RIVERS STATE UNIVERSITY
OF SCIENCE AND TECHNOLOGY
NKPOLU-OROWUROKWO, PORT
HARCOURT
MINI-PROJECT
ON
ELECTRIC FLOAT SWITCH
CAPABLE OF CONTROLLING A MOTOR
PRESENTED
BY
TARIAH TAMUNOBIRINENGI
DE.2010/0631
SUPERVISOR:
ENGR. F.M. ODEYEMI
MARCH, 2015
ABSTRACT
This
is a simple economical circuit switches on the motor pump when water in the
overhead tank falls below the lowest level it turned ON, and when the tank is
full it turns it OFF.
The
water level controller circuit is built around IC 555 to monitor the water
level in the overhead tank and the on/off status of the motor through the inverter
and driver circuits.
I
should like to thank my lecturer in Rivers State College of Arts and Science,
Rumuola Port Harcourt, Electrical Engineering Department Engr. Samuel Davies.
Who supported and encouraged me with a re-think of Electronics Engineering.
I
should like to thank my Lecturer Engr. F.M. Odeyemi, for is great approach in
teaching and impacting knowledge.
I
should like to thank Engr. T. Jenewari, for his teaching and ideas.
Many
thanks to all my friends, who have helped out along the way. By discussing
ideas or reading chapter.
Contents
CHAPTER ONE
1.0 INTRODUCTION
This is a simple, economical and
versatile circuit switches on the motor pump , when water in the overhead tank
falls below the lowest it turn on the pump and also when it is full it switch
it off automatically.
The water level controller circuit is
built around IC555 (IC2) to monitor the water level in the overhead
tank and ‘ON’/OFF statues of the motor through the water.
The circuit uses a transformer to step
down the ac voltage to 15v ac which is being rectified by the help of a diode
to give a dc voltage, and the capacitor help to reduce the ripple in converting
ac to dc voltage. The series-current limiting resistor R1, regulator
IC1, and noise filtering capacitors C2, C3. The constant
voltage regulator gives a steady voltage irrespective of the fluctuation in
input voltage. Electrodes are suspended into the tank such that they don’t
touch each other.
1.1 AIM
AND OBJECTIVE
·
To provide the
home with water at all time.
·
To save energy
and resources.
·
It used at home as
overhead tank water controller.
·
It brings better
understanding about transistor switching and how the works.
1.2 SCOPE
OF STUDY
The scope of this study is to design
and construct electric float switch capable of controlling 2 Hp electric pumps, for
home, office or any system where electricity is use.
LIMITATION
It cannot be used for ac voltage
greater than 240 volt.
CHAPTER TWO
2.1 TRANSISTORS
BJT (bipolar junction transistor) are widely
used an amplifier, oscillator, switch etc. It is a current-driven device (MOSFET is voltage
driven), the output current is equal to the input current times a factor which
is called Gain. A basic BJT has three pins: the Base, Collector, and Emitter.
The
output characteristic curve is useful as it shows the variations in collector
current Ic, for a given base current, Ib over a range of
collector-emitter voltage, Vce. This gives us the modes of the BJT
under different conditions. There are three modes in BJT – Forward-Active (Amplification), Saturation, and Cut-off.
Fig. 2.1
Saturation: high current
conduction from the emitter to the collector. This mode corresponds to a closed
switch. This could be also used for resistors simulation in small
circuits.
Cut-off: The biasing condition
is the opposite of saturation (both junctions reverse biased) which corresponds
to an open switch. The cut-off and saturation can be used together to form
a digital (1 or 0) type of circuit for computers.
Forward-active: This is the
linear region of the curves (shown as amplification mode in the diagram). The
collector-emitter current is approximately proportional to the base current,
but many times larger, for small base current variations. BJT amplifiers use
the Forward-active characteristics.
