1
PROJECT REPORT
ON
LAUNCHING MECHANISM OF
AEROPLANE
IN PARTIAL FULFILLMENT OF THE RECORD FOR THE AWARD OF
DEGREE
BACHELOR OF TECHNOLOGY
IN
ELECTRONICS AND COMMUNICATION
2008-2012
SUBMITTED BY :Sthitapragyan Rout
Smita Swain
Sriya Halder
Manorama Dash
Pradipta Ranjan Nayak
Srikant Sahu
Manisha Parida
(Reg.No.0801231040)
(Reg.No.0801231044)
(Reg.No.0801231051)
(Reg.No.0801231079)
(Reg.No.0801231174)
(Reg.No.0801231206)
(Reg.No.0801231214)
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
SAMANTA CHANDRASEKHAR INSTITUTE OF TECHNOLOGY &
MANAGEMENT
SEMILIGUDA, KORAPUT
BIJU PATNAIK UNIVERSITY OF TECHNOLOGY
ROURKELA, ORISSA
2
ACKNOWLEDGEMENT
We take this Opportunity to express our sincere gratitude to all those who
individually as well as collectively helped us in the successful completion of
this Project.
We are thankful to the Faculties of Department of Electronics and
Communication for their valuable guidance, expertise and motivation for the
accomplishment of this project work.
We also acknowledge the continuous encouragement rendered by our friends.
Sthitapragyan Rout
(Reg. No. 0801231040)
Smita Swain
(Reg. No. 0801231044)
Sriya Halder
(Reg. No. 0801231051)
Manorama Dash
(Reg. No. 0801231079)
Pradipta Ranjan Nayak
(Reg. No. 0801231174)
Srikant Sahu
(Reg. No. 0801231206)
Manisha Parida
(Reg. No. 0801231214)
3
ABSTRACT
A description is given of a rectractable aircraft landing gear consisting of two wheels located
one behind the other, a shock absorber (used for both wheels, placed parallel to the
longitudinal axis of the fuselage, and having two rods coming out the ends of the shock
absorber housing), and two levers for the suspension of these wheels, each of which is hinged
at its center or fastened to an eye on the shock absorber housing. To assure retraction and
lowering the shock absorber is articulately connected to the fuselage by the use of two eyes
located on the ends of the shock absorber housing. The mechanism for lowering and
retracting the landing gear is made in the form of a plane articulated parallelogram located in
a plane parallel to the longitudinal axis of the fuselage and formed by two breaking struts,
each of which is articulately fastened at one end to the fuselage and at the other to the
housing of the shock absorber. A crosspiece connects the center hinges of these struts and
contains a telescoping lift located outside the parallelogram in its plane. The housing of the
lift is connected with the fuselage and the rod is articulately connected to the fuselage by an
arm of the breaking strut nearest this lift. In the retracted and lowered position the
retractable landing gear can be spring-loaded in the direction corresponding to the turn axis
of the landing gear, the moment of which is produced by means of a telescoping springloaded mechanism articulately connected on one end to the fuselage.
4
INTRODUCTION
The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the
ground and allows it to taxi, takeoff and land. Typically wheels are used, but skids, skis, floats
or a combination of these and other elements can be deployed, depending on the surface.
The landing mechanism of aeroplane includes strut, shock absorber, extraction/retraction
mechanism, brakes, wheel, tyre. Shock absorber and extraction/retraction mechanism may
not be present in small airplanes.
Landing gear usually includes wheels equipped with shock absorbers for solid ground, but
some aircraft are equipped with skis for snow or floats for water, and/or skids or pontoons
(helicopters).The undercarriage is a relatively heavy part of the vehicle, it can be as much as 7%
of the takeoff weight, but more typically is 4-5%The landing gear is the interface of airplane to
ground, so that all the ground loads are transmitted by it to the aircraft structure. There is
then a high influence of the landing gear on the local structure, which must be taken into
account since the initial design stage.
The landing loads can reach factors of 2.5 for transport aircraft, 4.5 for small general aviation
vehicles and higher for combat aircraft. The system must then have considerable mechanical
resistance, which means in general that its mass is significant. Depending on aircraft
category, this can range from 3 to 7% of the aircraft total mass.
The main functions of the landing mechanism are energy absorption at landing, braking &
taxi control.
Landing is the main sizing conditions for the system and its surrounding structure; braking
also determines both vertical and horizontal loads that influence structural sizing. Taxi
control includes steering and taxi stability.
5
BLOCK DIAGRAM
POWER SUPPLY
The power supply designed for containing a fixed demand connected in this project. The
basic requirement for designing a power supply is as follows:
The voltage levels required for operating the devices is +5v.Here +5v required for operating
microcontroller and as well as required for drivers and amplifiers and transmitters and
receivers.
The current requirement of each device or load must be added to estimate the final capacity
of the power supply.
The power supply always specified with one or multiple voltage output along with a current
capacity. As it is estimate the requirement of power is approximately as follows,
a) Output voltage = +5v
b) Capacity = 1000mA
The power supply is basically consisting of three sections as follows,
a) Step down section
b) Rectifier section
c) Regulator section
6
CIRCUIT CONNECTION
In this we r using transformer (9-0-9)v/1mA,IC 7805,diods7004,LED and resisters.
Here 230v,50Hz ac signal is given as input to the primary and secondary of the transformer is
given to the bridge rectifier diode. The positive output of the bridge rectifier is given as i/p to
the voltage regulator is given to the LED through resister to act as the indicator.
CIRCUIT EXPLANATION
When ac signal is given to the primary of the transformer, due to the magnetic effect of the
coil magnetic effect of the coil magnetic flux is induced in the coil of the transformer due to
the transformer action. Transformer is an electromechanical static device which transformer
electrical energy from one coil to another without changing its frequency. Here the diodes
are connected to the two +12v output of the transformer. The secondary coil of the
transformer is given to the diode circuit for rectification purposes.
During the +ve cycle of the ac signal the diode D1 conduct due to the forward bias of the
diodes and diodes D2 doesn’t conduct due to the reversed bias of the diodes. Similarly during
the –ve cycle of the ac signal the diodes D2 conduct due to the forward bias of the diodes and
the diode D1 does not conducted due to reversed bias of the diodes. The output of the bridge
rectifier is not a power dc along with rippled ac is also present. To overcome this effect, a low
pass filter is connected to the output of the diodes. Which remover the unwanted ac signal
and thus a pure dc is obtained. Here we need a fixed voltage, that’s for we using IC
regulator(7805).”Voltage regulation is the circuit that supplies a constant voltage regardless
of change in load current”. This IC’s are designed as fixed voltage regulators are with
adequate heat sinking can deliver output current is excess of 1A. The o/p the full wave
rectifier is given as input the IC through low pass filter with respect to GND and thus a fixed
o/p is obtained. The output of the IC(7805) is given to the LED for indication purpose
through resister. Due to the forward bias of the LED, the LED glows on state, and the o/p are
obtain from the pin no3.
7
VOLTAGE REGULATOR
A popular three pin 12 V DC voltage regulator IC.
A voltage regulator is an electrical regulator designed to automatically maintain a constant
voltage level. A voltage regulator may be a simple "feed-forward" design or may include
negative feedback control loops. It may use an electromechanical mechanism, or electronic
components. Depending on the design, it may be used to regulate one or more AC or DC
voltages.
