The scheme below was collected in his youth, in the classroom of the radio engineering circle. And unsuccessfully. Perhaps the K155LA3 microcircuit is still not suitable for such a metal detector, perhaps the frequency of 465 kHz is not the most suitable for such devices, or perhaps it was necessary to shield the search coil as in the other circuits of the "Metal Detectors" section

In general, the resulting "scribble" reacted not only to metals, but also to the hand and other non-metallic objects. In addition, microcircuits of the 155th series are too uneconomical for portable devices.

Radio 1985 - 2 p. 61. Simple metal detector

Simple metal detector

The metal detector, the diagram of which is shown in the figure, can be assembled in just a few minutes. It consists of two almost identical LC oscillators, made on the elements DD1.1-DD1.4, a detector according to the scheme of doubling the rectified voltage on VD1 diodes. VD2 and high-resistance (2 kOhm) BF1 headphones, the change in the tone of the sound of which indicates the presence of a metal object under the coil-antenna.

The generator, assembled on the elements DD1.1 and DD1.2, is itself excited at the resonance frequency of the series oscillatory circuit L1C1 tuned to 465 kHz (using superheterodyne receiver IF filter elements). The frequency of the second generator (DD1.3, DD1.4) is determined by the inductance of the antenna coil 12 (30 turns of PEL 0.4 wire on a mandrel with a diameter of 200 mm) and the capacitance of the capacitor variable capacity C2. which allows you to configure the metal detector to detect objects of a certain mass before searching. The beats resulting from mixing the oscillations of both generators are detected by diodes VD1, VD2. are filtered by capacitor C5 and fed to headphones BF1.

The whole device is assembled on a small printed circuit board, which allows when powered by a flat battery for flashlight make it very compact and easy to handle

Janeczek A Prosty wykrywacz melali. - Radioelektromk, 1984, No. 9 p. 5.

Editorial note. When repeating the metal detector, you can use the K155LA3 chip, any high-frequency germanium diodes and KPE from the Alpinist radio receiver.

The same scheme is considered in more detail in the collection of Adamenko M.V. "Metal detectors" M.2006 (Download). Further article from this book

3.1 A simple metal detector on a K155LA3 chip

Beginning radio amateurs can be recommended to repeat the design of a simple metal detector, the basis for which was a circuit that was repeatedly published in the late 70s of the last century in various domestic and foreign specialized publications. This metal detector, made on just one K155LA3 chip, can be assembled in a few minutes.

circuit diagram

The proposed design is one of the many variants of metal detectors of the BFO (Beat Frequency Oscillator) type, that is, it is a device based on the principle of analyzing the beats of two signals that are close in frequency (Fig. 3.1). At the same time, in this design, the assessment of the change in the beat frequency is carried out by ear.

The device is based on measuring and reference oscillators, an RF oscillation detector, an indication circuit, and a supply voltage stabilizer.

In the design under consideration, two simple LC oscillators are used, made on the IC1 chip. Circuit solutions of these generators are almost identical. In this case, the first oscillator, which is a reference, is assembled on the elements IC1.1 and IC1.2, and the second, measuring or tunable generator, is made on the elements IC1.3 and IC1.4.

The reference oscillator circuit is formed by a 200 pF capacitor C1 and a coil L1. The measurement generator circuit uses a variable capacitor C2 with a maximum capacitance of approximately 300 pF, as well as a search coil L2. In this case, both generators are tuned to an operating frequency of approximately 465 kHz.

Rice. 3.1.
Schematic diagram of a metal detector on a K155LA3 chip

The outputs of the generators through decoupling capacitors C3 and C4 are connected to the RF oscillation detector, made on diodes D1 and D2 according to the rectified voltage doubling circuit. The load of the detector is BF1 headphones, on which the signal of the low-frequency component is extracted. In this case, the capacitor C5 shunts the load at higher frequencies.