As a switch:
Current-limiting resistors are usually
used between the Arduino or other micro controllers and BJT to prevent damage
and overheating from large current. Protection diodes are also sometimes
used in case of Back-EMF from an inductive load. For NPN BJT, the emitter is
always connected to either the negative voltage supply (i.e. GND) and the
collector is always connected to the load. The base is used to activate
the switch.
As an amplifier:
When
used as an amplifier, the biasing is arranged so that the transistor operates
in the linear region (shown above as almost horizontal sections). An
amplifier will usually be biased to about half the supply voltage to allow
for maximum output swing.
Type of BJT
There
are two types of BJT transistors PNP and NPN based on the doping types of the three main terminal
silicon layers.
PNP: usually used as
a high-side switch where the emitter of a PNP transistor connects to the
voltage supply, the collector connects to the load. To turn this transistor
off, we can connect the base to the emitter. Turning this transistor on is a
little confusing because a negative current or a 0v (GND) signal needs to
be applied to the base.
NPN: usually used as
a low-side switch, the emitter of an NPN transistor connects to the GND, the
collector connects to the load. To turn this transistor off, the base must
connect to the emitter (GND). This transistor is turned on by applying a
positive current to the base.
WORKING
THEORY
Power supply is obtained through step down transformer T1, diode D1 through D4, capacitor C1, series current limited
resistor R1, regulator IC1, and noise filtering capacitor C2 and C3. The set-up
for the water –level sensing electrodes is shown below:
Fig. 2.2: Water-level electrodes set-up for overhead tank
For the sensor electrodes, use a moulded-type
AC chord (used for tape recorders) with its pair of wires sleeved at the end
and connected together to form the electrode.
Other electrodes can be made similarly. The three AC chords are
suspended inside the tank from a longitudinally cut PVC pipe (used for
electrical wiring).
The arrangement for the dry pump sensor is
shown above at fig. 2.2. A moulded-type AC chord with its pair of wire sleeved
at the end can be attached firmly to the delivery pipe such that waterfalls
onto the plug lead.
A
BJT is formed of a three-layer sandwich of doped semiconductor materials,
either PNP or NPN. Each layer has a specific name, i.e. collector, emitter and
base.
Fig.
2.2
The
proper biasing of the junctions when operating is the functional difference
between a PNP transistor and an NPN transistor. For any given state of
operation the current directions and voltage polarities for each kind of
transistor are opposite.
Bipolar
Junctions Transistors is current controlled which means a smaller current at
the base controls the main current at the collector and emitter. For PNP
transistors the main current goes from collector to emitter and the small
controlling current goes from emitter to base, while for NPN transistors the main
current goes from emitter to collector and the controlling current goes
from base to emitter.
Fig. 2.3
For
example in an NPN transistor, when positive bias is applied to the base, the
equilibrium is disturbed between the thermally generated carriers and
the repelling electric field of the n-doped emitter depletion region. This
allows thermally excited electrons to inject from the emitter into the base.
These
electrons diffuse through the base from the high concentration
region near the emitter towards the low concentration region near the
collector. The electrons are minority carriers and hole
the majority carrier in the base, because the base is P-doped.
2.3 RELAYS
A relay is defined as an
electrically controlled device that opens and closes electrical contacts, or
activates and deactivates operation of other devices in the same or another
electrical circuit. Two types of relay technology are available, mechanical and
solid state. A mechanical relay is essentially a combination of an inductor and
a switch, where the electromagnetic force of the inductor causes a switch to
change position. A solid state relay accomplishes the same function with
semiconductor devices changing impedance to effectively activate or deactivate
a circuit open or closed.
2.4 555 TIMER
The 8-pin 555 timer must
be one of the most useful chips ever made and it is used in many projects. With
just a few external components it can be used to build many circuits, not all
of them involve timing.
A popular version is the
NE555 and this is suitable in most cases where a 555 timer' is specified. The
556 is a dual version of the 555 housed in a 14-pin package, the two timers (A
and B) share the same power supply pins. Low power versions of the 555 are
made, such as the ICM7555, but these should only be used when specified (to
increase battery life) because their maximum output current of about 20mA (with
a9V supply) is too low for many standard 555 circuits. The ICM 7555 has the
same pin arrangement as a standard 555.
