RADIO signal:
MULTIVIBRATOR-1
Just a theory or a simple theory
“MULTI” - a lot, “VIBRATO” - vibration, oscillation, therefore, “MULTIVIBRATOR” is a device that creates (generates) many, many vibrations.
Let us first understand how it creates vibrations, or how vibrations arise in it, and only then we will find out why there are many of them.
2. HOW TO CREATE A MULTIVIBRATOR?
Step #1. Let's take the simplest low-frequency amplifier (see my article “Transistor”, item 4 on the “Radio Components” page): 
(Here I do not describe its operating principle.)
Step #2. Let's combine two identical amplifiers so that we get a two-stage ULF: 
Step #3. Let's connect the output of this amplifier to its input: 
A so-called positive feedback (POF) will arise. You've probably heard the whistling sound that speakers made if the person with the microphone got too close to them. The same thing happens with the music center in karaoke mode if you bring the microphone to the speakers. In any such case, the signal from the output of the amplifier arrives at its own input, the amplifier enters the self-excitation mode and turns into a self-oscillator, and sound appears. Sometimes the amplifier can self-excite even at ultrasonic frequencies. In short, when making amplifiers, PIC is harmful and you have to fight it in every possible way, but that’s a slightly different story.
Let's return to our amplifier covered by PIC, i.e. MULTIVIBRATOR! Yes, it's already him! True, to depict exactly multivibrator accepted as in Fig. on right. By the way, there are a sufficient number of “perverts” on the Internet who draw this diagram both upside down and lying on its side. Why is this? Probably, as in the joke, “to be different.” Or in s share, or (there is such a Russian word!) in s show off.
The multivibrator can be assembled using n-p-n or p-n-p transistors: 
You can evaluate the operation of the multivibrator by ear or visually. In the first case, the load should be a sound emitter, in the second - a light bulb or LED: 
If low-impedance speakers are used, an output transformer or an additional amplifier stage will be required: 
The load can be included in both arms of the multivibrator: 
In the case of using LEDs, it is advisable to include additional resistors, the role of which is played, in this case, by R1 and R4.
3. HOW DOES A MULTIVIBRATOR WORK?
At the moment the power is turned on, the transistors of both arms of the multivibrator open, since positive (negative - hereinafter in parentheses for p-n-p transistors) bias voltages are applied to their bases through the corresponding resistors R2 and R3. At the same time, the coupling capacitors begin to charge: C1 - through the emitter junction of transistor VT2 and resistor R1; C2 - through the emitter junction of transistor V1 and resistor R4. These capacitor charging circuits, being voltage dividers of the power source, create at the bases of the transistors (relative to the emitters) positive (negative) voltages that are increasingly increasing in value, tending to open the transistors more and more. Turning on a transistor causes the positive (negative) voltage at its collector to decrease, which causes the positive (negative) voltage at the base of the other transistor to decrease, turning it off. This process occurs in both transistors at once, but only one of them closes, on the basis of which there is a higher negative (positive) voltage, for example, due to the difference in current transfer coefficients h21e (see my article “Transistor”, paragraph 4 on page “Radio components”), resistor and capacitor values, since even when selecting identical pairs, the parameters of the elements will still be slightly different. The second transistor remains open. But these states of transistors are unstable, because electrical processes in their circuits continue. Let's assume that some time after turning on the power, transistor V2 turned out to be closed, and transistor V1 turned out to be open. From this moment, capacitor C1 begins to discharge through open transistor V1, the resistance of the emitter-collector section of which is low at this time, and resistor R2. As capacitor C1 discharges, the negative (positive) voltage at the base of the closed transistor V2 decreases. As soon as the capacitor is completely discharged and the voltage at the base of transistor V2 becomes close to zero, a current appears in the collector circuit of this now opening transistor, which acts through capacitor C2 on the base of transistor V1 and lowers the positive (negative) voltage on it. As a result, the current flowing through transistor V1 begins to decrease, and through transistor V2, on the contrary, increases. This causes transistor V1 to turn off and transistor V2 to open. Now capacitor C2 will begin to discharge, but through the open transistor V2 and resistor R3, which ultimately leads to the opening of the first and closing of the second transistors, etc. The transistors interact all the time, causing the multivibrator to generate electrical oscillations.
The operation of the multivibrator is illustrated by graphs of the voltages Ube and Uk of one and the second transistor: 
As you can see, the multivibrator generates practically “rectangular” oscillations. Some violation of the rectangular shape is associated with transient processes at the moments when the transistors are turned on. From here it is clear that the signal can be “removed” from any transistor. It’s just that it’s most common to depict it exactly as shown above.
In practice, we can consider the oscillation shape of a multivibrator to be “purely rectangular”: 
On the one hand, the multivibrator waveform seems to be quite simple. But it is not so. More precisely, not like that at all. The simplest waveform is a sine wave: 
If the generator creates ideal sinusoidal signal, then it corresponds strictly one a certain oscillation frequency. The more the signal shape differs from a sinusoid, the more frequencies that are multiples of the fundamental frequency are present in the signal spectrum. And the multivibrator signal shape is quite far from a sinusoid. Therefore, if, for example, the frequency of its oscillations is 1000 Hz, then the spectrum will contain frequencies of 2000 Hz, and 3000 Hz, and 4000 Hz... etc. true amplitudes of these harmonics will be significantly less than the main signal. But they will! That's why this generator is called MULTI vibrator.
The oscillation frequency of the multivibrator depends both on the capacitance of the coupling capacitors and on the resistance of the base resistors. If the conditions are met in the multivibrator: R1=R4, R2=R3, R1
The approximate oscillation frequency of a symmetrical multivibrator can be calculated using a simplified formula:
, where f is the frequency in Hz, R is the resistance of the base resistor in kOhm, C is the capacitance of the coupling capacitor in μF.
4. CHANGE OF FREQUENCY and more
As noted above, the frequency of the pulses generated by the multivibrator is determined by the values of the coupling capacitors and base resistors. From the above formula it can be seen that an increase in the capacitance of the capacitors and/or an increase in the resistance of the base resistors leads to a decrease in the frequency of the multivibrator and, accordingly, vice versa. Of course, it is possible to solder capacitors of different capacities or resistors of different resistances, but only at the experimental stage. The frequency is quickly changed using a variable resistor R5 in the base circuits: 
The shape of the oscillation graph of a multivibrator is called a “meander”: 
The time from the beginning of one pulse to the beginning of another - period T - consists of:
tи – pulse duration and tп – pause duration.
The ratio S=T/ti is called duty cycle. For a symmetrical multivibrator S=2.
