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Contents: Introduction. Abstract AT89S52 Microcontroller. Infrared LED’S. 555 Timer . Photo Semiconductor. Light Emitting Diode. Circuit Diagram.


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.



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AT89S52 Microcontroller. LEDs. Crystal Oscillator 12 Mhz. LM7805. 12 V transformer. IR Tx -Rx Pair. 555 Timer . CL 100. Discrete components: Resistors, Capacitors .


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.

AT89S52 Microcontroller::

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 .

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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.

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. 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.

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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


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.

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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

555 timer::

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 .

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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.


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.

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Darlington connected photo transistors (two transistors together in one case) such as the 2N5777 are very sensitive with a h FE of 2.5K, a dark current of 100nA and a light current of 0.5-2.0mA for light flux density H=2mW/cm 2 . 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.


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.

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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.

Circuit Diagram::

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.

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