How to make a square wave generator. Generator based on NE555 timer. Video. Do-it-yourself high-voltage pulse generator

Stable square wave generator

Clock generators (GTI) are a kind of driving mechanisms in most complex digital circuits. At the GTI output, electrical impulses repeating with a certain frequency are formed. Most often they are rectangular in shape. Based on these oscillations, the operation of all digital microcircuits included in the device is synchronized. In one cycle, one atomic operation is performed (i.e., indivisible, one that cannot be performed or not partially performed).

Voltage pulses can be generated with varying degrees of accuracy and stability. But the more demanding the circuit is to the driving frequency, the more accurate and stable the generator should be.

The most common:

1.Classic (analogue) generators. They are easy to assemble, but have poor stability or generate not-quite-square-wave pulses. As the simplest example, LC circuits or circuits based on them.

2. Quartz (based on quartz crystals). Here quartz acts as a highly selective filter. The circuit is characterized by a high degree of stability and ease of assembly.

3.Based on programmable ICs (such as Arduino). Solutions also form stable pulses, but unlike quartz ones, they can be controlled within the specified ranges and form several reference frequencies at once.

4. Autogenerators. These are managed GTIs, working primarily with modern processors, most often integrated directly into the crystal.

Thus, the following are suitable for the role of stable square-wave generators in circuitry:

• Quartz
• And programmable (based on programmable microcircuits).

Separately, it is worth mentioning the circuits of classical single and multivibrators operating with the use of logical elements. This class of GTI can definitely be used in digital circuits, as it is able to generate a stable frequency.

High stability crystal oscillator

One of the implementation examples.

Rice. 1. Crystal oscillator circuit

The circuit is based on a quartz resonator and a CMOS inverter based on the Pierce generator principle.

Larger capacitors Ca and Cb are responsible for increasing stability.

Multivibrators based on logic elements

The simplest circuit multivibrator looks like this.

Rice. 2. Multivibrator circuit

In fact, this is an oscillatory circuit based on capacitors and resistances. Logic elements allow you to cut off the smooth fronts of the increase and decrease in voltage during the charge / discharge of the capacitor in the oscillatory circuit.

The stress generation graph will look like this.

Rice. 3. Graph of stress formation

Capacitor C1 is responsible for the pulse duration, and C2 is responsible for the pause between pulses. The steepness of the front depends on the response time of the logic element.

The indicated scheme has one drawback - a self-excitation mode is possible.

To eliminate this effect, another additional logic element is used (see the diagram below - LE3).

Rice. 4. C multivibrator circuit

Oscillators on operational amplifiers

The same oscillatory circuit, but with the integration of the op amp, will look like this.

Rice. 5. Scheme oscillatory circuit

Rice. 6. Graph of the formation of pulses at its output

The circuit mentioned above generates pulses whose time is equal to the pause time, which should not always be the case.

One can introduce asymmetry into the generation frequency in the following way.

Rice. 7. Pulse generator circuit

Here, the time of the pulses and the pauses between them are determined by different resistor values.

Generator based on NE555

The NE555 chip is universal timer, capable of operating in multi- or single vibrator mode.

There are many analogues of this microcircuit: 1006VI1, UPC617C, ICM7555, etc.

One of the simple options for building stable rectangular pulse generators with the ability to adjust the frequency can be seen below.

Rice. 8. Variant of the scheme of the generator of stable rectangular pulses

Here, various capacitors are included in the circuit (C1, C2, C3, there may be more of them), and trimmers (R2, R3, and R4 is responsible for the output current level).

The formula for calculating the frequency is as follows.

We will consider the Arduino-based generator in a separate article.

Publication date: 07.01.2018

Readers' opinions

• vitaly / 23.11.2018 - 17:11
  available

Rectangular pulses with wide range frequencies and duty cycle can be obtained using the uA741 operational amplifier.

A diagram of such a rectangular pulse generator is shown below.

In the diagram, the capacitor C1 and R1 forms a time-setting circuit. Resistors R2 and R3 form a voltage divider that supplies a fixed portion of the output voltage to the non-inverting terminal of the op amp as a reference voltage.

