Diagrams with explanations of simple devices for radio amateurs. How to read electrical diagrams. Schemes of homemade measuring instruments
Schemes of homemade measuring instruments
The circuit of the device, developed on the basis of a classic multivibrator, but instead of load resistors, transistors with the opposite main conductivity are included in the collector circuits of the multivibrator.
It's good if your lab has an oscilloscope. Well, if it is not there and it is not possible to buy it for one reason or another, do not worry. In most cases, it can be successfully replaced by a logic probe, which allows you to control the logical levels of signals at the inputs and outputs of digital integrated circuits, determine the presence of pulses in the controlled circuit and reflect the information received in visual (light-color or digital) or audio (tonal signals of various frequencies). ) forms. When setting up and repairing structures based on digital integrated circuits, it is far from always so necessary to know the characteristics of the pulses or the exact values of the voltage levels. Therefore, logic probes make it easy to set up, even if you have an oscilloscope.
A huge selection of different pulse generator circuits is presented. Some of them form a single pulse at the output, the duration of which does not depend on the duration of the triggering (input) pulse. Such generators are used for a wide variety of purposes: simulating the input signals of digital devices, when checking the performance of digital integrated circuits, the need to supply a certain number of pulses to a device with visual control of processes, etc. Others generate sawtooth and rectangular pulses of various frequencies, duty cycles and amplitude
Repair of various units and devices of low-frequency radio-electronic equipment and technology can be greatly simplified if you use a function generator as an assistant, which makes it possible to investigate the amplitude-frequency characteristics of any low-frequency device, transients and nonlinear characteristics of any analog devices, and also has the ability to generate rectangular pulses. form and simplify the process of setting up digital circuits.
When setting up digital devices, one more device is definitely needed - a pulse generator. An industrial generator is a rather expensive device and is rarely on sale, but its analogue, although not so accurate and stable, can be assembled from available radio elements at home
However, the creation of a sound generator that produces a sinusoidal signal is not an easy and rather painstaking task, especially in terms of adjustment. The fact is that any generator contains at least two elements: an amplifier and a frequency-dependent circuit that determines the frequency of oscillations. Usually it is connected between the output and input of the amplifier, creating a positive feedback (POS). In the case of an RF generator, everything is simple - a single-transistor amplifier and an oscillatory circuit that determines the frequency are enough. For the audio frequency range, it is difficult to wind the coil, and its quality factor turns out to be low. Therefore, in the audio frequency range, RC elements are used - resistors and capacitors. They filter the fundamental harmonic of the oscillations rather poorly, and therefore the sinusoidal signal turns out to be distorted, for example, limited in peaks. To eliminate distortion, amplitude stabilization circuits are used to maintain a low level of the generated signal when distortion is still invisible. It is the creation of a good stabilizing circuit that does not distort the sinusoidal signal that causes the main difficulties.
Often, having assembled the structure, the radio amateur sees that the device is not working. After all, a person does not have sense organs that allow him to see an electric current, an electromagnetic field, or processes occurring in electronic circuits Oh. Radio measuring instruments help to do this - the eyes and ears of a radio amateur.
Therefore, some means of testing and checking telephones and loudspeakers, audio frequency amplifiers, various sound recording and sound reproducing devices are needed. Such a tool is amateur radio circuits for audio frequency signal generators, or, more simply, a sound generator. Traditionally, it produces a continuous sinusoidal signal, the frequency and amplitude of which can be changed. This allows you to check all ULF stages, find faults, determine the gain, take amplitude-frequency characteristics (AFC) and much more.
A simple amateur radio home-made prefix is considered that turns your multimeter into a universal device for checking zener diodes and dinistors. PCB drawings available
amateur radio technology. The book tells about the technology of the radio amateur. Recommendations are given for processing materials, winding coils and transformers, assembling and soldering parts. It describes the manufacture of home-made parts of structural elements, the simplest machines, fixtures and tools.
Digital electronics for beginners. The basics of digital electronics are presented in a simple and accessible way for beginners - by creating fun and educational devices on transistors and microcircuits on a prototyping board, which start working immediately after assembly, without requiring soldering, adjustment and programming. The set of necessary parts is minimized both in terms of the number of items and in terms of cost.
In the course of the presentation, questions are given for self-examination and consolidation of the material, as well as creative tasks for independent development of schemes.
Oscilloscopes. Basic principles of measurements. Oscilloscopes are an indispensable tool for those who design, manufacture or repair electronic equipment. In today's fast-paced world, professionals need the best equipment to quickly and accurately solve their daily measurement tasks. As an engineer's "eye" into the world of electronics, oscilloscopes are a key tool for understanding the inner workings of electronic circuits.