The circuit symbol for a
555 (and 556) is a box with the pins arranged to suit the circuit diagram: for
example 555 pin 8 at the top for the +Vs supply, 555 pin 3 outputs on the right.
Usually just the pin numbers are used and they are not labeled with their function.
The 555 can be used with a
supply voltage (Vs) in the range 4.5 to 15V (18V absolute maximum).
Standard 555 chips create
a significant 'glitch' on the supply when their output changes state. This is
rarely a problem in simple circuits with no other ICs, but in more complex
circuits a smoothing capacitor (eg
100μF) should be connected across the +Vs and 0V supply near the 555.
The input and output pin
functions are described briefly below and there are fuller explanations
covering the various circuits:
1.
Astable - producing a square wave
2.
Monostable -
producing a single pulse when
triggered
3.
Bistable - a simple memory which can be set and reset Buffer - an
inverting buffer (Schmitt trigger).
Definition
of Pin Functions:
Pin 1
(Ground): The ground (or common) pin is the
most-negative supply potential of the device, which is normally connected to
circuit common (ground) when operated from positive supply voltages.
Pin 2
(Trigger): This pin is the input to the lower
comparator and is used to set the latch, which in turn causes the output to go
high. This is the beginning of the timing sequence in monostable operation.
Triggering is accomplished by taking the pin from above to below a voltage
level of 1/3 V+ (or, in general, one-half the voltage appearing at pin 5). The
action of the trigger input is level-sensitive, allowing slow rate-of-change
waveforms, as well as pulses, to be used as trigger sources. The trigger pulse
must be of shorter duration than the time interval determined by the external R
and C. If this pin is held low longer than that, the output will remain high
until the trigger input is driven high again.
One
precaution that should be observed with the trigger input signal is that it
must not remain lower than 1/3 V+ for a period of time longer than the
timing cycle. If this is allowed to happen, the timer will retrigger itself
upon termination of the first output pulse. Thus, when the timer is driven in
the monostable mode with input pulses longer than the desired output pulse
width, the input trigger should effectively be shortened by differentiation.
The
minimum-allowable pulse width for triggering is somewhat dependent upon pulse
level, but in general if it is greater than the 1uS (micro-Second), triggering
will be reliable.
A
second precaution with respect to the trigger input concerns storage time in
the lower comparator. This portion of the circuit can exhibit normal turn-off
delays of several microseconds after triggering; that is, the latch can still
have a trigger input for this period of time after the trigger pulse. In
practice, this means the minimum monostable output pulse width should be in the
order of 10uS to prevent possible double triggering due to this effect.
The
voltage range that can safely be applied to the trigger pin is between V+ and
ground. A dc current, termed the trigger current, must also flow from
this terminal into the external circuit. This current is typically 500nA
(nano-amp) and will define the upper limit of resistance allowable from pin 2
to ground. For an astable configuration operating at V+ = 5 volts, this
resistance is 3 Mega-ohm; it can be greater for higher V+ levels.
Pin 3
(Output): The output of the 555 comes from a
high-current totem-pole stage made up of transistors Q20 - Q24. Transistors Q21
and Q22 provide drive for source-type loads, and their Darlington connection
provides a high-state output voltage about 1.7 volts less than the V+ supply
level used. Transistor Q24 provides current-sinking capability for low-state
loads referred to V+ (such as typical TTL inputs). Transistor Q24 has a low
saturation voltage, which allows it to interface directly, with good noise
margin, when driving current-sinking logic. Exact output saturation levels vary
markedly with supply voltage, however, for both high and low states. At a V+ of
5 volts, for instance, the low state Vce(sat) is typically 0.25
volts at 5 mA. Operating at 15 volts, however, it can sink 200mA if an
output-low voltage level of 2 volts is allowable (power dissipation should be
considered in such a case, of course). High-state level is typically 3.3 volts
at V+ = 5 volts; 13.3 volts at V+ = 15 volts. Both the rise and fall times of
the output waveform are quite fast, typical switching times being 100nS.
