Evolution of Electronics and Solid State Control System

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ABSTRACT.
Evolution of electronics has given birth to
mother of all inventions. Solid state
control system is rapidly replacing
outdated mechanical technology that has
been in use over decades. During olden
days, a simple task such as amplification
of small signals seemed like a mountain
task. All credit to the changing dynamics
of the solid state controls whereby such
task are easily implemented with easily
accessible devices such as transistors. In
this report, experiments have been carried
in the laboratory. The transistor amplifier,
oscillators based on Nor gate and the 555
chip have been physically built. In
addition, delay unit has been implemented.
The characteristics of theof various
components used have been investigated
under different circumstances and
condition. Analysis of the findings have
also been dealt with and conclusion made
on the same.
LITERATURE REVIEW.
Transistor amplifier.
Signal amplification is the process by
which amplifier circuit records amplified
output signal that is a version of the input
signal. The transistor amplifier as the name
denotes is the amplification circuitry that is
purely dependent on the transistor [1].
Common emitter Amplifier is the most
used configuration for transistors that are
based on NPN transistors. The transistor
amplifier shown in the figure 1 is a single
stage amplifier that uses Voltage Divider
Biasing using Vcc and resistors R1 and R2
[2].In this type of the amplifier, resistor R3
is the current limiter which limits the
amount of base current to a value safe for
the normal operation of the amplifier. This
operation of this amplifier combines both
A.C and D.C voltage signals although the
designated purpose refers to the operation
of the AC signals.
The D.C analysis of the circuit is
determined by removing AC voltage
source and the coupling capacitors.
Thereafter, the DC biasing voltage ac then
be found using voltage divider. This
voltage is sometimes refers to as Thevenin
voltage. The AC voltage gain is a factor
determinant to the biasing voltage and
output voltage of the DC component.
Adc = V b
V a
Where Vb is voltage at node (b)
considered as the output and Vb is voltage
at point (a), taken as the input.
On the other hand, AC analysis is
performed by grounding Vcc and short
circuiting coupling capacitor C. The
impedance of the capacitor shown below is
inversely proportional to the frequency [3].
X c= 1
2 πCf
Where C is the capacitance and f is the
frequency of the voltage source Vs. The
AC voltage gain of the transistor is given
by;
Aac = V b−ac
V a−ac
In general, this amplifier is also called
Inverting Amplifier since variation of base
voltage is inversely proportion to the
corresponding variation of the output
voltage. In other words, the input and
output signals are out of phase by 1800.
Oscillator based Nor gate.
A Nor gate is a logic component whose
output is high and only goes when at least
one of its input is high. A group of Nor
gates are manufactured in a single chip
such as in CD4001BCN chip that consist

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of four Nor gates. A multiple switching
between high and low value can be
realized with integration of logic gate
family. These logic gates are fundamental
blocks that gives characteristic output
depending on the input signal [4]. They
can be connected in tandem an oscillator
based Nor gate is as shown figure 2.
Design of oscillator and delay unit using
555chip
555 chip is an IC that is mostly used to
produce fine timing pulses. It operates in
three modes namely astable, monostable
and bistable. In astable mode of operation,
the output oscillates between low and high.
Therefore in astable mode, the 555 chip
can be used as clock to generate square
waves to execute many application.
However, in the monostable mode, the
user inputs an external state which is
displayed at the output. When the interrupt
subsides, the output goes automatically to
high since at this state it is unstable at low.
Finally, bistable mode have both outcomes
stable, either high or low. So, depending
on the type of interrupt, the output remains
in the initialized status until it receives
another interrupt [5].
A voltage controlled oscillator (VCO)
based IC 555 chip is basically used to
controlled frequency of the digital signal
using the voltage. The digital signal
waveform reciprocates repeatedly between
high and low state thus displaying a square
wave. By varying the input voltage, variety
of the frequencies can therefore be
obtained at the output pin of the oscillator
[6]. The output signal can be useful to
applications that need clocking system
such as processors. The circuit of voltage
controlled oscillator based on the IC 555
chip is as shown in figure 5.
Using IC 555 chip to fabricate a delay unit,
it can be operated in two modes namely a
monostable mode of operation and astable
mode of operation. The delay unit is said
to be in astable operation mode when pin 2
is connected to pin 6 thus self-triggering.
On the other hand, the delay unit is
considered to be in monostable operation
mode when the triggering elements are
externally located from the chip [7]. An
example of a monostable-type delay unit is
as shown in the figure 6.
External triggering signal for the time
delay circuit above changes with variation
of resistor R3 and Capacitor C2.
INTRODUCTION.
The project has dealt with pertinent issues
concerning practical implementation of the
electronic circuits. This report is divided
into four section with each section
designated a particular project task.
Modelling of the each assignment has been
outlined and results and analysis have been
tackled in the next section. Each model
was individually investigated and results
discussed in the next section.
SYSTEM MODEL
Designing of the amplifier.
The circuit as shown in figure 1 was
constructed on a breadboard. The values
R1=51kΩ, R2=5.1 kΩ, R3=1 kΩ, R4=82
kΩ, C=0.47μF and Vcc=9V. The source
voltage was set to a magnitude of 0.1V
with 1kHz frequency.

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Fig 1: Common emitter transistor
amplifier.
AC and total voltages at node (a) and (b)
were determined using a digital multimeter
(DMM) and recorded simultaneously.
With values obtained above, it was
possible to calculate DC and AC voltage
gains of the transistor amplifier. The phase
different between AC components for
Va(AC) and Vb(AC) was also noted from
the equivalent signals in displayed the
oscilloscope.
Procedure for verifying input voltage
limitation to the output waveform was
conducted by resetting Vs gradually from
its initial value to 0.3V and concurrently
recording the output waveform Vb(Total)
and Vb(AC). In addition, the maximum
value of Vb(total) was deduced from the
oscilloscope.
Input frequency which is the factor that
directly influences output voltage was
proven experimentally by varying
frequency of Vs within a range of 10Hz
and 1MHz and noting the peak value of
Vb(AC). Values obtained were used to
determine the gain of the amplifier.
Furthermore, a plot of gain (A) against
frequency was plotted with help of Matlab
Software.
Designing of the oscillator based on Nor
gates.
The oscillator circuit was fabricated on the
breadboard as shown in the figure below.
Fig 2: Nor based oscillator
CD4001BCN chip was powered by
supplying Vcc=9V between Vcc pin (14)
and GND pin (7).
Waveforms at nodal points Va, Vb and Vc
were determined using the oscilloscope.
Besides waveforms, oscillating frequency
of the output waveform Vc was obtained
too.
Mounted oscillator was then coupled with
the amplifier by connecting output of the
oscillator to the input of the amplifier as
shown in the figure below.
Fig 3: Combined Nor gate
oscillator and the amplifier.