The reciprocal of the duty cycle is called the duty cycle D=1/S. For a symmetrical multivibrator D=0.5.
The multivibrator, the circuit of which is shown below, produces rectangular pulses. The frequency of their repetition can be varied within wide limits, while the duty cycle of the pulses remains unchanged.
The operation of the multivibrator is different in that at times when transistor VT1 is closed, capacitor C2 is discharged through a chain consisting of diode VD3 and resistor R4, as well as through resistor R3. Similarly, when transistor VT2 is closed, capacitor C1 is discharged through diode VD2 and resistors R4 and R5.
The pulse repetition rate can be adjusted within wide limits by changing only the resistance of resistor R4.
A multivibrator with the details shown in the diagram generates pulses with a repetition frequency from 140 to 1400 Hz.
In the multivibrator, you can use diodes D2V-D2I, D9V-D9L, and any low-power transistors with an n-p-n or p-n-p structure. When using transistors with a pnp structure, the switching polarity of all diodes and the power supply must be reversed.
If you slightly change the connection of resistor R7, then it swells multivibrator with variable duty cycle pulses: 
Depending on the position of the resistor R7 slider, this multivibrator becomes asymmetrical, and the graph of its oscillations can be, for example, like this: 
In one and the other case, the ratio T/ti changes - the duty cycle changes.
It is also clear, I hope, that the duty cycle can be roughly changed by installing capacitors of different capacities.
5. ASSYMMETRICAL MULTIVIBRATOR on transistors of different conductivities:
An asymmetrical multivibrator consists of an amplifier stage on two transistors, the output of which (the collector of transistor VT2) is connected to the input (the base of transistor VT1) through capacitor C1. The load is resistor R2, from which the signal is removed (an LED, an incandescent light bulb or a speaker can be turned on instead). Direct conduction transistor VT1 (p-n-p type) opens when a potential negative relative to the emitter is applied to the base. Transistor VT2 of reverse conductivity (n-p-n type), opens when a potential positive relative to the emitter is applied to the base. 
When turned on, capacitor C1 is charged through resistors R2 and R1, and the base potential decreases. When a negative potential arises at the base of VT1, transistor VT1 opens and the collector-emitter resistance drops. The base of transistor VT2 turns out to be connected to the positive pole of the source, transistor VT2 also opens, and the collector current increases. As a result, current flows through R2, capacitor C1 is discharged through resistor R1 and transistor VT2. The base potential of VT1 increases, transistor VT1 closes, causing transistor VT2 to close. After this, capacitor C1 is charged again, then discharged, etc. The frequency of the generated pulses is inversely proportional to the charging time of the capacitor T ~ R1×C. As the supply voltage increases, the capacitor charges faster, and the frequency of the generated pulses increases. As the resistance of resistor R1 or the capacitance of capacitor C1 increases, the oscillation frequency decreases.
In reality, the frequency is changed, for example, like this: 
6. STANDBY MULTIVIBRATOR
Such a multivibrator generates current (or voltage) pulses when triggering signals are applied to its input from another source, for example, from a self-oscillating multivibrator. To turn a self-oscillating multivibrator into a waiting multivibrator (see the diagram from point 3), you need to do the following: remove capacitor C2, and instead connect resistor R3 between the collector of transistor VT2 and the base of transistor VT1; between the base of transistor VT1 and the grounded conductor, connect a series-connected 1.5 V element and a resistor with resistance R5, but so that the positive pole of the element is connected to the base (via R5); connect capacitor C2 to the base circuit of transistor VT1, the second terminal of which will act as a contact input control signal. The initial state of transistor VT1 of such a multivibrator is closed, transistor VT2 is open. The voltage on the collector of the closed transistor should be close to the voltage of the power source, and on the collector of the open transistor - should not exceed 0.2 - 0.3 V. Include a milliammeter (for a current of 10-15 mA) in the collector circuit of transistor V1 and, observing it arrow, switch between contact UPR signal and with a grounded conductor, literally for a moment, one or two AAA elements connected in series (in the GB1 diagram). WARNING: The negative pole of this external electrical signal must be connected to the contact UPR signal. In this case, the milliammeter needle should immediately deviate to the value of the highest current in the transistor’s collector circuit, freeze for a while, and then return to its original position to wait for the next signal. If you repeat this experiment several times, then the milliammeter with each signal will show an instantaneous increase to 8 - 10 mA and after some time, the collector current of transistor VT1 also instantly decreases almost to zero. These are single current pulses generated by a multivibrator. Even if the GB1 battery is kept connected to the clamp longer UPR signal, the same thing will happen - only one pulse will appear at the output of the multivibrator. 
If you touch the terminal of the base of transistor VT1 with any metal object taken in your hand, then perhaps in this case the waiting multivibrator will work - from the electrostatic charge of the body. You can connect a milliammeter to the collector circuit of transistor VT2. When a control signal is applied, the collector current of this transistor should sharply decrease to almost zero, and then just as sharply increase to the value of the open transistor current. This is also a current pulse, but negative polarity.
What is the operating principle of a standby multivibrator? In such a multivibrator, the connection between the collector of transistor VT2 and the base of transistor VT1 is not capacitive, as in a self-oscillating one, but resistive - through resistor R3. A negative bias voltage that opens it is supplied to the base of transistor VT2 through resistor R2. Transistor VT1 is reliably closed by the positive voltage of element G1 at its base. This state of transistors is very stable. VT1 can remain in this state for any amount of time. When a voltage pulse of negative polarity appears at the base of transistor VT1, the transistors go into an unstable state. Under the influence of the input signal, transistor VT1 opens, and the changing voltage on its collector through capacitor C1 closes transistor VT2. The transistors remain in this state until capacitor C1 is discharged (through resistor R2 and open transistor VT1, the resistance of which is low at this time). As soon as the capacitor is discharged, transistor VT2 will immediately open, and transistor VT1 will close. From this moment on, the multivibrator is again in its original, stable standby mode. Thus, the waiting multivibrator has one stable And one unstable state.
During an unstable state it generates one square pulse
current (voltage), the duration of which depends on the capacitance of capacitor C1. The larger the capacitance of this capacitor, the longer the pulse duration. So, for example, with a capacitor capacity of 50 µF, the multivibrator generates a current pulse lasting about 1.5 s, and with a capacitor with a capacity of 150 µF - three times more. Through additional capacitors, positive voltage pulses can be removed from output 1, and negative ones from output 2. Is it only with a negative voltage pulse applied to the base of transistor VT1 that the multivibrator can be brought out of standby mode? No, not only. This can also be done by applying a voltage pulse of positive polarity, but to the base of transistor VT2.