When the search coil L2 of the oscillatory circuit of the tunable generator approaches a metal object, its inductance changes, which causes a change in the operating frequency of this generator. In this case, if there is an object made of ferrous metal (ferromagnet) near the coil L2, its inductance increases, which leads to a decrease in the frequency of the tunable oscillator. The non-ferrous metal reduces the inductance of the L2 coil, and increases the operating frequency of the generator.

The RF signal formed as a result of mixing the signals of the measuring and reference generators after passing through the capacitors C3 and C4 is fed to the detector. In this case, the amplitude of the RF signal changes with the beat frequency.

The low-frequency envelope of the RF signal is isolated by a detector made on diodes D1 and D2. Capacitor C5 provides filtering of the high-frequency component of the signal. Next, the beat signal is sent to the BF1 headphones.

Power is supplied to IC1 from a 9V source B1 through a voltage regulator formed by a zener diode D3, a ballast resistor R3 and a regulating transistor T1.

Details and construction

For the manufacture of the considered metal detector, you can use any prototyping board. Therefore, the used parts are not subject to any restrictions related to overall dimensions. Installation can be both hinged and printed.

When repeating the metal detector, you can use the K155LA3 chip, consisting of four 2I-NOT logic elements, powered by a common source direct current. As capacitor C2, you can use a tuning capacitor from a portable radio receiver (for example, from the Alpinist radio receiver). Diodes D1 and D2 can be replaced with any high frequency germanium diodes.

Coil L1 of the reference oscillator circuit should have an inductance of about 500 μH. As such a coil, it is recommended to use, for example, the IF filter coil of a superheterodyne receiver.

Measuring coil L2 contains 30 turns of PEL wire with a diameter of 0.4 mm and is made in the form of a torus with a diameter of 200 mm. This coil is easier to make on a rigid frame, but you can do without it. In this case, any suitable round object, such as a jar, can be used as a temporary frame. The turns of the coil are wound in bulk, after which they are removed from the frame and shielded with an electrostatic screen, which is an open aluminum foil tape wound over a bundle of turns. The gap between the beginning and the end of the tape winding (the gap between the ends of the screen) must be at least 15 mm.

In the manufacture of the L2 coil, it is especially necessary to ensure that the ends of the shielding tape do not close, since in this case a short-circuited coil is formed. In order to increase the mechanical strength, the coil can be impregnated with epoxy glue.

For source sound signals high-resistance headphones should be used with as much resistance as possible (about 2000 ohms). Suitable, for example, the well-known telephone TA-4 or TON-2.

As a power source V1, you can use, for example, a Krona battery or two 3336L batteries connected in series.

In a voltage stabilizer, the capacitance of the electrolytic capacitor C6 can be from 20 to 50 microfarads, and the capacitance of C7 can be from 3,300 to 68,000 pF. The voltage at the output of the stabilizer, equal to 5 V, is set by the trimming resistor R4. This voltage will be maintained unchanged even when the batteries are significantly discharged.

It should be noted that the K155LAZ chip is designed to be powered from a 5 V DC source. Therefore, if desired, the voltage stabilizer unit can be excluded from the circuit and one 3336L battery or similar can be used as a power source, which allows you to assemble a compact design. However, the discharge of this battery will very quickly affect functionality this metal detector. That is why you need a power supply that provides the formation of a stable voltage of 5 V.

It should be recognized that the author used four large imported imported round batteries connected in series as a power source. In this case, a voltage of 5 V was formed by an integral stabilizer of the 7805 type.

The board with the elements located on it and the power supply are placed in any suitable plastic or wooden case. A variable capacitor C2, a switch S1, as well as connectors for connecting a search coil L2 and headphones BF1 are installed on the housing cover (these connectors and switch S1 on circuit diagram not specified).

Establishment

As with the adjustment of other metal detectors, this device should be adjusted in conditions where metal objects are removed from the L2 search coil at a distance of at least one meter.

