Homemade square pulse generator. Useful diagrams for radio amateurs. Fig. 16.8. Timing diagrams of generator operation

5.6 Pulse generators

Pulse generators are used in many radio devices (electronic meters, time relays) and are used when setting up digital equipment. The frequency range of such generators can be from a few hertz to many megahertz.

In Fig. 116 shows a diagram of a generator that generates single rectangular pulses when the SB1 button is pressed. An RS trigger is assembled on the logical elements DD1.1 and DD1.2, which prevents the penetration of bounce pulses from the button contacts to the recalculating device. In the position of the contacts of the SB1 button, shown in the diagram, there will be a high level voltage at output 1, and a low level voltage at output 2; when the button is pressed - vice versa. This generator is convenient to use when checking the performance of various meters.

In Fig. Figure 117 shows a diagram of a simple pulse generator based on an electromagnetic relay. When power is applied, capacitor C1 is charged through resistor R1 and the relay is activated, turning off the power source with contacts K 1.1. But the relay does not release immediately, since for some time current will flow through its winding due to the energy accumulated by capacitor C1. When contacts K 1.1 close again, the capacitor begins to charge again - the cycle repeats.

The switching frequency of the electromagnetic relay depends on its parameters, as well as the values of capacitor C1 and resistor R1. When using the RES-15 relay (passport RS4.591.004), switching occurs approximately once per second.

Such a generator can be used, for example, to switch garlands on a New Year tree, to obtain other light

effects. Its disadvantage is the need to use a capacitor of significant capacity.

In Fig. 118 shows a diagram of another generator based on an electromagnetic relay, the operating principle of which is similar to the previous generator, but provides a pulse frequency of 1 Hz with a capacitor capacity 10 times smaller. When power is applied, capacitor C1 is charged through resistor R1. After some time, the zener diode VD1 will open and relay K1 will operate. The capacitor will begin to discharge through resistor R2 and the input resistance of the composite transistor VT1VT2. Soon the relay will release and a new cycle of generator operation will begin. Switching on transistors VT1 and VT2 according to a composite transistor circuit increases the input impedance of the cascade.

Relay K 1 can be the same as in the previous device. But you can use RES-9 (passport RS4.524.201) or any other relay that operates at a voltage of 15...17 V and a current of 20...50 mA.

In the pulse generator, the diagram of which is shown in Fig. 119, the logic elements of the DD1 microcircuit and the field-effect transistor VT1 are used. When changing the values of capacitor C1 and resistors R2 and R3, pulses with a frequency from 0.1 Hz to 1 MHz are generated. Such a wide range was obtained through the use of a field-effect transistor, which made it possible to use resistors R2 and R3 with a resistance of several megaohms. Using these resistors, you can change the duty cycle of the pulses: resistor R2 sets the duration of the high level voltage at the output of the generator, and resistor R3 sets the duration of the low level voltage. The maximum capacitance of capacitor C1 depends on its own leakage current. In this case it is 1...2 µF. The resistance of resistors R2, R3 is 10...15 MOhm. Transistor VT1 can be any of the KP302, KP303 series

If you have a CMOS chip (K176, K561 series), you can assemble a wide-range pulse generator without using a field-effect transistor.

The diagram is shown in Fig. 120. For the convenience of setting the frequency, the capacitance of the capacitor of the timing circuit is changed using the SA1 switch. The frequency range generated by the generator is 1...10,000 Hz.

In Fig. 121 shows a circuit of a pulse generator with adjustable duty cycle. The duty cycle, i.e. the ratio of the pulse repetition period to the duration of the high level voltage at the output of the logical element DD1.3, by resistor R1 can vary from 1 to several thousand. In this case, the pulse frequency also changes slightly. Transistor VT1, operating in key mode, amplifies the power pulses.

The generator, the diagram of which is shown in Fig. 122, produces pulses of both rectangular and sawtooth shapes. The master oscillator is made on logical elements DD 1.1-DD1.3. A differentiating circuit is assembled on capacitor C2 and resistor R2, thanks to which the output of the logical element DD1.5 forms

Short positive pulses are generated (about 1 µs in duration). An adjustable current stabilizer is made on field-effect transistor VT2 and variable resistor R4. This current charges the capacitor C3, and the voltage across it increases linearly. When a short positive pulse arrives at the base of transistor VT1, transistor VT1 opens, discharging capacitor S3. A sawtooth voltage is thus formed on its plates.