Voltage Regulator (regulator), usually having three legs, converts varying input voltage and
produces a constant regulated output voltage. They are available in a variety of outputs.
The most common part numbers start with the numbers 78 or 79 and finish with two digits
indicating the output voltage. The number 78 represents positive voltage and 79 negative
one. The 78XX series of voltage regulators are designed for positive input. And the 79XX
series is designed for negative input.
EXAMPLES:
·
5V DC Regulator Name: LM7805 or MC7805
·
-5V DC Regulator Name: LM7905 or MC7905
·
6V DC Regulator Name: LM7806 or MC7806
·
-9V DC Regulator Name: LM7909 or MC7909
The LM78XX series typically has the ability to drive current up to 1A. For application
requirements up to 150mA, 78LXX can be used. As mentioned above, the component has
three legs: Input leg which can hold up to 36VDC Common leg (GND) and an output leg
with the regulator's voltage. For maximum voltage regulation, adding a capacitor in parallel
between the common leg and the output is usually recommended. Typically a 0.1MF
capacitor is used. This eliminates any high frequency AC voltage that could otherwise
combine with the output voltage.
8
IC 7805 (VOLTAGE REGULATOR IC)
7805 is a voltage regulator integrated circuit. It is a member of 78xx series of fixed linear
voltage regulator ICs. The voltage source in a circuit may have fluctuations and would not
give the fixed voltage output. The voltage regulator IC maintains the output voltage at a
constant value. The xx in 78xx indicates the fixed output voltage it is designed to provide.
7805 provides +5V regulated power supply. Capacitors of suitable values can be connected at
input and output pins depending upon the respective voltage levels.
MC78XX/LM78XX/MC78XXA
3-TERMINAL 1A POSITIVE VOLTAGE REGULATOR
The MC78XX/LM78XX/MC78XXA series of three terminal positive regulators are available
in the TO-220/D-PAK package and with several fixed output voltages, making them useful in
a wide range of applications. Each type employs internal current limiting,
thermal shut down and safe operating area protection, making it essentially indestructible. If
adequate heat sinking is provided, they can deliver over 1A output current. Although
designed primarily as fixed voltage regulators, these devices can be used with external
components to obtain adjustable voltages and currents.
TO-220
D-PAK
9
ABSOLUTE MAXIMUM RATINGS
Parameter
Symbol
Value
Unit
Input Voltage (for
VO = 5V to 18V)
(for VO = 24V)
VI
VI
35
40
V
V
Thermal Resistance
Junction-Cases (TO220)
Thermal Resistance
Junction-Air
(TO220)
Operating
Temperature Range
Storage Temperature
Range
RθJC
5
oC/W
RθJA
65
oC/W
TOPR
0 ~ +125
oC
TSTG
-65 ~ +150
oC
10
ELECTRICAL CHARACTERISTICS (MC7805/LM7805)
Parameter
Output Voltage
Line Regulation
(Note1)
Load Regulation
(Note1)
Symbol
VO
Regline
Regload
Conditions
MC7805/LM7805
Unit
Min.
Typ.
Max.
TJ =+25 oC
4.8
5.0
5.2
5.0mA ≤ Io ≤
1.0A, PO ≤ 15W
VI = 7V to 20V
TJ=+25 VO = 7V
oC
to 25V
4.75
5.0
5.25
-
4.0
100
VI = 8V
to 12V
-
1.6
50
-
9
100
-
4
50
-
5.0
8.0
mA
mA
TJ=+25
oC
Quiescent
Current
IQ
IO
=
5.0mA
to1.5A
IO
=250mA
to
750mA
TJ =+25 oC
Quiescent
Current Change
IQ
IO = 5mA to 1.0A
-
0.03
0.5
VI= 7V to 25V
-
0.3
1.3
V
mV
mV
Output Voltage
Drift
VO/T
IO= 5mA
-
-0.8
-
mV/ oC
Output
Voltage
Noise
VN
f
=
10Hz
to
100KHz,TA=+25
oC
-
42
-
V/Vo
Ripple Rejection
RR
62
73
-
Dropout Voltage
VDrop
-
2
-
dB

V
Output
Resistance
Short
Circuit
Current
Peak Current
rO
f = 120Hz
VO = 8V to 18V
IO = 1A, TJ =+25
oC
f = 1KHz
-
15
-
m
VI = 35V, TA =+25
oC
TJ =+25 oC
-
230
-
mA
-
2.2
-
A
ISC
IPK
11
TRANSFORMER
Three-phase step-down transformer mounted between two utility poles
Laminated core transformer
A transformer is a device that transfers electrical energy from one circuit to another through
inductively coupled conductors—the transformer's coils. A varying current in the first or
primary winding creates a varying magnetic flux in the transformer's core and thus a varying
magnetic field through the secondary winding. This varying magnetic field induces a varying
electromotive force (EMF), or "voltage", in the secondary winding. This effect is called
inductive coupling.
If a load is connected to the secondary, current will flow in the secondary winding, and
electrical energy will be transferred from the primary circuit through the transformer to the
load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in
proportion to the primary voltage (Vp) and is given by the ratio of the number of turns in the
secondary (Ns) to the number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus enables an alternating
current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by
making Ns less than Np.
12
In the vast majority of transformers, the windings are coils wound around a ferromagnetic
core, air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling transformer hidden inside a
stage microphone to huge units weighing hundreds of tons used to interconnect portions of
power grids. All operate on the same basic principles, although the range of designs is wide.
While new technologies have eliminated the need for transformers in some electronic
circuits, transformers are still found in nearly all electronic devices designed for household
("mains") voltage. Transformers are essential for high-voltage electric power transmission,
which makes long-distance transmission economically practical.
BASIC PRINCIPLES
An ideal transformer. The secondary current arises from the action of the secondary EMF
on the (not shown) load impedance.
The transformer is based on two principles: first, that an electric current can produce a
magnetic field (electromagnetism) and second that a changing magnetic field within a coil of
wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the
current in the primary coil changes the magnetic flux that is developed. The changing
magnetic flux induces a voltage in the secondary coil.
An ideal transformer is shown in the adjacent figure. Current passing through the primary
coil creates a magnetic field. The primary and secondary coils are wrapped around a core of
very high magnetic permeability, such as iron, so that most of the magnetic flux passes
through both the primary and secondary coils. If a load is connected to the secondary
winding, the load current and voltage will be in the directions indicated, given the primary
current and voltage in the directions indicated (each will be alternating current in practice).
13
STEP DOWN TRANSFORMER
Step down transformers are designed to reduce electrical voltage. Their primary voltage is
greater than their secondary voltage. This kind of transformer "steps down" the voltage
applied to it. Step down transformers convert electrical voltage from one level or phase
configuration usually down to a lower level. They can include features for electrical
isolation, power distribution, and control and instrumentation applications. Step down
transformers typically rely on the principle of magnetic induction between coils to convert
voltage and/or current levels.Step down transformers are made from two or more coils of
insulated wire wound around a core made of iron. When voltage is applied to one coil
(frequently called the primary or input) it magnetizes the iron core, which induces a voltage
in the other coil, (frequently called the secondary or output). The turns ratio of the two sets
of windings determines the amount of voltage transformation.Step down transformers can be
considered nothing more than a voltage ratio device.
CIRCUIT SYMBOLS
Transformer with two windings and iron core.
Step-down or step-up transformer. The symbol shows which winding
has more turns, but not usually the exact ratio.
Transformer with three windings. The dots show the relative
configuration of the windings.