Rectangular pulse generator with adjustable frequency. Description of work

Initially, the voltage across capacitor C1 will be zero and the output of the op-amp will be high. As a result of this, the capacitor C1 begins to be charged from the positive voltage through the potentiometer R1.

When capacitor C1 is charged to a level at which the voltage at the inverting terminal of the op-amp becomes higher than the voltage at the non-inverting terminal, the output of the op-amp will switch to negative.

In this case, the capacitor is quickly discharged through R1, and then begins to charge towards the negative pole. When C1 is charged from a negative voltage, so that the voltage at the inverting terminal is more negative than at the non-inverting terminal, the output of the amplifier will switch to positive.

Now the capacitor is quickly discharged through R1 and begins to charge from the positive pole. This cycle will repeat indefinitely, and the result will be a continuous square wave at the output with amplitude from +Vcc to -Vcc.

The period of oscillation of a square wave generator can be expressed using the following equation:

As a rule, the resistance R3 is made equal to R2. Then the equation for the period can be simplified:

T = 2.1976R1C1

The frequency can be determined by the formula: F = 1 / T

Now a little about the uA741 operational amplifier

The uA741 op amp is a very popular IC that can be used in many circuits.

The LM741 op-amp comes in an 8-pin DIP plastic package containing one amplifier.

The uA741 operational amplifier can be used in various electronic circuits ah, such as: differentiator, integrator, adder, subtractor, differential amplifier, preamplifier, frequency generator, etc.

Although the uA741 typically runs on a dual power supply, it can also run on a single power supply just as well.

The pin assignment of the uA741 is shown in the following figure:

The uA741 supply voltage range is +/- 5 to +/- 18 volts.

Pin number 1 and 5 are for zero offset setting. This can be done by connecting a 10K variable resistor to pins 1 and 2, and a resistor slider to pin 4.

The maximum power dissipation of the uA741 is 500mW.

Pulse generators are designed to receive pulses of a certain shape and duration. They are used in many circuits and devices. And also they are used in measuring equipment for adjustment and repair of various digital devices. Rectangular pulses are great for checking the functionality of digital circuits, while triangular waves can be useful for sweep generators or oscillators.

The generator generates a single rectangular pulse at the push of a button. The scheme is assembled on logical elements which is based on a conventional RS-flip-flop, thanks to it the possibility of the penetration of bounce pulses of the button contacts to the counter is also excluded.

In the position of the button contacts, as shown in the diagram, a high level voltage will be present at the first output, and a high level voltage will be present at the second output. low level or a logical zero, when the button is pressed, the trigger state will change to the opposite. This generator is perfect for testing the operation of various counters.

In this circuit, a single pulse is formed, the duration of which does not depend on the duration of the input pulse. Such a generator is used in a wide variety of ways: to simulate the input signals of digital devices, when checking the operability of circuits based on digital microcircuits, the need to apply a certain number of pulses to some device under test with visual control of processes, etc.

As soon as the circuit is powered on, capacitor C1 starts charging and the relay is activated, opening the power supply circuit with its front contacts, but the relay will not turn off immediately, but with a delay, since the discharge current of capacitor C1 will flow through its winding. When the rear contacts of the relay are closed again, a new cycle will begin. The switching frequency of the electromagnetic relay depends on the capacitance of the capacitor C1 and the resistor R1.

You can use almost any relay, I took it. Such a generator can be used, for example, to switch Christmas tree garlands and other effects. The disadvantage of this circuit is the use of a large capacitor.

Another oscillator circuit on a relay, with a principle of operation similar to the previous circuit, but unlike it, the repetition rate is 1 Hz with a smaller capacitor capacitance. At the moment the generator is turned on, capacitor C1 begins to charge, then the zener diode opens and relay K1 is activated. The capacitor begins to discharge through the resistor and the composite transistor. After a short period of time, the relay turns off and a new generator cycle begins.

In the pulse generator, in Figure A, three AND-NOT logic elements and a unipolar transistor VT1 are used. Depending on the values ​​of the capacitor C1 and resistors R2 and R3, pulses are generated at output 8 with a frequency of 0.1 - up to 1 MHz. Such a huge range is explained by the use in the circuit field effect transistor, which made it possible to use megohm resistors R2 and R3. Using them, you can also change the duty cycle of the pulses: the resistor R2 sets the duration of the high level, and R3 - the duration of the low level voltage. VT1, you can take any of the KP302, KP303 series. - K155LA3.