The
state of the output pin will always reflect the inverse of the logic state of
the latch, and this fact may be seen by examining Fig. 3. Since the latch
itself is not directly accessible, this relationship may be best explained in
terms of latch-input trigger conditions. To trigger the output to a high
condition, the trigger input is momentarily taken from a higher to a lower
level. [see "Pin 2 - Trigger"]. This causes the latch to be set and
the output to go high. Actuation of the lower comparator is the only manner in
which the output can be placed in the high state. The output can be returned to
a low state by causing the threshold to go from a lower to a higher level [see
"Pin 6 - Threshold"], which resets the latch. The output can also be
made to go low by taking the reset to a low state near ground [see "Pin 4
- Reset"].
The
output voltage available at this pin is approximately equal to the Vcc applied
to pin 8 minus 1.7V.
Pin 4
(Reset): This pin is also used to reset the
latch and return the output to a low state. The reset voltage threshold level
is 0.7 volt, and a sink current of 0.1mA from this pin is required to reset the
device. These levels are relatively independent of operating V+ level; thus the
reset input is TTL compatible for any supply voltage.
The
reset input is an overriding function; that is, it will force the output to a
low state regardless of the state of either of the other inputs. It may thus be
used to terminate an output pulse prematurely, to gate oscillations from
"on" to "off", etc. Delay time from reset to output is
typically on the order of 0.5 μS, and the minimum reset pulse width is 0.5 μS.
Neither of these figures is guaranteed, however, and may vary from one manufacturer
to another. In short, the reset pin is used to reset the flip-flop that
controls the state of output pin 3. The pin is activated when a voltage level
anywhere between 0 and 0.4 volt is applied to the pin. The reset pin will force
the output to go low no matter what state the other inputs to the flip-flop are
in. When not used, it is recommended that the reset input be tied to V+ to
avoid any possibility of false resetting.
Pin 5
(Control Voltage): This pin allows direct access to the
2/3 V+ voltage-divider point, the reference level for the upper comparator. It
also allows indirect access to the lower comparator, as there is a 2:1 divider
(R8 - R9) from this point to the lower-comparator reference input, Q13. Use of
this terminal is the option of the user, but it does allow extreme flexibility
by permitting modification of the timing period, resetting of the comparator,
etc.
When
the 555 timer is used in a voltage-controlled mode, its voltage-controlled
operation ranges from about 1 volt less than V+ down to within 2 volts of
ground (although this is not guaranteed). Voltages can be safely applied
outside these limits, but they should be confined within the limits of V+ and
ground for reliability.
By
applying a voltage to this pin, it is possible to vary the timing of the device
independently of the RC network. The control voltage may be varied from 45 to
90% of the Vcc in the monostable mode, making it possible to control the width
of the output pulse independently of RC. When it is used in the astable mode,
the control voltage can be varied from 1.7V to the full Vcc. Varying the
voltage in the astable mode will produce a frequency modulated (FM) output. In
the event the control-voltage pin is not used, it is recommended that it be
bypassed, to ground, with a capacitor of about 0.01uF (10nF) for immunity to
noise, since it is a comparator input. This fact is not obvious in many 555
circuits since I have seen many circuits with 'no-pin-5' connected to anything,
but this is the proper procedure. The small ceramic cap may eliminate false
triggering.
Pin 6
(Threshold): Pin 6 is one input to the upper
comparator (the other being pin 5) and is used to reset the latch, which causes
the output to go low.
Resetting
via this terminal is accomplished by taking the terminal from below to above a
voltage level of 2/3 V+ (the normal voltage on pin 5). The action of the
threshold pin is level sensitive, allowing slow rate-of-change waveforms.
