3. Introduction:
Traffic lights have become an integral part of human’s day-
to-day life.
With this motivation in the mind, this project aims at
designing and implementing, a running model of traffic
light controller which is controlled according to the density
of vehicle on road.
We will use AT89s52 microcontroller and Infra red sensor
for performing all the computation and control related task.
6. Colors:
The most common colors used in traffic lights are red,
amber (yellow), and green. Red typically means stop or
high level of danger; amber typically means caution; and
green typically means proceed with care.
Usually, the red light contains some orange in its hue, and
the green light contains some blue, to provide some support
for people with red-green color blindness.
Some traffic lights typically have a white reflective border
which enables color blind users, during the hours of
darkness, to distinguish the lights from other similarly-
colored street or automobile lights, and to allow them to
distinguish the lights by vertical position.
7. AT89S52 Microcontroller:
When we have to learn about a new computer we have to
familiarize about the machine capability we are using, and
we can do it by studying the internal hardware design
(devices architecture), and also to know about the size,
number and the size of the registers.
A microcontroller is a single chip that contains the
processor (the CPU), non-volatile memory for the program
(ROM or flash), volatile memory for input and output
(RAM), a clock and an I/O control unit.
Also called a "computer on a chip," billions of
microcontroller units (MCUs) are embedded each year in a
myriad of products from toys to appliances to automobiles.
8. The AT89S52 is a low-power, high-performance CMOS 8-
bit microcontroller with 8K bytes of in-system
programmable Flash memory.
The device is manufactured using Atmel’s high-density
nonvolatile memory technology and is compatible with the
industry-standard 80C51 instruction set and pinout.
The AT89S52 provides the following standard features: 8K
bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog
timer, two data pointers, three 16-bit timer/counters, a six-
vector two-level interrupt architecture, a full duplex serial
port, on-chip oscillator, and clock circuitry.
In addition, the AT89S52 is designed with static logic for
operation down to zero frequency and supports two
software selectable power saving modes.
9. . The Idle Mode stops the CPU while
allowing the RAM, timer/counters,
serial port, and interrupt system to
continue functioning.
The Power-down mode saves the
RAM con-tents but freezes the
oscillator, disabling all other chip
functions until the next interrupt.
The hardware is driven by a set of
program instructions, or software.
Once familiar with hardware and
software, the user can then apply the
microcontroller to the problems
easily.
10. The 8051 architecture consists of these
specific features:
16 bit PC &data pointer (DPTR)
8 bit program status word (PSW)
8 bit stack pointer (SP)
Internal ROM 4k
Internal RAM of 128 bytes.
4 register banks, each containing
8 registers
80 bits of general purpose data
memory
32 input/output pins arranged as
four 8 bit ports:P0-P3
Two 16 bit timer/counters: T0-T1
Two external and three internal
interrupt sources
Oscillator and clock circuits
11. INFRARED LED'S:
Gallium arsenide is a direct-gap semiconductor with an
energy gap of 1.4eV at room temperature.
A typical GaPs LED is made by solid-state impurity
diffusion with zinc as the p-type impurity diffused into an
n-type substrate doped with tin, tellurium or silicon.
The external efficiency at room temperature is typically 5
percent.
A GaAs diode can also be fabricated by liquid-phase
epitaxial with silicon as both its n and p dopants.
If a silicon atom replaces a Ga atom, it provides one
additional electron, thus the resulting GaAs in as n-type.
12. If a silicon atom replaces arsenic atoms, an electron is missing
and the resulting GaAs is a p-type. In Si doped GaAs diode, the
emission peak shifts down to 1.32eV.
Since the emission is in infrared region, GaAs light sources are
suitable for application such as the optical isolator.
The high switching speed, with a recovery time between 2 and
10ns, makes them ideal for data transmission.
The disadvantages of the GaAs emitter are emitted wavelength
and the associated attenuation an dispersion.
A critical issue of using an LED for the fibre optics is the
coupling of light from the semiconductor to the fibre.
Because of the larger refractive index of GaAs relative to air,
the internal efficiency of LED can be quite low
13. 555 timer:
The buffer circuit's input has a very high impedance (about
1M ) so it requires only a few µA, but the output can sink
or source up to 200mA.
This enables a high impedance signal source (such as an
LDR) to switch a low impedance output transducer (such as
a lamp).
It is an inverting buffer or NOT gate because the output
logic state (low/high) is the inverse of the input state.
Input low (< 1/3 Vs) makes output high, +Vs.
Input high (> 2/3 Vs) makes output low, 0V .
14. When the input voltage is between 1/3
and 2/3 Vs the output remains in its
present state.
This intermediate input region is a dead
space where there is no response, a
property called hysteresis, it is like
backlash in a mechanical linkage. This
type of circuit is called a Schmitt
trigger.
If high sensitivity is required the
hysteresis is a problem, but in many
circuits it is a helpful property.
It gives the input a high immunity to
noise because once the circuit output
has switched high or low the input must
change back by at least 1/3 Vs to make
the output switch back.
15. PHOTO SEMICONDUCTOR:
A Germanium or silicon diode or transistor, which has a
transparent encasing, can serve as a photodiode or
transistor because the light photons can initiate conduction
in the p-n- junction region.
Early devices such as the OCP 71 were Ge-devices. Later,
silicon types became available with lower leakage current
and better light sensitivity
In a phototransistor, the base lead is not used; but, if a
resistor is connected form base to emitter it reduced the
light sensitivity.
16. Darlington connected photo transistors (two transistors
together in one case) such as the 2N5777 are very sensitive
with a hFE of 2.5K, a dark current of 100nA and a light
current of 0.5-2.0mA for light flux density H=2mW/cm2.
The device is rated 200mW and voltage of 25V maximum.
SCRs with a light window are also available, called as
LASCR, which are very sensitive and can turn mains power
ON and OFF, with light.
The switching speed of phototransistors far exceeds those
of LDRs, made of CdS. The rise time for the 2N5777 is 75s
and fall time is 50s.
Maximum switching speed is 1KHz. Photo devices are
useful in optical encoding, intrusion alarms, tape readers,
level control, character recognition etc.
17. LIGHT EMITTING DIODE:
Light emitting diode (LED) is basically a P-N junction
semiconductor diode particularly designed to emit visible
light.
There are infrared emitting LEDs which emit invisible
light. The LEDs are now available in many colors red,
green and yellow.
A normal LED emits at 2.4V and consumes MA of current.
The LEDs are made in the form of flat tiny P-N junction
enclosed in a semi-spherical dome made up of clear colored
epoxy resin.
The dome of a LED acts as a lens and diffuser of light. The
diameter of the base is less than a quarter of an inch.
18. The actual diameter varies somewhat with
different makes.
It is similar to the conventional rectifier diode
symbol with two arrows pointing out.
There are two leads- one for anode and the other
for cathode.
LEDs often have leads of dissimilar length and
the shorter one is the cathode.
All manufacturers do not strictly adhere this to.
Sometimes the cathode side has a flat base.
If there is doubt, the polarity of the diode should
be identified.
19. Circuit Diagram: As shown in the circuit a microcontroller is
programmed to automatically “ON” and
“OFF” the LEDs (traffic light).
The crystal oscillator is provides the
necessary clocking for the microcontroller to
work properly.
The four traffic lights, shown as 4 groups of 3
LEDs (Red, Green, Yellow), is actually
installed at each of the four roads.
The necessary stabilized power source is
designed by the use of LM7805, as shown
above (in the lower figure).
The whole circuit will be implemented on a
zero PCB. The programming of the
Microcontroller can be done either in C or in
Assembly, using a programmer.