Designing and building a Tesla coil is pretty easy. For a beginner this seems like a daunting task (I also found it difficult), but you can get a working coil by following the instructions in this article and doing a little calculation. Of course, if you want a very powerful coil, there is no way other than learning the theory and doing a lot of calculations.
Homemade young radio amateur. The book describes sound simulators, hidden wiring finders, acoustic switches, automatic sound control models, electric musical instruments, electric guitar attachments, color music consoles and other structures assembled from available parts.
School radio station ShK-2 - Alekseev S.M. The brochure describes two transmitters and two receivers operating on the 28 and 144 MHz bands, an anode-screen modulator, a power supply and simple antennas. It also tells about the organization of the work of students at a collective radio station, about the training of operators, the content of their work, about research work schoolchildren in the field of distribution of HF and VHF.
Electronics For Dummies
Build your electronics workbench - and begin creating fun electronics projects right away
Packed with hundreds of colorful diagrams and photographs, this book provides step-by-step instructions for experiments that show you how electronic components work, advice on choosing and using essential tools, and exciting projects you can build in 30 minutes or less. You "ll get charged up as you transform theory into action in chapter after chapter!
The book consists of descriptions of simple designs containing electronic components and experiments with them. In addition to traditional designs, whose operation logic is determined by their circuitry, descriptions of products that are functionally implemented using programming have been added. Subjects of products - electronic toys and souvenirs.
How to master radio electronics from scratch. If you have a great desire to be friends with electronics, if you want to create your own homemade products, but don't know where to start, use this tutorial. You'll learn how to read circuit diagrams, work with a soldering iron, and create quite a few interesting homemade. You will learn how to use a measuring instrument, design and build printed circuit boards, learn the secrets of many professional radio amateurs. In general, get enough knowledge to further master electronics on your own.
Soldering is easy step by step guide for beginners. The comic, despite its format and volume, explains in small details the basic principles of this process, which are not at all obvious to people who have never held a soldering iron in their hands (as practice shows, for many who held it too). If you have long wanted to learn how to solder yourself, or plan to teach your children this, then this comic is for you.
Electronics for the curious. This book is written specifically for you, who are starting an exciting ascent to the heights of electronics. Helps to master the dialogue of the author of the book with the beginner. Measuring instruments, breadboard, books and PCs also become assistants in mastering knowledge.
Encyclopedia of a young radio amateur. Here you will find many practical diagrams of both individual nodes and blocks, and entire devices. In resolving many issues, a special guide will help. Taking advantage convenient system search, you will find the desired section, and to it, as illustrative examples, superbly executed drawings.
The book was created specifically for beginner radio amateurs, or, as we like to say, "dummies". She talks about the basics of electronics and electrical engineering necessary for a radio amateur. Theoretical questions are told in a very accessible form and in the volume necessary for practical work. The book teaches how to properly solder, measure, analyze circuits. But, rather, this is a book about entertaining electronics. After all, the basis of the book is amateur radio homemade products that are accessible to a beginner radio amateur and useful in everyday life.
This is the second book in a series of publications addressed to the novice radio amateur as an educational and practical aid. In this book, on a more serious level, the acquaintance with various circuits based on a semiconductor and radio-vacuum base, the basics of sound engineering, electrical and radio measurements is continued. The presentation is accompanied by a large number of illustrations and practical diagrams.
Radio amateur's alphabet. The main and only purpose of this book is to introduce children who do not have the slightest idea about it to amateur radio creativity. The book is built on the principle of `from the basics - through acquaintance - to understanding` and can be recommended to middle and high school students as a guide to the beginnings of radio engineering.
Below are simple light and sound circuits, mainly assembled on the basis of multivibrators, for beginner radio amateurs. In all circuits, the simplest element base is used, complex adjustment is not required, and elements can be replaced with similar ones within a wide range.
Electronic duck
A toy duck can be equipped with a simple two-transistor "quack" simulator circuit. The circuit is a classic two-transistor multivibrator with an acoustic capsule in one arm, and two LEDs that can be inserted into the eyes of the toy serve as the load of the other. Both of these loads work alternately - either a sound is heard, or LEDs flash - the eyes of a duck. A reed switch can be used as a power switch SA1 (can be taken from the SMK-1, SMK-3, etc. sensors used in security alarm systems as door opening sensors). When a magnet is brought to the reed switch, its contacts are closed and the circuit starts to work. This can happen when the toy is tilted to a hidden magnet or a kind of “magic wand” with a magnet is brought up.
Transistors in the circuit can be any pnp type, low or medium power, for example MP39 - MP42 (old type), KT 209, KT502, KT814, with a gain of more than 50. You can also use transistors n-p-n structures, for example KT315, KT 342, KT503, but then you need to change the polarity of the power supply, turn on the LEDs and the polar capacitor C1. As an acoustic emitter BF1, you can use a capsule type TM-2 or a small-sized speaker. Establishing the circuit is reduced to the selection of the resistor R1 to obtain a characteristic quacking sound.