The
voltage range that can safely be applied to the threshold pin is between V+ and
ground. A dc current, termed the threshold current, must also flow into
this terminal from the external circuit. This current is typically 0.1μA, and
will define the upper limit of total resistance allowable from pin 6 to V+. For
either timing configuration operating at V+ = 5 volts, this resistance is 16 MΩ
For 15 volt operation, the maximum value of resistance is 20 MΩ.
Pin 7
(Discharge): This pin is connected to the open
collector of a NPN transistor (Q14), the emitter of which goes to ground, so
that when the transistor is turned "on", pin 7 is effectively shorted
to ground. Usually the timing capacitor is connected between pin 7 and ground
and is discharged when the transistor turns "on". The conduction
state of this transistor is identical in timing to that of the output stage. It
is "on" (low resistance to ground) when the output is low and
"off" (high resistance to ground) when the output is high.
In both the monostable and astable time modes,
this transistor switch is used to clamp the appropriate nodes of the timing
network to ground. Saturation voltage is typically below 100mV (milli-Volt) for
currents of 5 mA or less, and off-state leakage is about 20nA (these parameters
are not specified by all manufacturers, however).
Maximum
collector current is internally limited by design, thereby removing
restrictions on capacitor size due to peak pulse-current discharge. In certain
applications, this open collector output can be used as an auxiliary output
terminal, with current-sinking capability similar to the output (pin 3).
Pin 8 (V +): The V+ pin (also referred to as Vcc) is the
positive supply voltage terminal of the 555 timer IC. Supply-voltage operating
range for the 555 is +4.5 volts (minimum) to +16 volts (maximum), and it is specified
for operation between +5 volts and + 15 volts. The device will operate
essentially the same over this range of voltages without change in timing
period. Actually, the most significant operational difference is the output
drive capability, which increases for both current and voltage range as the
supply voltage is increased.
Inputs of 555
Trigger input: when < 1/3 Vs ('active low') this makes
the output high (+Vs). It monitors the discharging of the timing capacitor in
an astable circuit. It has a high input impedance > 2M .Threshold input:
when > 2/3 Vs ('active high') this makes the output low (0V). It monitors
the charging of the timing capacitor in astable and monostable circuits. It has
a high input impedance > 10M providing the trigger input is < 1/3 Vs (the
trigger input overrides the threshold input).Reset input: when less than about
0.7V ('active low') this makes the output low (0V), overriding other inputs.
When not required it should be connected to +Vs. It has an input impedance of
about 10k .Control input: this can be used to adjust the threshold voltage
which is set internally to be 2/3 Vs. Usually this function is not required and
the control input is connected to 0V with a 0.01μF capacitor to eliminate electrical
noise. It can be left unconnected if noise is not a problem. The discharge pin
is not an input, but it is listed here for convenience. It is connected to 0V
when the timer output is low and is used to discharge the timing capacitor in
astable and monostable circuits.
Output of 555
The output of a standard 555 or 556
can sink and source up to 200mA. This is more than most chips and it is
sufficient to supply many output transducers directly, including LEDs (with a
resistor in series), low current lamps, piezotransducers, loudspeakers (with a
capacitor in series), relay coils (with diode protection) and some motors (with
diode protection). The output voltage does not quite reach 0V and +Vs,
especially if a large current is flowing. To switch larger currents you can
connect a transistor. The ability to both sink and source current means that
two devices can be connected to the output so that one is on when the output is
low and the other is on when the output is high. The top diagram shows two LEDs
connected in this way. This arrangement is used in the Level Crossing project
to make the red LEDs flash alternately Loudspeakers.
CHAPTER THREE
3.0 DESIGN
AND CALCULATION
Fig. 3.1 circuit of the water level controller
3.2
POWER SUPPLY
The power supply unit is a 2-way
automatic power supply system. It gets input from both mains supply and battery
supply. The two independent supply systems are connected to a relay switch which
acts as an automatic change over switch to switch on any of the available input
supply to the main circuit. The power supply unit provides power supply to the
other two units of the circuit.
