scrap collecting robot
TRANSCRIPT
Dissertation submitted in partial fulfillment of the A.M.I.E.T.E. course.
Scrap Collecting Robot
Submitted ByAbhishek Kaushik
SG-119836.
Table of Contents
1. Acknowledgements.
2. Certificate.
3. Introduction to the Project.
4. Circuit Diagram.
5. Component List.
6. Hardware
a. Power Supply for the circuit.
b. Integrated Circuits.
c. Transistors.
d. Diode.
e. Relays.
f. Transformer.
g. Resistors.
h. Capacitors.
7. Project Working.
8. Project Synopsis.
9. Bibliography.
Introduction -
Project is very interesting. We are using Tsop1738 as a IR – infrared
receiver. We using relay coil to collect scrap. Coil need 5 to 12v DC.
Better voltage- better collecting power. Robot help us to collect scrap
from every corner and from everywhere.
In this project we will control robot with infrared sensor remote. We
will control different functions of moving robot. As we know the value
of robotics it can be used in biomedical industry, domestic, food,
leather, autoparts etc. In this project we will make remote which will
have functions to control robot like forward, backward, right and left.
There will be six functions. We will use 89c051 microcontroller for this
function. We will give 9v supply to remote with 9v dc battery available
in the market. We will use 7805 voltage regulator for 5v dc supply.
For input to microcontroller there will be microswitches. There will be
complementary push pull power amplifier after Microcontroller output.
For that we will use 548 npn transistors 558 pnp. It will amplify data
so that it will not destroy in the way. After that it will be amplify and
led will convert that signal into phpt signal . On receiver end
phototransistor will amplify that signal and will give it to
microcontroller. Microcontroller will give signal to optocoupler. Here
optocoupler will work as a isolator after that h bridge will amplify that
signal and will give signal according to rxed signal
Automation requires precisely rotating motor which accelerates / decelerates
very fast & stops at precise predetermined position without any error, and
also has holding torque so that the motor-shaft position is maintained.
AUTO CONTROLS make stepper motor controllers are based on H-bridge
configuration with facility of having constant current supplied to the motor.
Stepper motor controllers are MOSFET based and utilize high voltage D.C.
Supply at constant current mode. Hence, the stepper motor can run at higher
speed up to 1000 rpm and above. Stepper motor controllers can achieve the
acceleration of 100 m/Sec2. to zero speed to stop the motor from running
speed, with rated torque. The time of Acc & Dec. will vary as per the load
and GD2 of the load to overcome inertia force.
the smallest step available is 0.9o. Hence stepper motor follows the step of
0.9o per step, It can be used in open loop system. Hence, the controllers
become simpler.
Working –
In this project we will use microcontroller 89s51.in which
we divide project in two portions. In transmitter
WELCOME TO THE WORLD OF THE MICROCONTROLLERS.
Look around. Notice the smart “intelligent” systems? Be it the T.V, washing
machines, video games, telephones, automobiles, aero planes, power
systems, or any application having a LED or a LCD as a user interface, the
control is likely to be in the hands of a micro controller!
Measure and control, that’s where the micro controller is at its best.
Micro controllers are here to stay. Going by the current trend, it is obvious
that micro controllers will be playing bigger and bigger roles in the different
activities of our lives.
So where does this scenario leave us? Think about it……
The world of Micro controllers
What is the primary difference between a microprocessor and a micro
controller? Unlike the microprocessor, the micro controller can be
considered to be a true “Computer on a chip”.
In addition to the various features like the ALU, PC, SP and registers found
on a microprocessor, the micro controller also incorporates features like the
ROM, RAM, Ports, timers, clock circuits, counters, reset functions etc.
While the microprocessor is more a general-purpose device, used for read,
write and calculations on data, the micro controller, in addition to the above
functions also controls the environment.
We have used a whole lot of technical terms already! Don’t get worried
about the meanings at this point. We shall understand these terms as we
proceed further
For now just be aware of the fact, that all these terms literally mean what
they say.