The sound of a bouncing metal ball
The circuit quite accurately imitates such a sound, as the capacitor C1 discharges, the volume of the “beats” decreases, and the pauses between them decrease. At the end, a characteristic metallic rattle will be heard, after which the sound will stop.
Transistors can be replaced with similar ones, as in the previous circuit.
The total duration of the sound depends on the capacitance C1, and C2 determines the duration of the pauses between the “beats”. Sometimes, for a more believable sound, it is useful to choose a transistor VT1, since the operation of the simulator depends on its initial collector current and gain (h21e).
Engine Sound Simulator
They can, for example, sound a radio-controlled or other model of a mobile device.
Transistor and speaker replacement options - as in the previous circuits. Transformer T1 is the output from any small-sized radio receiver (a speaker is also connected through it in the receivers).
There are many schemes for imitating the sounds of birdsong, animal voices, the whistle of a locomotive, etc. The circuit proposed below is assembled on just one digital microcircuit K176LA7 (K561 LA7, 564LA7) and allows you to simulate many different sounds depending on the resistance value connected to the X1 input contacts.
It should be noted that the microcircuit here works “without power”, that is, no voltage is applied to its positive output (leg 14). Although, in fact, the microcircuit is still powered, but this happens only when the resistance-sensor is connected to the X1 contacts. Each of the eight inputs of the microcircuit is connected to the internal power bus through diodes that protect against static electricity or incorrect connection. Through these internal diodes, the microcircuit is powered due to the presence of a positive feedback power supply through the input resistor-sensor.
The circuit consists of two multivibrators. The first one (on the elements DD1.1, DD1.2) immediately starts generating rectangular pulses with a frequency of 1 ... 3 Hz, and the second one (DD1.3, DD1.4) starts working when the logic level " one". It generates tone pulses with a frequency of 200 ... 2000 Hz. From the output of the second multivibrator, pulses are fed to a power amplifier (transistor VT1) and a modulated sound is heard from the dynamic head.
If you now connect a variable resistor with a resistance of up to 100 kOhm to the input jacks X1, then there is a feedback on the power supply and this transforms the monotonous intermittent sound. By moving the slider of this resistor and changing the resistance, you can achieve a sound reminiscent of the trill of a nightingale, the chirping of a sparrow, the quacking of a duck, the croaking of a frog, etc.
Details
The transistor can be replaced with KT3107L, KT361G, but in this case, you need to put R4 with a resistance of 3.3 kOhm, otherwise the sound volume will decrease. Capacitors and resistors - of any type with ratings close to those indicated on the diagram. It must be borne in mind that the above-mentioned protective diodes are absent in the K176 series microcircuits of early releases and such instances will not work in this circuit! It is easy to check the presence of internal diodes - just measure the resistance between pin 14 of the microcircuit (“+” power supply) and its input terminals (or at least one of the inputs) with a tester. As with testing diodes, resistance should be low in one direction and high in the other.
The power switch in this circuit can be omitted, since in rest mode the device consumes less than 1 μA current, which is much less than even the self-discharge current of any battery!
Adjustment
A correctly assembled simulator does not require any adjustment. To change the tone of the sound, you can select a capacitor C2 from 300 to 3000 pF and resistors R2, R3 from 50 to 470 kOhm.
flasher
The flashing frequency of the lamp can be adjusted by selecting the elements R1, R2, C1. The lamp can be from a flashlight or a car 12 V. Depending on this, you need to choose the supply voltage of the circuit (from 6 to 12 V) and the power of the switching transistor VT3.
Transistors VT1, VT2 - any low-power corresponding structures (KT312, KT315, KT342, KT 503 (n-p-n) and KT361, KT645, KT502 (p-n-p), and VT3 - medium or high power (KT814, KT816, KT818).
A simple device for listening to the sound of TV programs on headphones. It does not require any power and allows you to move freely within the room.
Coil L1 is a "loop" of 5 ... 6 turns of wire PEV (PEL) -0.3 ... 0.5 mm, laid along the perimeter of the room. It is connected in parallel with the TV speaker through the SA1 switch as shown in the figure. For normal operation of the device, the output power of the TV sound channel must be within 2 ... 4 W, and the loop resistance must be 4 ... 8 Ohms. The wire can be laid under the plinth or in the cable duct, while it must be placed as far as possible no closer than 50 cm from the wires of the 220 V network to reduce AC voltage interference.
Coil L2 is wound on a frame made of thick cardboard or plastic in the form of a ring with a diameter of 15 ... 18 cm, which serves as a headband. It contains 500 ... 800 turns of PEV (PEL) wire 0.1 ... 0.15 mm fixed with glue or electrical tape. A miniature volume control R and an earphone (high-resistance, for example, TON-2) are connected in series to the coil terminals.