Resistor R4 regulates the charging current of the capacitor and, consequently, the steepness of the increase in the sawtooth voltage and its amplitude. Capacitors C1 and SZ are selected based on the required pulse frequency.

Sometimes there is a need to build a generator that generates a number of pulses corresponding to the number of the button pressed.

A schematic diagram of a device (first option) that implements this possibility is shown in Fig. 123. Functionally, it includes a pulse generator, a counter and a decoder. The rectangular pulse generator is assembled using logic elements DD1.3 and DD1.4. The pulse repetition rate is about 10 Hz. From the output of the generator, pulses are supplied to the input of a binary-decimal counter made on the DD2 chip. The four outputs of the counter are connected to the inputs of the DD3 microcircuit, which is a decoder with 4 inputs and 16 outputs.

When supply voltage is applied to the right (according to the diagram) contacts of all fifteen SB I-SB 15 buttons, there will be a low level voltage provided by the presence of a low-resistance resistor R5. This voltage is supplied to the input of the standby multivibrator, made on elements DD1.1, DD1.2 and capacitor C1, and

dampening impulses from bouncing of button contacts. The output of the standby multivibrator is low, so the pulse generator does not work. When one of the buttons is pressed, capacitor C3 is instantly charged through diode VD1 to a high level voltage, as a result of which a low level voltage appears at pins 2 and 3 of counter DD2, setting it into operating condition. At the same time, through the closed contact of the pressed button, a high-level voltage is supplied to the input of the standby multivibrator, and the generator pulses are sent to the counter input. In this case, a low level voltage consistently appears at the decoder outputs. As soon as it appears at the output to which the contact of the pressed button is connected, the supply of pulses to the counter input will stop. The number of pulses corresponding to the number of the pressed button will be removed from pin 11 of element DD1.4. If you continue to hold the button pressed, then after some time the capacitor SZ will discharge through resistor R2, the counter DD2 will be set to zero and the generator will issue a new series of pulses. The button cannot be released until the series of pulses ends.

The device uses MLT-0.25 resistors; oxide capacitors - K50-6. Transistors VT1, VT2 can be of the KT312, KT315, KT503, KT201 series, diode VD1 - of the D7, D9, D311 series. Buttons SB 1 -SB 15 - types P2K, KM 1-1, etc.

Setting up a pulse number generator involves setting the required generator pulse repetition rate by selecting resistor R1 and capacitor C2, which can range from a few hertz to tens of kilohertz. At a frequency above 100 Hz, it takes no more than 0.15 s to issue a full series of pulses, so you don’t have to hold the button with your finger - a short press is enough to form a train of pulses.

In Fig. 124 shows a diagram of another pulse number generator (second option), based on an operating principle similar to that described above. Thanks to the use of K176 series microcircuits, the generator circuit has been simplified. The generator generates from 1 to 9 pulses.

In the two variants of number-pulse generators described above, it is necessary to hold the button pressed until the end of the series of pulses, otherwise an incomplete train of pulses will be output. This is a disadvantage. In Fig. 125 shows a diagram of the third version of the pulse number generator, in which pulses begin to be generated after the button is released.

An encoder is assembled on microcircuits DD1, DD2 and diodes VD1-VD3, which converts a decimal number into binary code. Signals from the outputs of the encoder are supplied to inputs D1, D2, D4, D8 of the microcircuit

DD4 (up/down counter) and to the inputs of the 4OR-HE (DD3.1) logic element.

Let's consider the operation of the generator when the SB3 button is pressed. When the button is pressed, a high level voltage will be established at the outputs of logic elements DD1.1 and DD1.2, and a low level voltage will remain at the outputs DD2.1, DD2.2. A low level voltage will appear at the output of logic element DD3.1, which, through the differentiating circuit C1R11, will be sent to input C of the downward counter DD4 and set it to state 1100. At the same time, a low level voltage will be established at the output of logic element DD3.2, which is inverted by logic element DD5 .1 and prepares the generator for operation using logic elements DD5.2-DD5.4. After releasing the SB3 button, a high-level voltage will appear at the output of element DD3.1, which will be applied to output 12 of the DD5 microcircuit; the generator will start working. Pulses from its output (pin 11 of the DD5 chip) are sent to input -1 of the up/down counter. In this case, the number recorded in the counter decreases, and combinations of logical levels 0100, 1000, 0000 appear successively at outputs 1, 2, 4, 8 of the counter. When the counter is set to state 0000, a high level voltage will be established at the output of logic element DD3.2, and the generator will stop. Three pulses will be output.

