Pc to pc laser communication pdf download

Figure 4. Lasers generally have a narrower frequency distribution, much higher intensity, a greater degree of collimation or much shorter pulse duration than available from more common types of light sources. Therefore we use them in compact displayers, in super markets checkout scanners, in surviving instruments and in medical applications as a surgical knifes or for welding detached retinas.

We also use them in communication systems and in radar and military targeting applications as well as many other areas. Different parts of the laser beam are related to each other in phase. These phase relationships are maintained over long enough time so that interference effects may be seen or recorded photographically.

This coherence property is what makes holograms possible. Figure 7. So the laser light has a single spectral color and is almost the purest monochromatic light available. Because of bouncing back between mirrored ends of a laser cavity, those paths which sustain amplification must pass between the mirrors many times and be very nearly perpendicular to the mirrors. As a result, laser beams are very narrow and do not spread very much.

A parallel port sends and receives data eight bits at a time over 8 separate wires. This allows data to be transferred very quickly; however, the cable required is more bulky because of the number of individual wires it must contain.

A serial port sends and receives data one bit at a time over one wire. While it takes eight times as long to transfer each byte of data this way, only a few wires are required. In fact, two-way full duplex communications is possible with only three separate wires - one to send, one to receive, and a common signal ground wire. The serial port on the PC is a full-duplex device meaning that it can send and receive data at the same time.

In order to be able to do this, it uses separate lines for transmitting and receiving data. Some types of serial devices support only one-way communications and therefore use only two wires in the cable - the transmit line and the signal ground.

Once the start bit has been sent, the transmitter sends the actual data bits. There may either be 5, 6, 7, or 8 data bits, depending on the number we have selected. Both receiver and the transmitter must agree on the number of data bits, as well as the baud rate. Almost all devices transmit data using either 7 or 8 data bits. After the data has been transmitted, a stop bit is sent. A stop bit has a value of 1 - or a mark state - and it can be detected correctly even if the previous data bit also had a value of 1.

This is accomplished by the stop bit's duration. Stop bits can be 1, 1. Besides the synchronization provided by the use of start and stop bits, an additional bit called a parity bit may optionally be transmitted along with the data. A parity bit affords a small amount of error checking, to help detect data corruption that might occur during transmission.

We can choose either even parity, odd parity, mark parity, space parity or none at all. When even or odd parity is being used, the number of marks logical 1 bits in each data byte are counted, and a single bit is transmitted following the data bits to indicate whether the number of 1 bits just sent is even or odd.

When even parity is chosen, the parity bit is transmitted with a value of 0 if the number of preceding marks is an even number. For the binary value of the parity bit would be 0. Odd parity is just the opposite, and the parity bit is 0 when the number of mark bits in the preceding word is an odd number. Parity error checking is very rudimentary. It tells us if there is a single bit error in the character, it doesn't show which bit was received in error. Also, if even number of bits are in error then the parity bit would not reflect any error at all.

Mark parity means that the parity bit is always set to the mark signal condition and likewise space parity always sends the parity bit in the space signal condition. Since these two parity options serve no useful purpose whatsoever, they are almost never used. These terms are used to indicate the pin-out for the connectors on a device and the direction of the signals on the pins.

However, to connect two like devices, we must instead use a null modem cable. Null modem cables cross the transmit and receive lines in the cable.

The listing below shows the connections and signal directions for both 25 and 9-pin connectors. This name can be deceiving, because this wire is used by a DCE device to receive its data. The DTE device puts this line in a mark condition to tell the remote device that it is ready and able to receive data.

If the DTE device is not able to receive data typically because its receive buffer is almost full , it will put this line in the space condition as a signal to the DCE to stop sending data. When the DTE device is ready to receive more data i. Likewise, if the DCE device is unable to receive data, it will place this line in the space condition. Software flow control uses special control characters transmitted from one device to another to tell the other device to stop or start sending data.

The Software Wedge sets DTR to the mark state when the serial port is opened and leaves it in that state until the port is closed. CD stands for Carrier Detect.

Carrier Detect is used by a modem to signal that it has a made a connection with another modem, or has detected a carrier tone. The last remaining line is RI or Ring Indicator. A modem toggles the state of this line when an incoming call rings your phone. Because most modems transmit status information to a PC when either a carrier signal is detected i.

