08-10-2010, 04:01 PM
This article is presented by:
DEPARTMENT OF ELECTRONICS AND COMMUNICATIONS
ENGINEERING
KONERU LAKSHMAIAH COLLEGE OF ENGINEERING
Ch.Ravi Kishore
ABSTRACT
Using this circuit you can communicate with your neighbors wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up to a distance of about 500 meters. The phototransistor of the receiver must be accurately oriented towards the laser beam from the torch. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver. The transmitter circuit (Fig. 1) comprises condenser microphone transistor amplifier BC548 (T1) followed by an opamp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm pot meter VR1. The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam. The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit—with the body of the torch connected to the emitter of BD139 and the spring-loaded lead protruding from inside the torch to circuit ground. The receiver circuit (Fig. 2) uses an NPN phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio power amplifier. The receiver does not need any complicated alignment. Just keep the phototransistor oriented towards the remote transmitter’s laser point and adjust the volume control for a clear sound. To avoid 50Hz hum noise in the speaker, keep the phototransistor away from AC light sources such as bulbs.
GENERAL
Laser communications systems are wireless connections through the atmosphere. They work similarly to fiber optic links, except the beam is transmitted through free space. While the transmitter and receiver must require line-of-sight conditions, they have the benefit of eliminating the need for broadcast rights and buried cables. Laser communications systems can be easily deployed since they are inexpensive, small, low power and do not require any radio interference studies. The carrier used for the transmission signal is typically generated by a laser diode. Two parallel beams are needed, one for transmission and one for reception. Due to budget restrictions, the system implemented in this project is only one way.
Laser communications have been a hot topic lately, as solutions for how to satisfy ever increasing bandwidth needs are in high demand. Some have suggested that bandwidth could be distributed in neighborhoods by putting laser communication systems on top of homes and pointing them towards a common transceiver with a fast page link to the Internet. With possible transmit speeds of up to a gigabit per second, this is an exciting area. Other applications for this technology include temporary connectivity needs (e.g. sporting events, disaster scenes, or conventions), or space based communications.
Using this circuit you can communicate with your neighbors wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up to a distance of about 500 meters. The phototransistor of the receiver must be accurately oriented towards the laser beam from the torch. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver. The transmitter circuit (Fig. 1) comprises condenser microphone transistor amplifier BC548 (T1) followed by an opamp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm pot meter VR1. The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam. The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit—with the body of the torch connected to the emitter of BD139 and the spring-loaded lead protruding from inside the torch to circuit ground. The receiver circuit (Fig. 2) uses an NPN phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio power amplifier. The receiver does not need any complicated alignment. Just keep the phototransistor oriented towards the remote transmitter’s laser point and adjust the volume control for a clear sound. To avoid 50Hz hum noise in the speaker, keep the phototransistor away from AC light sources such as bulbs.
DEPARTMENT OF ELECTRONICS AND COMMUNICATIONS
ENGINEERING
KONERU LAKSHMAIAH COLLEGE OF ENGINEERING
Ch.Ravi Kishore
ABSTRACT
Using this circuit you can communicate with your neighbors wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up to a distance of about 500 meters. The phototransistor of the receiver must be accurately oriented towards the laser beam from the torch. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver. The transmitter circuit (Fig. 1) comprises condenser microphone transistor amplifier BC548 (T1) followed by an opamp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm pot meter VR1. The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam. The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit—with the body of the torch connected to the emitter of BD139 and the spring-loaded lead protruding from inside the torch to circuit ground. The receiver circuit (Fig. 2) uses an NPN phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio power amplifier. The receiver does not need any complicated alignment. Just keep the phototransistor oriented towards the remote transmitter’s laser point and adjust the volume control for a clear sound. To avoid 50Hz hum noise in the speaker, keep the phototransistor away from AC light sources such as bulbs.
GENERAL
Laser communications systems are wireless connections through the atmosphere. They work similarly to fiber optic links, except the beam is transmitted through free space. While the transmitter and receiver must require line-of-sight conditions, they have the benefit of eliminating the need for broadcast rights and buried cables. Laser communications systems can be easily deployed since they are inexpensive, small, low power and do not require any radio interference studies. The carrier used for the transmission signal is typically generated by a laser diode. Two parallel beams are needed, one for transmission and one for reception. Due to budget restrictions, the system implemented in this project is only one way.
Laser communications have been a hot topic lately, as solutions for how to satisfy ever increasing bandwidth needs are in high demand. Some have suggested that bandwidth could be distributed in neighborhoods by putting laser communication systems on top of homes and pointing them towards a common transceiver with a fast page link to the Internet. With possible transmit speeds of up to a gigabit per second, this is an exciting area. Other applications for this technology include temporary connectivity needs (e.g. sporting events, disaster scenes, or conventions), or space based communications.
Using this circuit you can communicate with your neighbors wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up to a distance of about 500 meters. The phototransistor of the receiver must be accurately oriented towards the laser beam from the torch. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver. The transmitter circuit (Fig. 1) comprises condenser microphone transistor amplifier BC548 (T1) followed by an opamp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm pot meter VR1. The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in turn, modulates the laser beam. The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuit—with the body of the torch connected to the emitter of BD139 and the spring-loaded lead protruding from inside the torch to circuit ground. The receiver circuit (Fig. 2) uses an NPN phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio power amplifier. The receiver does not need any complicated alignment. Just keep the phototransistor oriented towards the remote transmitter’s laser point and adjust the volume control for a clear sound. To avoid 50Hz hum noise in the speaker, keep the phototransistor away from AC light sources such as bulbs.