Automatic light switch
This one differs from many schemes of similar automata by its extreme simplicity and reliability and does not need a detailed description. It allows you to turn on the lighting or some electrical appliance for a specified short time, and then automatically turns it off.
To turn on the load, it is enough to briefly press the switch SA1 without fixing. In this case, the capacitor has time to charge and opens the transistor, which controls the switching on of the relay. The turn-on time is determined by the capacitance of the capacitor C and with the nominal value indicated on the diagram (4700 mF) is about 4 minutes. An increase in the on-time is achieved by connecting additional capacitors in parallel with C.
The transistor can be any n-p-n type of medium power or even low power, such as KT315. It depends on the operating current of the relay used, which can also be any other for an actuation voltage of 6-12 V and capable of switching the load of the power you need. You can also use p-n-p type transistors, but you will need to change the polarity of the supply voltage and turn on the capacitor C. Resistor R also affects the response time to a small extent and can be 15 ... 47 kOhm, depending on the type of transistor.
List of radio elements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad | |
|---|---|---|---|---|---|---|---|
| Electronic duck | |||||||
| VT1, VT2 | bipolar transistor | KT361B | 2 | MP39-MP42, KT209, KT502, KT814 | To notepad | ||
| HL1, HL2 | Light-emitting diode | AL307B | 2 | To notepad | |||
| C1 | 100uF 10V | 1 | To notepad | ||||
| C2 | Capacitor | 0.1uF | 1 | To notepad | |||
| R1, R2 | Resistor | 100 kOhm | 2 | To notepad | |||
| R3 | Resistor | 620 ohm | 1 | To notepad | |||
| BF1 | Acoustic emitter | TM2 | 1 | To notepad | |||
| SA1 | reed switch | 1 | To notepad | ||||
| GB1 | Battery | 4.5-9V | 1 | To notepad | |||
| Bouncing metal ball sound simulator | |||||||
| bipolar transistor | KT361B | 1 | To notepad | ||||
| bipolar transistor | KT315B | 1 | To notepad | ||||
| C1 | electrolytic capacitor | 100uF 12V | 1 | To notepad | |||
| C2 | Capacitor | 0.22uF | 1 | To notepad | |||
| dynamic head | GD 0.5...1Watt 8 Ohm | 1 | To notepad | ||||
| GB1 | Battery | 9 Volt | 1 | To notepad | |||
| Engine Sound Simulator | |||||||
| bipolar transistor | KT315B | 1 | To notepad | ||||
| bipolar transistor | KT361B | 1 | To notepad | ||||
| C1 | electrolytic capacitor | 15uF 6V | 1 | To notepad | |||
| R1 | Variable resistor | 470 kOhm | 1 | To notepad | |||
| R2 | Resistor | 24 kOhm | 1 | To notepad | |||
| T1 | Transformer | 1 | From any small radio receiver | To notepad | |||
| Universal sound simulator | |||||||
| DD1 | Chip | K176LA7 | 1 | K561LA7, 564LA7 | To notepad | ||
| bipolar transistor | KT3107K | 1 | KT3107L, KT361G | To notepad | |||
| C1 | Capacitor | 1 uF | 1 | To notepad | |||
| C2 | Capacitor | 1000 pF | 1 | To notepad | |||
| R1-R3 | Resistor | 330 kOhm | 1 | To notepad | |||
| R4 | Resistor | 10 kOhm | 1 | To notepad | |||
| dynamic head | GD 0.1...0.5Watt 8 Ohm | 1 | To notepad | ||||
| GB1 | Battery | 4.5-9V | 1 | To notepad | |||
| flasher | |||||||
| VT1, VT2 | bipolar transistor | ||||||
When studying electronics, the question arises how to read electrical circuits. The natural desire of a novice electronics engineer or radio amateur is to solder some interesting electronic device. However, on the initial path, sufficient theoretical knowledge and practical skills, as always, are not enough. Therefore, the device is assembled blindly. And it often happens that a soldered device, on which a lot of time, effort and patience was spent, does not work, which only causes disappointment and discourages a novice radio amateur from doing electronics, without feeling all the delights of this science. Although, as it turns out, the scheme did not work due to the assumption of a trifling error. It would take less than a minute for a more experienced radio amateur to correct such an error.
This article provides useful tips to help you minimize errors. They will help a novice radio amateur to assemble various electronic devices that will work the first time.
Any radio-electronic equipment consists of separate radio components soldered (connected) to each other in a certain way. All radio components, their connections and additional designations are displayed on a special drawing. Such a drawing is called an electrical circuit. Each radio component has its own designation, which is correctly called conditional graphic designation, abbreviated - UGO. We will return to UGO later in this article.