If you use CMOS chips instead of K155LA3, for example K561LN2, you can make a wide-range pulse generator without using a field effect transistor in the circuit. The diagram of this generator is shown in Figure B. To expand the number of generated frequencies, the capacitance of the timing circuit capacitor is selected by switch S1. The frequency range of this generator is 1Hz to 10kHz.

The last figure shows a pulse generator circuit in which the possibility of adjusting the duty cycle is incorporated. For those who have forgotten, we recall. The pulse duty cycle is the ratio of the repetition period (T) to the duration (t):

The duty cycle at the output of the circuit can be set from 1 to several thousand, using the resistor R1. The transistor operating in the key mode is designed to amplify power pulses

If there is a need for a highly stable pulse generator, then it is necessary to use quartz at the appropriate frequency.

The generator circuit shown in the figure is capable of generating rectangular and sawtooth pulses. The master oscillator is made on the logic elements DD 1.1-DD1.3 of the K561LN2 digital microcircuit. Resistor R2 paired with capacitor C2 form a differentiating circuit, which at the output of DD1.5 generates short pulses with a duration of 1 μs. An adjustable current stabilizer is assembled on a field effect transistor and resistor R4. From its output, a current flows charging capacitor C3 and the voltage across it increases linearly. At the moment of receipt of a short positive pulse, the transistor VT1 opens, and the capacitor C3 is discharged. Thereby forming a sawtooth voltage on its plates. With a variable resistor, you can adjust the capacitor charge current and the slope of the sawtooth voltage pulse, as well as its amplitude.

The circuit is built using two op-amps of the LM741 type. The first op amp is used to generate a rectangular shape, and the second one generates a triangular one. The generator circuit is built as follows:

In the first LM741, the inverting input from the output of the amplifier is connected Feedback(OS) performed on resistor R1 and capacitor C2, and the OS also goes to the non-inverting input, but through a voltage divider, based on resistors R2 and R5. The output of the first op-amp is directly connected to the inverting input of the second LM741 through the resistance R4. This second op-amp, together with R4 and C1, form an integrator circuit. Its non-inverting input is grounded. Both op amps are supplied with +Vcc and -Vee supply voltages, as usual on the seventh and fourth pins.

The scheme works as follows. Assume that initially there is +Vcc at the output of U1. Then the capacitance C2 starts charging through the resistor R1. At a certain point in time, the voltage at C2 will exceed the level at the non-inverting input, which is calculated using the formula below:

V 1 \u003d (R 2 / (R 2 + R 5)) × V o \u003d (10 / 20) × V o \u003d 0.5 × V o

The output signal V 1 becomes -Vee. So, the capacitor starts to discharge through the resistor R1. When the voltage across the capacitance becomes less than the voltage given by the formula, the output signal will again be + Vcc. Thus, the cycle is repeated, and due to this, rectangular pulses are generated with a time period determined by the RC circuit consisting of resistance R1 and capacitor C2. These square-shaped formations are also input signals to the integrator circuit, which converts them into a triangular shape. When the output of op-amp U1 is +Vcc, capacitance C1 is charged to its maximum level and produces a positive, rising slope of the triangle at the output of op-amp U2. And, accordingly, if there is -Vee at the output of the first op-amp, then a negative, downward slope will be formed. That is, we get a triangular wave at the output of the second op-amp.

The pulse generator in the first circuit is built on the TL494 chip, which is great for setting up any electronic circuits. The peculiarity of this circuit is that the amplitude of the output pulses can be equal to the supply voltage of the circuit, and the microcircuit is capable of operating up to 41 V, because it is not just that it can be found in power supplies for personal computers.

Wiring printed circuit board you can download from the link above.