Transformer with electrostatic screen preventing capacitive coupling
between the windings.
14
DIODES
A Diode is the simplest two-terminal unilateral semiconductor device. It allows current to
flow only in one direction and blocks the current that flows in the opposite direction. The
two terminals of the diode are called as anode and cathode. The symbol of diode symbol is as
shown in the figure below.
The characteristics of a diode closely match to that of a switch. An ideal switch when open
does not conduct current in either directions and in closed state conducts in both directions.
The characteristic of a diode is as shown in the figure below.
Ideally, in one direction that is indicated by the arrow head diode must behave short
circuited and in other one that opposite to that of the direction of arrow head must be open
circuited. By ideal characteristics, the diodes is designed to meet these features theoretically
but are not achieved practically. So the practical diode characteristics are only close to that of
the desired.
APPLICATION OF DIODE:
Diodes are used in various applications like rectification, clipper, clamper, voltage multiplier,
comparator, sampling gates and filters.
RECTIFICATION
The rectification means converting AC voltage into DC voltage. The common rectification
circuits are half wave rectifier (HWR), full wave rectifier (FWR) and bridge rectifier.
15
· Half wave rectifier: This circuit rectifies either positive or negative pulse of the input AC.
The figure is as shown below:
· Full wave rectifier: This circuit converts the entire AC signal into DC. The figure is as
shown below:
· Bridge rectifier: This circuit converts the entire AC signal into DC. The figure is as shown
below:
16
IDENTIFICATION:
A diode is marked with a bar which indicates the cathode terminal of a diode which is as
shown in the figure below:
PRINCIPLE AND OPERATION:
The possible configurations for a diode are:
1. Forward biased
2. Reverse biased
1. FORWARD BIAS: In forward bias condition, higher or positive potential is applied at
the anode and negative or lower potential is applied at the cathode of a diode. The positive
potential at anode repels the holes in p-region towards n-region while negative potential at
the cathode repels electrons in n-region towards p-region. Thus, the height of the potential
barrier reduces. The depletion region disappears when the applied voltage equals to the
potential barrier and a large current flows through the diode. The voltage required to drive
the diode into a state of conduction is called as the ‘Cut in/Offset/Threshold/Firing voltage’.
The current is of considerable magnitude as it is dominantly constituted by the majority
charge currents that is the hole current in the p-region and the electron current in the nregion. The current that flows from anode to cathode is limited by the crystal bulk
resistance, recombination of charges and the ohmic contact resistances at the two metal
semiconductor junctions. The current is restricted to mille Amperes order.
2.REVERSE BIAS: In reverse bias condition, the higher or positive potential is applied at
the cathode and negative or lower potential is applied at the anode. The negative potential at
anode attracts the holes in p-region that are away from the n-region while positive potential
at the cathode attracts electrons in n-region that are away from the p-region. The applied
voltage increases the height of the potential barrier. The current flows dominantly due to the
17
minority charge currents that is the electron current in p-region and the hole current in nregion. Thus a constant current of negligible magnitude flows in the reverse direction which
is called as the ‘Reverse saturation current’. Practically, the diode remains in a state of non –
conduction. The reverse saturation current is of the order of microamperes in a germanium
diode or nanoamperes in a silicon diode If the reverse voltage exceeds the limit of
‘breakdown/zener/Peak inverse/Peak reverse voltage’, the potential breakdown that occurs
leads to a large reverse current.
TYPES OF DIODES:
The other variant of diodes have different construction, characteristics and applications. The
different types of diodes are:
Light emitting diodes (LED) - This is the most popular kind of diode. When it works in
the forward bias condition, the current flows through the junction to produce the light.
Schottky diode - These diodes are used in RF applications and clamping circuits. This
diode has lower forward voltage drop as against the silicon PN junction diodes.
18
GENERIC DIODES (SMALL SIGNAL AND LARGE SIGNAL):
A p-n junction diode is the simplest semiconductor device. It is a two-terminal, bipolar,
unilateral rectifying device that conducts only in one direction. The generic diodes are used
in the following fields:
· Rectification in power supply circuits
· Extraction of modulation from radio signals in a radio receiver and in protection circuits
where large transient currents may appear on low current transistors or ICs in interfacing
with relays or other high power devices.
· Used in series with power inputs to electronic circuits where only one of negative or
positive polarity voltage is desired.
RECTIFIER DIODES (LARGE CURRENT)
Rectifier diodes are used in power supplies to convert alternating current (AC) to direct
current (DC), a process called rectification. They are also used elsewhere in circuits where a
large current must pass through the diode. All rectifier diodes are made from silicon and
therefore have a forward voltage drop of 0.7V.
BRIDGE RECTIFIERS
Various types of Bridge Rectifiers
There are several ways of connecting diodes to make a rectifier to convert AC to DC. The
bridge rectifier is one of them and it is available in special packages containing the four
diodes required. Bridge rectifiers are rated by their maximum current and maximum reverse
voltage. They have four leads or terminals: the two DC outputs are labelled + and -, the two
AC inputs are labelled . The diagram shows the operation of a bridge rectifier as it converts
AC to DC.
19
CAPACITORS
Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is
the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer
infinite reactance to zero frequency so they are used for blocking DC components or
bypassing the AC signals. The capacitor undergoes through a recursive cycle of charging and
discharging in AC circuits where the voltage and current across it depends on the RC time
constant. For this reason, capacitors are used for smoothing power supply variations. Other
uses include, coupling the various stages of audio system, tuning in radio circuits etc. These
are used to store energy like in a camera flash. Capacitors may be non-polarized/polarized
and fixed/variable. Electrolytic capacitors are polarized while ceramic and paper capacitors
are examples of non polarized capacitors. Since capacitors store charge, they must be
carefully discharged before troubleshooting the circuits. The maximum voltage rating of the
capacitors used must always be greater than the supply voltage.
FUNCTION
Capacitors store electric charge. They are used with resistors in timing circuits because it
takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by
acting as a reservoir of charge. They are also used in filter circuits because capacitors easily
pass AC (changing) signals but they block DC (constant) signals.
CAPACITANCE
This is a measure of a capacitor's ability to store charge. A large capacitance means that more
charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large,
so prefixes are used to show the smaller values.
Three prefixes (multipliers) are used, μ (micro), n (nano) and p (pico):
l μ means 10-6 (millionth), so 1000000μF = 1F
l n means 10-9 (thousand-millionth), so 1000nF = 1μF
l p means 10-12 (million-millionth), so 1000pF = 1nF
20
CIRCUIT SYMBOL
PIN DIAGRAM:
DETERMINING CAPACITOR VALUES
21
AT89C51 MICROCONTROLLER
AT89C51 is an 8-bit microcontroller and belongs to Atmel's 8051 family. ATMEL 89C51 has
4KB of Flash programmable and erasable read only memory (PEROM) and 128 bytes of
RAM. It can be erased and program to a maximum of 1000 times.
The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes
of Flash programmable and erasable read only memory (PEROM). The device is
manufactured using Atmel’s high-density nonvolatile memory technology and is compatible
with the industry-standard MCS-51 instruction set and pinout. The on-chip Flash allows the
program memory to be reprogrammed in-system or by a conventional nonvolatile memory
programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel
AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective
solution to many embedded control applications.