Fig. 3.2: The schematic diagram of the
power supply unit is shown below.
Fig. 3.2: The schematic diagram of the power
supply unit
F1 is a protective fuse used to
prevent excess current from entering the circuit. T1 is a step down transformer.
D1, D2, D3, and D4 are rectifier diodes. C1 is a filter capacitor. IC1 is a
regulator IC. R1 is current limiting resistors protecting the circuit.
3.2.1 Operation of the Power Supply Unit
The operation of the power supply unit
can be illustrated by the block diagram shown in Fig. 3 below.
Fig.3.3: Block diagram of the power supply
unit
The block diagram consist of 4 stages
for rectification of 240V (A.C) mains supply to 12V (D.C), and a relay switch.
The description of each stage is given below:
3.2.2. Transformer Stage
This stage consists of a 240V/18V,
step down transformer. It converts the 240V (A.C) voltage supply from mains to
18V (A.C), a 1A fuse (F1) was incorporated at the primary side of the
transformer to protect it from excess current. The 18V (A.C) supply is then
passed to the rectifier stage. A 220V/18V step down transformer was chosen
because the regulator used required more than 15V for its operation.
3.2.3. Rectifier Stage
In this stage, the rectifier converts
the 18V (A.C) supply from the transformer into a pulsating D.C voltage. A full
bridge rectifier was used for this purpose. It consist of four diodes (1N
4001series) arranged as shown in Fig. 2. During the positive half cycles diodes
D2 and D3 are forward biased and current flows through the terminals. In the
negative half cycle, diodes D1 and D4 are forward biased. Since load current is
in the same direction in both half cycles, full wave rectifier signal appears
across the terminals.
3.2.4. Filter Stage
The pulsating D.C voltage that comes
out from the rectifier stage is converted into constant D.C voltage with the
aid of a filter capacitor (C1). This capacitor is large value electrolytic
capacitor. It charges up (i.e. store energy) during the conduction half cycle
thereby opposing any changes in voltage. The filter stage therefore filters out
voltage pulsations (or ripple).
3.2.5. Regulator Stage
The output of the filter stage varies
slightly when the load current or output voltage varies and it is an 18V D.C
supply which is higher than the circuit requirement. For these reasons, a 7812
Regulator was used to stabilize the voltage and also reduce it from 18V to a 15V
steady D.C supply.
3.3
ASTABLE AND MONOSTABLE VIBRATOR
Fig. 3.4 astable and monostable vibrator
Standard 555 astable circuit in astable mode, the 555 timer puts
out a continuous stream of rectangular pulses having a specified frequency.
Resistor R1 is connected between VCC and the
discharge pin (pin 7) and another resistor (R2) is connected between
the discharge pin (pin 7), and the trigger (pin 2) and threshold (pin 6) pins
that share a common node. Hence the capacitor is charged through R1 and
R2, and discharged only through R2, since pin 7 has low
impedance to ground during output low intervals of the cycle, therefore
discharging the capacitor.
In the astable mode, the frequency of the pulse stream depends
on the values of R1, R2 and C:
The high time from each pulse is given by:
And the low time from each pulse is given by:
Where R1 and R2 are the values
of the resistors in ohms and C is the value of the
capacitor in farads.
The power capability of R1 must be greater than
.
Particularly with bipolar 555s, low values of
must be avoided so that the output stays saturated near
zero volts during discharge, as assumed by the above equation. Otherwise the
output low time will be greater than calculated above. The first cycle will take
appreciably longer than the calculated time, as the capacitor must charge from
0V to 2/3 of VCC from power-up, but only from 1/3 of VCC to
2/3 of VCC on subsequent cycles.
To achieve a duty cycle of
less than 50% a small diode (that is fast enough for the application) can be
placed in parallel with R2, with the cathode on the capacitor side.