First, using a frequency meter or oscilloscope, you need to adjust the operating frequencies of the reference and measuring oscillators. The frequency of the reference oscillator is set to approximately 465 kHz by adjusting the core of the coil L1 and, if necessary, by selecting the capacitance of the capacitor C1. Before adjustment, you will need to disconnect the corresponding terminal of the capacitor C3 from the diodes of the detector and capacitor C4. Next, you need to disconnect the corresponding terminal of the capacitor C4 from the diodes of the detector and from the capacitor C3 and adjust the capacitor C2 to set the frequency of the measuring generator so that its value differs from the frequency of the reference generator by about 1 kHz. After all connections are restored, the metal detector is ready for operation.

Operating procedure

Holding prospecting work using the considered metal detector does not have any features. In practical use of the device, the variable capacitor C2 should support required frequency beat signal that changes with battery discharge, temperature change environment or deviations in the magnetic properties of the soil.

If the frequency of the signal in the headphones changes during operation, this indicates the presence of a metal object in the area of ​​​​the search coil L2. When approaching some metals, the frequency of the beat signal will increase, and when approaching others, it will decrease. By changing the tone of the beat signal, having a certain experience, one can easily determine what metal, magnetic or non-magnetic, the detected object is made of.

Getting to know the digital circuit

In the second part of the article, it was told about the conventional graphic symbols of logical elements and about the functions performed by these elements.

To explain the principle of operation, contact circuits were given that perform the logical functions AND, OR, NOT and AND-NOT. Now you can start a practical acquaintance with the K155 series microcircuits.

Appearance and design

The basic element of the 155th series is the K155LA3 chip. It is a plastic case with 14 pins, on the upper side of which there is a marking and a key indicating the first pin of the microcircuit.

The key is a small round label. If you look at the microcircuit from above (from the side of the case), then the counting of the conclusions should be carried out counterclockwise, and if from below, then clockwise.

A drawing of the microcircuit housing is shown in Figure 1. Such a housing is called DIP-14, which in English means a plastic housing with a two-row pin arrangement. Many microcircuits have a larger number of pins and therefore packages can be DIP-16, DIP-20, DIP-24 and even DIP-40.

Figure 1. DIP-14 package.

What's in this box

The DIP-14 package of the K155LA3 chip contains 4 2I-NOT elements independent of each other. The only thing that unites them is only common power pins: the 14th pin of the microcircuit is the + of the power source, and pin 7 is the negative pole of the source.

In order not to clutter up the diagrams extra elements, power lines are usually not shown. This is not done also because each of the four elements 2I-NOT can be in different places scheme. Usually, they simply write on the diagrams: “Connect + 5V to terminals 14 DD1, DD2, DD3 ... DDN. -5V lead to pins 07 DD1, DD2, DD3…DDN.». separately located elements are designated as DD1.1, DD1.2, DD1.3, DD1.4. Figure 2 shows that the K155LA3 chip consists of four 2I-NOT elements. As already mentioned in the second part of the article, input terminals are located on the left, outputs are on the right.

The foreign analogue of K155LA3 is the SN7400 chip and it can be safely used for all the experiments described below. To be more precise, the entire series of K155 microcircuits is an analogue of the foreign SN74 series, so sellers on the radio markets offer it.

Figure 2. K155LA3 chip pinout.

To conduct experiments with a microcircuit, you will need a voltage of 5V. The easiest way to make such a source is by using the K142EN5A stabilizer microcircuit or its imported version, which is called 7805. In this case, it is not at all necessary to wind the transformer, solder the bridge, and install capacitors. After all, there is always some Chinese network adapter with a voltage of 12V, to which it is enough to connect the 7805, as shown in Figure 3.

Figure 3. A simple power supply for experiments.

To conduct experiments with a microcircuit, you will need to make a small breadboard. It is a piece of getinaks, fiberglass or other similar insulating material with dimensions of 100 * 70 mm. Even simple plywood or thick cardboard is suitable for such purposes.

