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3.2 HARDWARE DESCRIPTION
3.2.1 POWER SUPPLY
Power supply is a supply of electrical power. A device or system that supplies
electrical or other types of energy to an output load or group of loads is called a power supply
unit or PSU. The term is most commonly applied to electrical energy supplies, less often to
mechanical ones, and rarely to others.
The electric power normally is not used in the form in which it was produced or
distributed. Practically all of electronic systems require some form of power conversion. The
device that transfers electric energy from the source to the load, using electronic circuits is
referred to as power supply, although a more accurate term for such a device is a power
converter. A typical application of a power supply is to convert utility AC voltage to
regulated DC voltages required for electronic equipments. Nowadays, in most power supplies
providing more than a few watts the energy flow is controlled with power semiconductors
that are continuously switching on and off with high frequency. Such devices are referred to
as switch mode power supplies or SMPS.
3.2.2 ULTRASONIC TRANSDUCERS
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Ultrasonic sensors (also known as transceivers when they both send and receive) work
on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the
echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency
sound waves and evaluate the echo which is received back by the sensor. Sensors calculate
the time interval between sending the signal and receiving the echo to determine the distance
to an object.
40 kHz ultrasonic transducer matched pair (transmitter and receiver). The general
transducer design features a piezo ceramic disc bender that is resonant at a nominal frequency
of 20-60 kHz and radiates or receives ultrasonic energy. They are distinguished from the
piezo ceramic transducer in that they produce sound waves above 20 kHz that are inaudible
to humans and the ultrasonic energy is radiated or received in a relatively narrow beam.
The “open” type ultrasonic transducer design exposes the piezo bender bonded with a
metal conical cone behind a protective screen. The “enclosed” type transducer design has the
piezo bender mounted directly on the underside of the top of the case which is then machined
to resonant at the desired frequency. The “PT and EP” type transducer has more internal
damper for minimizing ringing”, which usually operates as a transceiver-oscillating in a short
period and then switching to receiving mode.
In order to properly select a transducer for a given application, it is important to be
aware of the principles of sound propagation. Since sound is a wave phenomenon, its
propagation and directivity are related to its wavelength. A typical radiation power pattern for
either a generator or receiver of waves is shown in fig 3.22. due to the reciprocity of
transmission and reception the graph portrays both power radiated along a given direction (in
case of wave production), and the sensitivity along a given direction (in case of wave
reception).
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ULTRASONIC WAVE PROPAGATION
3.2.3 555 TIMER IC
The 555 timer is one of the most remarkable integrated circuits ever developed. It
comes in a single or dual package and even low power CMOS versions exists –ICM755.
Common part numbers are LM555, NE555, LM556 and NE556. The 555 timer consists of
two voltage comparators, bitable flip-flop discharge transistors, and a resistor divider
network.
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INTERNAL DIAGRAM OF 555 IC
PINS OF 555
The Power Supply
Pin 8 is where you connect the positive power supply (Vs) to the 555. This can be any
voltage between 3V and 15V DC, but is commonly 5V DC when working with digital IC’s.
Pin 1 is the 0V connection to the power supply.
Trigger and Reset Inputs
Pin 2 is called the Trigger input as it is this input that sets the output to the high state.
Pin 4 is called the Reset input as it is this input that resets the output to the low state. Both
pins may be connected to push buttons to control the operations of the 555. Sometimes the
Reset input is not used in a circuit, in which case it is connected directly to Vs so that
unwanted resetting cannot occur.
Threshold and Discharge
Pins 6 and 7 (and sometimes the Trigger input, pin 2) are used to set up the timing
aspect of the 555 IC. They are normally connected to a combination of resistors and a
capacitor.
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Offset
Pin 5 can be used to alter the timing aspect of the 555 IC in applications such as
frequency modulation.
FEATURES
 Turn-off time less than 2ms
 Maximum operating frequency greater than 500 KHz
 Timing from microseconds to hours
 Operates in both astable and monostable modes
 High output current
 Adjustable duty cycle
 TTL compatible
 Temperature stability of 0.005% per degree Celsius
APPLICATIONS
 Precision timing
 Pulse generation
 Sequential timing
 Time delay generation
 Pulse width modulation
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555 TIMERS IN ASTABLE OPERATION
This circuit is configured in astable mode of operation, which is basic oscillator
circuit using a 555 type of timer. The circuit is also sometimes referred to as a free running
oscillator, with the oscillation frequency given by f=1.46/((Ra +2Rb)*c). Initially, capacitor C
charged towards 2/3 V + via Ra and Rb when voltage on C reaches that threshold level, the
discharge output on pin 7 is turned on ,discharging C. When voltage on C is discharged to 1/3
V +, it triggers the comparator inside pin2, turning off the discharge output and starts the c
charging cycle again. Hence through the charging and discharging cycles, an oscillator circuit
is implemented. The output high time period is determined by T=0.693(Ra+Rb)*C. The
output low time period is determined by T=0.693(Rb*C).