He is credited with devising the first uniform-length 5-bit code for characters of the alphabet in the late 19th century. Baud refers to the modulation rate or the number of times per second that a line changes state. This is not always the same as bits per second BPS. If we connect two serial devices together using direct cables then baud and BPS are in fact the same. Because modems transfer signals over a telephone line, the baud rate is actually limited to a maximum of baud. This is a physical restriction of the lines provided by the phone company.

The increased data throughput achieved with or higher baud modems is accomplished by using sophisticated phase modulation, and data compression techniques. This module is primary of interest for people building their own electronics with an RS interface. Off-the-shelf computers with RS interfaces already contain the necessary electronics, and there is no need to add the circuitry as described here.

Serial RS V. On the other hand, classic TTL computer logic operates between 0V Modern low-power logic operates in the range of 0V So, the maximum RS signal levels are far too high for today's computer logic electronics, and the negative RS voltage can't be grokked at all by the computer logic.

Therefore, to receive serial data from an RS interface the voltage has to be reduced, and the 0 and 1 voltage levels inverted. In the other direction sending data from some logic over RS the low logic voltage has to be "bumped up", and a negative voltage has to be generated, too.

However, since more than a decade it has become standard in amateur electronics to do the necessary signal level conversion with an integrated circuit IC from the MAX family typically a MAXA or some clone. This greatly simplified the design of circuitry.

Circuitry designers no longer need to design and build a power supply with three voltages e. All it does is to convert signal voltage levels. It has also helped that many companies now produce clones ie.

These clones sometimes need different external circuitry, e. It is recommended to check the data sheet of the particular manufacturer of an IC instead of relying on Maxim's original data sheet. The original manufacturer and now some clone manufacturers, too offers a large series of similar ICs, with different numbers of receivers and drivers, voltages, built-in or external capacitors, etc.

V- 6 is connected to GND via a capacitor C4. A photodiode is a type of photodetector capable of converting light into either current orvoltage, depending upon the mode of operation. Photodiodes are similar to regular semiconductor diodes except that they may be either exposed to detect vacuum UV or X-rays or packaged with a window or optical fiberconnection to allow light to reach the sensitive part of the device.

Many diodes designed for use specifically as a photodiode will also use a PIN junction rather than the typical PN junction. When a photon of sufficient energy strikes the diode, it excites an electron, thereby creating a mobile electron and a positively charged electron hole. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in field of the depletion region.

Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is produced. The responsivity may also be expressed as aquantum efficiency, or the ratio of the number of photogenerated carriers to incident photons and thus a unitless quantity.

The dark current includes photocurrent generated by background radiation and the saturation current of the semiconductor junction. Dark current must be accounted for by calibration if a photodiode is used to make an accurate optical power measurement, and it is also a source of noise when a photodiode is used in an optical communication system. The NEP is roughly the minimum detectable input power of a photodiode.

When a photodiode is used in an optical communication system, these parameters contribute to the sensitivity of the optical receiver, which is the minimum input power required for the.

LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in ,[2] early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.

The LED is based on the semiconductor diode. When a diode is forward biased switched on ,electrons are able to recombine with holes within the device, releasing energy in the form ofphotons. This effect is called electroluminescence and the color of the light corresponding to the energy of the photon is determined by the energy gap of the semiconductor.

An LED is usually small in area less than 1 mm2 , and integrated optical components are used to shape its radiation pattern and assist in reflection. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Current LED products for general lighting are more expensive to buy than fluorescent lamp sources of comparable output. They also enjoy use in applications as diverse as replacements for traditional light sources inautomotive lighting particularly indicators and in traffic signals.

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To implement the idea a working prototype of a system will be designed using low-cost laser LEDs available in the local electronic Market. By using the proposed system, we can establish data communication between two PCs in some industrial applications where conventional wireless and wired network technologies can not be used due to technical or legal reasons.

Laser, acronym for light amplification by stimulated emission of radiation. Lasers are devices that amplify light and produce coherent light beams, ranging from infrared to ultraviolet. A light beam is coherent when its waves, or photons, propagate in step with one another. Laser light, therefore, can be made extremely intense, highly directional, and very pure in color frequency. Laser devices now extend into the X-ray frequency range.

Masers are similar devices for microwaves see Maser. Laser-based projects used to be expensive, until the development of solid state lasers.

This project is designed for the entry-level laser experimenter.