How can you practically use a standby multivibrator? Differently. For example, to convert sinusoidal voltage into rectangular voltage (or current) pulses of the same frequency, or to turn on another device for some time by applying a short-term electrical signal to the input of a waiting multivibrator.
An example of using a waiting multivibrator is a maximum speed indicator.
When running in a new car, the engine speed should not exceed for a certain time the maximum permissible value recommended by the manufacturer.
To control the engine speed, you can use a device assembled according to the diagram given here. An incandescent lamp is used as an indicator of the maximum engine speed. 
The main parts of the tachometer are a standby multivibrator on transistors T1 and T2 and a Schmitt trigger on transistors T5 and T6. The input signal coming from the breaker is fed to the differentiating chain R4C1 (this is necessary to obtain pulses of the same duration). Further signal formation is performed by the multivibrator. Diode D1 does not transmit negative half-waves of the input signal to the base of transistor T2. The pulses generated by the multivibrator are fed to the Schmitt trigger through an emitter follower made on transistor T3 and an integrating circuit R7C3. Indicator lamp L1, connected to the emitter circuit of transistor T6, lights up only when the engine speed exceeds a preset one (using variable resistor R8).
The finished device can be calibrated using a standard tachometer or a sound generator. So, for example, for a four-stroke four-cylinder engine, 1500 rpm corresponds to a sound generator frequency of 60 Hz, 3000 rpm - 100 Hz, 6000 rpm - 200 Hz, and so on.
When using parts with the data indicated in the diagram, the tachometer allows you to register from 500 to 10,000 rpm. Current consumption - 20 mA.
Transistors BC107 can be replaced with KT315 with any letter index. Any silicon diode can be used as diode D1. The use of germanium transistors and diodes is not recommended due to the severe temperature conditions.
7. MULTIPHASE MULTIVIBRATORS
are obtained by adding amplification stages and PICs.
Three-phase multivibrator: 
Example from the site http://www.votshema.ru/324-simmetrichnyy-multivibrator.html
A four-phase multivibrator requires special measures to ensure stable operation: 
Example from the site http://www.moyashkola.net/krugok/r_begog.htm
8. MULTIVIBRATORS ON LOGIC ELEMENTS
The multivibrator can be made using logical elements, for example, NAND. A diagram of a possible option, for example, is as follows: 
The function of the active elements here is performed by 2I-NOT logic elements (see my article “CHICROCIRCUIT” on page “RADIO components”), connected by inverters. Thanks to the PIC between the output DD1.2 and the input DD1.1, as well as the output DD1.1 and the input DD1.2, created by capacitors C1 and C2, the device is excited and generates electrical pulses. The pulse repetition rate depends on the values of capacitors and resistors R1 and R2. By reducing the capacitance of the capacitors to 1...5 µF we obtain an audio frequency of 500...1000 Hz. The headphone must be connected to one of the outputs of the multivibrator through a capacitor with a capacity of 0.01...0.015 μF.
Sometimes the same multivibrator is depicted like this: 
The multivibrator can be made on three logical elements: 
All elements are switched on by inverters and connected in series. The timing chain is formed by C1 and R1. An incandescent light bulb can be used as an indicator. To smoothly change the frequency, instead of R1, you should include a 1.5 kOhm variable resistor. 
If the capacitance of the capacitor is 1 µF, then the oscillation frequency will become sound.
How does such a multivibrator work? After switching on, one of the logical elements will be the first to take one of the possible states and thereby affect the state of other elements. Let it be element DD1.2, which turns out to be in a single state. Through elements DD1.1 and DD1.2, the capacitor is instantly charged, and element DD1.1 is in the zero state. The DD1.3 element finds itself in the same state, since its input is logical 1. This state is unstable, because the output of DD1.3 is logical 0, and the capacitor begins to discharge through the resistor and the output stage of the DD1.3 element. As the discharge progresses, the positive voltage at the input of element DD1.1 decreases. As soon as it becomes equal to the threshold, this element will switch to the single state, and the DD1.2 element will switch to the zero state. The capacitor will begin to charge through element DD1.3 (its output is now at logical level 1), a resistor and element DD1.2. Soon the voltage at the input of the first element will exceed the threshold, and all elements will switch to opposite states. This is how electrical pulses are formed at the output of the multivibrator - at the inverse output of element DD1.3.
The “three-element” multivibrator can be simplified by removing DD1.3 from it: 
It works similarly to the previous one. It is this kind of multivibrator that is most often used in various radio-electronic devices.
You can also make a waiting multivibrator using logic elements. Like the previous one, it is built on 2 logical elements. 
The first DD1.1 is used for its intended purpose - as a 2I-NOT element. Button SB1 acts as a trigger signal sensor. To indicate pulses, for example, an LED is used. The pulse duration can be increased by increasing the capacitance C1 and resistance R1. Instead of R1, you can turn on a variable (tuning) resistor with a resistance of about 2 kOhm (but not more than 2.2 kOhm) to change the pulse duration within certain limits. But if the resistance is less than 100 Ohms, the multivibrator will stop working.
Operating principle. At the initial moment, the lower pin of the DD1.1 element is not connected to anything - it has a logical level of 1. And for the 2I-NOT element, this is enough for it to be in the zero state. The DD1.2 input is also at a logical 0 level, since the voltage drop across the resistor created by the input current of the element keeps the input transistor of the element in the closed state. The logic 1 voltage at the output of this element maintains the first element in the zero state. When the button is pressed, a trigger pulse of negative polarity is applied to the input of the first element, which switches element DD1.1 to the single state. The positive voltage jump that occurs at this moment at its output is transmitted through a capacitor to the inputs of the second element and switches it from a single state to a zero state. This state of the elements remains even after the end of the triggering pulse. From the moment a positive pulse appears at the output of the first element, the capacitor begins to charge - through the output stage of this element and a resistor. As charging occurs, the voltage across the resistor drops. As soon as it reaches the threshold, the second element will switch to the one state, and the first to the zero state. The capacitor will quickly discharge through the output stage of the first element and the water stage of the second, and the device will be in standby mode.
It should be borne in mind that for normal operation of the multivibrator, the duration of the triggering pulse must be less than the duration of the generated one.
P.S. The topic "MULTIVIBRATOR" is an example of a creative approach to the study of electrical vibrations in a school physics course. And not only. Creating simple circuits, modeling their operation, observing and measuring electrical quantities is going far beyond the scope of ordinary school physics and computer science. And the creation of real devices completely changes the idea of young people about what and how they can STUDY at school (I hate the word “TEACH”).