Bits and Bytes
Before starting on the 8051, here is a quick run through on the bits and
bytes. The basic unit of data for a computer is a bit. Four bits make a nibble.
Eight bits or two nibbles make a byte. Sixteen bits or four nibbles or two
bytes make a word.
1024 bytes make a kilobyte or 1KB, and 1024 KB make a Mega Byte or
1MB.
Thus when we talk of an 8-bit register, we mean the register is capable of
holding data of 8 bits only.
The 8051
The 8051 developed and launched in the early 80`s, is one of the most
popular micro controller in use today. It has a reasonably large amount of
built in ROM and RAM. In addition it has the ability to access external
memory.
The generic term `8x51` is used to define the device. The value of x defining
the kind of ROM, i.e. x=0, indicates none, x=3, indicates mask ROM, x=7,
indicates EPROM and x=9 indicates EEPROM or Flash.
A note on ROM
The early 8051, namely the 8031 was designed without any ROM. This
device could run only with external memory connected to it. Subsequent
developments lead to the development of the PROM or the programmable
ROM. This type had the disadvantage of being highly unreliable.
The next in line, was the EPROM or Erasable Programmable ROM. These
devices used ultraviolet light erasable memory cells. Thus a program could
be loaded, tested and erased using ultra violet rays. A new program could
then be loaded again.
An improved EPROM was the EEPROM or the electrically erasable PROM.
This does not require ultra violet rays, and memory can be cleared using
circuits within the chip itself.
Finally there is the FLASH, which is an improvement over the EEPROM.
While the terms EEPROM and flash are sometimes used interchangeably,
the difference lies in the fact that flash erases the complete memory at one
stroke, and not act on the individual cells. This results in reducing the time
for erasure.
Understanding the basic features of the 8051 core
Let’s now move on to a practical example. We shall work on a simple
practical application and using the example as a base, shall explore the
various features of the 8051 microcontroller.
Consider an electric circuit as follows,
The positive side (+ve) of the battery is connected to one side of a switch.
The other side of the switch is connected to a bulb or LED (Light Emitting
Diode). The bulb is then connected to a resistor, and the other end of the
resistor is connected to the negative (-ve) side of the battery.
When the switch is closed or ‘switched on’ the bulb glows. When the switch
is open or ‘switched off’ the bulb goes off
If you are instructed to put the switch on and off every 30 seconds, how
would you do it? Obviously you would keep looking at your watch and
every time the second hand crosses 30 seconds you would keep turning the
switch on and off.
Imagine if you had to do this action consistently for a full day. Do you think
you would be able to do it? Now if you had to do this for a month, a year??
No way, you would say!
The next step would be, then to make it automatic. This is where we use the
Microcontroller.
But if the action has to take place every 30 seconds, how will the
microcontroller keep track of time?
Execution time
Look at the following instruction,
clr p1.0
This is an assembly language instruction. It means we are instructing the
microcontroller to put a value of ‘zero’ in bit zero of port one. This
instruction is equivalent to telling the microcontroller to switch on the bulb.
The instruction then to instruct the microcontroller to switch off the bulb is,
Setb p1.0
This instructs the microcontroller to put a value of ‘one’ in bit zero of port
one.
Don’t worry about what bit zero and port one means. We shall learn it in
more detail as we proceed.
There are a set of well defined instructions, which are used while
communicating with the microcontroller. Each of these instructions requires
a standard number of cycles to execute. The cycle could be one or more in
number.
How is this time then calculated?
The speed with which a microcontroller executes instructions is determined
by what is known as the crystal speed. A crystal is a component connected
externally to the microcontroller. The crystal has different values, and some
of the used values are 6MHZ, 10MHZ, and 11.059 MHz etc.
Thus a 10MHZ crystal would pulse at the rate of 10,000,000 times per
second.
The time is calculated using the formula
No of cycles per second = Crystal frequency in HZ / 12.
