The purpose of these devices is clear from the name. With their help, they create impulses that have certain parameters. If necessary, you can purchase a device made using factory technologies. But this article will discuss the circuit diagrams and do-it-yourself assembly technologies. This knowledge will be useful for solving various practical problems.
What does the G5-54 pulse generator look like?
When you press a key on an electric musical instrument, electromagnetic vibrations are amplified and sent to the loudspeaker. A sound of a certain tone is heard. In this case, a sinusoidal signal generator is used.
For the coordinated operation of memory, processors, and other computer components, precise synchronization is necessary. A sample signal with a constant frequency is created by a clock generator.
To check the operation of meters and other electronic devices, and to identify malfunctions, single pulses with the necessary parameters are used. Such problems are solved using special generators. A regular manual switch will not work, since it will not be able to provide a specific signal shape.
Before choosing one scheme or another, it is necessary to clearly formulate the purpose of the project. The following figure shows an enlarged view of a typical square wave.
Square pulse circuit
Its shape is not ideal:
Also, to determine the parameters of the future circuit, the concept of duty cycle is used. This parameter is calculated using the following formula:
If the duty cycle is low, it is difficult to detect a short-term signal. This provokes failures in information transmission systems. If the time distribution of highs and lows is the same, the parameter will be equal to two. Such a signal is called a meander.
Square wave and basic pulse parameters
For simplicity, only rectangular pulse generators will be considered in the following.
Using the following examples, you can understand the operating principles of the simplest devices of this class.
Square Pulse Generator Circuits
The first circuit is designed to generate single rectangular pulses. It is created on two logic elements, which are connected to perform the functions of an RS type flip-flop. If the button is in the indicated position, the third leg of the microcircuit will have high voltage, and the sixth leg will have low voltage. When pressed, the levels will change, but contact bounce and corresponding distortion of the output signal will not occur. Since operation requires external influence (in this case, manual control), this device does not belong to the group of self-generators.
A simple generator, but performing its functions independently, is shown in the second half of the figure. When power is applied through the resistor, the capacitor is charged. The relay does not operate immediately, since after the contact is broken, the flow of current through the winding for some time is ensured by the charge of the capacitor. Once the circuit is closed, this process is repeated repeatedly until the power is turned off.
By changing the resistance and capacitor values, you can observe the corresponding transformations in frequency and other signal parameters on an oscilloscope. It will not be difficult to create such a square wave generator with your own hands.
In order to expand the frequency range, the following circuit is useful:
Generator with variable pulse parameters
To implement a plan, two logical elements are not enough. But it’s not difficult to choose one suitable microcircuit (for example, in the K564 series).
Signal parameters that can be changed by manual adjustment, other important parameters
| Circuit diagram element | Purpose and features |
|---|---|
| VT1 | This field effect transistor is used so that high resistance resistors can be used in the feedback circuit. |
| C1 | The permissible capacitance of the capacitor is from 1 to 2 µF. |
| R2 | The resistance value determines the duration of the upper parts of the pulses. |
| R3 | This resistor sets the duration of the lower parts. |
To ensure the stability of the frequency of rectangular signals, circuits based on quartz elements are used:
To make it easier to assemble a pulse generator of a certain frequency with your own hands, it is better to use a universal circuit board. It will be useful for experiments with different electrical circuits. Once you have acquired the skills and relevant knowledge, it will not be difficult to create the ideal device to successfully solve a specific task.
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.
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 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 principle of operation 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 the supply voltage is applied, pin 9 of element D1.3 will have a low level voltage, and pulses from the generator output will not arrive at 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.
Rectangular pulses having a wide range of frequencies and duty cycles can be obtained using the uA741 operational amplifier.
The diagram of such a square pulse generator is shown below.
In the diagram, capacitor C1 and R1 form a time-setting circuit. Resistors R2 and R3 form a voltage divider that supplies a fixed portion of the output voltage to the op-amp's non-inverting pin as a reference voltage.
Initially, the voltage across capacitor C1 will be zero and the output of the op-amp will be high. As a result, capacitor C1 begins to charge from a positive voltage through potentiometer R1.
When capacitor C1 is charged to a level at which the voltage at the inverting pin of the op-amp becomes higher than the voltage at the non-inverting pin, the output of the op-amp switches to negative.
In this case, the capacitor quickly discharges through R1, and then begins to charge to 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 amplifier output switches to positive.
Now the capacitor quickly discharges through R1 and begins to charge from the positive pole. This cycle will be repeated endlessly, and its result will be a continuous square wave at the output with an amplitude from + Vcc to -Vcc.
The oscillation period of a square wave generator can be expressed using the following equation:
As a rule, 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
The uA741 operational amplifier is a very popular IC that can be used in many circuits.
The LM741 op amp is available in an 8-pin plastic DIP package containing one amplifier.
uA741 operational amplifier can be applied in various electronic circuits, such as: differentiator, integrator, adder, subtractor, differential amplifier, preamplifier, frequency generator, etc.
Although uA741, as a rule, operates from a bipolar power supply, it can also successfully operate from a unipolar one.
The pin assignments of uA741 are 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 500 mW.