In 40 pin AT89C51, there are four ports designated as P1, P2, P3 and P0. All these ports are 8bit bi-directional ports, i.e., they can be used as both input and output ports. Except P0 which
needs external pull-ups, rest of the ports have internal pull-ups. When 1s are written to these
port pins, they are pulled high by the internal pull-ups and can be used as inputs. These ports
are also bit addressable and so their bits can also be accessed individually.
Port P0 and P2 are also used to provide low byte and high byte addresses, respectively, when
connected to an external memory. Port 3 has multiplexed pins for special functions like serial
communication, hardware interrupts, timer inputs and read/write operation from external
memory. AT89C51 has an inbuilt UART for serial communication. It can be programmed to
operate at different baud rates. Including two timers & hardware interrupts, it has a total of
six interrupts.
22
PIN DIAGRAM:
23
Pin Description:
Pin No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Function
8 bit input/output port (P1) pins
Reset pin; Active high
I/o (rxr)for serial comm RxD
O/p(txr)for serialcomm TxD
External interrupt 1
Int0
8
bit
External interrupt 2
Int1
input/output port
Timer1 external input
T0
(P3) pins
Timer2 external input
T1
Write to ext data mem Write
Rd from ext data mem Read
Quartz crystal oscillator (up to 24 MHz)
Ground (0V)
8 bit input/output port (P2) pins
/
High-order address bits when interfacing with external
memory
Prog store enable; Read from ext program memory
Address Latch Enable
Program pulse input during Flash programming
Ext Access Enable; Vcc for int program executions
Prog enable voltage; 12V (during Flash programming)
8 bit input/output port (P0) pins
Low-order address bits when interfacing with external
memory
Supply voltage; 5V (up to 6.6V)
Name
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
Reset
P3.0
P3.1
P3.2
P3.3
P3.4
P3.5
P3.6
P3.7
Crystal 2
Crystal 1
Ground
P2.0/ A8
P2.1/ A9
P2.2/ A10
P2.3/ A11
P2.4/ A12
P2.5/ A13
P2.6/ A14
P2.7/ A15
PSEN
ALE
Prog
EA
Vpp
P0.7/ AD7
P0.6/ AD6
P0.5/ AD5
P0.4/ AD4
P0.3/ AD3
P0.2/ AD2
P0.1/ AD1
P0.0/ AD0
Vcc
24
VCC(PIN 40)
Supply voltage.
GND(PIN 20)
Ground.
PORT 0(PIN 32-39)
Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink
eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance
inputs. Port 0 may also be configured to be the multiplexed low order address/data bus
during accesses to external program and data memory. In this mode P0 has internal pull ups.
Port 0 also receives the code bytes during Flash programming, and outputs the code bytes
during program verification. External pullups are required during program verification.
PORT 1(PIN 1-8)
Port 1 is an 8-bit bi-directional I/O port with internal pull ups. The Port 1 output buffers can
sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the
internal pullups and can be used as inputs. As inputs, Port 1 pins that are externally being
pulled low will source current (IIL) because of the internal pull ups. Port 1 also receives the
low-order address bytes during Flash programming and verification.
PORT 2(PIN 21-28)
Port 2 is an 8-bit bi-directional I/O port with internal pull ups. The Port 2 output buffers can
sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the
internal pullups and can be used as inputs. As inputs, Port 2 pins that are externally being
pulled low will source current (IIL) because of the internal pull ups. Port 2 emits the highorder address byte during fetches from external program memory and during accesses to
external data memory that use 16-bit addresses (MOVX @ DPTR). In this application, it uses
strong internal pull-ups when emitting 1s. During accesses to external data memory that use
8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register.
Port 2 also receives the high-order address bits and some control signals during Flash
programming and verification.
PORT 3(PIN 10-17)
Port 3 is an 8-bit bi-directional I/O port with internal pullups. The Port 3 output buffers can
sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the
internal pullups and can be used as inputs. As inputs, Port 3 pins that are externally being
pulled low will source current (IIL) because of the pul lups.
25
Port 3 also serves the functions of various special features of the AT89C51 as listed below:
Port Pin
Alternate Functions
P3.0
RXD (serial input
port)
P3.1
TXD (serial output
port)
P3.2
INT0
(external
interrupt 0)
P3.3
INT1
(external
interrupt 1)
P3.4
T0 (timer 0 external
input)
P3.5
T1 (timer 1 external
input)
P3.6
WR (external data
memory
write
strobe)
P3.7
RD (external data memory read strobe)
Port 3 also receives some control signals for Flash programming and verification.
RST(PIN 9)
Reset input. A high on this pin for two machine cycles while the oscillator is running resets
the device.
ALE/PROG(PIN 30)
Address Latch Enable output pulse for latching the low byte of the address during accesses to
external memory. This pin is also the program pulse input (PROG) during Flash
programming. In normal operation ALE is emitted at a constant rate of 1/6 the oscillator
frequency, and may be used for external timing or clocking purposes. Note, however, that
one ALEpulse is skipped during each access to external Data Memory. If desired, ALE
operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active
only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high.
Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.
PSEN(PIN 29)
Program Store Enable is the read strobe to external program memory. When the AT89C51 is
executing code from external program memory, PSEN is activated twice each machine cycle,
except that two PSEN activations are skipped during each access to external data memory.
26
EA/VPP(PIN 31)
External Access Enable. EA must be strapped to GND in order to enable the device to fetch
code from external program memory locations starting at 0000H up to FFFFH. Note,
however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should
be strapped to VCC for internal program executions. This pin also receives the 12-volt
programming enable voltage (VPP) during Flash programming, for parts that require 12-volt
VPP.
XTAL1(PIN 19)
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
XTAL2(PIN 18)
Output from the inverting oscillator amplifier.
OSCILLATOR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which
can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz
crystal or ceramic resonator may be used. To drive the device from an external clock source,
XTAL2 should be left unconnected while XTAL1 is driven. There are no requirements on the
duty cycle of the external clock signal, since the input to the internal clocking circuitry is
through a divide-by-two flip-flop, but minimum and maximum voltage high and low time
specifications must be observed.
IDLE MODE
In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The
mode is invoked by software. The content of the on-chip RAM and all the special functions
registers remain unchanged during this mode. The idle mode can be terminated by any
enabled interrupt or by a hardware reset. It should be noted that when idle is terminated by
a hardware reset, the device normally resumes program execution, from where it left off, up
to two machine cycles before the internal reset algorithm takes control. On-chip hardware
inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To
eliminate the possibility of an unexpected write to a port pin when Idle is terminated by
reset, the instruction following the one that invokes Idle should not be one that writes to a
port pin or to external memory.
27
POWER-DOWN MODE
In the power-down mode, the oscillator is stopped, and the instruction that invokes powerdown is the last instruction executed. The on-chip RAM and Special Function Registersretain
their values until the power-down mode is terminated. The only exit from power-down is a
hardware reset. Reset redefines the SFRs but does not change the on-chip RAM. The reset
should not be activated before VCC is restored to its normal operating level and must be held
active long enough to allow the oscillator to restart and stabilize.
PROGRAM MEMORY LOCK BITS
On the chip are three lock bits which can be left unprogrammed (U) or can be programmed
(P) to obtain the additional features. When lock bit 1 is programmed, the logic level at the
EA pin is sampled and latched during reset. If the device is powered up without a reset, the
latch initializes to a random value, and holds that value until reset is activated. It is necessary
that the latched value of EA be in agreement with the current logic level at that pin in order
for the device to function properly.