For a 10MHZ crystal the number of cycles would be,
10,000,000/12=833333.33333 cycles.
This means that in one second, the microcontroller would execute
833333.33333 cycles.
Therefore for one cycle, what would be the time? Try it out.
The instruction clr p1.0 would use one cycle to execute. Similarly, the
instruction setb p1.0 also uses one cycle.
So go ahead and calculate what would be the number of cycles required to
be executed to get a time of 30 seconds!
Getting back to our bulb example, all we would need to do is to instruct the
microcontroller to carry out some instructions equivalent to a period of 30
seconds, like counting from zero upwards, then switch on the bulb, carry out
instructions equivalent to 30 seconds and switch off the bulb.
Just put the whole thing in a loop, and you have a never ending on-off
sequence.
Simple isn’t it?
Let us now have a look at the features of the 8051 core, keeping the above
example as a reference,
1. 8-bit CPU.( Consisting of the ‘A’ and ‘B’ registers)
Most of the transactions within the microcontroller are carried out through
the ‘A’ register, also known as the Accumulator. In addition all arithmetic
functions are carried out generally in the ‘A’ register. There is another
register known as the ‘B’ register, which is used exclusively for
multiplication and division.
Thus an 8-bit notation would indicate that the maximum value that can be
input into these registers is ‘11111111’. Puzzled?
The value is not decimal 111, 11,111! It represents a binary number, having
an equivalent value of ‘FF’ in Hexadecimal and a value of 255 in decimal.
We shall read in more detail on the different numbering systems namely the
Binary and Hexadecimal system in our next module.
2. 4K on-chip ROM
Once you have written out the instructions for the microcontroller, where do
you put these instructions?
Obviously you would like these instructions to be safe, and not get deleted
or changed during execution. Hence you would load it into the ‘ROM’
The size of the program you write is bound to vary depending on the
application, and the number of lines. The 8051 microcontroller gives you
space to load up to 4K of program size into the internal ROM.
4K, that’s all? Well just wait. You would be surprised at the amount of stuff
you can load in this 4K of space.
Of course you could always extend the space by connecting to 64K of
external ROM if required.
3. 128 bytes on-chip RAM
This is the space provided for executing the program in terms of moving
data, storing data etc.
4. 32 I/O lines. (Four- 8 bit ports, labeled P0, P1, P2, P3)
In our bulb example, we used the notation p1.0. This means bit zero of port
one. One bit controls one bulb.
Thus port one would have 8 bits. There are a total of four ports named p0,
p1, p2, p3, giving a total of 32 lines. These lines can be used both as input or
output.
5. Two 16 bit timers / counters.
A microcontroller normally executes one instruction at a time. However
certain applications would require that some event has to be tracked
independent of the main program.
The manufacturers have provided a solution, by providing two timers. These
timers execute in the background independent of the main program. Once
the required time has been reached, (remember the time calculations
described above?), they can trigger a branch in the main program.
These timers can also be used as counters, so that they can count the number
of events, and on reaching the required count, can cause a branch in the main
program.
6. Full Duplex serial data receiver / transmitter.
The 8051 microcontroller is capable of communicating with external devices
like the PC etc. Here data is sent in the form of bytes, at predefined speeds,
also known as baud rates.
The transmission is serial, in the sense, one bit at a time
7. 5- interrupt sources with two priority levels (Two external and three
internal)
During the discussion on the timers, we had indicated that the timers can
trigger a branch in the main program. However, what would we do in case
we would like the microcontroller to take the branch, and then return back to
the main program, without having to constantly check whether the required
time / count has been reached?
This is where the interrupts come into play. These can be set to either the
timers, or to some external events. Whenever the background program has
reached the required criteria in terms of time or count or an external event,
the branch is taken, and on completion of the branch, the control returns to
the main program.
Priority levels indicate which interrupt is more important, and needs to be
executed first in case two interrupts occur at the same time.