In principle, two stages of improving the reading of electrical circuits can be distinguished. The first stage is typical for assemblers of radio-electronic equipment. They simply assemble (solder) devices without delving into the purpose and principle of operation of its main components. In fact, this is a boring job, although soldering is good, you still need to learn. Personally, I'm much more interested in soldering something that I fully understand how it works. There are many options for maneuvers. You understand which denomination, for example, or critical in this case, and which one can be neglected and replaced by another. Which transistor can be replaced with an analogue, and where should only a transistor of the specified series be used. Therefore, the second stage is closer to me personally.
The second stage is inherent in the developers of electronic equipment. This stage is the most interesting and creative, since it is possible to improve in the development of electronic circuits endlessly.
Entire volumes of books have been written in this direction, the most famous of which is The Art of Circuitry. It is to this stage that we will strive to approach. However, deep theoretical knowledge is already required here, but it's all worth it.
Designation of power supplies
Any electronic device is able to perform its functions only in the presence of electricity. Basically, there are two types of power sources: direct and alternating current. This article deals exclusively with sources. These include batteries or galvanic cells, rechargeable batteries, various kinds of power supplies, etc.
There are thousands of thousands of different batteries, galvanic cells, etc. in the world, which differ as appearance, as well as by design. However, they all have one thing in common functional purpose- supply electronic equipment with direct current. Therefore, in the drawings of electrical circuits, the sources are designated uniformly, but still with some slight differences.
It is customary to draw electrical circuits from left to right, that is, in the same way as writing text. However, this rule is not always followed, especially by radio amateurs. But, nevertheless, such a rule should be adopted and applied in the future.
A galvanic cell or one battery, no matter "finger", "little" or tablet type, is indicated as follows: two parallel lines of different lengths. A longer dash indicates a positive pole - plus "+", and a short one - minus "-".
Also, for greater clarity, signs of the polarity of the battery can be affixed. A galvanic cell or battery has a standard letter designation G.
However, radio amateurs do not always adhere to such encryption and often instead of G write a letter E, which indicates that this galvanic cell is a source of electromotive force (EMF). Also, the EMF value can be indicated nearby, for example, 1.5 V.
Sometimes, instead of the image of the power source, only its terminals are shown.
A group of galvanic cells that can be repeatedly recharged, battery. In the drawings of electrical circuits, they are indicated in the same way. Only between parallel lines is a dotted line and letter designation is applied GB. The second letter just means "battery".
Designation of wires and their connections in the diagrams
Electrical wires perform the function of combining all electronic elements into a single circuit. They act as a "pipeline" - they supply electronic components with electrons. Wires are characterized by many parameters: cross section, material, insulation, etc. We will deal with mounting flexible wires.
On the printed circuit boards conductors are conductive paths. Regardless of the type of conductor (wire or track), in the drawings of electrical circuits they are designated in the same way - a straight line.
For example, in order to light an incandescent lamp, it is necessary to supply voltage from the battery with the help of connecting wires to the light bulb. Then the circuit will be closed and a current will begin to flow in it, which will cause the filament of the incandescent lamp to heat up to glow.
The conductor should be denoted by a straight line: horizontal or vertical. According to the standard, wires or current-carrying tracks can be drawn at an angle of 90 or 135 degrees.
In branched circuits, conductors often cross. If this does not form an electrical connection, then the point at the intersection is not set.
Common wire designation
In complex electrical circuits, in order to improve the readability of the circuit, the conductors connected to the negative terminal of the power source are often not depicted. And instead of them, signs are used that indicate the negative wire, which is also called general th or weight or chassis or h earth.
Next to the ground sign, often, especially in English-language diagrams, the inscription GND is made, short for GRAUND - Earth.
However, you should know that the common wire does not have to be negative, it can also be positive. Especially often it was taken as a positive common wire in old Soviet circuits, in which transistors were mainly used p— n— p structures.
Therefore, when they say that the potential at some point in the circuit is equal to some voltage, this means that the voltage between the specified point and the “minus” of the power supply is equal to the corresponding value.
For example, if the voltage at point 1 is 8 V, and at point 2 it is 4 V, then you need to install the positive probe of the voltmeter at the corresponding point, and the negative probe to the common wire or negative terminal.
This approach is quite often used, since it is very convenient from a practical point of view, since it is enough to specify only one point.
This is especially often used when setting up or adjusting electronic equipment. Therefore, learning to read electrical circuits is much easier, using the potentials at specific points.
Conditional graphic designation of radio components
Radio components form the basis of any electronic device. These include LEDs, transistors, various microcircuits, etc. To learn how to read electrical circuits, you need to know well the graphic symbols of all radio components.