A transistor multivibrator is a square wave generator. Below in the photo is one of the oscillograms of a symmetrical multivibrator.
A symmetrical multivibrator generates rectangular pulses with a duty cycle of two. You can read more about duty cycle in the article frequency generator. We will use the operating principle of a symmetrical multivibrator to alternately turn on the LEDs.
The scheme consists of:
– two KT315B (can be with any other letter)
– two capacitors with a capacity of 10 microFarads
– four, two 300 Ohm each and two 27 KiloOhm each
– two Chinese 3 Volt LEDs
This is what the device looks like on a breadboard:
And this is how it works:
To change the blinking duration of the LEDs, you can change the values of capacitors C1 and C2, or resistors R2 and R3.
There are also other types of multivibrators. You can read more about them. It also describes the operating principle of a symmetrical multivibrator.
If you are too lazy to assemble such a device, you can buy a ready-made one;-) I even found a ready-made device on Alika. You can look it up at this link.
Here is a video that describes in detail how a multivibrator works:
In this article we will talk about the multivibrator, how it works, how to connect a load to the multivibrator and the calculation of a transistor symmetrical multivibrator.
Multivibrator is a simple rectangular pulse generator that operates in self-oscillator mode. To operate it, you only need power from a battery or other power source. Let's consider the simplest symmetrical multivibrator using transistors. Its diagram is shown in the figure. The multivibrator can be more complicated depending on the necessary functions performed, but all the elements presented in the figure are mandatory, without them the multivibrator will not work.
The operation of a symmetrical multivibrator is based on the charge-discharge processes of capacitors, which together with resistors form RC circuits.
I wrote earlier about how RC circuits work in my article Capacitor, which you can read on my website. On the Internet, if you find material about a symmetrical multivibrator, it is presented briefly and not intelligibly. This circumstance does not allow novice radio amateurs to understand anything, but only helps experienced electronics engineers remember something. At the request of one of my site visitors, I decided to eliminate this gap.
At the initial moment of power supply, capacitors C1 and C2 are discharged, so their current resistance is low. The low resistance of the capacitors leads to the “fast” opening of the transistors caused by the flow of current:
— VT2 along the path (shown in red): “+ power supply > resistor R1 > low resistance of discharged C1 > base-emitter junction VT2 > — power supply”;
— VT1 along the path (shown in blue): “+ power supply > resistor R4 > low resistance of discharged C2 > base-emitter junction VT1 > — power supply.”
This is the “unsteady” mode of operation of the multivibrator. It lasts for a very short time, determined only by the speed of the transistors. And there are no two transistors that are absolutely identical in parameters. Whichever transistor opens faster will remain open—the “winner.” Let's assume that in our diagram it turns out to be VT2. Then, through the low resistance of the discharged capacitor C2 and the low resistance of the collector-emitter junction VT2, the base of the transistor VT1 will be short-circuited to the emitter VT1. As a result, transistor VT1 will be forced to close - “become defeated.”
Since transistor VT1 is closed, a “fast” charge of capacitor C1 occurs along the path: “+ power supply > resistor R1 > low resistance of discharged C1 > base-emitter junction VT2 > — power supply.” This charge occurs almost up to the voltage of the power supply.
At the same time, capacitor C2 is charged with a current of reverse polarity along the path: “+ power source > resistor R3 > low resistance of discharged C2 > collector-emitter junction VT2 > — power source.” The charge duration is determined by the ratings R3 and C2. They determine the time at which VT1 is in the closed state.
When capacitor C2 is charged to a voltage approximately equal to the voltage of 0.7-1.0 volts, its resistance will increase and transistor VT1 will open with the voltage applied along the path: “+ power supply > resistor R3 > base-emitter junction VT1 > - power supply.” In this case, the voltage of the charged capacitor C1, through the open collector-emitter junction VT1, will be applied to the emitter-base junction of transistor VT2 with reverse polarity. As a result, VT2 will close, and the current that previously passed through the open collector-emitter junction VT2 will flow through the circuit: “+ power supply > resistor R4 > low resistance C2 > base-emitter junction VT1 > — power supply.” This circuit will quickly recharge capacitor C2. From this moment, the “steady-state” self-generation mode begins.
The first half-cycle of operation (oscillation) of the multivibrator begins.
When transistor VT1 is open and VT2 is closed, as I just wrote, capacitor C2 is quickly recharged (from a voltage of 0.7...1.0 volts of one polarity, to the voltage of the power source of the opposite polarity) along the circuit: “+ power supply > resistor R4 > low resistance C2 > base-emitter junction VT1 > - power supply.” In addition, capacitor C1 is slowly recharged (from the power source voltage of one polarity to a voltage of 0.7...1.0 volts of the opposite polarity) along the circuit: “+ power source > resistor R2 > right plate C1 > left plate C1 > collector- emitter junction of transistor VT1 > - - power source.”
When, as a result of recharging C1, the voltage at the base of VT2 reaches a value of +0.6 volts relative to the emitter of VT2, the transistor will open. Therefore, the voltage of the charged capacitor C2, through the open collector-emitter junction VT2, will be applied to the emitter-base junction of the transistor VT1 with reverse polarity. VT1 will close.
The second half-cycle of operation (oscillation) of the multivibrator begins.
When transistor VT2 is open and VT1 is closed, capacitor C1 is quickly recharged (from a voltage of 0.7...1.0 volts of one polarity, to the voltage of the power source of the opposite polarity) along the circuit: “+ power supply > resistor R1 > low resistance C1 > base emitter junction VT2 > - power supply.” In addition, capacitor C2 is slowly recharged (from the voltage of the power source of one polarity, to a voltage of 0.7...1.0 volts of the opposite polarity) along the circuit: “right plate of C2 > collector-emitter junction of transistor VT2 > - power supply > + source power > resistor R3 > left plate C2". When the voltage at the base of VT1 reaches +0.6 volts relative to the emitter of VT1, the transistor will open. Therefore, the voltage of the charged capacitor C1, through the open collector-emitter junction VT1, will be applied to the emitter-base junction of transistor VT2 with reverse polarity. VT2 will close. At this point, the second half-cycle of the multivibrator oscillation ends, and the first half-cycle begins again.
The process is repeated until the multivibrator is disconnected from the power source.
Rectangular pulses are removed from two points of a symmetrical multivibrator– transistor collectors. When there is a “high” potential on one collector, then there is a “low” potential on the other collector (it is absent), and vice versa - when there is a “low” potential on one output, then there is a “high” potential on the other. This is clearly shown in the time graph below.