This bypasses R2 during the high part of the cycle so that the
high interval depends approximately only on R1 and C. The
presence of the diode is a voltage drop that slows charging on the capacitor so
that the high time is longer than the expected and often-cited ln(2)*R1C
= 0.693 R1C. The low time will be the same as without the diode as shown
above. With a diode, the high time is
Where Vdiode is when the diode has a current of
1/2 of Vcc/R1 which can be determined from its
datasheet or by testing. As an extreme example, when Vcc= 5 and Vdiode=
0.7, high time = 1.00 R1C which is 45% longer than the
"expected" 0.693 R1C. At the other extreme, when Vcc=
15 and Vdiode= 0.3, the high time = 0.725 R1C which is
closer to the expected 0.693 R1C. The equation reduces to the
expected 0.693 R1C if Vdiode= 0.
The operation of RESET in this mode is not well defined, some
manufacturers' parts will hold the output state to what it was when RESET is
taken low, and others will send the output either high or low.
Monostable
Fig.
3.4: Schematic of a 555 in monostable mode
Fig.
3.5
The relationships of the trigger signal, the voltage on C and
the pulse width in monostable mode in the monostable mode, the 555 timer acts
as a "one-shot" pulse generator. The pulse begins when the 555 timer
receives a signal at the trigger input that falls below a third of the voltage
supply. The width of the output pulse is determined by the time constant of an
RC network, which consists of a capacitor (C)
and a resistor (R).
The output pulse ends when the voltage on the capacitor equals 2/3 of the
supply voltage. The output pulse width can be lengthened or shortened to the
need of the specific application by adjusting the values of R and C.
The output pulse width of time t, which is the time
it takes to charge C to 2/3 of the
supply voltage, is given by
While using the timer IC in monostable mode, the main
disadvantage is that the time span between any two triggering pulses must be
greater than the RC time constant.
CHAPTER FOUR
4.0 CALCULATION, TESTING AND DISCUSSIONS
4.1 CALCULATION
A 240/18V transformer was chosen
because its rating is capable of meeting the current demand of the circuit and
it is protected by the 1A fuse against excess current.
The peak inverse voltage (PIV)
obtainable at the secondary terminal transformer is twice the terminal voltage
Vs.
That is: PIV = 2 x Vs =2 x 15 = 30V.
At the full bridge rectifier circuit
1N4001 diode was used because its PIV which is 50V is greater than the PIV of
the secondary of the secondary terminal which is 36V [13]. This was done to
avoid damage to the diodes in case reverse operation occurs. The value of the
filter capacitor C1 was obtained as:
(For full wave rectifier
circuits)[13], where: f= frequency of ripple voltage = 50Hz y= tipple factor=
5%0.05
V = Constant output voltage from the
regulator = 12v, I = Constant output current from the regulator = 500mA = 0.5A
To ensure that the current is
sufficient to drive the transistor into saturation, the quantity of the current
is doubled i.e.
‘B 0.00 12x2 = 0.024A
4.3. TESTING AND CASING
In testing the designed and
constructed system, basic steps were taken. These steps are sequentially listed
below as:
·
To ensure that
all the components to be used are functionally operating, they were first
tested with a digital multi meter and failed ones replaced before finally
soldering them on the veroboard.
·
To ensure that
there was no breakage in the circuit path on the veroboard, immediately after
soldering on veroboard, the circuit path was tested using the Digital
Multi-meter. This was done to also ensure continuity of circuit on the
veroboard.
·
Using Circuit
WIZARD (Student Edition), the circuit was simulated. The result obtained from
the simulation closely corresponds to the desired result, with only some slight
variations.
·
Switch On the
power to the circuit.
·
LED! Glows and
relay R1 energizes, the energized relay indicates ‘ON’ statue of the motor.
·
Immerse points B
an Lin water, as would be the case when the water level rises. Momentarily
touch point U to water. LED! Goes ‘OFF’ and the relay reenergizes to turn the
pump ‘OFF’. This would be the case when water touches the overflow limit.
·
Remove points U
and B from water, assuming that water has fallen below the lowest limit because
of consumption. Two second later, LED1 glows and the relay energize.