For example, consider the following drawing. It consists of a battery of galvanic cells GB1 , resistor R1 and LED VD1 . The conditional graphic designation (UGO) of the resistor has the form of a rectangle with two leads. In the drawings, it is indicated by the letter R, after which its serial number is placed, for example R1 , R2 , R5 etc.
Since an important resistor parameter, in addition to resistance, is , its value is also indicated in the designation.
The UGO of the LED has the form of a triangle with a risk at its top; and two arrows, the tips of which are directed from the triangle. One end of the LED is called the anode and the other is called the cathode.
An LED, like a "normal" diode, passes current in only one direction - from the anode to the cathode. This semiconductor device is designated VD, and its type is indicated in the specification or in the description of the scheme. The characteristics of a particular type of LED are given in reference books or "datasheets".
How to read electrical schematics for real
Let's go back to the simplest circuit, consisting of a battery of galvanic cells GB1 , resistor R1 and LED VD1 .
As we can see, the circuit is closed. Therefore, an electric current flows through it. I, which has same value because all elements are connected in series. Direction electric current I from the positive terminal GB1 through a resistor R1 , Light-emitting diode VD1 to the negative terminal.
The purpose of all elements is quite clear. The end goal is for the LED to glow. However, so that it does not overheat and fail, the resistor limits the amount of current.
The voltage value, according to the second law of Kirchhoff, on all elements may differ and depends on the resistance of the resistor R1 and LED VD1 .
If you measure the voltage across R1 And VD1 , and then add the obtained values, then their sum will be equal to the voltage on GB1 : V1 = V2 + V3 .
Let's assemble a real device according to this drawing.
Adding radio components
Consider the following circuit, consisting of four parallel branches. The first is just a battery. GB1, voltage 4.5 V. Normally closed contacts are connected in series in the second branch K1.1 electromagnetic relay K1 , resistor R1 and LED VD1 . Next in the drawing is the button SB1 .
The third parallel branch consists of an electromagnetic relay K1 shunted in the reverse direction by a diode VD2 .
The fourth branch has normally open contacts K1.2 and boozer BA1 .
There are elements here that we have not previously considered in this article: SB1 - This is a button without fixing the position. As long as it is pressed down, the contacts are closed. But as soon as we stop pressing and remove our finger from the button, the contacts will open. Such buttons are also called clock buttons.
The next element is an electromagnetic relay K1 . Its principle of operation is as follows. When voltage is applied to the coil, its open contacts close and closed contacts open.
All contacts that match the relay K1 , denoted K1.1 , K1.2 etc. The first digit means that they belong to the corresponding relay.
Boozer
FROM The next element, previously unknown to us, is the boozer. Boozer to some extent can be compared with a small speaker. When an alternating voltage is applied to its outputs, a sound of the corresponding frequency is heard. However, there is no AC voltage in our circuit. Therefore, we will use an active booster, which has a built-in alternator.
Passive Boozer - for AC .
Active Boozer - for direct current.
An active booster has a polarity, so you should stick to it.
Now we can already consider how to read the electrical circuit as a whole.
In the original state of the contacts K1.1 are in a closed position. Therefore, the current flows through the circuit from GB1 across K1.1 , R1 , VD1 and goes back to GB1 .
When you press a button SB1 its contacts are closed, and a path is created for the flow of current through the coil K1 . When the relay is energized, its normally closed contacts K1.1 open, and normally closed contacts K1.2 close. As a result, the LED turns off. VD1 and the boomer sound BA1 .
Now back to the parameters of the electromagnetic relay K1 . The specification or drawing must indicate the series of relays used, for example HLS‑4078‑ DC5 V. Such a relay is designed for a rated operating voltage of 5 V. However, GB1 = 4.5 V, but the relay has some allowable operating range, so it will work well at a voltage of 4.5 V.
To select a booster, it is often enough to know only its voltage, but sometimes you need to know the current as well. You should also not forget about its type - passive or active.
Diode VD2 series 1 N4148 designed to protect the elements that open the circuit from overvoltage. IN this case you can do without it, because the circuit opens the button SB1 . But if it is opened by a transistor or thyristor, then VD2 must be installed.
Learning to read circuits with transistors
In this drawing we see VT1 and engine M1 . For definiteness, we will use a transistor of the type 2 N2222 , which works in .
In order for the transistor to open, it is necessary to apply a positive potential to its base relative to the emitter - for n— p— n type; for p— n— p type, you need to apply a negative potential relative to the emitter.
Button SA1 latching, that is, it retains its position after being pressed. Engine M1 direct current.
In the initial state, the circuit is open by contacts SA1 . When you press a button SA1 multiple paths for current to flow. The first way - "+" GB1 - contacts SA1 - resistor R1 - transistor base-emitter junction VT1 – «-» GB1 . Under the action of the current flowing through the base-emitter junction, the transistor opens and a second current path is formed - “+” GB1 – SA1 - relay coil K1 – collector-emitter VT1 – «-» GB1 .