The pulse frequency of the generator is determined by elements C2 and R 12 and can vary over a wide range (from a few hertz to hundreds of kilohertz).

In the pulse generators described here, you can use MLT-0.25 resistors and K50-6, KM-6 capacitors. KT315B transistors can be replaced with transistors from the KT312, KT315, KT316, KT503 series. Diodes - any of the D7, D9, D311 series. Buttons - types P2K, KM1, etc. Microcircuits can be of the K 133, K 134, K 136, K158, KR531, K555 series for the first and third options; K561 - for the second option.

The 555 integrated timer chip was developed 44 years ago, in 1971, and is still popular today. Perhaps not a single microcircuit has served people for so long. They collected everything on it, they even say that number 555 is the number of options for its application :) One of the classic applications of the 555 timer is an adjustable square pulse generator.
This review will describe the generator, specific application will be next time.

The board was sent sealed in an antistatic bag, but the microcircuit is very wooden and static cannot easily kill it.

The installation quality is normal, the flux has not been washed off

The generator circuit is standard to obtain a pulse duty cycle of ≤2

The red LED is connected to the generator output and blinks when the output frequency is low.
According to Chinese tradition, the manufacturer forgot to put a limiting resistor in series with the upper trimmer. According to the specification, it must be at least 1 kOhm so as not to overload the internal switch of the microcircuit, however, in reality the circuit works with lower resistance - up to 200 Ohms, at which generation fails. Adding a limiting resistor to the board is difficult due to the layout of the printed circuit board.
The operating frequency range is selected by installing a jumper in one of four positions
The seller indicated the frequencies incorrectly.

Really measured generator frequencies at a supply voltage of 12V
1 - from 0.5Hz to 50Hz
2 - from 35Hz to 3.5kHz
3 - from 650Hz to 65kHz
4 - from 50kHz to 600kHz

The lower resistor (according to the diagram) sets the pulse pause duration, the upper resistor sets the pulse repetition period.
Supply voltage 4.5-16V, maximum output load - 200mA

The stability of output pulses in ranges 2 and 3 is low due to the use of capacitors made of ferroelectric ceramics of the Y5V type - the frequency creeps away not only when the temperature changes, but even when the supply voltage changes (by several times). I didn’t draw any graphs, just take my word for it.
On other ranges the pulse stability is acceptable.

This is what it produces on range 1
At maximum resistance of trimmers

In meander mode (upper 300 Ohm, lower at maximum)

In maximum frequency mode (upper 300 ohms, lower to minimum)

In the minimum pulse duty cycle mode (upper trimmer at maximum, lower at minimum)

For Chinese manufacturers: add a 300-390 Ohm limiting resistor, replace the 6.8uF ceramic capacitor with a 2.2uF/50V electrolytic capacitor, and replace the 0.1uF Y5V capacitor with a higher quality 47nF X5R (X7R)
Here is the finished modified diagram

I didn’t modify the generator myself, because... These disadvantages are not critical for my application.

Conclusion: the usefulness of the device becomes clear when any of your homemade products require pulses to be sent to it :)
To be continued…

I'm planning to buy +31 Add to favorites I liked the review +28 +58

Rectangular pulse generators are used in many radio devices: electronic meters, slot machines, and used when setting up digital equipment. The frequency range of such generators can be from a few hertz to many megahertz.

In Fig. Figure 51 shows a diagram of a generator that generates single rectangular pulses when the S1 button is pressed. An RS trigger is assembled on logic elements D1.1 and D1.2, which prevents the penetration of bounce pulses from the button contacts to the recalculating device. In the position of the contacts of button S1, shown in the diagram, output 1 will have a high level voltage, output 2 will have a low level voltage; when the button is pressed - vice versa. This generator is convenient to use when checking the performance of various meters.

And in Fig. Figure 52 shows a diagram of the simplest pulse generator based on an electromagnetic relay. When power is applied, capacitor C1 is charged through resistor R1 and the relay is activated, turning off the power source with contacts K1.1. But the relay does not release immediately, since for some time current will flow through its winding due to the energy accumulated by capacitor C1. When the contacts K1.1 close again, the capacitor will begin to charge again - the cycle will repeat.