The multivibrator load must be connected in parallel with one of the collector resistors, but in no case in parallel with the collector-emitter transistor junction. You cannot bypass the transistor with a load. If this condition is not met, then at a minimum the duration of the pulses will change, and at a maximum the multivibrator will not work. The figure below shows how to connect the load correctly and how not to do it.
In order for the load not to affect the multivibrator itself, it must have sufficient input resistance. For this purpose, buffer transistor stages are usually used.
The example shows connecting a low-impedance dynamic head to a multivibrator. An additional resistor increases the input resistance of the buffer stage, and thereby eliminates the influence of the buffer stage on the multivibrator transistor. Its value should be no less than 10 times the value of the collector resistor. Connecting two transistors in a “composite transistor” circuit significantly increases the output current. In this case, it is correct to connect the base-emitter circuit of the buffer stage in parallel with the collector resistor of the multivibrator, and not in parallel with the collector-emitter junction of the multivibrator transistor.
For connecting a high-impedance dynamic head to a multivibrator a buffer stage is not needed. The head is connected instead of one of the collector resistors. The only condition that must be met is that the current flowing through the dynamic head must not exceed the maximum collector current of the transistor.
If you want to connect ordinary LEDs to the multivibrator– to make a “flashing light”, then buffer cascades are not required for this. They can be connected in series with collector resistors. This is due to the fact that the LED current is small, and the voltage drop across it during operation is no more than one volt. Therefore, they do not have any effect on the operation of the multivibrator. True, this does not apply to super-bright LEDs, for which the operating current is higher and the voltage drop can be from 3.5 to 10 volts. But in this case, there is a way out - increase the supply voltage and use transistors with high power, providing sufficient collector current.
Please note that oxide (electrolytic) capacitors are connected with their positives to the collectors of the transistors. This is due to the fact that on the bases of bipolar transistors the voltage does not rise above 0.7 volts relative to the emitter, and in our case the emitters are the minus of the power supply. But at the collectors of the transistors, the voltage changes almost from zero to the voltage of the power source. Oxide capacitors are not able to perform their function when connected with reverse polarity. Naturally, if you use transistors of a different structure (not N-P-N, but P-N-P structures), then in addition to changing the polarity of the power source, you need to turn the LEDs with the cathodes “up in the circuit”, and the capacitors with the pluses to the bases of the transistors.
Let's figure it out now What parameters of the multivibrator elements determine the output currents and generation frequency of the multivibrator?
What do the values of collector resistors affect? I have seen in some mediocre Internet articles that the values of collector resistors do not significantly affect the frequency of the multivibrator. This is all complete nonsense! If the multivibrator is correctly calculated, a deviation of the values of these resistors by more than five times from the calculated value will not change the frequency of the multivibrator. The main thing is that their resistance is less than the base resistors, because collector resistors provide fast charging of capacitors. But on the other hand, the values of collector resistors are the main ones for calculating the power consumption from the power source, the value of which should not exceed the power of the transistors. If you look at it, if connected correctly, they do not even have a direct effect on the output power of the multivibrator. But the duration between switchings (multivibrator frequency) is determined by the “slow” recharging of the capacitors. The recharge time is determined by the ratings of the RC circuits - base resistors and capacitors (R2C1 and R3C2).
A multivibrator, although it is called symmetrical, this refers only to the circuitry of its construction, and it can produce both symmetrical and asymmetrical output pulses in duration. The pulse duration (high level) on the VT1 collector is determined by the ratings of R3 and C2, and the pulse duration (high level) on the VT2 collector is determined by the ratings R2 and C1.
The duration of recharging capacitors is determined by a simple formula, where Tau– pulse duration in seconds, R– resistor resistance in Ohms, WITH– capacitance of the capacitor in Farads:
Thus, if you have not already forgotten what was written in this article a couple of paragraphs earlier:
If there is equality R2=R3 And C1=C2, at the outputs of the multivibrator there will be a “meander” - rectangular pulses with a duration equal to the pauses between pulses, which you see in the figure.
The full period of oscillation of the multivibrator is T equal to the sum of the pulse and pause durations:
Oscillation frequency F(Hz) related to period T(sec) through the ratio:
As a rule, if there are any calculations of radio circuits on the Internet, they are meager. That's why Let's calculate the elements of a symmetrical multivibrator using the example .
Like any transistor stages, the calculation must be carried out from the end - the output. And at the output we have a buffer stage, then there are collector resistors. Collector resistors R1 and R4 perform the function of loading the transistors. Collector resistors have no effect on the generation frequency. They are calculated based on the parameters of the selected transistors. Thus, first we calculate the collector resistors, then the base resistors, then the capacitors, and then the buffer stage.
Initial data:
Supply voltage Ui.p. = 12 V.
Required multivibrator frequency F = 0.2 Hz (T = 5 seconds), and the pulse duration is equal to 1 (one) second.
A car incandescent light bulb is used as a load. 12 volts, 15 watts.
As you guessed, we will calculate a “flashing light” that will blink once every five seconds, and the duration of the glow will be 1 second.
Selecting transistors for the multivibrator. For example, we have the most common transistors in Soviet times KT315G.
For them: Pmax=150 mW; Imax=150 mA; h21>50.
Transistors for the buffer stage are selected based on the load current.
In order not to depict the diagram twice, I have already signed the values of the elements on the diagram. Their calculation is given further in the Decision.
Solution:
1. First of all, you need to understand that operating a transistor at high currents in switching mode is safer for the transistor itself than operating in amplification mode. Therefore, there is no need to calculate the power for the transition state at the moments of passage of an alternating signal through the operating point “B” of the static mode of the transistor - the transition from the open state to the closed state and back. For pulse circuits built on bipolar transistors, the power is usually calculated for the transistors in the open state.
First, we determine the maximum power dissipation of the transistors, which should be a value 20 percent less (factor 0.8) than the maximum power of the transistor indicated in the reference book. But why do we need to drive the multivibrator into the rigid framework of high currents? And even with increased power, energy consumption from the power source will be large, but there will be little benefit. Therefore, having determined the maximum power dissipation of transistors, we will reduce it by 3 times. A further reduction in power dissipation is undesirable because the operation of a multivibrator based on bipolar transistors in low current mode is an “unstable” phenomenon. If the power source is used not only for the multivibrator, or it is not entirely stable, the frequency of the multivibrator will also “float”.