PROGRAMMING THE FLASH
The AT89C51 is normally shipped with the on-chip Flash memory array in the erased state
(that is, contents = FFH) and ready to be programmed. The programming interface accepts
either a high-voltage (12-volt) or a low-voltage (VCC) program enable signal. The lowvoltage programming mode provides a convenient way to program the AT89C51 inside the
user’s system, while the high-voltage programming mode is compatible with conventional
third party Flash or EPROM programmers. The AT89C51 is shipped with either the highvoltage or low-voltage programming mode enabled.
PROGRAMMING ALGORITHM
Before programming the AT89C51, the address, data and control signals should be set up
according to the Flash programming mode table. To program the AT89C51, take the
following steps.
1. Input the desired memory location on the address lines.
2. Input the appropriate data byte on the data lines.
3. Activate the correct combination of control signals.
4. Raise EA/VPP to 12V for the high-voltage programming mode.
5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The bytewrite cycle is self-timed and typically takes no more than 1.5 ms.
Repeat steps 1 through 5, changing the addressand data for the entire array or until the end
of the object file is reached.
28
DATA POLLING: The AT89C51 features Data Polling to indicate the end of a write cycle.
During a write cycle, an attempted read of the last byte written will result in the
complement of the written datum on PO.7. Once the write cycle has been completed, true
data are valid on all outputs, and the next cycle may begin. Data Polling may begin any time
after a write cycle has been initiated.
READY/BUSY: The progress of byte programming can also be monitored by the RDY/BSY
output signal. P3.4 is pulled low after ALE goes high during programming to indicate BUSY.
P3.4 is pulled high again when programming is done to indicate READY.
PROGRAM VERIFY: If lock bits LB1 and LB2 have not been programmed, the
programmed code data can be read back via the address and data lines for verification. The
lock bits cannot be verified directly. Verification of the lock bits is achieved by observing
that their features are enabled.
CHIP ERASE: The entire Flash array is erased electrically by using the proper combination
of control signals and by holding ALE/PROG low for 10 ms. The code array is written with
all “1”s. The chip erase operation must be executed before the code memory can be
reprogrammed.
READING THE SIGNATURE BYTES: The signature bytes are read by the same
procedure as a normal verification of locations 030H, 031H, and 032H, except that P3.6 and
P3.7 must be pulled to a logic low. The values returned are as follows.
(030H) = 1EH indicates manufactured by Atmel
(031H) = 51H indicates 89C51
(032H) = FFH indicates 12V programming
(032H) = 05H indicates 5V programming
PROGRAMMING INTERFACE
Every code byte in the Flash array can be written and the entire array can be erased by using
the appropriate combination of control signals. The write operation cycle is self timed and
once initiated, will automatically time itself to completion. All major programming vendors
offer worldwide support for the Atmel microcontroller series. Please contact your local
programming vendor for the appropriate software revision.
AC CHARACTERISTICS
Under operating conditions, load capacitance for Port 0, ALE/PROG, and PSEN = 100 pF;
load capacitance for all other outputs = 80 pF.
29
RESISTORS
A resistor is a component of an electrical circuit that resists the flow of electrical current. A
resistor has two terminals across which electricity must pass, and is designed to drop the
voltage of the current as it flows from one terminal to the next. A resistor is primarily used to
create and maintain a known safe current within an electrical component.
Because resistors are often too small to be written on, a standardized color-coding system is
used to identify them. The first three colors represent ohm value, and a fourth indicates the
tolerance, or how close by percentage the resistor is to its ohm value. This is important for
two reasons: the nature of resistor construction is imprecise, and if used above its maximum
current, the value of the resistor can alter or the unit itself can burn up.
• The internal resistance is usually drawn into a circuit diagram (schematic) as shown in
Figure 1.
Figure 1: A schematic diagram showing internal resistance and a battery.
The squiggly line just before the positive terminal of the battery shows the internal
resistance of the circuit.
• That symbol, drawn any other place in the circuit, represents an actual resistor placed in the
circuit.
• A resistor is a device found in circuits that has a certain amount of resistance.
• The most common reason to add resistance to a circuit by using a resistor is that we need to
be able to adjust the current flowing through a particular part of the circuit.
• If voltage is constant, then we can change the resistor to change the current. I=V R If “V” is
constant and we change “R”, “I” will be different.
•
ACTUAL RESISTORS
The colored lines tell you the resistance and error range (tolerance) for a resistor according
to the following rules and table of numbers. You do NOT have to memorize this table… it
will be given to you if you need it.
• To use the table you need to remember the following rules:
1. The first line is the first digit
2. The second line is the second digit
3. The third line is the multiplier
4. The last line (if any) is the tolerance
• Some resistors may have additional colored bands, but we will ignore them here.
• They usually have something to do with measuring things like failure rates or temperature
coefficients.
30
Figure 2: Three resistors used in electronic devices
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
whiteite
Gold
Silver
No Color •
Number Multiplier
0
1
2
3
4
5
6
7
8
Tolerance
100
101
102 •
103
104
105
106
107
108
9
109
10-1 •
10-2 •
+_ 1%
+_ 2%
+_5%
+_ 10%
+_ 20%
31
CRYSTAL OSCILLATOR
A miniature 4 MHz quartz crystal enclosed in a hermetically sealed HC-49/US package, used
as the resonator in a crystal oscillator.
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a
vibrating crystal of piezoelectric material to create an electrical signal with a very precise
frequency. This frequency is commonly used to keep track of time (as in quartz
wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize
frequencies for radio transmitters and receivers. The most common type of piezoelectric
resonator used is the quartz crystal, so oscillator circuits designed around them became
known as "crystal oscillators."
MODELING
ELECTRICAL MODEL
Electronic symbol for a piezoelectric crystal resonator
A quartz crystal can be modeled as an electrical network with a low impedance (series) and a
high impedance (parallel) resonance point spaced closely together.
32
Mathematically (using the Laplace transform) the impedance of this network can be written
as:
or,
where s is the complex frequency(
),
is the series resonant frequency in radians
per second and
is the parallel resonant frequency in radians per second.
Adding additional capacitance across a crystal will cause the parallel resonance to shift
downward. This can be used to adjust the frequency at which a crystal oscillates. Crystal
manufacturers normally cut and trim their crystals to have a specified resonance frequency
with a known 'load' capacitance added to the crystal. For example, a crystal intended for a 6
pF load has its specified parallel resonance frequency when a 6.0 pF capacitor is placed across
it. Without this capacitance, the resonance frequency is higher.
Schematic symbol and equivalent circuit for a quartz crystal in an oscillator
33
PUSH TO ON SWITCH
A push switch is is a momentary or non-latching switch which causes a temporary change in
the state of a electrical circuit only while the switch is physically actuated. An automatic
mechanism (ie a spring) returns the switch to its default position immediately afterwards,
restoring the initial circuit condition. There are two types:
 A push to make switch allows electricity to flow between its two contacts when held
in. When the button is released, the circuit is broken.
 A push to break switch does the opposite, i.e when the button is not pressed,
electricity can flow, but when it is pressed the circuit is broken.
(ON)-OFF (PUSH-TO-MAKE = SPST MOMENTARY)
A push-to-make switch returns to its normally open (off) position when you release the
button, this is shown by the brackets around ON. This is the standard doorbell switch.
CIRCUIT SYMBOL
34
L293D MOTOR DRIVER IC
L293D is a dual H-bridge motor driver integrated circuit (IC). Motor drivers act as current
amplifiers since they take a low-current control signal and provide a higher-current signal.