Such a generator can be used, for example, to switch garlands on a New Year tree or to obtain other lighting effects. Its disadvantage is the need to use a capacitor of significant capacity.

Rice. 51 Single pulse generator circuit

Rice. 52 Pulse circuit on an electromagnetic relay

In Fig. Figure 53 shows a diagram of another generator based on an electromagnetic relay, the operating principle of which is similar to the previous generator, but less powerful. When power is applied, capacitor C1 is charged through resistor R1. After a pulse frequency of 1 Hz is reached, the capacitor capacity is ten times less - for some time the zener diode V1 will open and relay K1 will operate. The capacitor will begin to discharge through resistor R2 and the input resistance of the composite transistor V2V3. Soon the relay will release and a new cycle of generator operation will begin. The inclusion of transistors V2 and V3 according to the emitter follower circuit increases the input impedance of the cascade.

Rice. 53. Circuit of a pulse generator using a transistor and an electromagnetic relay

Figure 54. Pulse generator based on logic elements and field-effect transistor

Relay K1 may be the same as in the previous device. But you can use RES-9 (passport RS4.524.201) or any other relay that operates at a voltage of 15...17 V and a current of 20...50 mA.

In the pulse generator, the diagram of which is shown in Fig. 54, logic chip D1 and field-effect transistor V1 are used. When the values of capacitor C1 and resistors R2 and S3 change, it generates pulses with a frequency from 0.1 Hz to 1 MHz. Such a wide range was obtained through the use of a field-effect transistor, which made it possible to use resistors R2 and R3 with a resistance of several megaohms. Using these resistors, you can change the duty cycle of the pulses: resistor R2 sets the duration of the high potential at the output of the generator, and resistor R3 sets the duration of the low potential. The maximum capacitance of capacitor C1 depends on its own leakage current. In this case it is 1 ... 2 µF. The resistance of resistors R2, R3 can be 10...15 MOhm. Transistor V1 can be any of the KP302, KP303 series.

It is advisable to assemble this generator in a housing and use it as an independent device for configuring digital devices.

Sometimes there is a need to build a generator that generates the number of pulses. Corresponding to the number of the pressed button. It can be used, for example, when setting up characterographs or examiners, in which each answer corresponds to a certain number of points. A schematic diagram of such a pulse number generator is shown in Fig. 55.

This device consists of a pulse generator, a counter and a decoder. The generator, which produces rectangular pulses with a repetition rate of about 10 Hz, is assembled using logic elements D1.3, D1.4. From the output of element D1.4, pulses are sent to a binary decimal counter assembled on chip D2.

Rice. 55. Pulse generator circuit (see original)

The four outputs of this counter (pins 12, 9, 8 and 11) are connected to the inputs of the D3 chip, which is a decoder with 4 inputs and 16 outputs. When the counter is operating, a low level voltage is present at one of the decoder outputs, and the number of this output corresponds to the decimal equivalent of the binary number supplied in binary code to the decoder input.

When supply voltage is applied, pin 9 of element D1.3 will have a low level voltage, and no pulses will be received from the generator output to the counter input. When you press one of the buttons S1-S15, capacitor C3 is instantly charged through diode V1 to a high level voltage, at pins 2 and 3 of microcircuit D2 at this time a low level voltage appears, setting the counter to the input pulse counting state. At the same time, through the closed contact of the pressed button, a high-level voltage is supplied to the input of element D1.1 (pin 2) and pulses are sent to the counter. When the counter is operating, a low level voltage consistently appears at the decoder outputs. As soon as it appears at the output to which the left (according to the diagram) contact of the pressed button is connected, the supply of pulses to the counter input will stop. The number of pulses corresponding to the number of the pressed button will be removed from pin 11 of element D1.4. If you continue to hold the button pressed, then after some time the capacitor C3 will discharge through the resistor R2, the counter D2 will be set to zero, and the generator will issue a new series of pulses. It is quite clear that the pressed button cannot be released until the series of pulses ends.

The pulse former on elements D1.1 and D1.2, which is a standby multivibrator, prevents the penetration of pulses created by the bouncing of the button contacts into the counter input.

