DESIGN AND
SIMULATION OF MULTIVIBRATORS
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‘Multi’ means ‘Many’ and ‘vibrator’ means
‘oscillator’. Thus, a multivibrator can be defined in the simplest terms as
the circuit which vibrates of oscillates in different frequencies.
Multivibrators are those forms of electronic circuit
that employ positive feedback to cross-couple two devices so that two
distinct states are possible, for example, one device ON and the other device
OFF, and in which the states of the two devices can be interchanged either by
use of external pulses or by internal capacitance coupling. When the circuit
is switched between states, transition times are normally very short compared
to the ON and OFF periods. Hence, the output waveforms are essentially
rectangular in form.
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Multivibrators may be classified as bistable,
monostable, or astable.
A bistable
multivibrator, often referred to as a flip-flop, has two possible stable
states; each with one device ON and the other OFF, and the states of the two
devices can be interchanged only by the application of external pulses.
A monostable multivibrator, sometimes referred to as
a one-shot, also has two possible states, only one of which is stable. If it
is forced to the opposite state by an externally applied trigger, it will
recover to the stable state in a period of time usually controlled by a
resistance-capacitance (RC) coupling circuit.
An astable multivibrator has two possible states,
neither of which is stable, and switches between the two states, usually
controlled by two RC coupling time constants. The astable circuit is
one form of relaxation oscillator, which generates recurrent waveforms at a
controllable rate.
In this project, we discover the real purpose behind
the invention of multivibrators. We learn about the different aspects of use
and applications of multivibrators. We learn the causes and effects of using
a particular kind of multivibrator in a particular field in accordance to the
fact that there are numerous kinds of multivibrators used for different
purposes.
We must admit
that we’ve been guilty of using a microcontroller to make two LEDs blink
alternately in the past. It’s not the worst transgression, but it stems from
our discomfort with analog circuits. Luckily, [Ray] published an illustrated
guide on building multivibrator circuits. This is a simple method of
assembling a two-output oscillator. All it takes is a pair of NPN
transistors, which are then switched by on and off based on a
resistor-capacitor (RC) timer.
Through this project, we do the good job of walking
through how the circuit works at each stage of one complete cycle. The carefully read, studies and used
supplementary schematics to water down snap shots of the various electrical
states are mentioned in the different parts of this project.
Of course, blinking LEDs isn’t the sole purpose of a
multivibrator. It is a method of producing a clean square wave which can be
used as a clock signal for TTL logic chips. Multivibrator is much more and
all the study has been reported through the project names as ‘Design and
Simulation of Multivibrators’.
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