8. On-chip clock oscillator.
This represents the oscillator circuits within the microcontroller. Thus the
hardware is reduced to just simply connecting an external crystal, to achieve
the required pulsing rate.
The Basic Registers of the 8051
For more details contact the course coordinator at
Block Diagram:-
Receiver
SensorsPhotodio
Programmable
Motor control circuit,
DC Motors
Wheels of the
COMPONENT DESCRIPTION
TRANSFORMER
Transformer works on the principle of mutual inductance. We know
that if two coils or windings are placed on the core of iron, and if we
pass alternating current in one winding, back emf or induced voltage
is produced in the second winding. We know that alternating current
always changes with the time. So if we apply AC voltage across one
winding, a voltage will be induced in the other winding. Transformer
works on this same principle. It is made of two windings wound
around the same core of iron. The winding to which AC voltage is
applied is called primary winding. The other winding is called as
secondary winding.
Voltage and current relationship:
Let V1 volts be input alternating voltage applied to primary winding. I1
Amp is input alternating current through primary winding. V2 volt is
output alternating voltage produced in the secondary. I2 amp be the
current flowing through the secondary.
Then relationship between input and output voltages is given by
V1/V2 = N1/N2
Relationship between input and output currents is
I1/I2 = N2/N1
(Where N1 is no. of turns of coil in primary and N2 is number of turns
in secondary )
We know that Power = Current X Voltage. It is to be noted that input power
is equal to output power. Power is not changed. If V2 is greater than V1, then
I2 will be less than I1. This type of transformer is called as step up
transformer. If V1 is
greater than V2, then I1 will be less than I2. This type of transformer is called
as step down transformer.
For step up transformer, N2>N1, i.e., number of turns of secondary winding
is more than those in primary.
For step down transformer, N1>N2, i.e., numbers of turns of primary winding
is more than those in secondary.
RESISTORS
The flow of charge (or current) through any material, encounters an opposing
force similar in many respect to mechanical friction. This opposing force is called
resistance of the material. It is measured in ohms. In some electric circuits
resistance is deliberately introduced in the form of the resistor.
Resistors are of following types:
1. Wire wound resistors.
2. Carbon resistors.
3. Metal film resistors.
Wire Wound Resistors:
Wire wound resistors are made from a long (usually Ni-Chromium) wound on a
ceramic core. Longer the length of the wire, higher is the resistance. So
depending on the value of resistor required in a circuit, the wire is cut and wound
on a ceramic core. This entire assembly is coated with a ceramic metal. Such
resistors are generally available in power of 2 watts to several hundred watts and
resistance values from 1ohm to 100k ohms. Thus wire wound resistors are used
for high currents.
Carbon Resistors:
Carbon resistors are divided into three types:
a. Carbon composition resistors are made by mixing carbon grains with
binding material (glue) and moduled in the form of rods. Wire leads
are inserted at the two ends. After this an insulating material seals the
resistor. Resistors are available in power ratings of 1/10, 1/8, 1/4 ,
1/2 , 1.2 watts and values from 1 ohm to 20 ohms.
b. Carbon film resistors are made by deposition carbon film on a ceramic
rod. They are cheaper than carbon composition resistors.
c. Cement film resistors are made of thin carbon coating fired onto a
solid ceramic substrate. The main purpose is to have more precise
resistance values and greater stability with heat. They are made in a
small square with leads.
Metal Film Resistors:
They are also called thin film resistors. They are made of a thin metal coating
deposited on a cylindrical insulating support. The high resistance values are not
precise in value; however, such resistors are free of inductance effect that is
common in wire wound resistors at high frequency.
Variable Resistors:
Potentiometer is a resistor where values can be set depending on the
requirement. Potentiometer is widely used in electronics systems. Examples are
volume control, tons control, brightness and contrast control of radio or T.V. sets.
Fusible Resistors:
These resistors are wire wound type and are used in T.V. circuits for protection.