Setting up the device consists of setting the required generator pulse repetition rate from units of hertz to tens of kilohertz by selecting resistor R1 and capacitor C2.

In the pulse generators described here, you can use MLT-0.25 resistors and K50-6 capacitors. KT315B transistors can be replaced with transistors from the KT312, KT315, KT316 series. Diodes - any of the D7, D9, D311 series. Buttons S1 - S15 type P2K, KM1-G, etc. Microcircuits can be of the K133, K134, K136, K158 series.

Measurement technique

Stable Square Pulse Generator

Clock generators (GTIs) are a kind of master mechanisms in most complex digital circuits. At the output of the GTI, electrical pulses repeating at a certain frequency are formed. Most often they have a rectangular shape. Based on these oscillations, the operation of all digital chips included in the device is synchronized. In one clock 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 regarding the reference frequency, the more accurate and stable the generator must be.

The most common:

1.Classical (analog) generators. They are easy to assemble, but have low stability or generate pulses that are not quite square. As a simple 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 chips (such as Arduino). The solutions also generate stable pulses, but unlike quartz ones, they can be controlled in specified ranges and generate several reference frequencies at once.

4. Autogenerators. These are controlled GTIs, working primarily with modern processors, and are most often integrated directly into the chip.

Thus, the following are suitable for the role of stable rectangular pulse generators in circuit design:

Quartz
And programmable (based on programmable chips).

Separately, it is worth mentioning the circuits of classical single- and multivibrators operating using logic elements. This class of GTI can definitely be used in digital circuits, since it is capable of generating 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 principle of a Pierce oscillator.

Capacitors of increased capacity Ca and Cb are responsible for increasing stability.

Multivibrators based on logic elements

The simplest multivibrator circuit looks like this.

Rice. 2. Multivibrator circuit

In fact, this is an oscillatory circuit based on capacitors and resistances. Logic elements make it possible to cut off smooth edges of increasing and decreasing voltage when charging/discharging a capacitor in an oscillatory circuit.

The stress generation graph will look like this.

Rice. 3. Stress generation graph

Capacitor C1 is responsible for the pulse duration, and C2 is responsible for the pause between pulses. The slope of the edge depends on the reaction time of the logic element.

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

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

Rice. 4. C multivibrator circuit

Operational amplifier generators

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

Rice. 5. Oscillatory circuit diagram

Rice. 6. Graph of pulse formation at its output

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

You can introduce asymmetry into the generation frequency as follows.

Rice. 7. Pulse generator circuit

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

Generator based on NE555

The NE555 chip is a universal timer that can operate in multi- or one-shot mode.

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

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

Rice. 8. Variant of the stable rectangular pulse generator circuit

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

The frequency calculation formula is as follows.

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

Publication date: 07.01.2018

Readers' opinions

Vitaly / 11/23/2018 - 17:11
available

This device will find application in various automation devices for periodically interrupting current in load circuits or to generate pulses with widely variable duration and duration. Pulse duty cycle can reach several thousand, their repetition period and duration are tens of seconds.

When the power source is turned on (see diagram), all transistors generator are closed, capacitor C1 begins charging through the circuit VD1, R3, R H. When the voltage at the emitter of transistor VT1 becomes less than at the base, it will open. Following it, transistors VT2 and VT3 will open. Now capacitor C1 will be discharged through the circuit VT2, R4, VT1. After the capacitor discharges, the transistors will close again and the process will repeat.

In addition to the one indicated, another discharge circuit for this capacitor is introduced into the generator - VT3, R5, VD2. The use of a composite transistor VT2VT3 makes it possible to increase the resistance of resistor R4, thereby reducing the influence of the circuit VT2, R4, VT1 on the duration of discharge of capacitor C1. At the same time, the generator received a number of advantages compared to the original one; it became possible to widely regulate the duration of pulses; The dependence of the pulse duration on their repetition period has been eliminated; improved shape of output pulses; voltage practically ceased to influence the parameters of the pulse sequence.

The load RH (incandescent lamp, LED, relay winding, etc.) can be connected to both the negative and positive power wires. Transistor VT3 is selected in accordance with the current consumed by the load. There are no special requirements for other elements of the generator.

With the values of the timing elements indicated in the diagram - C1, R3, R4, R5 - the pulse repetition period can be adjusted from 20 to 1500 ms, and their duration - from 0.5 to 12 ms.

A. DRYKOV