derive_cicuitry_for_led

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Mehran University Of Engineering & Technology Page 1

DERIVECIRCUITRYFORLED/LASER

AbstractA derive circuit comprising of LED/LASER can be made by designing a circuit of Infrared

Transmitter & Receiver. One of the main problems to design such a circuit would be noise. To

overcome this problem we have to make transmitter/receiver immune to noise, for that the

transmitted signal needs Look different than the noise. This can be achieved by modulating the

IR LED diode on and off at an appropriate chosen frequency through the use of an Astable 555

Timer IC. Then, a receiver will be build which is much more sensitive to that frequency than any

other frequencies.

EQUIPMENTS

The equipments that are needed to design this circuitry are divided in to transmitter and

receiver section.

Transmitter SectionTransmitter SectionTransmitter SectionTransmitter Section

555 TIMER IC:The 555 Timer IC is an integrated circuit (chip) implementing a variety oftimer and

multi-vibrator applications. The IC was designed by Hans R. Camenzind in 1970 and brought to

market in 1971by Signetics (later acquired by Philips). The original name was the SE555 (metal

can)/NE555 (plastic DIP) and the part was described as "The IC Time Machine". It has been

claimed that the 555 gets its name from the three 5 k resistors used in typical early

implementations,[2] but Hans Camenzind has stated that the number was arbitrary. The part is

still in wide use, thanks to its ease of use, low price and good stability. As of 2003, it is estimated

that 1 billion units are manufactured every year. Depending on the manufacturer, the standard

555 package includes over 20 transistors, 2 diode sand 15 resistors on a silicon chip installed in

an 8-pin mini dual-in-line package (DIP-8).[4] Variants available include the 556 (a 14-pin DIP

combining two 555s on one chip), and the 558 (a 16-pin DIP combining four slightly modified

555s with DIS & THR connected internally, and TR falling edge sensitive instead of levelsensitive). Ultra-low power versions of the 555 are also available, such as the 7555 and

TLC555.[5] The 7555 is designed to cause less supply glitching than the classic 555 and the

manufacturer claims that it usually does not require a "control" capacitor and in many cases

does not require a power supply bypass capacitor.
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The 555 has three operating modes:

MONOSTABLE MODE: In this mode, the 555 functions as a "one-shot". Application include

timers, missing pulse detection, bounce free switches, touch switches, frequency divider,

capacitance measurement, pulse-width modulation (PWM) etc

ASTABLE MODE:Astable - free running mode: the 555 can operate as an oscillator. Uses

include LED and lamp flashers, pulse generation, logic clocks, tone generation, security

alarms, pulse position modulation, etc.

BISTABLE MODE:Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS

pin is not connected and no capacitor is used. Uses include bounce free latched switches, etc.

RESISTORS:

A resistor is a two-terminalelectronic component that produces a voltage across its terminals

that is proportional to the electric current through it in accordance with Ohm's law (V = IR)

Resistors are elements ofelectrical networks and electronic circuits and are ubiquitous in most

electronic equipment. Practical resistors can be made of various compounds and films, as well

as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). The primary

characteristics of a resistor are the resistance, the tolerance, the maximum working voltage and

the power rating. Other characteristics include temperature coefficient, noise, and inductance.Less well-known is critical resistance, the value below which power dissipation limits the

maximum permitted current, and above which the limit is applied voltage. Critical resistance is

determined by the design, materials and dimensions of the resistor. Resistors can be integrated

into hybrid and printed circuits, as well as integrated circuits. Size, and position of leads (or
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terminals), are relevant to equipment designers; resistors must be physically large enough not

to overheat when dissipating their power.

SWITCH:In electronics, a switch is an electrical component that can break an electrical circuit,

interrupting the current or diverting it from one conductor to another. The most familiar form of

switch is a manually operated electromechanical device with one or more sets ofelectrical

contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts

are touching and electricity can flow between them, or 'open', meaning the contacts are

separated and non-conducting.

A switch may be directly manipulated by a human as a control signal to a system, such as a

computer keyboard button, or to control power flow in a circuit, such as alight switch.

Automatically-operated switches can be used to control the motions of machines, for example,

to indicate that a garage door has reached its full open position or that a machine tool is in a

position to accept another work piece. Switches may be operated by process variables such as

pressure, temperature, flow, current, voltage, and force, acting as sensors in a process and used

to automatically control a system. For example, a thermostat is a temperature-operated switch

used to control a heating process. A switch that is operated by another electrical circuit is called

a relay. Large switches may be remotely operated by a motor drive mechanism. Some switches

are used to isolate electric power from a system, providing a visible point of isolation that can be

pad-locked if necessary to prevent accidental operation of a machine during maintenance, or to

prevent electric shock.

CAPACITOR:A capacitor is a passive electronic component consisting of a pair ofconductors separated by

a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a

static electric field develops in the dielectric that stores energy and produces a mechanical force

between the conductors. An ideal capacitor is characterized by a single constant

value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor
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Mehran University Of Engin

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INFRARED LED:Aninfraredlight-emittingdiode(LED) is a type of electronic device that emits infrared light not

visible to the naked eye. An infrared LED operates like a regular LED, but may use different

materials to produce infrared light. This infrared light may be used for a remote control, to

transfer data between devices, to provide illumination for night visionequipment, or for a variety

of other purposes. An infrared LED is, like all LEDs, a type of diode, or simple semi-conductor.