They have resistance of less than 15 ohms. Their function is similar to a fuse
made to blow off whenever current in the circuit exceeds the limit.
Resistance of a wire is directly proportional to its length and inversely
proportional to its thickness.
R L
R 1/A
RESISTOR COLOR CODE
Example: 1k or 1000 ohms
1st 2nd 3rd 4th
Band1
Band 2
Band 3
Band 4
COLOUR CODES
COLOUR NUMBER MULTIPLIER COLOUR TOLERANCE
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Gold
Silver
0
1
2
3
4
5
6
7
8
9
100
101
102
103
104
105
106
107
108
109
10-1
10-2
Gold
Silver
No colour
5%
10%
20%
CAPACITORS
A capacitor can store charge, and its capacity to store charge is called
capacitance. Capacitors consist of two conducting plates, separated by an
insulating material (known as dielectric). The two plates are joined with two
leads. The dielectric could be air, mica, paper, ceramic, polyester, polystyrene,
etc. This dielectric gives name to the capacitor. Like paper capacitor, mica
capacitor etc.
Types of capacitors:
Capacitors can be broadly classified in two categories, i.e., Electrolytic capacitors
and Non-Electrolytic capacitors as shown if the figure above.
Capa
Fixed Variable
Electr Non- Gang condenser
Trimmer
Mica Paper Ceramic
Electrolytic Capacitor:
Electrolytic capacitors have an electrolyte as a dielectric. When such an
electrolyte is charged, chemical changes takes place in the electrolyte. If its one
plate is charged positively, same plate must be charged positively in future. We
call such capacitors as polarized. Normally we see electrolytic capacitor as
polarized capacitors and the leads are marked with positive or negative on the
can. Non-electrolyte capacitors have dielectric material such as paper, mica or
ceramic. Therefore, depending upon the dielectric, these capacitors are
classified.
Mica Capacitor:
It is sandwich of several thin metal plates separated by thin sheets of mica.
Alternate plates are connected together and leads attached for outside
connections. The total assembly is encased in a plastic capsule or Bakelite case.
Such capacitors have small capacitance value (50 to 500pf) and high working
voltage (500V and above). The mica capacitors have excellent characteristics
under stress of temperature variation and high voltage application. These
capacitors are now replaced by ceramic capacitors.
Ceramic Capacitor:
Such capacitors have disc or hollow tabular shaped dielectric made of ceramic
material such as titanium dioxide and barium titanate. Thin coating of silver
compounds is deposited on both sides of dielectric disc, which acts as capacitor
plates. Leads are attached to each sides of the dielectric disc and whole unit is
encapsulated in a moisture proof coating. Disc type capacitors have very high
value up to 0.001uf. Their working voltages range from 3V to 60000V. These
capacitors have very low leakage current. Breakdown voltage is very high.
Paper Capacitor:
It consists of thin foils, which are separated by thin paper or waxed paper. The
sandwich of foil and paper is then rolled into a cylindrical shape and enclosed in
a paper tube or encased in a plastic capsules. The lead at each end of the
capacitor is internally attached to the metal foil. Paper capacitors have
capacitance ranging from 0.0001uf to 2.0uf and working voltage rating as high as
2000V.
THE DIODE
Diodes are polarized, which means that they must be inserted into the PCB the
correct way round. This is because an electric current will only flow through them
in one direction (like air will only flow one way trough a tyre valve). Diodes have
two connections, an anode and a cathode. The cathode is always identified by a
dot, ring or some other mark.
The PCB is often marked with a +sign for the cathode end. Diodes come in all
shapes and sizes. They are often marked with a type number. Detailed
characteristics of a diode can be found by looking up the type number in a data
book. If you know how to measure resistance with a meter then test some
diodes. A good one has low resistance in one direction and high in other. They
are specialized types of diode available such as the zener and light emitting
diode (LED).