Along the long sides of the board, tinned conductors should be strengthened, about 1.5 mm thick, through which power will be supplied to the microcircuits (power rails). Holes with a diameter of no more than 1 mm should be drilled between the conductors over the entire area of ​​the breadboard.

When conducting experiments, it will be possible to insert segments of tinned wire into them, to which capacitors, resistors and other radio components will be soldered. Low legs should be made at the corners of the board, this will make it possible to place the wires from below. The design of the breadboard is shown in Figure 4.

Figure 4. Breadboard.

After the breadboard is ready, you can start experimenting. To do this, you should install at least one K155LA3 chip on it: solder pins 14 and 7 to the power buses, and bend the rest of the pins so that they are adjacent to the board.

Before starting experiments, you should check the reliability of soldering, the correct connection of the supply voltage (connecting the supply voltage in reverse polarity can damage the microcircuit), and also check if there is a short circuit between adjacent terminals. After this check, you can turn on the power and start the experiments.

For measurements, it is best suited, the input resistance of which is at least 10Kom / V. This requirement is fully satisfied by any tester, even a cheap Chinese one.

Why is arrow better? Because, by observing the fluctuations of the arrow, one can notice voltage pulses, of course, of a sufficiently low frequency. A digital multimeter does not have this capability. All measurements must be carried out relative to the "minus" of the power source.

After the power is turned on, measure the voltage at all pins of the microcircuit: at input pins 1 and 2, 4 and 5, 9 and 10, 12 and 13, the voltage should be 1.4V. And at the output pins 3, 6, 8, 11 about 0.3V. If all voltages are within the specified limits, then the microcircuit is working.

Figure 5 Simple experiments with a logical element.

Checking work logic element 2AND-NOT can start, for example, with the first element. Its input terminals are 1 and 2, and the output is 3. In order to apply a logic zero signal to the input, it is enough to simply connect this input to the negative (common) wire of the power source. If it is required to apply a logical unit to the input, then this input should be connected to the + 5V bus, but not directly, but through a limiting resistor with a resistance of 1 ... 1.5 KΩ.

Suppose that we connected input 2 to a common wire, thereby applying a logical zero to it, and a logical unit was applied to input 1, as just indicated through the limiting resistor R1. This connection is shown in Figure 5a. If, with such a connection, the voltage at the output of the element is measured, then the voltmeter will show 3.5 ... 4.5V, which corresponds to a logical unit. A logical unit will give a measurement of the voltage at pin 1.

This completely coincides with what was shown in the second part of the article using the example of a relay-contact circuit 2I-NOT. Based on the results of the measurements, we can draw the following conclusion: when one of the inputs of the 2I-NOT element has a high level, and the other one has a low level, a high level is necessarily present at the output.

Next, we will do the following experiment - we will apply a unit to both inputs at once, as shown in Figure 5b, but one of the inputs, for example 2, will be connected to a common wire using a wire jumper. (For such purposes, it is best to use an ordinary sewing needle soldered to a flexible wire). If we now measure the voltage at the output of the element, then, as in the previous case, there will be a logical unit.

Without interrupting the measurement, remove the wire jumper - the voltmeter will show a high level at the output of the element. This is fully consistent with the logic of the 2I-NOT element, which can be seen by referring to the contact diagram in the second part of the article, as well as looking at the truth table shown there.

If now with this jumper we periodically close any of the inputs to a common wire, simulating the supply of a low and high level, then using a voltmeter at the output, voltage pulses can be detected - the arrow will oscillate in time with the touches of the microcircuit input jumper.

From the experiments carried out, the following conclusions can be drawn: a low-level voltage at the output will appear only if there is a high level at both inputs, that is, the 2I condition is met at the inputs. If at least one of the inputs has a logical zero, there is a logical unit at the output, we can repeat that the logic of the microcircuit is fully consistent with the logic of the 2I-NOT contact circuit considered in.