Once powered, the relay K1 closes its open contacts K1.1 in the engine circuit M1 . Thus, a third path is created: "+" GB1 – SA1 – K1.1 – M1 – «-» GB1 .
Now let's summarize everything. In order to learn how to read electrical circuits, at first it is enough to clearly understand the laws of Kirchhoff, Ohm, electromagnetic induction; ways of connecting resistors, capacitors; you should also know the purpose of all elements. Also, at first, you should collect those devices for which there are maximum detailed descriptions assignment of individual components and assemblies.
To understand the general approach to the development of electronic devices according to drawings, with many practical and illustrative examples, my very useful course for beginners will help. After completing this course, you will immediately feel that you have moved from a beginner to a new level.
Several schemes are given simple devices and nodes that can be made by novice radio amateurs.
Single stage AF amplifier
This simplest design, which allows you to demonstrate the amplifying capabilities of the transistor True, the voltage gain is small - it does not exceed 6, so the scope of such a device is limited.
Nevertheless, it can be connected to, say, a detector radio (it must be loaded with a 10 kΩ resistor) and, using the BF1 headphone, listen to the transmission of a local radio station.
The amplified signal is fed to the input sockets X1, X2, and the supply voltage (as in all other designs of this author, it is 6 V - four galvanic cells with a voltage of 1.5 V connected in series) is fed to the X3, X4 sockets.
Divider R1R2 sets the bias voltage at the base of the transistor, and resistor R3 provides current feedback, which contributes to the temperature stabilization of the amplifier.
Rice. 1. Scheme of a single-stage AF amplifier on a transistor.
How does stabilization take place? Suppose that under the influence of temperature, the collector current of the transistor has increased. Accordingly, the voltage drop across the resistor R3 will increase. As a result, the emitter current will decrease, and hence the collector current - it will reach its original value.
The load of the amplifying stage is a headphone with a resistance of 60 .. 100 Ohms. It is not difficult to check the operation of the amplifier, you need to touch the X1 input jack, for example, a weak buzz should be heard with tweezers in the phone, as a result of alternating current pickup. The collector current of the transistor is about 3 mA.
Two-stage ultrasonic frequency converter on transistors of different structures
It is designed with direct coupling between stages and deep negative DC feedback, which makes its mode independent of temperature. environment. The basis of temperature stabilization is the resistor R4, which works similarly to the resistor R3 in the previous design.
The amplifier is more "sensitive" compared to a single-stage one - the voltage gain reaches 20. An alternating voltage with an amplitude of no more than 30 mV can be applied to the input jacks, otherwise there will be distortion heard in the headphone.
They check the amplifier by touching the X1 input jack with tweezers (or just a finger) - a loud sound will be heard in the phone. The amplifier consumes a current of about 8 mA.
Rice. 2. Scheme of a two-stage AF amplifier on transistors of different structures.
This design can be used to amplify weak signals such as from a microphone. And of course, it will significantly amplify the signal 34 taken from the load of the detector receiver.
Two-stage ultrasonic frequency converter on transistors of the same structure
Here, a direct connection between the cascades is also used, but the stabilization of the operating mode is somewhat different from previous designs.
Assume that the collector current of the transistor VT1 has decreased. The voltage drop across this transistor will increase, which will lead to an increase in the voltage across the resistor R3 included in the emitter circuit of the transistor VT2.
Due to the connection of the transistors through the resistor R2, the base current of the input transistor will increase, which will lead to an increase in its collector current. As a result, the initial change in the collector current of this transistor will be compensated.
Rice. 3. Scheme of a two-stage AF amplifier on transistors of the same structure.
The sensitivity of the amplifier is very high - the gain reaches 100. The gain is highly dependent on the capacitance of the capacitor C2 - if you turn it off, the gain will decrease. The input voltage should be no more than 2 mV.
The amplifier works well with a detector receiver, an electret microphone, and other weak signal sources. The current consumed by the amplifier is about 2 mA.
It is made on transistors of different structures and has a voltage gain of about 10. The highest input voltage can be 0.1 V.
The first two-stage amplifier is assembled on a VT1 transistor, the second - on VT2 and VTZ of different structures. The first stage amplifies signal 34 in terms of voltage, and both half-waves are the same. The second one amplifies the current signal, but the cascade on the VT2 transistor “works” with positive half-waves, and on the VТЗ transistor - with negative ones.
Rice. 4. Push-pull AF power amplifier on transistors.
The DC mode is chosen so that the voltage at the junction point of the emitters of the transistors of the second stage is approximately half the voltage of the power source.
