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Introduction

74LS04 contains six independent gates each of which performs the logic INVERT function. The output signals of the six inverters are opposite to the input signals.

Catalog

Introduction

I Circuit of Ring Oscillator

II Symmetrical Square-wave Oscillator

III Simple self-excited Multivibrator

IV Circuit of Crystal Oscillator and Frequency Divider  

V FM Wireless Microphone

FAQ

Ordering & Quantity

I Circuit of Ring Oscillator

Figure 1. Ring oscillator

The experimental circuit of a non gate ring self-excited multivibrator with RC delay circuit is shown in the figure. The oscillation circuit is composed of non gate IC1, IC2, IC3, and timing circuit elements RP and C. The rectangular wave signal is output by IC3. R1 is a protective resistor to avoid damage to IC 3 gate circuit when timing capacitor C is reverse discharged. Not gate IC4 makes the oscillator output rectangular wave with better waveform.

Oscillation frequency estimation f > 1 / 2.3RC T> 2.3RC

The resistance value of the timing resistor is selected in the range of 100-10002. The timing capacitor C has a large value range, from several hundred picofarads (pF) to several hundred microfarads, which can make the oscillation frequency range from several megahertz to several hertz. Replace the timing resistor with a potentiometer  (1.5k92), which can continuously adjust the oscillation frequency and has larger coverage. The chip used is 74LS04.

II Symmetrical Square-wave Oscillator

The figure shows the experimental circuit of the non-gate symmetrical square-wave self-excited multivibrator. Because the circuit is symmetrical, the duty cycle of output oscillation waveform is 1:1, which is a square wave, so it is called a symmetrical square wave oscillator. In the oscillation circuit, the output of non gate IC1 is coupled to the input of non gate IC2 via a timing capacitor C2. Also, the IC2 output is coupled to the IC1 input via C1. Two non gates are coupled with each other through capacitors to form a positive feedback closed-loop circuit, which can produce square-wave oscillation. When R1 = R4 = R, C1 = C2 = C, the estimation formula of oscillation frequency is as follows: f≈1/RC. The oscillation period T ≈ RC.

Figure 2. Symmetrical Square-wave Oscillator

III Simple self-excited Multivibrator

The figure shows a simple non gate self-excited multivibrator experimental circuit. It is composed of non-gate oscillator IC1, IC2, inverter IC3, red and green light-emitting diodes and power supply system GB. IC1 and IC2 are the switching links of the oscillator. R1 and C timing circuits produce delay positive feedback signals to control the switch to turn on and off periodically, so that IC2 outputs rectangular wave. The inverter IC3 makes the red and green LEDs and the oscillator flash alternately.

Figure 3. Simple self-excited multivibrator

IV Circuit of Crystal Oscillator and Frequency Divider

Figure 4. Circuit of Crystal oscillator and frequency divider

V FM Wireless Microphone

Wireless microphones are available everywhere on the market, but their circuits are all made up of LC oscillators or quartz crystal oscillator circuits. As we all know, the NAND gate has the function of magnification and phase inversion. Therefore, as long as three NAND gates are connected, a ring oscillator is formed. Coupled with the FM circuit, it can also be made into a wireless microphone.

Figure 5. FM wireless microphone

74LS04 is a TTL integrated circuit with six single-input NAND gates. The author uses three of them to make an oscillator. When the supply voltage is 5V, the oscillation frequency is about 90mhz. When the power supply voltage decreases, the frequency decreases; when the supply voltage increases, the frequency also increases. Of course, its oscillation amplitude will also change, but the effect is not significant. In this way, the author uses the method of changing the power supply voltage to change the frequency (that is, to achieve frequency modulation). The specific method is to use the output of BA328, an audio amplifier integrated circuit, as its power supply.

BA328 is an amplifying circuit of the recording head. When it is used for tape signal compensation and equalization, an RC series-parallel network should be connected between the first and the second pins, but it is used for linear amplification, so only a 100kw-130kw resistor is needed. The voltage of the output terminal (pin) of BA328  should be equal to one-half of the voltage of the pin (power supply). If the power supply voltage is 12V, there should be a 6V output. If it is not correct, the resistance should be adjusted. In addition, the 1kW resistor in the figure is used to adjust the magnification. If it is reduced, the gain will be increased. When speaking to an electret microphone, the voltage at the output (PIN) can change rapidly from 5.8v to 6.2V. This voltage is sent to the foot of 74LS04  to make it generate an FM signal, which is amplified and isolated by the fourth NAND gate and sent to the antenna.


FAQ

  • What does 74LS04 contain?

Six gates that perform the logic INVERT function

  • What is 74LS04?

74LS04 is a member of 74XXYY IC series. The 74-series are digital logic integrated circuits. 74LS04 IC has six NOT gates. These NOT gates perform Inverting function. Hence name HEX INVERTING GATES.

  • What is the function of ic 74ls04?

74LS04 Hex NOT Gate IC. 74LS04 is a 2 input quadruple 8-bit NOT gate IC. Inverter in logic converters is an electronics device whose basic functions are to invert the incoming logic weather it is HIGH or LOW. They are also known as NOT gates.

  • What is a hex inverter?

A hex inverter is a type of an integrated circuit that contains six inverters. Many sophisticated digital devices use inverters, including multiplexers, decoders, and state machines.  An inverter circuit's main function is to output the voltage representing the opposite level to its input.

  • Why is NOT gate called an inverter?

A NOT gate, often called an inverter, is a nice digital logic gate to start with because it has only a single input with simple behavior. A NOT gate performs logical negation on its input. In other words, if the input is true, then the output will be false.

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