Here it is appropriate to do another experiment. Its meaning is to turn off all input pins, just leave them in the "air" and measure output voltage element. What is going to be there? That's right, there will be a logic zero voltage. This suggests that the unconnected inputs of logic elements are equivalent to inputs with a logical one applied to them. This feature should not be forgotten, although unused inputs, as a rule, are recommended to be connected somewhere.

Figure 5c shows how the 2I-NOT logic element can simply be turned into an inverter. To do this, it is enough to connect both of its inputs together. (Even if there are four or eight inputs, such a connection is quite acceptable).

To make sure that the output signal has a value opposite to the input signal, it is enough to connect the inputs with a wire jumper to a common wire, that is, apply a logical zero to the input. In this case, the voltmeter connected to the output of the element will show a logical unit. If the jumper is opened, then a low level voltage will appear at the output, which is just the opposite of the input.

This experience suggests that the operation of the inverter is completely equivalent to the operation of the NOT contact circuit discussed in the second part of the article. These are, in general, the wonderful properties of the 2I-NOT microcircuit. To answer the question of how all this happens, one should consider the electrical circuit of the 2I-NOT element.

The internal structure of the element 2I-NOT

Until now, we have considered a logical element at the level of its graphic designation, taking it, as they say in mathematics, for a “black box”: without going into details of the internal structure of the element, we have studied its response to input signals. Now is the time to explore internal organization our logical element, which is shown in Figure 6.

Figure 6 Wiring diagram logical element 2I-NOT.

The circuit contains four transistors n-p-n structures, three diodes and five resistors. There is a direct connection between the transistors (without coupling capacitors), which allows them to work with constant voltages. The output load of the microcircuit is conditionally shown as a resistor Rn. In fact, this is most often an input or several inputs of the same digital microcircuits.

The first transistor is multi-emitter. It is he who performs the input logical operation 2I, and the following transistors perform amplification and inversion of the signal. Microcircuits made according to a similar scheme are called transistor-transistor logic, abbreviated as TTL.

This abbreviation reflects the fact that the input logical operations and the subsequent amplification and inversion are performed by the transistor circuit elements. In addition to TTL, there is also diode-transistor logic (DTL), the input logic stages of which are made on diodes, located, of course, inside the microcircuit.

Figure 7

At the inputs of the 2I-NOT logic element, diodes VD1 and VD2 are installed between the emitters of the input transistor and the common wire. Their purpose is to protect the input from a voltage of negative polarity, which may arise as a result of self-induction of the mounting elements when the circuit operates at high frequencies, or simply applied by mistake from external sources.

The input transistor VT1 is connected according to a common base circuit, and its load is the transistor VT2, which has two loads. In the emitter, this is the resistor R3, and in the collector R2. Thus, a phase inverter is obtained for the output stage on transistors VT3 and VT4, which makes them work in antiphase: when VT3 is closed, VT4 is open and vice versa.

Let's assume that both inputs of the 2I-NOT element are low. To do this, simply connect these inputs to a common wire. In this case, the transistor VT1 will be open, which will lead to the closing of transistors VT2 and VT4. The transistor VT3 will be in the open state and through it and the diode VD3 current flows to the load - at the output of the element, a high level state (logical unit).

In the event that a logic unit is applied to both inputs, the transistor VT1 will close, which will lead to the opening of transistors VT2 and VT4. Due to their opening, the transistor VT3 will close and the current through the load will stop. At the output of the element, a zero state or a low level voltage is set.

The low-level voltage is due to the voltage drop at the collector-emitter junction of the open transistor VT4 and, according to the specifications, does not exceed 0.4V.

The high-level voltage at the output of the element is less than the supply voltage by the amount of voltage drop across the open transistor VT3 and the diode VD3 in the case when the transistor VT4 is closed. The high level voltage at the output of the element depends on the load, but should not be less than 2.4V.