We determine the maximum power dissipation: Pdis.max = 0.8 * Pmax = 0.8 * 150 mW = 120 mW
We determine the rated dissipated power: Pdis.nom. = 120 / 3 = 40mW
2. Determine the collector current in the open state: Ik0 = Pdis.nom. / Ui.p. = 40mW / 12V = 3.3mA
Let's take it as the maximum collector current.
3. Let’s find the value of the resistance and power of the collector load: Rk.total = Ui.p./Ik0 = 12V/3.3mA = 3.6 kOhm
We select resistors from the existing nominal range that are as close as possible to 3.6 kOhm. The nominal series of resistors has a nominal value of 3.6 kOhm, so we first calculate the value of the collector resistors R1 and R4 of the multivibrator: Rк = R1 = R4 = 3.6 kOhm.
The power of the collector resistors R1 and R4 is equal to the rated power dissipation of the transistors Pras.nom. = 40 mW. We use resistors with a power exceeding the specified Pras.nom. - type MLT-0.125.
4. Let's move on to calculating the basic resistors R2 and R3. Their rating is determined based on the gain of transistors h21. At the same time, for reliable operation of the multivibrator, the resistance value must be within the range: 5 times greater than the resistance of the collector resistors, and less than the product Rк * h21. In our case Rmin = 3.6 * 5 = 18 kOhm, and Rmax = 3.6 * 50 = 180 kOhm
Thus, the values of resistance Rb (R2 and R3) can be in the range of 18...180 kOhm. We first select the average value = 100 kOhm. But it is not final, since we need to provide the required frequency of the multivibrator, and as I wrote earlier, the frequency of the multivibrator directly depends on the base resistors R2 and R3, as well as on the capacitance of the capacitors.
5. Calculate the capacitances of capacitors C1 and C2 and, if necessary, recalculate the values of R2 and R3.
The values of the capacitance of capacitor C1 and the resistance of resistor R2 determine the duration of the output pulse on the collector VT2. It is during this impulse that our light bulb should light up. And in the condition the pulse duration was set to 1 second.
Let's determine the capacitance of the capacitor: C1 = 1 sec / 100 kOhm = 10 µF
A capacitor with a capacity of 10 μF is included in the nominal range, so it suits us.
The values of the capacitance of capacitor C2 and the resistance of resistor R3 determine the duration of the output pulse on the collector VT1. It is during this pulse that there is a “pause” on the VT2 collector and our light bulb should not light up. And in the condition, a full period of 5 seconds with a pulse duration of 1 second was specified. Therefore, the duration of the pause is 5 seconds – 1 second = 4 seconds.
Having transformed the recharge duration formula, we Let's determine the capacitance of the capacitor: C2 = 4 sec / 100 kOhm = 40 μF
A capacitor with a capacity of 40 μF is not included in the nominal range, so it does not suit us, and we will take the capacitor with a capacity of 47 μF that is as close as possible to it. But as you understand, the “pause” time will also change. To prevent this from happening, we Let's recalculate the resistance of resistor R3 based on the duration of the pause and the capacitance of capacitor C2: R3 = 4sec / 47 µF = 85 kOhm
According to the nominal series, the closest value of the resistor resistance is 82 kOhm.
So, we got the values of the multivibrator elements:
R1 = 3.6 kOhm, R2 = 100 kOhm, R3 = 82 kOhm, R4 = 3.6 kOhm, C1 = 10 µF, C2 = 47 µF.
6. Calculate the value of resistor R5 of the buffer stage.
To eliminate the influence on the multivibrator, the resistance of the additional limiting resistor R5 is selected to be at least 2 times greater than the resistance of the collector resistor R4 (and in some cases more). Its resistance, together with the resistance of the emitter-base junctions VT3 and VT4, in this case will not affect the parameters of the multivibrator.
R5 = R4 * 2 = 3.6 * 2 = 7.2 kOhm
According to the nominal series, the nearest resistor is 7.5 kOhm.
With a resistor value of R5 = 7.5 kOhm, the buffer stage control current will be equal to:
Icontrol = (Ui.p. - Ube) / R5 = (12v - 1.2v) / 7.5 kOhm = 1.44 mA
In addition, as I wrote earlier, the collector load rating of the multivibrator transistors does not affect its frequency, so if you do not have such a resistor, then you can replace it with another “close” rating (5 ... 9 kOhm). It is better if this is in the direction of decrease, so that there is no drop in the control current in the buffer stage. But keep in mind that the additional resistor is an additional load for transistor VT2 of the multivibrator, so the current flowing through this resistor adds up to the current of collector resistor R4 and is a load for transistor VT2: Itotal = Ik + Icontrol. = 3.3mA + 1.44mA = 4.74mA
The total load on the collector of transistor VT2 is within normal limits. If it exceeds the maximum collector current specified in the reference book and multiplied by a factor of 0.8, increase resistance R4 until the load current is sufficiently reduced, or use a more powerful transistor.
7. We need to provide current to the light bulb Iн = Рн / Ui.p. = 15W / 12V = 1.25 A
But the control current of the buffer stage is 1.44 mA. The multivibrator current must be increased by a value equal to the ratio:
In / Icontrol = 1.25A / 0.00144A = 870 times.
How to do it? For significant output current amplification use transistor cascades built according to the “composite transistor” circuit. The first transistor is usually low-power (we will use KT361G), it has the highest gain, and the second must provide sufficient load current (let’s take the no less common KT814B). Then their transmission coefficients h21 are multiplied. So, for the KT361G transistor h21>50, and for the KT814B transistor h21=40. And the overall transmission coefficient of these transistors connected according to the “composite transistor” circuit: h21 = 50 * 40 = 2000. This figure is greater than 870, so these transistors are quite enough to control a light bulb.
Well, that's all!
Multivibrators are another form of oscillators. An oscillator is an electronic circuit that is capable of maintaining an alternating current signal at its output. It can generate square, linear or pulse signals. To oscillate, the generator must satisfy two Barkhausen conditions:
T loop gain should be slightly greater than unity.
The cycle phase shift must be 0 degrees or 360 degrees.
To satisfy both conditions, the oscillator must have some form of amplifier, and part of its output must be regenerated into the input. If the gain of the amplifier is less than one, the circuit will not oscillate, and if it is greater than one, the circuit will be overloaded and produce a distorted waveform. A simple generator can generate a sine wave, but cannot generate a square wave. A square wave can be generated using a multivibrator.
A multivibrator is a form of generator that has two stages, thanks to which we can get a way out of any of the states. These are basically two amplifier circuits arranged with regenerative feedback. In this case, none of the transistors conducts simultaneously. Only one transistor is conducting at a time, while the other is in the off state. Some circuits have certain states; the state with fast transition is called switching processes, where there is a rapid change in current and voltage. This switching is called triggering. Therefore, we can run the circuit internally or externally.