+
SYMBOLS OF DIFFERENT DIODES
anode cathode
simple diode zener diode
RELAYS
Error: Reference source not found
A relay is an electrically operated switch. The relay contacts can be made to
operate in the pre-arranged fashion. For instance, normally open contacts close
and normally closed contacts open. In electromagnetic relays, the contacts
however complex they might be, they have only two position i.e. OPEN and
CLOSED, whereas in case of electromagnetic switches, the contacts can have
multiple positions.
STRIP
OUT N/C
OUT N/O
SPRING
MAGNET
230V P
NEED FOR THE USE OF RELAY
The reason behind using relay for switching loads is to provide complete
electrical isolation. The means that there is no electrical connection between the
driving circuits and the driven circuits. The driving circuit may be low voltage
operated low power circuits that control several kilowatts of power. In our
circuit where a high fan could be switched on or off depending upon the output
from the telephone.
Since the relay circuit operated on a low voltage, the controlling circuit is quite
safe. In an electromagnetic relay the armature is pulled by a magnetic force
only. There is no electrical connection between the coil of a relay and the
switching contacts of the relay. If there are more than one contact they all are
electrically isolated from each other by mounting them on insulating plates and
washers. Hence they can be wired to control different circuits independently.
Some of the popular contacts forms are described below:
1. Electromagnetic relay
2. Power Relay.
3. Time Delay Relay.
4. Latching Relay.
5. Crystal Can Relay.
6. Co-axial Relay.
1. Electromagnetic relay:
An electromagnetic relay in its simplest form consists of a coil, a DC current
passing through which produces a magnetic field. This magnetic field attracts
an armature, which in turn operates the contacts. Normally open contacts close
and normally closed contacts open. Electromagnetic relays are made in a large
variety of contacts forms.
2. Power relays:
Power relays are multi-pole heavy duty lapper type relays that are capable of
switching resistive loads of upto 25amp.. These relays are widely used for a
variety of industrial application like control of fractional horse power motors,
solenoids, heating elements and so on. These relays usually have button like
silver alloy contacts and the contact welding due to heavy in rush current is
avoided by wiping action of the contacts to quench the arc during high voltage
DC switching thus avoiding the contact welding.
3. Time Delay Relay:
A time delay relay is the one in which there is a desired amount of time delay
between the application of the actuating signal and operation of the load
switching devices.
4. Latching Relay:
In a Latching Relay, the relay contacts remain in the last energized position
even after removal of signal in the relay control circuit. The contacts are held in
the last relay-energized position after removal of energisation either electrically
or magnetically. The contacts can be released to the normal position electrically
or mechanically.
5. Crystal Can Relay:
They are so called, as they resemble quartz crystal in external shapes. These are
high performance hermetically sealed miniature or sub-miniature relay widely
used in aerospace and military application. These relays usually have gold
plated contacts and thus have extremely low contact resistance. Due to low
moment of inertia of the armature and also due to statically and dynamically
balanced nature of armature, these relays switch quite reliably even under
extreme condition of shock and vibration.
6. Co-axial Relay:
A Co-axial Relay has two basic parts, an actuator which is nothing but some
kind of a coil and a cavity, housing the relay contacts. The co-axial relay are
extensively used for radio frequency switching operations of equipment
THE JUNCTION TRANSISTOR
Collector Collector
Base Base
Emitter Emitter
C C
B B
E E
NPN PNP
_ _ _ _ _ _ _ _ _ _
+ + + + + + + + + + + + + -- --
Junction transistors consists of two junctions made from N-type and P-type
semiconductor materials and are called bipolar transistors (two polarities).
They have three connections emitter, base, and collector.
TRANSISTOR CURRENTS
Collector
Current Ic
Ib
Base current
Emitter Ie current
Ie = Ib+Ic
The forward biased base/emitter junction causes electrons to be attracted
from the emitter area towards the base. Arriving in the base area, most of
the negative electrons come under the influence of the more positive
collector and are attracted by it. This is shown in the left hand drawing,
where the base current plus collector current equals the emitter current.