If a very slowly changing voltage, varying from 0 ... 5V, is applied to the inputs of the element, connected together, then it can be seen that the transition of the element from a high level to a low level occurs abruptly. This transition is performed at the moment when the voltage at the inputs reaches a level of approximately 1.2V. Such a voltage for the 155th series of microcircuits is called threshold.

Boris Alaldyshkin

Article continued:

Electronic book -

This bug does not require painstaking configuration.This device collected on the well-known chip k155la3

The range of the bug in an open area at which it is clearly audible and distinguishable is 120 meters. This device is suitable do-it-yourself novice radio amateur. And it doesn't cost much.

The circuit uses a digital carrier frequency generator. Generally beetle consists of three parts: microphone, amplifier and modulator. This scheme uses the simplest amplifier on the one transistor KT315.

Principle of operation. Thanks to your conversation, the microphone begins to pass current through itself, which enters the base of the transistor. The transistor, due to the incoming voltage, begins to open - to pass current from the emitter to the collector in proportion to the current at the base. The louder you yell, the more current flows to the modulator. Connecting the microphone to the oscilloscope and we see that the output voltage does not exceed 0.5V and sometimes drops to minus (i.e. there is a negative wave, where U<0). Подключив усилитель к оцилографу,амплитута стала 5в (но теперь начали обрезаться и приводить к этой амплитуде громкие звуки) и напряжение всегда выше 0. Именно такой сигнал и поступает на модулятор, который состоит из генератора несущей частоты, собранного из четырех 2И-НЕ элементов.

For constant frequency generation, the inverter is closed to itself through a variable resistor. There are no capacitors in the generator. Where is the frequency delay then? The fact is that microcircuits have a so-called response delay. It is thanks to it that we obtain a frequency of 100 MHz and such a small circuit size.

Collect the beetle in parts. That is, I assembled the block - checked it; collected the next one, checked it, and so on. We also do not recommend doing the whole thing on cardboard or circuit boards.

After assembly, tune the FM receiver to 100 MHz. Say something. If this is something you can hear, then everything is fine, the beetle is working. If you hear only weak interference or even silence, then try to drive the receiver on other frequencies. The same bug is caught on Chinese receivers with an autoscan.

Every radio amateur has a k155la3 chip somewhere “littered around”. But often they cannot find a serious application for them, since in many books and magazines there are only schemes for flashing lights, toys, etc. with this detail. This article will consider circuits using the k155la3 chip.
First, consider the characteristics of the radio component.
1. The most important thing is nutrition. It is supplied to 7 (-) and 14 (+) legs and amounts to 4.5 - 5 V. More than 5.5 V should not be applied to the microcircuit (it starts to overheat and burns out).
2. Next, you need to determine the purpose of the part. It consists of 4 elements, 2 and not (two inputs). That is, if you apply 1 to one input and 0 to the other, then the output will be 1.
3. Consider the pinout of the microcircuit:

To simplify the diagram, separate elements of the part are depicted on it:

4. Consider the location of the legs relative to the key:

It is necessary to solder the microcircuit very carefully, without heating it (you can burn it).

Here are the circuits using the k155la3 chip:

1. Voltage stabilizer (can be used as a phone charger from the car's cigarette lighter).
Here is the diagram:


Up to 23 volts can be applied to the input. Instead of the P213 transistor, you can put a KT814, but then you have to install a radiator, since it can overheat under heavy load.
Printed circuit board:

Another option for a voltage stabilizer (powerful):


2. Car battery charge indicator.
Here is the diagram:

3. Tester of any transistors.
Here is the diagram:

Instead of diodes D9, you can put d18, d10.
Buttons SA1 and SA2 have switches for testing forward and reverse transistors.