Circuits have two states.
One is the steady state, in which the circuit remains forever without any triggering.
The other state is unstable: in this state, the circuit remains for a limited period of time without any external triggering and switches to another state. Hence, the use of multivibartors is done in two state circuits such as timers and flip-flops.
It is a free-running generator that continuously switches between two unstable states. In the absence of an external signal, the transistors alternately switch from the off state to the saturation state at a frequency determined by the RC time constants of the communication circuits. If these time constants are equal (R and C are equal), then a square wave with a frequency of 1/1.4 RC will be generated. Hence, an astable multivibrator is called a pulse generator or square wave generator. The greater the value of the base load R2 and R3 relative to the collector load R1 and R4, the greater the current gain and the sharper the signal edge will be.
The basic principle of operation of an astable multivibrator is a slight change in the electrical properties or characteristics of the transistor. This difference causes one transistor to turn on faster than the other when power is first applied, causing oscillation.
Diagram Explanation
An astable multivibrator consists of two cross-coupled RC amplifiers.
The circuit has two unstable states
When V1 = LOW and V2 = HIGH then Q1 ON and Q2 OFF
When V1 = HIGH and V2 = LOW, Q1 is OFF. and Q2 ON.
In this case, R1 = R4, R2 = R3, R1 must be greater than R2
C1 = C2
When the circuit is first turned on, none of the transistors are turned on.
The base voltage of both transistors begins to increase. Either transistor turns on first due to the difference in doping and electrical characteristics of the transistor.
Rice. 1: Schematic diagram of the operation of a transistor astable multivibrator
We can't tell which transistor conducts first, so we assume Q1 conducts first and Q2 is off (C2 is fully charged).
Q1 is conducting and Q2 is off, hence VC1 = 0V since all current to ground is due to Q1 short circuit, and VC2 = Vcc since all voltage across VC2 drops due to TR2 open circuit (equal to supply voltage) .
Due to the high voltage of VC2, capacitor C2 starts charging through Q1 through R4 and C1 starts charging through R2 through Q1. The time required to charge C1 (T1 = R2C1) is longer than the time required to charge C2 (T2 = R4C2).
Since the right plate C1 is connected to the base of Q2 and is charging, then this plate has a high potential and when it exceeds the voltage of 0.65V, it turns on Q2.
Since C2 is fully charged, its left plate has a voltage of -Vcc or -5V and is connected to the base of Q1. Therefore it turns off Q2
TR Now TR1 is off and Q2 is conducting, hence VC1 = 5 V and VC2 = 0 V. The left plate of C1 was previously at -0.65 V, which begins to rise to 5 V and connects to the collector of Q1. C1 first discharges from 0 to 0.65V and then begins to charge through R1 through Q2. During charging, the right plate C1 is at low potential, which turns off Q2.
The right plate of C2 is connected to the collector of Q2 and is pre-positioned at +5V. So C2 first discharges from 5V to 0V and then starts charging through resistance R3. The left plate C2 is at high potential during charging, which turns on Q1 when it reaches 0.65V.
Rice. 2: Schematic diagram of the operation of a transistor astable multivibrator
Now Q1 is conducting and Q2 is off. The above sequence is repeated and we get a signal at both the collectors of the transistor which is out of phase with each other. To obtain a perfect square wave by any collector of the transistor, we take both the collector resistance of the transistor, the base resistance, i.e. (R1 = R4), (R2 = R3), and also the same value of the capacitor, which makes our circuit symmetrical. Therefore, the duty cycle for low and high output is the same that generates a square wave
Constant The time constant of the waveform depends on the base resistance and collector of the transistor. We can calculate its time period by: Time constant = 0.693RC
In this video tutorial from the Soldering Iron TV channel, we will show how the elements of an electrical circuit are interconnected and get acquainted with the processes occurring in it. The first circuit on the basis of which the operating principle will be considered is a multivibrator circuit using transistors. The circuit can be in one of two states and periodically transitions from one to another.
All we see now are two LEDs blinking alternately. Why is this happening? Let's consider first first state.
The first transistor VT1 is closed, and the second transistor is completely open and does not interfere with the flow of collector current. The transistor is in saturation mode at this moment, which reduces the voltage drop across it. And therefore the right LED lights up at full strength. Capacitor C1 was discharged at the first moment of time, and the current freely passed to the base of transistor VT2, completely opening it. But after a moment, the capacitor begins to quickly charge with the base current of the second transistor through resistor R1. After it is fully charged (and as you know, a fully charged capacitor does not pass current), the transistor VT2 therefore closes and the LED goes out.
The voltage across capacitor C1 is equal to the product of the base current and the resistance of resistor R2. Let's go back in time. While transistor VT2 was open and the right LED was on, capacitor C2, previously charged in the previous state, begins to slowly discharge through the open transistor VT2 and resistor R3. Until it is discharged, the voltage at the base of VT1 will be negative, which completely turns off the transistor. The first LED is not lit. It turns out that by the time the second LED fades out, capacitor C2 has time to discharge and becomes ready to pass current to the base of the first transistor VT1. By the time the second LED stops lighting, the first LED lights up.
A in the second state the same thing happens, but on the contrary, transistor VT1 is open, VT2 is closed. The transition to another state occurs when capacitor C2 is discharged, the voltage across it decreases. Having completely discharged, it begins to charge in the opposite direction. When the voltage at the base-emitter junction of transistor VT1 reaches a voltage sufficient to open it, approximately 0.7 V, this transistor will begin to open and the first LED will light up.
Through resistors R1 and R4, the capacitors are charged, and through R3 and R2, discharge occurs. Resistors R1 and R4 limit the current of the first and second LEDs. Not only the brightness of the LEDs depends on their resistance. They also determine the charging time of the capacitors. The resistance of R1 and R4 is selected much lower than R2 and R3, so that the charging of the capacitors occurs faster than their discharge. A multivibrator is used to produce rectangular pulses, which are removed from the collector of the transistor. In this case, the load is connected in parallel to one of the collector resistors R1 or R4.
The graph shows the rectangular pulses generated by this circuit. One of the regions is called the pulse front. The front has a slope, and the longer the charging time of the capacitors, the greater this slope will be.