The pulse repetition rate can be changed by switch S2 and variable resistor RV1, resistor RV2 is used to adjust the duty cycle. Switch SA1 is designed to change the operating modes of the generator from in-phase to anti-phase. Resistor R3 should cover the frequency range, and the duty cycle adjustment range is regulated by the selection of R1, R2

Capacitors C1-4 from 1000 pF to 10 uF. Transistors any high-frequency KT972

A selection of circuits and designs of generators of rectangular pulses. The amplitude of the generated signal in such generators is very stable and close to the supply voltage. But the shape of the oscillations is very far from sinusoidal - the signal is pulsed, and the duration of the pulses and pauses between them is easily adjustable. It is easy to give pulses the appearance of a meander when the duration of the pulse is equal to the duration of the pause between them

It generates powerful short single pulses that set the input or output of any digital element to a logic level opposite to the existing one. The pulse duration is chosen so as not to disable the element, the output of which is connected to the tested input. This makes it possible not to disturb the electrical connection of the tested element with the rest.

Pulse generators are devices that are capable of creating waves of a certain shape. The clock frequency in this case depends on many factors. The main purpose of generators is considered to be the synchronization of processes in electrical appliances. Thus, the user has the opportunity to configure various digital equipment.

Examples include clocks and timers. The main element of devices of this type considered to be an adapter. Additionally, capacitors and resistors are installed in the generators along with diodes. The main parameters of the devices include the indicator of excitation of oscillations and negative resistance.

Generators with inverters

You can make a pulse generator with your own hands with inverters at home. This adapter will require a capacitorless type. Resistors are best used precisely field. Their momentum transfer parameter is quite high level. Capacitors to the device must be selected based on the power of the adapter. If its output voltage is 2 V, then the minimum should be at the level of 4 pF. Additionally, it is important to monitor the negative resistance parameter. On average, it must fluctuate around 8 ohms.

Rectangular pulse model with regulator

To date, a square-wave generator with regulators is quite common. In order for the user to be able to adjust the limiting frequency of the device, it is necessary to use a modulator. On the market, they are presented by manufacturers of a rotary and push-button type. In this case, it is best to stop at the first option. All this will allow you to more finely tune and not be afraid of a failure in the system.

The modulator is installed in the rectangular pulse generator directly on the adapter. In this case, soldering must be done very carefully. First of all, you should thoroughly clean all contacts. If we consider capacitorless adapters, then they have outputs on the upper side. Additionally, there are analog adapters, which are often available with a protective cover. In this situation, it must be removed.

In order for the device to have a high bandwidth, it is necessary to install resistors in pairs. The oscillation excitation parameter in this case must be at the level. As the main problem, the rectangular pulse generator (the circuit is shown below) has a sharp increase operating temperature. In this case, you should check the negative resistance of the capacitorless adapter.

Overlapping pulse generator

To make a pulse generator with your own hands, it is best to use an analog adapter. Regulators in this case are not required. This is due to the fact that the level of negative resistance can exceed 5 ohms. As a result, a rather large load is placed on the resistors. Capacitors to the device are selected with a capacity of at least 4 ohms. In turn, the adapter is connected to them only by output contacts. As a main problem, the pulse generator has an asymmetric oscillation, which occurs due to overloading of the resistors.

Device with symmetrical pulses

A simple pulse generator of this type can only be made using inverters. In such a situation, it is best to select an adapter of the analog type. It costs much less on the market than the capacitorless modification. Additionally, it is important to pay attention to the type of resistors. Many experts for the generator are advised to select quartz models. However, their throughput is quite low. As a result, the oscillation excitation parameter will never exceed 4 ms. Plus, the risk of overheating of the adapter is added to this.

Given all of the above, it is more appropriate to use field resistors. in this case will depend on their location on the board. If you choose the option when they are installed in front of the adapter, in this case the vibration excitation index can reach up to 5 ms. Otherwise, good results cannot be expected. You can check the pulse generator for operability simply by connecting a 20 V power supply. As a result, the level of negative resistance must be in the region of 3 ohms.

To minimize the risk of overheating, it is additionally important to use only capacitive capacitors. The regulator can be installed in such a device. If we consider rotary modifications, then the modulator of the PPR2 series is suitable as an option. According to its characteristics, today it is quite reliable.

triggered generator

A trigger is a device that is responsible for transmitting a signal. Today they are sold unidirectional or bidirectional. Only the first option is suitable for the generator. The above element is installed near the adapter. In this case, soldering must be done only after a thorough cleaning of all contacts.

