is no signal - a logical one is output).
The disadvantage of such a generator is the inability to regulate the frequency (it is fixed and determined by the value of the capacitor with a resistor) and influence the pause time, pulse duration (or their ratio - that is, duty cycle).
Regulated generator
The circuit indicated below allows you to separately adjust the pause time and pulse duration.
Rice. 4. A circuit that allows you to separately adjust the pause time and pulse duration
The tuning resistors R2 and R3 are responsible for this logic. The frequency range is slightly adjustable, and therefore, to change it radically, it is possible to include several capacitors of different capacities (to replace C1), which are included in the circuit alternately.
Another version with the ability to regulate the duty cycle (based on the circuit of the same multivibrator).
Rice. 5. Circuit option with the ability to regulate the duty cycle
We can call it almost universal for various kinds of experiments with GTIs (clock pulse generators).
It looks like this.
Rice. 6. Circuit with different waveforms
The values of resistors and capacitors are not particularly important and can be changed to suit your needs.
As you can see above, there are three outputs with a rectangular signal (meander), triangular and sine.
Each of them can be changed by the corresponding trimming resistors.
Publication date: 06.03.2018
Readers' opinions
- Vitaly / 05/17/2019 - 16:50
Tell me how to increase the amplitude of the signal if in the first circuit we set c1 to 100p for example? And how to calculate the correct resistor? - Anton / 08/31/2018 - 22:04
Not bad enough.
In the last lesson we were introduced to simple logical elements NOT, AND, OR, NAND, NOR. Now let’s start getting acquainted directly with the microcircuits of the K561 or K176 series, using the example of the K561LA7 microcircuit (or K176LA7, in principle they are the same, only some electrical parameters differ).
The microcircuit contains four AND-NOT elements; this is one of the most commonly used microcircuits in amateur radio practice. The K561LA7 (or K176LA7) chip has a rectangular plastic black, brown or gray case with 14 pins located along its long edges. These leads are bent to one side. Figures 1A, 1B and 1C show how pins are numbered. You take the microcircuit with the markings facing you, and the pins are turned in the direction opposite to you. The first output is determined by the "key". The “key” is a stamped, recessed mark on the body of the microcircuit; it can be in the form of a groove (Figure 1A), in the form of a small indented dot placed near the first pin (Figure 1B), or in the form of a large recessed circle (Figure 1B) . In any case, the pins are counted from the end of the microcircuit body marked with a “key”. How the pins are counted is shown in these figures. If the microcircuit is turned “on its back,” that is, with the markings facing away from you, and with its “legs” (pins) toward you, then the positions of pins 1-7 and 8-14 will naturally change places. This is understandable, but many novice radio amateurs forget this little detail and this leads to incorrect wiring of the microcircuit, as a result of which the design does not work, and the microcircuit may fail.
Figure 2 shows the contents of the microcircuit (the microcircuit is shown with its feet facing you, upside down). The microcircuit has four 2I-NOT elements and shows how their inputs and outputs are connected to the pins of the microcircuit. The power is connected like this: plus - to pin 14, and minus - to pin 7. In this case, the common wire is considered to be minus. You need to solder the pins of the microcircuit very carefully and use a power of no more than 25 W. The tip of this must be sharpened so that the width of its working part is 2-3 mm. The soldering time for each pin should not exceed 4 seconds. It is best to place microcircuits for experiments on special breadboards, like the one proposed by our regular author Sergei Pavlov in the journal IRK-12-99" (page 46).
Let us recall that digital microcircuits understand only two levels of input voltage “O” - when the input voltage is near zero supply voltage, and “1” - when the voltage is close to the supply voltage. Let's conduct an experiment (Figure 3) turn the 2I-NOT element into a NOT element (to do this, its inputs need to be connected together) and we will apply voltage to these inputs from the variable resistor R1 (any one will do for any resistance from 10 kOhm to 100 kOhm), and to output, connect LED VD1 through resistor R2 (The LED can be any emitting visible light, for example AL307). Then we connect the power (do not mix up the poles) - two series-connected “flat” batteries of 4.5 V each (or one “Krona” of 9V). Now, turning the slider of resistor R1, watch the LED, at some point the LED will go out, and at another it will light up (if the LED does not light up at all, it means that you soldered it incorrectly, swap its pins and everything will be fine).