The main reason for testing all the
components before they were finally soldered on the Veroboard is to avoid the
painstaking effort it will take to dis-solder faulty components at the end of
the day. From the continuity test carried out on the veroboard to check the
circuit path, it was discovered that the circuit was in a perfect working
condition as continuity was ensured. Simulation of the circuit design was also
done as mentioned. This section described the steps taken in the verification
of calculated results through the real time implementation and measurements.
The construction of the system is in 2 stages; the soldering of the components
and the coupling of the entire system to the casing. The power supply stage was
first soldered stage by stage. Each stage was tested using the multi-meter to
make sure it is working properly before the next stage is done. This helps to
detect mistakes and faults easily. The soldering of the circuit was done on a
10cm by 24cm Veroboard. The second stage of the system construction is the
casing of the soldered circuit. Casing refers to the outer covering or something
that serves as a container or covering. For the purpose of this system, the
material used for the casing was a plastic box. Proper dimensioning of the
casing was marked out to give the desired shape based on the size of the
constructed project work on Vero-board. After fabricating the file and painting
the casing to give aesthetic values to the system.
4.4 PRECAUTIONS:
·
Make
sure that water being delivered from the water pipe does not touch any of the
suspended water level sensors.
·
Use a
properly shield cable to carry signals from the tank to the water level
controller unit.
Fig. 4.1 final circuit of the water level
controller
Fig. 4.2: PCB Layout of circuit of the water
level controller
BILL OF MATERIALS
NAME
|
COST (NAIRA)
|
QUANTITY
|
TOTAL(NAIRA)
|
0.01UF
|
50
|
1
|
50
|
0.1UF ELECTROLYTIC CAPACITOR
|
50
|
2
|
100
|
1UF ELECTROLYTIC CAPACITOR
|
50
|
3
|
150
|
10 OHMS RESISTOR
|
20
|
1
|
20
|
1000UF ELECTROLYTIC CAPACITOR
|
150
|
1
|
150
|
10K OHM REISITOR
|
20
|
2
|
40
|
13(W)BY 11(H)
|
200
|
1
|
200
|
1M OHMS RESISTOR
|
20
|
3
|
60
|
1N4001 DIODE
|
20
|
5
|
100
|
7812(12V,1A)VOLTAGE REGULATOR
|
100
|
1
|
100
|
BC548B NPN TRANSISTOR
|
100
|
1
|
100
|
LED(RED)
|
30
|
1
|
30
|
NE555 BIPOLAR TIMER
|
200
|
1
|
200
|
TRANSFORMER(15V, 1A)
|
800
|
1
|
800
|
TOTAL
|
2100
|
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
The project was design and constructed
with the appropriate equations to make sure the arms and objective goals was
achieved, after the design every step was follow carefully and changes were
necessarily taken care off, the project works effectively with a pulsating
sound when there is power on and also ring with a full sound when there is
power off for the duration of time set by the monostable vibrator.
5.2 RECOMMENDATION
Provision of laborites and research
center should be made to encourage student in project and research work and
also engineering journals and other related work should be provided in the
libraries which will make the work easier and interesting.
REFERENCES
Edward Hughes, Hughes
Electrical technology, Addition Wesley Longman
(Singapore) plc Ltd, India, Seventh Edition, (pp 395-399). (2001)
Electronics for you.
Electronicsforu.com/electronicsforu/circuitarchives/view_article.asp?sno=221.
Mechnical and Nuclear
Engineering, The 555 Timer IC, John Cimbala (2010-01-12)
J. Shepherd, A.H Morton
and L.F Spence, Basic Electrical Engineering”,
Pitman Publishing Reprinted 1973, Page 274- 278.
Paul Horonitz and
Weinbeild Hill, the Art of Electronics, second Edition,
Cambridge University Ulc.(1995)
Ray Marston, “Relay Output
Circuits”, Electronics Now Magazine, July
1994
download pdf here
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