WIRELESS LASER BASED VOICE TRANSMITTER AND RECEIVER.

. WIRELESS LASER BASED VOICE TRANSMITTER AND RECEIVER. Deepak Kumar 1, Kundan Kumar Singh 2,Anand Mohan. 3 ABSTRACT: In this paper, we are designing the circuit through which we can communicate with our neighbours wirelessly and this paper is based on exchanging data between two persons. By implementing this circuit we have a new means of voice transfer between persons. Instead of RF signals, we are using LASER torch as the carrier in the circuit. The LASER torch can transmit light up to a distance of about 500 meters. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver. The transmitter circuit comprises of condenser microphone and transistor amplifier BC548 followed by an op amp stage built around μa741. The gain of the op-amp can be controlled with the help of 1-mega-ohm potentiometer VR1.The output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the LASER beam. The phototransistor of the receiver must be accurately oriented towards the LASER beam from the torch. Keywords LASER;RF; BC548;LM386;wireless. I. INTRODUCTION By using LASER as a communication medium we can improve the communication systems as the problem of interference faced in electromagnetic waves is not there and high secrecy is available[1]. LASER used in communication systems in the future because of advantages of the full channel speeds, no communication licenses is required at present. Besides this there are no recurring of line costs, portability, transparency to networks or protocol. The main operation of our paper is based upon the two sections one is LASER transmitter section and other is receiver section. The combination of these two sections constitutes the entire circuit block which is shown in the fig. A1 below. The audio signal is transmitted along with the LASER beam and transmitted in air by LASER torch. This audio signal fed to the amplifier circuit which converts the given signal and transmits to the listeners speaker. Condenser microphone converts the voice into electric pulse which is then amplified and transmitted through LASER. Photo transistor at receiver detects the LASER light and voice is the output through loud speaker. Fig-A 1 Block Diagram. Deepak Kumar, Kundan Kumar Singh and Anand Mohan. 1

WIRELESS LASER BASED VOICE TRANSMITTER AND RECEIVER. II. OBJECTIVES A LASER communication system by using low cost laser torch and electronic equipment which can be got easily form local electronics and people can construct for their personal use. 1. A light based voice transmission and reception system is implemented by using light from a laser torch as the carrier of the signal. 2. To design and implement a new circuit by the substitution of photo transistor available at local electronics market. 3. We used this circuit to communicate with the neighbor place wirelessly. 4. Calculate the total implementation cost to compare with the previous implemented design. III. THEORY LASER is a device which emits light by a process of optical amplification. LASER are distinguished from other light sources by their coherence. Spatial coherence is typically expressed through the output being a narrow beam, which is diffraction-limited. We can focus the LASER beam to very tiny spots, achieving a very high irradiance, or they can have very low divergence in order to concentrate their power at a great distance. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively great distance (the coherence length) along the beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length. The principle of a laser is based on three separate features: Stimulated emission within an amplifying medium, Population inversion of electronics and an optical resonator. LASER communication has High data rate, small antenna size, and narrow beam divergence. Photo transistor A transistor that uses light rather than electricity to cause an electrical current to flow from one side to the other. It is used in a variety of sensors that detect the presence of light. Phototransistors co mbine a photodiode and transistor together to generate more output current than a photodiode by itself. A Phototransistor consist of a single crystal Ge or Si semiconductor wafer in which three region are present to perform technological process. A.TRANSMITTER Deepak Kumar, Kundan Kumar Singh and Anand Mohan 2

In the above transmitter circuit (Fig. 1) comprises condenser microphone, transistor amplifier BC548 (T1) followed by an amp stage μa741 (IC1). The circuit is based upon principle of Light Modulation. The gain of the op-amp can be controlled by the help of 1-mega-ohm potmeter VR1.The AF output from IC1 is coupled to the base of transistor BD139 (T2), in turns to modulate the LASER beam. The transmitter uses 9V power supply. In the transmitter circuit, audio signal of the non-sinusoidal and few of mv of amplitude is taken as input from condenser mic. Power dissipation rate of UA741 is very high, which is not useful for the driving of other electronics devices, so heat sink power transistor BD139 is used. The Power transistor BD139 absorbs most of the power and supplies the suitable power to drive the LASER torch. This in turns modulates the LASER beam. So, LASER beam modulates and transmits the signals to large distances. B. RECEIVER. The above receiver circuit (Fig. 2) uses an npn phototransistor which is act as the light sensor which is followed by a two-stage transistor preamplifier and IC LM386 is based upon audio Power amplifier. The pre amplifier stage is RC coupled amplifier in CE configuration. The receiver circuit does not need any complicated alignment. We have to keep the phototransistor oriented towards the transmitter s LASER beam and volume of the sound is adjusted for a clear sound with the help of potentiometer. To avoid 50Hz hum noise in the speaker, keep away the phototransistor from AC light sources such as bulbs. LM386 provides suitable output power useful for drive the loudspeaker. From the loudspeaker, the audio output is heard. IV.RESULT We obtained the voice signal from the receiver at the loudspeaker when we apply the ac signal to the condenser microphone in the transmitter circuit Deepak Kumar, Kundan Kumar Singh and Anand Mohan. 3

WIRELESS LASER BASED VOICE TRANSMITTER AND RECEIVER. V.ADVANTAGES The advantage of this system is high reliability as it is impossible to track the data on the way of transmission. The design of LASER voice transmission system can be made at home with minimum cost. It can be used for frequent conversation between neighboring house at free of cost. A remarkable feature of laser is the concentration of its energy to extremely high intensities that s remaining almost constant over long distances because oflow divergence [6]. VI. APPLICATIONS Using this circuit we can easily communicate with our neighbors wirelessly. It can be used in inaccessible areas. In future, it can be commissioned in satellites for communication and also it can be used in conference halls. VII. FUTURE SCOPE Multiple voice, data, pictures, video can be multiplied simultaneously to perform communication using multiplexer. Half-duplex or even full-duplex can be achieved by software implementation. A more power LASER can be used for communication. LASER can be replaced by IR LASER which can be visible by bare eye. Improved design of this system can be used to transmit confidential voice data from one hill top to other hill top in remote area where cell phone communication is not possible due to the lack of mobile operator s tower by using extra amplifying circuit at the receiver end for having higher efficiency of the system. VIII.CONCLUSION It is concluded that Wireless LASER based voice transmitter and receiver is suitable for easy communication. There can be further upgradations in the paper which could lead to a much better system for communication. Some of the possible ways are as follows:-instead of the short range laser, high range lasers can be used which range a few hundred meters. Provisions have to be made for cases when there is no heavy traffic. LASER Torch Based Transmission and Reception are cheaper and simpler in construction than RF transmitter and receiver. Infra-Red and Blue-Tooth can also be used for voice transmission and Reception purpose, but their range is small compared with their price. This project can be made and used successfully at conference room, political assembly, and class room and for general conversation between two houses. Deepak Kumar, Kundan Kumar Singh and Anand Mohan 4

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