Now connect the voltmeter (PA1) as shown in Figure 3 (any tester or multimeter connected to change the DC voltage can be used as a voltmeter). By turning the R1 slider, notice at what voltage at the inputs of the microcircuit element the LED lights up and at what voltage it goes out.
Figure 4 shows the circuit of a simple time relay. Let's look at how it works. At the moment when the contacts of switch S1 are closed, capacitor C1 is discharged through them, and the voltage at the inputs of the element is equal to logical one (close to the supply voltage). Since this element works as NOT (both inputs AND are closed together), its output will be logical zero, and the LED will not light up. Now we open the contacts S1. Capacitor C1 begins to slowly charge through resistor R1. And the voltage on this capacitor will increase, and the voltage on R1 will fall. At some point, this voltage will reach the level of logical zero and the microcircuit will switch, the output of the element will be a logical one - the LED will light up. You can experiment by installing resistors of different resistances in place of R1, and capacitors of different capacities in place of C1, and discover an interesting relationship - how the greater the capacitance and resistance, the longer the time will pass from the moment S1 opens until the LED lights up. And vice versa, the lower the capacitance and resistance, the less time passes from the moment S1 opens until the LED lights up. If resistor R1 is replaced with a variable one, you can change the time by turning its slider each time. This time relay will work. This time relay is activated by briefly closing the contacts S1 (you can simply use tweezers or a wire to close the terminals of C1 instead of S1, thus discharging C1.
If the connection points of the resistor and capacitor are changed (Figure 5), the circuit will work the other way around - when the contacts S1 are closed, the LED lights up immediately, and goes out some time after they open.
By assembling the circuit shown in Figure 6 - a multivibrator from two logic elements, you can make a simple “flashing light” - the LED will blink, and the frequency of this blinking will depend on the resistance of the resistor R1 and the capacitance of the capacitor C1. The smaller these values are, the faster the LED will blink, and vice versa, the more, the slower (if the LED does not blink at all, this means that it is not connected correctly, you need to swap its pins).
Now let's make changes to the multivibrator circuit (Figure 7) - disconnect pin 2 from pin 1 of the first element (D1.1) and connect pin 2 to the same circuit of a capacitor and resistor as in the experiments with a time relay. Now watch what happens : while S1 is closed, the voltage at one of the inputs of element D1.1 is zero. But this is an AND-NOT element, which means that if zero is applied to its one input, then no matter what happens at its second input, everything is at its output. will be equal to 1 unit. This unit is supplied to both inputs of the element D 1.2, and the output of D 1.2 will be zero. And if so, the LED will light up and remain lit with a constant light. After opening S1, capacitor C2 will slowly charge through R3 and the voltage on C2. will increase. At some point it will become equal to logical one. At this moment, the output level L of element D1.1 will depend on the level at its second input - pin 1 and the multivibrator will start working and the LED will blink.
If C2 and R3 are swapped (Figure 8), the circuit will work the other way around - at first the LED will blink, and after some time after opening S1 it will stop blinking and will remain on continuously.
Now let's move on to the area of audio frequencies - assemble the circuit shown in Figure 9. When you connect the power, a squeak will be heard in the speaker. The more C1 and R1, the lower the squeak tone will be, and the smaller they are, the higher the sound tone. Assemble the circuit shown in Figure 10.
This is a ready-made time relay. If you put a scale on the R3 handle, then it can be used, for example, for photo printing. YOU close S1, set resistor R3 to the required time, and then open S1. After this time has elapsed, the speaker will begin to beep. The circuit works almost the same as shown in Figure 7.
In the next lesson, we will try to assemble several useful devices in everyday life using K561LA7 (or K176J1A7) microcircuits.