Directly adapter can be selected even analog type. The load in this case will be small, and the level of negative resistance with a successful assembly will not exceed 5 ohms. The oscillation excitation parameter with a trigger is on average 5 ms. The main problem of the pulse generator is this: increased sensitivity. As a result, these devices are not able to work with a power supply above 20 V.

increased load?

Let's take a look at microchips. Pulse generators of this type imply the use of a powerful inductor. Additionally, only an analog adapter should be selected. In this case, it is necessary to achieve a high throughput of the system. For this, capacitors are used only capacitive type. They must be able to withstand at least 5 ohms of negative resistance.

Resistors for the device are suitable for a wide variety. If you choose them of a closed type, then it is necessary to provide for them a separate contact. If you still stop at field resistors, then the phase change in this case will take quite a long time. Thyristors for such devices are practically useless.

Models with quartz stabilization

The pulse generator circuit of this type provides for the use of only a capacitorless adapter. All this is necessary so that the oscillation excitation index is at least at the level of 4 ms. All this will also reduce thermal losses. Capacitors for the device are selected based on the level of negative resistance. Additionally, the type of power supply must be taken into account. If we consider pulse models, then their output current level is on average at around 30 V. All this can ultimately lead to overheating of the capacitors.

To avoid such problems, many experts advise installing zener diodes. They are soldered directly to the adapter. To do this, clean all contacts and check the cathode voltage. Auxiliary adapters for such generators are also used. In this situation, they play the role of a switched transceiver. As a result, the oscillation excitation parameter is increased to 6 ms.

Generators with PP2 capacitors

The generator of high-voltage pulses with capacitors of this type is formed quite simply. Finding elements for such devices on the market is not a problem. However, it is important to choose a quality chip. Many for this purpose acquire multi-channel modifications. However, they are quite expensive in the store compared to the usual types.

Transistors for generators are most suitable single-junction. In this case, the negative resistance parameter should not exceed 7 ohms. In such a situation, one can hope for the stability of the system. To increase the sensitivity of the device, many advise using zener diodes. However, triggers are rarely used. This is due to the fact that the throughput of the model is significantly reduced. The main problem of capacitors is considered to be the amplification of the limiting frequency.

As a result, the phase change occurs with a large margin. To set up the process properly, you must first configure the adapter. If the negative resistance level is at around 5 ohms, then the limiting frequency of the device should be approximately 40 Hz. As a result, the load from the resistors is removed.

Models with PP5 capacitors

A high-voltage pulse generator with the indicated capacitors can be found quite often. At the same time, it can be used even with 15 V power supplies. Bandwidth it depends on the adapter type. In this case, it is important to decide on the resistors. If you select field models, then it is more expedient to install the adapter of the non-condenser type. In that case, the negative resistance parameter will be in the region of 3 ohms.

Zener diodes in this case are used quite often. This is due to a sharp decrease in the level of the limiting frequency. In order to align it, zener diodes are ideal. They are installed, as a rule, near the output port. In turn, resistors are best soldered near the adapter. The oscillatory excitation index depends on the capacitance of the capacitors. Considering 3 pF models, we note that the above parameter will never exceed 6 ms.

Main problems of the generator

The main problem of devices with PP5 capacitors is considered to be increased sensitivity. At the same time, thermal indicators are also at a low level. Due to this, there is often a need to use a trigger. However, in this case, it is still necessary to measure the output voltage indicator. If it exceeds 15 V with a block of 20 V, then the trigger can significantly improve the performance of the system.

Devices on regulators MKM25

The pulse generator circuit with this regulator includes only closed-type resistors. At the same time, even the PPR1 series of microcircuits can be used. In this case, only two capacitors are required. The level of negative resistance directly depends on the conductivity of the elements. If the capacitance of the capacitors is less than 4 pF, then the negative resistance can rise even up to 5 ohms.

To solve this problem, it is necessary to use zener diodes. The regulator in this case is installed on the pulse generator near the analog adapter. The output contacts must be carefully cleaned. You should also check the threshold voltage of the cathode itself. If it exceeds 5 V, then an adjustable pulse generator can be connected to two contacts.