This higher current signal is used to drive the motors.L293D contains two inbuilt H-bridge
driver circuits. In its common mode of operation, two DC motors can be driven
simultaneously, both in forward and reverse direction. The motor operations of two motors
can be controlled by input logic at pins 2 & 7 and 10 & 15. Input logic 00 or 11 will stop the
corresponding motor.Logic 01 and 10 will rotate it in clockwise and anticlockwise directions,
respectively. Enable pins 1 and 9 (corresponding to the two motors) must be high for motors
to start operating. When an enable input is high, the associated driver gets enabled. As a
result, the outputs become active and work in phase with their inputs. Similarly, when the
enable input is low, that driver is disabled, and their outputs are off and in the highimpedance state.
PIN DIAGRAM:
35
PIN DESCRIPTION:
Pin No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Function
Enable pin for Motor 1; active high
Input 1 for Motor 1
Output 1 for Motor 1
Ground (0V)
Ground (0V)
Output 2 for Motor 1
Input 2 for Motor 1
Supply voltage for Motors; 9-12V (upto 36V)
Enable pin for Motor 2; active high
Input 1 for Motor 1
Output 1 for Motor 1
Ground (0V)
Ground (0V)
Output 2 for Motor 1
Input2 for Motor 1
Supply voltage; 5V (up to 36V)
Name
Enable 1,2
Input 1
Output 1
Ground
Ground
Output 2
Input 2
Vcc 2
Enable 3,4
Input 3
Output 3
Ground
Ground
Output 4
Input 4
Vcc 1
36
CODE
; Motor1 connected with the p1.0 and p1.1
; Motor2 connect with the p1.2 and p1.3
; Motor 3 connect with the p1.4 and p1.5
;Seven segment is conneccted with the port 0
org 00h
main:
acall display
; ------------------ Motor operation from this point ----------setb p1.0
clr p1.1
; Motor 1 forward
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
CLR P1.0
CLR P1.1
Acall delay
Acall delay
Acall delay
setb p1.2
clr p1.3
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
CLR P1.2
CLR P1.3
acall delay
Acall delay
Acall delay
; Motor 2 forward
37
setb p1.4
clr p1.5
; Motor 3 forward
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
CLR P1.4
CLR P1.5
acall delay
Acall delay
Acall delay
; -------------------------- display ----------------------acall display
; ---------------------------- Motor operation -----------------setb p1.5
clr p1.4
;motor 3 reversed
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
clr p1.5
clr p1.4
acall delay
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
setb p1.3
clr p1.2
Acall delay
;Motor 2 reversed
38
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
clr p1.3
clr p1.2
acall delay
Acall delay
Acall delay
setb p1.1
clr p1.0
;Motor 1 reversed
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
clr p1.1
clr p1.0
acall delay
Acall delay
Acall delay
Ljmp main
; ------------------------------ TIME DELAY --------------------delay:mov R1,#255
here1:mov R2,#255
here:Djnz R2,here
Djnz R1,here1
ret
; ----------------------------- SEVEN SEGMENT DISPLAY ------------------display:
MOV P0,#00H
mov p0,#01011111b ;Display9
Acall delay
39
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#01111111b ;Display 8
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#00001110b ; Display 7
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#01111011b ;Display 6
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#01011011b ;Display 5
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#01001101b ;Display 4
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#01011110b ;Display 3
40
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#01110110b ;Display 2
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#00001100b ;Display 1
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
mov p0,#00111111b ;Display 0
Acall delay
Acall delay
Acall delay
Acall delay
Acall delay
MOV P0,#00H
ret
; -------------------------------------------------------------------------------------end
41
SEVEN-SEGMENT DISPLAY
A typical 7-segment LED display component, with decimal point
A seven-segment display (SSD), or seven-segment indicator, is a form of electronic display
device for displaying decimal numerals that is an alternative to the more complex dot-matrix
displays. Seven-segment displays are widely used in digital clocks, electronic meters, and
other electronic devices for displaying numerical information.
The idea of the seven-segment display is quite old. In 1910, for example, a seven-segment
display illuminated by incandescent bulbs was used on a power-plant boiler room signal
panel.
CONCEPT AND VISUAL STRUCTURE
The individual segments of a seven-segment display
42
16x8-grid showing the 128 states of a seven-segment display
A seven segment display, as its name indicates, is composed of seven elements. Individually
on or off, they can be combined to produce simplified representations of the arabic numerals.
Often the seven segments are arranged in an oblique (slanted) arrangement, which aids
readability. In most applications, the seven segments are of nearly uniform shape and size
(usually elongated hexagons, though trapezoids and rectangles can also be used), though in
the case of adding machines, the vertical segments are longer and more oddly shaped at the
ends in an effort to further enhance readability.
IMPLEMENTATIONS
An incandescent light A mechanical seventype early seven-segment display for
segment display
displaying automotive
fuel prices
Seven-segment displays may use a liquid crystal display (LCD), arrays of light-emitting
diodes (LEDs), or other light-generating or controlling techniques such as cold cathode gas
discharge, vacuum fluorescent, incandescent filaments, and others. In a simple LED package,
typically all of the cathodes (negative terminals) or all of the anodes (positive terminals) of
the segment LEDs are connected and brought out to a common pin; this is referred to as a
"common cathode" or "common anode" device. Hence a 7 segment plus decimal point
package will only require nine pins (though commercial products typically contain more
pins, and/or spaces where pins would go, in order to match industry standard pinouts).
Multiple-digit LED displays as used in pocket calculators and similar devices used
multiplexed displays to reduce the number of IC pins required to control the display.
DISPLAY PATTERN TABLES
.HINDU-ARABIC NUMERAL
0
1
2
3
4
5
6
7
8
9
43
THE LED
Light emitting diodes (LEDs) are semiconductor light sources. The light emitted from LEDs
varies from visible to infrared and ultraviolet regions. They operate on low voltage and
power. LEDs are one of the most common electronic components and are mostly used as
indicators in circuits. They are also used for luminance and optoelectronic applications.
Based on semiconductor diode, LEDs emit photons when electrons recombine with holes on
forward biasing. The two terminals of LEDs are anode (+) and cathode (-) and can be
identified by their size. The longer leg is the positive terminal or anode and shorter one is
negative terminal.
The forward voltage of LED (1.7V-2.2V) is lower than the voltage supplied (5V) to drive it in
a circuit. Using an LED as such would burn it because a high current would destroy its p-n
gate. Therefore a current limiting resistor is used in series with LED. Without this resistor,
either low input voltage (equal to forward voltage) or PWM (pulse width modulation) is
used to drive the LED.
Besides red, they can also be yellow, green and blue. The letters LED stand for Light
Emitting Diode.. The important thing to remember about diodes (including LEDs) is that
current can only flow in one direction.
PIN DIAGRAM:
44
FUNCTION
LEDs emit light when an electric current passes through them.
CONNECTING AND SOLDERING
LEDs must be connected the correct way round, the diagram may be labelled a or + for
anode and k or - for cathode (yes, it really is k, not c, for cathode!). The cathode is the short
lead and there may be a slight flat on the body of round LEDs. If you can see inside the LED
the cathode is the larger electrode (but this is not an official identification method). LEDs
can be damaged by heat when soldering, but the risk is small unless you are very slow.
No special precautions are needed for soldering most LEDs.