Diodes are designed so that electric current can only flow in one direction. As the current flows,

electrons fall from one part of the diode into holes on another part. In order to fall into these

holes, the electrons must shed energy in the form of photons, which produce light.

Thewavelengthand color of the light produced depend on the material used in the diode.

Infrared LEDs use material that produces light in the infrared part of the spectrum, that is, just

below what the human eye can see. Different infrared LEDs may produce infrared light of

differing wavelengths, just like different LEDs produce light of different colors. A very common

place to find an infrared LED is in a remote control for a television or other device. One or more

LEDs inside the remote transmit rapid pulses of infrared light to a receiver on the television. The

receiver then decodes and interprets these pulses as a command and carries out the desired

operation. Infrared light can also be used to transfer data between electronic devices. Mobile

phones, personal digital assistants (PDAs), and some laptops may have an infrared LED and

receiver designed for short-range data transfer. Some wireless keyboards andcomputermice also

use an infrared LED and receiver to replace a cable. Although invisible to human eyes, many

types of cameras and other sensors can see infrared light. This makes infraredLED

technology well-suited to applications like security systems and night visiongoggles. Many

security cameras and camcorders use infrared LEDs to provide a night-vision mode. Hunters may

use similar equipment to spot game at night, and some companies sell flashlights with an

infrared LED to provide extra illumination for night-vision cameras or devices.

2 Receiver Section2 Receiver Section2 Receiver Section2 Receiver Section

The other equipments such as resistors, capacitors and transistors used in receiver

are very much same as in transistor. The only new device which is used in receiver is a phoro-

detector, which is described below:
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PHOTODETECTOR:Photodetectors are devices capable of sensing electromagnetic energy, typically light, which

contains photon particles that are a type of electromagnetic energy. Although there are many

types, the most common are mechanical, biological, chemical. Photodetectors can also be used

as thermometers to measure radiation, to generate voltage, to amplify an existing current,

and to record images. Plants even use a form of photodetection to guide their growth, as their

cells react to the light and grow towards it. Whether natural or artificial, all photodetectors

share a common principle: a reaction triggered by the presence of light. An example of a

mechanical sensor of this sort would be a lasersecurity system that detects the presence of laser

light, and its interruption, to determine intrusions and trigger an alarm. The most commonly

known biological sensor is the eye, which detects and reacts to light to interpret optical signals,

which it then sends to the brain as an image. Photographic film is one of the simplest forms of

chemical sensors it uses light to imprint an image onto its surface. Photographers develop

their film in darkrooms to avoid ruining it, should the film have a chemical reaction to the light.

With a wide range of uses, photodetectors appear everywhere from particle-detectingtelescopes to the Large Hadron Collider to UV-sensitive sunglasses. The majority of

photodetectors are calibrated to detect light and radiation on a very specific spectrum, ranging

from ultra-violet to infrared. Infrared devices, such as heat sensors and television remote

controls, use light on the infrared spectrum to transmit a signal, which is captured and

interpreted by a detector. When a button is pressed on a television remote control, the remote

control emits an infrared signal on a wavelength invisible to the human eye. The television

intercepts and interprets the signal as a command to turn the volume down, change the

channel, or turn power on or off.

Depending on their purpose, photodetectors can have a variety of other functions. For

example, semiconductors and semiconducting circuits use photodetectors to conduct anelectrical current by changing light into electricity. When the semiconductor is exposed to light

in its target spectrum, the semiconductor material absorbs photons that act on electrons to

separate electron-hole pairs and create electrons in an excited state. This outcome allows the

electrons to travel freely as a conductive medium, which creates a photo-current. This

conductive action makes semiconductors a key base component of virtually all modern

electronics.
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WORKING

To explain its working we have explained both the Transmitter & Receiver section

separately, which are being discussed below:

TRANSMITTER

Above circuit diagram shows the transmitter section, here we see when the button is

pushed , the astable 555 timer oscillates and causes the IR LEDto emit a modulated or pulsed ,

infrared signal. Further the signal is transferred to the receiver. The 555 timer integrated circuit

to to modulate the transmitted slight, the timing of which is controlled by externally connected

resistors and capacitors. For IR LED we want a resistance R that will limit the current to 50-

100mA. Pin 3 on the 555IC derives the transistor and the indicator LED, and the transistor

derives the IR LED. This is necessary, as the 555 cannot supply the necessary current to activate

the IR LED. It is necessary that appropriate resistors are selected, in order to ensure that neither

the IR LED nor the 555 chip are damaged.


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RECEIVER

The above circuit diagram shows the receiver section, here the transmitted

signal is received via our receiver circuit phototransistor. The high pass amplifier allows us to

preserve only the high frequency component of our received signal. The bandpass filter is tuned

to our modulation frequency, thus removing more noise at higher and lower frequencies. The

signal at this point is a high frequency AC signal, the rectifier and the lowpass filter convert the

signal from AC to DC and the comparator allows us to adjust the sensitivity threshold so that we

do not detect spurious noise signals.

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