basic 555 and opamp design!!!!!

8/7/2019 basic 555 and opamp design!!!!!

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a one pulse of variable length. In the astable mode the 555 will retrigger itself to output a streamof pulses of variable length. Basic information about the timers are shown below.

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Monostable Mode

In the basic monostable mode the timer will be triggered by applying a negative pulse to pin 2.

That will cause the output of the timer to output a pulse on pin 3 for a time period determined bythe values of R1 and C1 in the circuit below. The supply voltage has no effect on the length of the

pulse. The formula to determine the duration of the output pulse is as follows T = R1 x C1. Forexample if R1= 100k ohms and C1= 10uf then the length of the pulse would be 1 second. Typically

circuit designers already know what the length of the pulse is going to be, they would then need tocalculate the values of R1 and C1. In this case we will have to pick a value for either R1 or C1 and

then calculate the value of the other component. To obtain a 10 second timing pulse we will use a

100k ohm resistor for R1 and calculate C1's value. C1 = T / R1. C1 = 100uf. To calculate the valueof R1 when the value of C1 is known the formula would be R1 = T / C1.

Astable Mode

In the astable mode of operation pin 2 and 6 are tied together to cause the timer to retrigger itself.

The output pulse is on pin 3. The output pulse is shown in the diagram below. To calculate the T1

time (output high) use the following formula T1 = .693(R1 + R2)C1. To calculate the T2 time(output low) use the formula T2 = .693( R1 x C1 ). If you need to know the frequency of the output

use this formula Freq. = 1.44 / (R1 + 2R2)C1.




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P $ P heory ' esign

he per ational $ mplifier p $ mp can e used in many differ ent Z ays. he p amp has t Z o

inputs an inY er ting input and a non inY er ting input and one output. $ signal applthe inY er ting input Z ill haY e its polar ity r eY er sed on the output. $ signal applied to the non

inY er ting input Z ill r etain its polar ity on the output. he gain or amplification of the signal isdeter mined y a feed acN r esistor that feeds some of the output signal acN to the inY er ting input he smaller the r esistor the loZ er the gain. Some typical op amp pin outs ar e shoZ n eloZ . he

most common ar e the 7 1 and 1 dual op amp. her e ar e many mor e aY aila le.




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Another common way that opamps are used are in comparator circuits. A comparator circuit willcompare the voltage on the two inputs and then making the output high or low. This is

accomplished by having one input the voltage reference (Vref) and the other input is the voltageinput (Vin). Shown below are the two ways to hook up a comparator circuit.

The circuit below shows a basic comparator circuit that you can experiment with.

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PIC Theory and Design

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basic 555 and opamp design!!!!!

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