TESTING AN LED
Never connect an LED directly to a battery or power supply! It will be destroyed almost
instantly because too much current will pass through and burn it out. LEDs must have a
resistor in series to limit the current to a safe value, for quick testing purposes a 1k resistor is
suitable for most LEDs if your supply voltage is 12V or less.
FLASHING LEDS
Flashing LEDs look like ordinary LEDs but they contain an integrated circuit (IC) as well as
the LED itself. The IC flashes the LED at a low frequency, typically 3Hz (3 flashes per
second). They are designed to be connected directly to a supply, usually 9 - 12V, and no
series resistor is required. Their flash frequency is fixed so their use is limited and you may
prefer to build your own circuit to flash an ordinary LED, for example our Flashing LED
project which uses a 555 astable circuit.
45
TRANSISTORS
Transistors are basic components in all of today's electronics. They are just simple switches
that we can use to turn things on and off. Even though they are simple, they are the most
important electrical component. For example, transistors are almost the only components
used to build a Pentium processor. A single Pentium chip has about 3.5 million transistors.
The ones in the Pentium are smaller than the ones we will use but they work the same way.
Transistors that we will use in projects look like this:
The transistor has three legs, the Collector (C), Base (B), and Emitter (E). Sometimes they are
labeled on the flat side of the transistor. Transistors always have one round side and one flat
side. If the round side is facing you, the Collector leg is on the left, the Base leg is in the
middle, and the Emitter leg is on the right.
TRANSISTOR BC548
BC548 is general purpose silicon, NPN, bipolar junction transistor. It is used for amplification
and switching purposes. The current gain may vary between 110 and 800. The maximum DC
current gain is 800.Its equivalent transistors are 2N3904 and 2SC1815. These equivalent
transistors however have different lead assignments. The variants of BC548 are 548A, 548B
and 548C which vary in range of current gain and other characteristics.The transistor
terminals require a fixed DC voltage to operate in the desired region of its characteristic
curves. This is known as the biasing. For amplification applications, the transistor is biased
such that it is partly on for all input conditions. The input signal at base is amplified and
taken at the emitter. BC548 is used in common emitter configuration for amplifiers. The
voltage divider is the commonly used biasing mode. For switching applications, transistor is
biased so that it remains fully on if there is a signal at its base. In the absence of base signal, it
gets completely off.
46
TRANSISTOR SYMBOL
The following symbol is used in circuit drawings (schematics) to represent a transistor.
Basic Circuit
The Base (B) is the On/Off switch for the transistor. If a current is flowing to the Base, there
will be a path from the Collector (C) to the Emitter (E) where current can flow (The Switch
is On.) If there is no current flowing to the Base, then no current can flow from the Collector
to the Emitter. (The Switch is Off.)
Below is the basic circuit we will use for all of our transistors.
47
FUNCTION
Transistors amplify current, for example they can be used to amplify the small output current
from a logic chip so that it can operate a lamp, relay
or other high current device. In many circuits a resistor is used to convert the changing
current to a changing voltage, so the transistor is being used to amplify voltage.
A transistor may be used as a switch (either fully on with maximum current, or fully off with
no current) and as an amplifier (always partly on). The amount of current amplification is
called the current gain, symbol hFE.
TYPES OF TRANSISTOR
There are two types of standard transistors, NPN and PNP, with
different circuit symbols. The letters refer to the layers of
semiconductor material used to make the transistor. Most
transistors used today are NPN because this is the easiest type to
make from silicon. If you are new to electronics it is best to start
by learning how to use NPN transistors.
Transistor circuit symbols
The leads are labelled base (B), collector (C) and emitter (E).
These terms refer to the internal operation of a transistor but they are not much help in
understanding how a transistor is used, so just treat them as labels!
A Darlington pair is two transistors connected together to give a very high current gain.
In addition to standard (bipolar junction) transistors, there are field-effect transistors which
are usually referred to as FETs. They have different circuit symbols and properties and they
are not (yet) covered by this page.
CONNECTING
Transistors have three leads which must be connected the correct way round. Please take
care with this because a wrongly connected transistor may be damaged instantly when you
switch on.
If you are lucky the orientation of the transistor will be clear from the PCB or stripboard
layout diagram, otherwise you will need to refer to a supplier's catalogue to identify the
leads.
The drawings on the right show the leads for some of the most common case styles.
Please note that transistor lead diagrams show the view from below with the leads towards
you. This is the opposite of IC (chip) pin diagrams which show the view from above.
48
SOLDERING
Transistors can be damaged by heat when soldering so if you are not
an expert it is wise to use a heat sink clipped to the lead between the
joint and the transistor body. A standard crocodile clip can be used as
a heat sink.
Crocodile clip.
Do not confuse this temporary heat sink with the permanent heat
sink (described below) which may be required for a power transistor to prevent it
overheating during operation.
HEAT SINKS
Waste heat is produced in transistors due to the current flowing through
them. Heat sinks are needed for power transistors because they pass large
currents. If you find that a transistor is becoming too hot to touch it Heat sink
certainly needs a heat sink! The heat sink helps to dissipate (remove) the
heat by transferring it to the surrounding air. .
CHOOSING A TRANSISTOR
Most projects will specify a particular transistor, but if necessary you can usually substitute
an equivalent transistor from the wide range available. The most important properties to look
for are the maximum collector current IC and the current gain hFE. To make selection easier
most suppliers group their transistors in categories determined either by their typical use or
maximum power rating.
To make a final choice you will need to consult the tables of technical data which are
normally provided in catalogues. They contain a great deal of useful information but they
can be difficult to understand if you are not familiar with the abbreviations used. The table
below shows the most important technical data for some popular transistors, tables in
catalogues and reference books will usually show additional information but this is unlikely
to be useful unless you are experienced.
49
The quantities shown in the table are explained below.
Code
Case
ICMax
VCE.max hFEmin Ptotmax.
Category(typicaluse)
BC107
BC108
TO18
TO18
100mA 45V
100mA 20V
110
110
300mW Audio,Low Power
BC182 BC547
NPN
300mW Generalpurpose,Low BC108C
BC183 NPN
Power
BC548
BC108C TO18
100mA 20V
420
BC109
TO18
200mA 20V
200
BC182
TO92C
100mA 50V
100
BC182L
TO92A 100mA 50V
100
600mW Audio(low
noise),Low Power
300mW General
purpose,Low Power
350mW General
purpose,Low Power
350mW Audio,Low Power
BC547B
2C
100mA 45V
200
BC548B
2C
100mA 30V
220
BC549B
TO39
100mA 30V
240
2N3053
TO39
700mA 40V
50
BFY51
TO39
1A
30V
40
BC639
TO92A 1A
80V
40
TIP29A
TO220
1A
60V
40
TIP31A
TO220
3A
60V
10
TIP31C
TO220
3A
100V
10
TIP41A
TO220
6A
60V
15
2N3055
TO3
15A
60V
20
500mW General
purpose,Low Power
500mW Audio(low
noise),Low Power
625mW General
purpose,Low Power
500mW General
purpose,Medium
Power
800mW General
purpose,Medium
Power
800mW General
purpose,Medium
Power
30W
Genpurpose,High
Power
40W
General
purpose,High Power
40W
General
purpose,High Power
65W
General
purpose,High Power
117W
General
purpose,High Power
Possiblesubstitutes Structure
NPN
BC184 BC549
NPN
BC107 BC182L
NPN
BC107 BC182
NPN
BC107B
NPN
BC108B
NPN
BC109
NPN
BFY51
NPN
BC639
NPN
BFY51
NPN
NPN
TIP31 TIP41A
NPN
TIP31A TIP41A
NPN
This shows the type of transistor, NPN or PNP. The polarities of the two types are different,
so if you are looking for a substitute it must be the same type.