Alpha gain is collector current divided by emitter current, and is always
less than 1. Beta gain is collector current divided by base current and can
be fairly high number. Therefore, causing a small base current to flow
makes a much larger collector current to flow. A small base current
controls a large collector current. There is 0.6 volts across the base\emitter
junction, where it is forward biased (0.3 volts for germanium).
MOBILE CONTROL ELECTRICAL APPLIANCES
Project Introduction.
This unit talks about the basic definitions needed to understand the Project better and further defines the technical criteria to be implemented as a part of this project.
Why automation?
Earlier, we are looking into the face of future
when we talked about automated devices, which
could do anything on instigation of a controller,
but today it has become a reality.
1. An automated device can replace good
amount of human working force, moreover
humans are more prone to errors and in
intensive conditions the probability of error
increases. Whereas an automated device can
work with diligence, versatility and with almost
zero error.2. This is why this project looks into construction and implementation of a system
involving hardware to control a variety of electrical and electronics instruments.
POWER SUPPLY
IN 4007
1
3 +12V
7812
A.C
2 supply 4700 uf
1000 uf
How to control sensors
What is a voltage divider?
You are going to find out but don't be in too much of a hurry. Work through the Chapter and allow the explanation to develop.
The diagram below shows a light dependent resistor, or LDR, together with its circuit symbol:
The light-sensitive part of the LDR is a wavy track of cadmium sulphide. Light energy triggers the release of extra charge carriers in this material, so that its resistance falls as the level of illumination increases.
A light sensor uses an LDR as part of a voltage divider.
The essential circuit of a voltage divider, also called a potential divider, is:
What happens if one of the resistors in the voltage divider is replaced by an LDR? In the circuit below, Rtop is a 10 resistor, and an LDR is used as Rbottom :
Suppose the LDR has a resistance of 500 , 0.5 , in bright light, and 200 in the shade (these values are reasonable).
When the LDR is in the light, Vout will be:
In the shade, Vout will be:
In other words, this circuit gives a LOW voltage when the LDR is in the light, and a HIGH voltage when the LDR is in the shade. The voltage divider circuit gives an output voltage which changes with illumination.
A sensor subsystem which functions like this could be thought of as a 'dark sensor' and could be used to control lighting circuits which are switched on automatically in the evening.
Perhaps this does not seem terribly exciting, but almost every sensor circuit you can think of uses a voltage divider. There's just no other way to make sensor subsystems work.
Here is the voltage divider built with the LDR in place of Rtop :
Temperature sensors
A temperature-sensitive resistor is called a thermistor. There are several different types:
The resistance of most common types of thermistor decreases as the temperature rises. They are called negative temperature coefficient, or ntc, thermistors. Note the -t° next to the circuit symbol. A typical ntc thermistor is made using semiconductor metal oxide materials. (Semiconductors have resistance properties midway between those of conductors and insulators.) As the temperature rises, more charge carriers become available and the resistance falls.
Although less often used, it is possible to manufacture positive temperature coefficient, or ptc, thermistors. These are made of different materials and show an increase in resistance with temperature.
How could you make a sensor circuit for use in a fire alarm? You want a circuit which will deliver a HIGH voltage when hot conditions are detected. You need a voltage divider with the ntc thermistor in the Rtop position:
How could you make a sensor circuit to detect temperatures less than 4°C to warn motorists that there may be ice on the road? You want a circuit which will give a HIGH voltage in cold conditions. You need a voltage divider with the thermistor in place of Rbottom :
This last application raises an important question: How do you know what value of Vout you are going to get at 4°C?