Using the CMOS version of the 555 timer circuit, a very wide frequency range at a
low level of voltage spikes and power dissipation can be achieved. Selection of the values of
Ra and Rb is limited by the input leakage specifications of timer at pin7,2 and 6. The values
are limited by the internal leakage current at capacitor C. C usually has the range 10,000uF
down to 0. When C is at 0 value, timer oscillates without an external C, relying entirely on
the internal parasitic capacitor inside the 555 for oscillation. One interesting and very useful
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features of the 555 timer in either mode is that the timing interval for either charge or
discharge is independent of the supply voltage, Vcc. This is because the same Vcc is used
both as charging voltage and as the basis voltages for the two comparators inside the 555.
Thus the timing equations above depend only on the values for R and C in either operating
mode.
3.2.4 741 OPERATIONAL AMPLIFIER IC
An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain
electronic voltage amplifier with a differential input and, usually, a single-ended output.[1] An
op-amp produces an output voltage that is typically millions of times larger than the voltage
difference between its input terminals.
Typically the op-amp's very large gain is controlled by negative feedback, which
largely determines the magnitude of its output ("closed-loop") voltage gain in amplifier
applications, or the transfer function required (in analog computers). Without negative
feedback, and perhaps with positive feedback for regeneration, an op-amp essentially acts as
a comparator. High input impedance at the input terminals (ideally infinite) and low output
impedance at the output terminal(s) (ideally zero) are important typical characteristics.
In an inverting amplifier, the output voltage changes in an opposite direction to the
input voltage.
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3.2.5 7809-7909 VOLTAGE REGULATOR
A voltage regulator is an electrical regulator designed to automatically maintain a
constant voltage level.
It may use an electromechanical mechanism, or passive or active electronic
components. Depending on the design, it may be used to regulate one or more AC or DC
voltages.
With the exception of passive shunt regulators, all modern electronic voltage
regulators operate by comparing the actual output voltage to some internal fixed reference
voltage. Any difference is amplified and used to control the regulation element in such a way
as to reduce the voltage error. This forms a negative feedback control loop; increasing the
open-loop gain tends to increase regulation accuracy but reduce stability (avoidance of
oscillation, or ringing during step changes). There will also be a trade-off between stability
and the speed of the response to changes. If the output voltage is too low (perhaps due to
input voltage reducing or load current increasing), the regulation element is commanded, up
to a point, to produce a higher output voltage - by dropping less of the input voltage (for
linear series regulators and buck switching regulators), or to draw input current for longer
periods (boost-type switching regulators); if the output voltage is too high, the regulation
element will normally be commanded to produce a lower voltage.
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3.2.6 DC MOTOR
Brushless DC motors use a rotating permanent magnet in the rotor, and stationary
electrical magnets on the motor housing. A motor controller converts DC to AC. This design
is simpler than that of brushed motors because it eliminates the complication of transferring
power from outside the motor to the spinning rotor. Advantages of brushless motors include
long life span, little or no maintenance, and high efficiency. Disadvantages include high
initial cost, and more complicated motor speed controllers.
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3.3 CIRCUIT DIAGRAM
TRANSMITTER SECTION
GND
1
2
3
4
IC1
8
7
6
5
555
1k
VR110k
INPUT
R1
R3
1N4148DO35-7
D2
R4 220
Q1
D1BD139
1N4148DO35-7
OUTPUT
Q2
BD140
GND
4.7k
R5 220
R2 10k
C1
GND
.001uf
GND
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TRANSMITTER SECTION PCB LAYOUT
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TRANSMITTER SECTION COMPONENT POSITION LAYOUT
T1
VR1
BSY34
3
1
10k
IC1
D1
555
R1
4.7k
1N4148DO35-7
R4
220
OUTPUT
.01uf
INPUT
1k
R3
D2
R2
10k
C2
.001uf
C1
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1N4148DO35-7 R5
220
T2
BSV17
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