NPN
NPN
50
IC max. Maximum collector current.
VCE
max.
Maximum
voltage
across
the
collector-emitter
junction.
hFE This is the current gain (strictly the DC current gain). The guaranteed minimum value is
given because the actual value varies from transistor to transistor - even for those of the same
type!
Ptot max. Maximum total power which can be developed in the transistor, note that a
heat sink will be required to achieve the maximum rating. This rating is important for
transistors operating as amplifiers, the power is roughly IC × VCE. For transistors operating as
switches the maximum collector current (IC max.) is more important.
DARLINGTON PAIR
This is two transistors connected together so that the amplified
current from the first is amplified further by the second
transistor. This gives the Darlington pair a very high current gain
such as 10000. Darlington pairs are sold as complete packages
containing the two transistors. They have three leads (B, C and E)
which are equivalent to the leads of a standard individual
transistor.
You can make up your own Darlington pair from two transistors.
For example:
 For TR1 use BC548B with hFE1 = 220.
 For TR2 use BC639 with hFE2 = 40.
The overall gain of this pair is hFE1 × hFE2 = 220
The pair's maximum collector current IC(max) is the same as TR2.
Absolute Maximum Ratings Ta=25 C unless otherwise note
Symbol
VCBO
Parameter
Value
×
40
=
Units
IC
Collector-Base Voltage : BC546
: BC547/550
: BC548/549
Collector-Emitter Voltage : BC546
: BC547/550
: BC548/549
Emitter-Base Voltage : BC546/547
: BC548/549/550
Collector Current (DC)
80
50
30
65
45
30
6
5
100
V
V
V
V
V
V
V
V
mA
PC
Collector Power Dissipation
500
mW
TJ
Junction Temperature
150
°C
TSTG
Storage Temperature
-65 ~ 150
°C
VCEO
VEBO
8800.
51
MECHANISM OF AEROPLANE
GEAR ARRANGEMENTS
Wheeled undercarriages normally come in two types: conventional or "taildragger"
undercarriage, where there are two main wheels towards the front of the aircraft and a
single, much smaller, wheel or skid at the rear; or tricycle undercarriage where there are two
main wheels (or wheel assemblies) under the wings and a third smaller wheel in the nose.
The taildragger arrangement was common during the early propeller era, as it allows more
room for propeller clearance. Most modern aircraft have tricycle undercarriages. Taildraggers
are considered harder to land and take off (because the arrangement is unstable, that is, a
small deviation from straight-line travel is naturally amplified by the greater drag of the
mainwheel which has moved farther away from the plane's centre of gravity due to the
deviation), and usually require special pilot training. Sometimes a small tail wheel or skid is
added to aircraft with tricycle undercarriage, in case of tail strikes during take-off. The
Concorde, for instance, had a retractable tail "bumper" wheel, as delta winged aircraft need a
high angle when taking off. The Boeing 727 also had a retractable tail bumper. Some aircraft
with retractable conventional landing gear have a fixed tailwheel, which generates minimal
drag (since most of the airflow past the tailwheel has been blanketed by the fuselage) and
even improves yaw stability in some cases.
EXTRACTION AND RETRACTION
A retractable landing gear is installed whenever a drag improvement is worthy. This means
in all aircraft with exception of agricultural and small general aviation airplanes, where the
installation of a movable landing gear would increase the costs beyond the requirements of
the aircraft category.
Landing gear extraction is a primary operation and always its actuation has high redundancy.
There are different solutions for the mechanism to obtain suitable landing gear movement.
Some are schematically shown in fig.1. Many solutions are based on the four bar linkage
(cases A to C), where one bar is represented by the aircraft frame. In other solutions (case D)
one bar end can slide along a slot. More complex kinematics include three-dimensional
motion and the deflection of the bogie, that for the main landing gear of large airplanes is
made of double tandem wheels.
Actuators, normally of the hydraulic type, control the extraction/retraction operation. In
general the mechanism should be designed in such a way that gravity and aerodynamic
drag favour extraction; if the conditions on gravity and drag are satisfied, the extraction is
possible with no power from the hydraulic system; a diagram reporting piston load vs.
52
stroke will be of the type shown in fig.2, with a constant sign: this means that retraction
is obtained by applying a force to contrast drag and movable equipment weight, while
extraction can initiate by gravity and be completed by drag. The area under the load line
represents the necessary work. If this is divided by the area of the rectangle defined by
the max load and stroke, one obtains the efficiency of the kinematic mechanism, which
commonly is in the range
Fig1.
In both extracted and retracted configurations, the mechanism must be blocked (downlock
and uplock respectively). A kinematic lock at extraction can be obtained by making the
four bar linkage to reach its dead centre at full extraction. In any case a downlock based
on a hydraulic or electric device is activated to prevent any movement of the strut when
the aircraft is taxiing. An uplock is also activated when the landing gear is fully retracted,
to prevent non-intentional extraction during flight, which also could be a dangerous
operation at high velocity. Uplocks and downlocks are normally provided for the landing
gear doors too.
53
Fig2.Load Vs Stroke
RETRACTABLE GEAR
Fig3. Main and nosewheel undercarriage of an Airbus A330
To decrease drag in flight some undercarriages retract into the wings and/or fuselage with
wheels flush against the surface or concealed behind doors; this is called retractable gear.If
the wheels rest protruding and partially exposed to the air stream after being retracted, the
system is called semi-retractable.
54
Schematic showing hydraulically operated landing gear, with the wheel stowed into the
wing root of the aircraft
Most retraction systems are hydraulically operated, though some are electrically operated or
even manually operated. This adds weight and complexity to the design. In retractable gear
systems, the compartment where the wheels are stowed are called wheel wells, which may
also diminish valuable cargo or fuel space.
55
A Boeing 737-700 with main undercarriage retracted in the wheel wells without landing
gear doors
Pilots confirming that their landing gear is down and locked refer to "three green" or "three
in the green.", a reference to electrical indicator lights from the nosewheel and the two main
gears. Amber lights indicate the gears are in the up-locked position; red lights indicates that
the landing gear is in transit (neither down and locked nor fully retracted).
56
CONCLUSION
Malfunctions or human errors (or a combination of these) related to retractable landing gear
have been the cause of numerous accidents and incidents throughout aviation history. In the
event of a failure of the aircraft's landing gear extension mechanism a back-up is provided.
This may be an alternate hydraulic system, a hand-crank, compressed air (nitrogen),
pyrotechnic or free-fall system. A free-fall or gravity drop system uses gravity to deploy the
landing gear into the down and locked position. To accomplish this the pilot activates a
switch or mechanical handle in the cockpit, which releases the up-lock. Gravity then pulls
the landing gear down and deploys it. Once in position the landing gear is mechanically
locked and safe to use and land on. Some aircraft have a stiffened fuselage bottom or added
firm structures, designed to minimise structural damage in a wheels-up landing.
57
REFERENCE
www.google.com
www.wikipedia.com
www.reynoldelectronics.com
www.engineersgarage.com
www.datasheetcatalogue.com
www.electricityforum.com