Key point: The biggest change in Vout from a voltage divider is obtained when Rtop and Rbottom are equal in value
Sound sensors
Another name for a sound sensor is a microphone. The diagram shows a cermet microphone:
Cermet' stands for 'ceramic' and 'metal'. A mixture of these materials is used in making the sound-sensitive part of the microphone. To make them work properly, cermet microphones need a voltage, usually around 1.5 V across them. A suitable circuit for use with a 9 V supply is:
The 4.7 and the 1 resistors make a voltage divider which provides 1.6 V across the microphone. Sound waves generate small changes in voltage, usually in the range 10-20 mV. To isolate these small signals from the steady 1.6 V, a capacitor is used.
Signals from switches
When a switch is used to provide an input to a circuit, pressing the switch usually generates a voltage signal. It is the voltage signal which triggers the circuit into action. What do you need to get the switch to generate a voltage signal? . . . You need a voltage divider. The circuit can be built in either of two ways:
The pull down resistor in the first circuit forces Vout to become LOW except when the push button switch is operated. This circuit delivers a HIGH voltage when the switch is pressed. A resistor value of 10 is often used.
In the second circuit, the pull up resistor forces Vout to become HIGH except when the switch is operated. Pressing the switch connects Vout directly to 0 V. In other words, this circuit delivers a LOW voltage when the switch is pressed.
In circuits which process logic signals, a LOW voltage is called 'logic 0' or just '0', while a HIGH voltage is called 'logic1' or '1'. These voltage divider circuits are perfect for providing input signals for logic systems.
What kinds of switches could you use. One variety of push button switch is called a miniature tactile switch. These are small switches which work well with prototype board:
As you can see, the switch has four pins which are linked in pairs by internal metal strips. Pressing the button bridges the contacts and closes the switch. The extra pins are useful in designing printed circuit boards for keyboard input and also stop the switch from being moved about or bent once soldered into position.
There are lots of other switches which you might want to use in a voltage divider configuration. These include magnetically-operated reed switches, tilt switches and pressure pads, all with burglar alarm applications.
;**************************** My code tx*********************************
org 00h
jnb p1.0,reverse
jnb p1.1,forward
jnb p1.2,right
jnb p1.3,left
right:
Mov a,#01100000
Mov sbuf,a
Acall delay
ret
left:
Mov a,#10010000
Mov sbuf,a
Acall delay
ret
forward:
Mov a,#01010000
Mov sbuf,a
Acall delay
ret
reverse:
Mov a,#10100000
Mov sbuf,a
Acall delay
ret
delay:
mov r2,#50
here : mov r3,#150
here1: djnz r3,here1
djnz r2,here
ret
end
;**************************** My code rx*********************************
org 00h
out equ p2
mov a,sbuf
mov p2,a
acall delay
delay:
mov r2,#50
here : mov r3,#150
here1: djnz r3,here1
djnz r2,here
ret
end
BIBILIOGRAPHY
1. HAND BOOK OF ELECTRONICS A.K. MAINI.
2.HAND BOOK OF ELECTRONICS GUPTA & KUMAR.
3.LET US C YASHWANT KANITKAR.
4.SHYAM SERIES TATA MC GRILL.
5.DIGITAL SYSTEMS PRINCIPLES AND APPLICATION RONALD LTOCCI.
(Sixth addition)
6.ELECTRONICS FOR YOU (MARCH 1998).
7.DIGITAL DESIGN MORIS MANO.
(Second addition)
8.RELAYS AND ITS APPLICATION SHARMA, MC.
(Bpb-publishers)
9.MODERN ALL ABOUT MOTHERBOARD LOTHIA, M.
(Bpb-publishers)
10.POWER SUPPLY FOR ALL OCCASION SHARMA, MC.
(Bpb-publishers)
11.CMOS DATA BOOK (74SERIES) ECA.
(Bpb-publishers)
12.PRACTICAL VALUE AND TRANSISTOR DATA POPE.
(Bpb-publishers)
13.PRACTICAL TRANSFORMER DESIGN HAND BOOK LABON. E.
(Bpb-publishers)
14 MODERN IC MANAHAR LOTIA.
(DATA AND SUBSTITUTIONAL MANUAL)
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