This is achieved by turning on the feedback resistor R2. The collector current of the input transistor, flowing through the diode VD1, leads to a voltage drop across it. which is the bias voltage at the bases of the output transistors (relative to their emitters) - it allows you to reduce the distortion of the amplified signal.
The load (several parallel-connected headphones or a dynamic head) is connected to the amplifier through an oxide capacitor C2.
If the amplifier will work on a dynamic head (with a resistance of 8 -.10 ohms), the capacitance of this capacitor should be at least twice as large , but with a lower load output.
This is the so-called voltage boost circuit, in which a small positive feedback voltage is supplied to the base circuit of the output transistors, which equalizes the operating conditions of the transistors.
Two-level voltage indicator
Such a device can be used. for example, to indicate the “depletion” of the battery or to indicate the level of the reproduced signal in a household tape recorder. The layout of the indicator will allow you to demonstrate the principle of its operation.
Rice. 5. Scheme of a two-level voltage indicator.
In the lower position of the variable resistor R1 engine according to the diagram, both transistors are closed, the LEDs HL1, HL2 are off. When moving the slider of the resistor up, the voltage across it increases. When it reaches the opening voltage of the transistor VT1, the HL1 LED will flash
If you continue to move the engine. there will come a moment when, after the diode VD1, the transistor VT2 opens. The HL2 LED will also flash. In other words, a low voltage at the input of the indicator causes only the HL1 LED to glow, and more than both LEDs.
By smoothly reducing the input voltage with a variable resistor, we note that the HL2 LED goes out first, and then HL1. The brightness of the LEDs depends on the limiting resistors R3 and R6 as their resistances increase, the brightness decreases.
To connect the indicator to a real device, you need to disconnect the top terminal of the variable resistor from the positive wire of the power source and apply a controlled voltage to the extreme terminals of this resistor. By moving its engine, the threshold of the indicator is selected.
When monitoring only the voltage of the power source, it is permissible to install the AL307G green LED in place of HL2.
It gives out light signals according to the principle less than the norm - the norm - more than the norm. To do this, the indicator uses two red LEDs and one green LED.
Rice. 6. Three-level voltage indicator.
At a certain voltage on the engine of the variable resistor R1 (the voltage is normal), both transistors are closed and only the green LED HL3 (works). Moving the resistor slider up the circuit leads to an increase in voltage (more than normal), the transistor VT1 opens on it.
LED HL3 goes out, and HL1 lights up. If the engine is moved down and thus the voltage on it is reduced ('less than normal'), the transistor VT1 will close, and VT2 will open. The following picture will be observed: first, the HL1 LED will go out, then it will light up and soon HL3 will go out, and finally HL2 will flash.
Due to the low sensitivity of the indicator, a smooth transition is obtained from the extinction of one LED to the ignition of the other, for example, HL1 has not yet completely gone out, but HL3 is already on.
Schmitt trigger
As you know, this device is usually used to convert a slowly changing voltage into a rectangular signal. When the engine of the variable resistor R1 is in the lower position according to the circuit, the transistor VT1 is closed.
The voltage on its collector is high, as a result, the transistor VT2 is open, which means that the HL1 LED is lit. A voltage drop forms on the resistor R3.
Rice. 7. Simple Schmitt trigger on two transistors.
By slowly moving the variable resistor slider up the circuit, it will be possible to reach the moment when the transistor VT1 suddenly opens and VT2 closes. This will happen when the voltage on the base of VT1 exceeds the voltage drop across the resistor R3.
The LED will turn off. If after that you move the slider down, the trigger will return to its original position - the LED will flash. This will happen when the voltage on the slider is less than the LED off voltage.
Waiting multivibrator
Such a device has one stable state and switches to another only when an input signal is applied. In this case, the multivibrator generates an impulse of its duration, regardless of the duration of the input. We will verify this by conducting an experiment with the layout of the proposed device.
Rice. 8. circuit diagram waiting multivibrator.
In the initial state, the transistor VT2 is open, the LED HL1 is lit. Now it is enough to briefly close the sockets X1 and X2 so that the current pulse through the capacitor C1 opens the transistor VT1. The voltage on its collector will decrease and the capacitor C2 will be connected to the base of the transistor VT2 in such polarity that it will close. The LED will turn off.
The capacitor starts to discharge, the discharge current will flow through the resistor R5, keeping the transistor VT2 in the closed state. As soon as the capacitor is discharged, the transistor VT2 will open again and the multivibrator will go back to standby mode.
The duration of the pulse generated by the multivibrator (the duration of being in an unstable state) does not depend on the duration of the trigger, but is determined by the resistance of the resistor R5 and the capacitance of the capacitor C2.
If you connect a capacitor of the same capacity in parallel with C2, the LED will remain off twice as long.
I. Bokomchev. R-06-2000.