If a multivibrator uses identical transistors, capacitors of the same capacity, and if resistors have symmetrical resistances, then such a multivibrator is called symmetrical. It has the same pulse duration and pause duration. And if there are differences in parameters, then the multivibrator will be asymmetrical. When we connect the multivibrator to a power source, at the first moment of time both capacitors are discharged, which means that current will flow to the base of both capacitors and an unsteady operating mode will appear, in which only one of the transistors should open. Since these circuit elements have some errors in ratings and parameters, one of the transistors will open first and the multivibrator will start.
If you want to simulate this circuit in the Multisim program, then you need to set the values of resistors R2 and R3 so that their resistances differ by at least a tenth of an ohm. Do the same with the capacitance of the capacitors, otherwise the multivibrator may not start. In the practical implementation of this circuit, I recommend supplying voltage from 3 to 10 Volts, and now you will find out the parameters of the elements themselves. Provided that the KT315 transistor is used. Resistors R1 and R4 do not affect the pulse frequency. In our case, they limit the LED current. The resistance of resistors R1 and R4 can be taken from 300 Ohms to 1 kOhm. The resistance of resistors R2 and R3 is from 15 kOhm to 200 kOhm. Capacitor capacity is from 10 to 100 µF. Let's present a table with the values of resistances and capacitances, which shows the approximate expected pulse frequency. That is, to get a pulse lasting 7 seconds, that is, the duration of the glow of one LED is equal to 7 seconds, you need to use resistors R2 and R3 with a resistance of 100 kOhm and a capacitor with a capacity of 100 μF.
The timing elements of this circuit are resistors R2, R3 and capacitors C1 and C2. The lower their ratings, the more often the transistors will switch, and the more often the LEDs will flicker.
A multivibrator can be implemented not only on transistors, but also on microcircuits. Leave your comments, don’t forget to subscribe to the “Soldering Iron TV” channel on YouTube so you don’t miss new interesting videos.
Another interesting thing about the radio transmitter.
A multivibrator is the simplest pulse generator that operates in the self-oscillation mode, that is, when voltage is applied to the circuit, it begins to generate pulses.
The simplest diagram is shown in the figure below:
Moreover, the capacitances of capacitors C1, C2 are always selected as identical as possible, and the nominal value of the base resistances R2, R3 should be higher than the collector ones. This is an important condition for proper operation of the MV.
How does a transistor-based multivibrator work? So: when the power is turned on, capacitors C1 and C2 begin to charge.
The first capacitor in the chain R1-C1-transition BE of the second body.
The second capacitance will be charged through the circuit R4 - C2 - transition BE of the first transistor - housing.
Since there is a base current on the transistors, they almost open. But since there are no two identical transistors, one of them will open a little earlier than its colleague.
Let's assume that our first transistor opens earlier. When it opens, it will discharge capacity C1. Moreover, it will discharge in reverse polarity, closing the second transistor. But the first one is in the open state only for the moment until capacitor C2 is charged to the supply voltage level. At the end of the charging process C2, Q1 is locked.
But by this time C1 is almost discharged. This means that a current will flow through it, opening the second transistor, which will discharge capacitor C2 and will remain open until the first capacitor is recharged. And so on from cycle to cycle until we turn off the power from the circuit.
As is easy to see, the switching time here is determined by the capacitance rating of the capacitors. By the way, the resistance of the basic resistances R1, R3 also contributes a certain factor here.
Let's return to the original state, when the first transistor is open. At this moment, capacitance C1 will not only have time to discharge, but will also begin to charge in reverse polarity along the circuit R2-C1-collector-emitter of open Q1.
But the resistance of R2 is quite large and C1 does not have time to charge to the level of the power source, but when Q1 is locked, it will discharge through the base chain of Q2, helping it to open faster. The same resistance also increases the charging time of the first capacitor C1. But the collector resistances R1, R4 are a load and do not have much effect on the frequency of pulse generation.
As a practical introduction, I propose to assemble, in the same article the design with three transistors is also discussed.
Let's look at the operation of an asymmetrical multivibrator using two transistors using the example of a simple homemade amateur radio circuit that makes the sound of a bouncing metal ball. The circuit works as follows: as capacitance C1 discharges, the volume of the blows decreases. The total duration of the sound depends on the value of C1, and capacitor C2 sets the duration of pauses. Transistors can be absolutely any p-n-p type.
There are two types of domestic micro multivibrators - self-oscillating (GG) and standby (AG).
Self-oscillating ones generate a periodic sequence of rectangular pulses. Their duration and repetition period are set by the parameters of external elements of resistance and capacitance or the level of control voltage.
Domestic microcircuits of self-oscillating MVs, for example, are 530GG1, K531GG1, KM555GG2 You will find more detailed information on them and many others in, for example, Yakubovsky S.V. Digital and analogue integrated circuits or ICs and their foreign analogues. Directory in 12 volumes edited by Nefedov
For waiting MVs, the duration of the generated pulse is also set by the characteristics of the attached radio components, and the pulse repetition period is set by the repetition period of the trigger pulses arriving at a separate input.
Examples: K155AG1 contains one standby multivibrator that generates single rectangular pulses with good duration stability; 133AG3, K155AG3, 533AG3, KM555AG3, KR1533AG3 contains two standby MVs that generate single rectangular voltage pulses with good stability; 533AG4, KM555AG4 two waiting MVs that form single rectangular voltage pulses.
Very often in amateur radio practice they prefer not to use specialized microcircuits, but to assemble it using logical elements.
The simplest multivibrator circuit using NAND gates is shown in the figure below. It has two states: in one state DD1.1 is locked and DD1.2 is open, in the other - everything is the opposite.
For example, if DD1.1 is closed, DD1.2 is open, then capacitance C2 is charged by the output current of DD1.1 passing through resistance R2. The voltage at the DD1.2 input is positive. It keeps DD1.2 open. As capacitor C2 charges, the charging current decreases and the voltage across R2 drops. At the moment the threshold level is reached, DD1.2 begins to close and its output potential increases. The increase in this voltage is transmitted through C1 to output DD1.1, the latter opens, and the reverse process develops, ending with complete locking of DD1.2 and unlocking of DD1.1 - the transition of the device to the second unstable state. Now C1 will be charged through R1 and the output resistance of the microcircuit component DD1.2, and C2 through DD1.1. Thus, we observe a typical self-oscillatory process.
Another simple circuit that can be assembled using logic elements is a rectangular pulse generator. Moreover, such a generator will operate in self-generation mode, similar to a transistor one. The figure below shows a generator built on one logical digital domestic microassembly K155LA3
multivibrator circuit on K155LA3
A practical example of such an implementation can be found on the electronics page in the design of the calling device.
A practical example of the implementation of the operation of a waiting MV on a trigger in the design of an optical lighting switch using IR rays is considered.
