Photo Sensor

7/30/2019 Photo Sensor

http://slidepdf.com/reader/full/photo-sensor 1/3

IRE/IRD

A sensor is required to find out that case and to keep in form to the

computer for further actions.We use INFRARED EMITTER and

DETECTOR to over come the problem. In early days to find out humanentry in unauthorized places achieved by using LDR'S and LIGHT

OPERATED SYSTEM, which had a problem, that may work in sunlights

and cross sectional luminaries and provides false information to monitoring

station.

To avoid this we are using invisible INFRARED RADIATIONSYSTEM,

which is harmless. In basic I.R. rays has highest wave length than the

existing VIBGYOR color spectrum. According to manufacturer's

instruction we found that I.R. rays can be generated by applying electric

current to GALLIUM ARSENIDE semiconductor material.

Here we are using a current limiting resistor to safeguard

I.R.EMITTER as well as to produce enough rays density, which is

necessary to drive I.R. DETECTOR.

We have used 1K resistor from 5V dc to the I.R. EMITTER to restrict

current flow beyond 5mA. Even though I.R.EMITTER can withstand upto

35mA, we have used 5mA due to shortest distance. If the distance is more

we have to increase the current flow to the emitter.

Beyond the limitation of I.R. EMITTER can be achieved by

using additional lenses (OPTICAL SYSTEM) in front of the emitter.I.R.

DETECTOR I.R. DETECTOR is having reverse characteristics of the I.R.

EMITTER. That is we cannot consume more current from it on account of

positive sensitivity. For the above grounds we have used 100K from the

supply Voltage. So the sink current will be as per the OHM's LAW I=V/R.

So 5/100K will be less than a microamphere which may improve the

detecting characteristics.I.R. DETECTOR will conduct as long as the rays

falls on it.

So the level will be low which may goes to CUT OFF RANGE, when ever

there is no rays. Status will be high.From the above we are clearly known

that if there is no entry signal will be low, if there is entry signal will be

high.

I.R. DETECTOR drives a NPN transistor which provides inverse output at

collector end and given to a two stages SCHMITT TRIGGER. Which will

give at ultimate inversion of the I.R. DETECTOR.(If there is no entry =

high).



If there is any entry the signal output of SCHMITT TRIGGER will be low,

which creates a false information to the computer.

THEORY

I.R. EMITTER

Early emitters, both visible and infrared, suffered from low power output

deterioration(degradation) when compared to present day devices. Emitter

chip materials, commonly referred to as III-V compounds, are combinations

of elements from the III and Vcolumns of the periodic chart. The P-N

junction is formed by either diffusing or epitaxially growing the junction.

Typical materials used for emitters include GALLIUM ARSENIDE and

GALLIUM ALUMINUM ARSENIDE, among others. When a forward bias

current flows through the emitter's P-N junction, photons are emitted. The

total output power is a function of the forward current, and is measured in

mW. Likewise, the axial radiant intensity of an emitting device, which is the

portion of thetotal emitted power radiated within a specified cone angle directly on axis,

is also a function of this forward current, and is measured in mW per

steradian.

Motorola's line of emitter's operate at wavelengths of either 660,850, or 940

nanometers. This encompasses the red and the near I.R. portions of the

electromagnetic frequency specrum. Emitters of various wavelengths are

produced for the purpose of optimizing system with a variety of applications

and environments.

The 940nm emitters are the most cost effective, however, their

spectral emission is not ideally matched to that of the Silicon

detectors. Most applications can tolerate certain justified by the

devices lower price. Almost all optoisolators, for example, use the

940nm emitter.

The 850nm emitters are not well matched to silicon, but are

ideal for use in plastic fiber optic systems. Plastic fiber has a

characteristic attenuation curve which reaches a minimum at 660nm.

This attenuation is the predominant factor to consider when designing a

plastic fiber system.

The above emitters find wide usage in a variety of isolating, remote controland fiber optic applications.

Newly developed materials and refinements in chip processing and handling

have led to more efficient and more reliable emitters. New packaging

techniques have made low cost plastic devices suitable for applications

formerly requiting glass lensed units, by providing efficient modeled-in

lenses. In this way, higher on-axis radiant intensities can be achieved, for a



given amount of total radiated power. A narrow radiation angle provides for

a lower drive current when operating in a configuration where the opto

detector is on-axis with the power into an optical fiber.

When a very wide or off-axis viewing angle is required,such as in a

remote control emitters are generally used.Motorola's selection of emitters

includes the low-cost plastic Case 422A devices, such as MLED91,

MLED96 and MLED97. Also in a plastic package is the remote control

emitter, MLED81.Metal and glass packages, such as the TO-

18(MLED930)are utilized in applications where high axial intensity or

absolute hermeticity are essential.

DETECTORS

As emitters have developed over the years, photodetectors have alsoadvanced dramatically. Early photo transistors and photo diodes were soon

joined by photodarlington detectors, and then by light-activated SCRs.

Innovations in design have created devices having higher sensitivity, speed

and voltage capabilities.

Recent developments in detector technology have led to larger and more

complex circuit integration. Photodetectors incorporating SCHMITT

TRIGGER logic outputs are becoming increasingly popular in applications

requiring very fast speed, hysteresis for noise immunity, and logic level

outputs.

Motorola introduced the world's first photo-triac driver, a planar silicondevice capable of controlling loads on an ac power line. This was followed

by the zero-crossing triac driver, also a Motorola development. This device

stands as a classic circuitry, photo-optic technology, high voltage solid state

physics and field effect transistor (FET) technology are all incorporated on a

monolithic integrated circuit chip inside this device.

Future trends point to even higher performance characteristics and

more circuit integration in photodetectors.Detectors, are like emitters, are

available in plastic and in lensed metal packages.

Documents

Photo Sensor