4. Two options for the rodent repeller.
Here is the first diagram:


C1 - 2200 uF, C2 - 4.7 uF, C3 - 47 - 100 uF, R1-R2 - 430 Ohm, R3 - 1 kohm, V1 - KT315, V2 - KT361. You can also put transistors of the MP series. Dynamic head - 8 ... 10 ohms. Power supply 5V.

Second option:

C1 - 2200 uF, C2 - 4.7 uF, C3 - 47 - 200 uF, R1-R2 - 430 Ohm, R3 - 1 kohm, R4 - 4.7 ohm, R5 - 220 Ohm, V1 - KT361 (MP 26, MP 42, kt 203, etc.), V2 - GT404 (KT815, KT817), V3 - GT402 (KT814, KT816, P213). Dynamic head 8...10 ohm.
Power supply 5V.

Such a beacon can be assembled as a complete signaling device, for example, on a bicycle or just for fun.

A beacon on a microcircuit is arranged nowhere simpler. It consists of one logic chip, a bright LED of any glow color and several strapping elements.

After assembly, the beacon starts working immediately after power is supplied to it. Almost no settings are required, with the exception of adjusting the duration of the flashes, but this is optional. You can leave everything as it is.

Here is the schematic diagram of the "beacon".

So, let's talk about the parts used.

The K155LA3 microcircuit is a logic microcircuit based on transistor-transistor logic - abbreviated as TTL. This means that this microcircuit is made of bipolar transistors. The microcircuit inside contains only 56 parts - integrated elements.

There are also CMOS or CMOS chips. Here they are already assembled on MOS field-effect transistors. It is worth noting the fact that TTL chips have higher power consumption than CMOS chips. But they are not afraid of static electricity.

The K155LA3 microcircuit includes 4 2I-NOT cells. The number 2 means that there are 2 inputs at the input of the base logic element. If you look at the diagram, you can see that this is indeed the case. On the diagrams, digital microcircuits are denoted by the letters DD1, where the number 1 indicates the serial number of the microcircuit. Each of the basic elements of the microcircuit also has its own letter designation, for example, DD1.1 or DD1.2. Here, the number after DD1 indicates the serial number of the base element in the chip. As already mentioned, the K155LA3 chip has four basic elements. In the diagram, they are designated as DD1.1; DD1.2; DD1.3; DD1.4.

If you look at the circuit diagram more closely, you will notice that the letter designation of the resistor R1* has an asterisk * . And this is no accident.

So on the diagrams, elements are indicated, the value of which must be adjusted (selected) during the establishment of the circuit in order to achieve the desired mode of operation of the circuit. In this case, using this resistor, you can adjust the duration of the LED flash.

In other circuits that you may come across, by selecting the resistance of the resistor indicated by an asterisk, you need to achieve a certain mode of operation, for example, a transistor in an amplifier. As a rule, the tuning procedure is given in the description of the circuit. It describes how you can determine that the circuit is configured correctly. This is usually done by measuring the current or voltage in a certain section of the circuit. For the lighthouse scheme, everything is much simpler. The adjustment is purely visual and does not require measuring voltages and currents.

On circuit diagrams, where the device is assembled on microcircuits, as a rule, it is rarely possible to find an element whose value needs to be selected. Yes, this is not surprising, since microcircuits are, in fact, already configured elementary devices. And, for example, on old circuit diagrams that contain dozens of individual transistors, resistors and asterisk capacitors * next to the letter designation, radio components can be found much more often.

Now let's talk about the pinout of the K155LA3 chip. If you do not know some rules, then you may encounter an unexpected question: "How to determine the pin number of the microcircuit?" Here the so-called key. The key is a special label on the microcircuit case that indicates the starting point for the pin numbering. The countdown of the pin number of the microcircuit, as a rule, is counterclockwise. Take a look at the picture and everything will become clear to you.

The positive “+” of the power supply is connected to the output of the K155LA3 microcircuit at number 14, and the minus “-” is connected to output 7. The minus is considered a common wire, in foreign terminology it is designated as GND .