08-10-2010, 02:30 PM
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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 pomp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm potmeter VR1.The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, inturn, 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 ofBD139 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. The reflected sunlight, however, does not cause any problem. But the sensor should not directly face the sun.
A BRIEF DISCRIPTION OF LASER TORCH BASED
TRANSMITTER AND RECEIVER
PROJECT DESCRIPTION
(a) A. LASER BASED VOICE TRANSMITTER
The circuit is based upon the principle of LIGHT MODULATION where instead of radio frequency signals; light from a laser torch is used as the carrier in the circuit.
Here, the transmitter uses 9V power supply.
Audio signal or voice is taken as input from the condenser mic, which is, followed transistor amplifier BC548 along with op-amp stage built around UA741.
The gain of the op-amp can be controlled with the help of 1 mega ohms potmeter.
The AF output from op-amp UA741 is coupled to the base of the power transistor BD139, which in turn, modulates the laser.
However, the three volts laser torch can be directly connected to the emitter of BD139 and the spring loaded lead protruding from inside the torch to the ground.
In the transmitter circuit, audio signal of the non-sinusoidal waveform and having a few mV of amplitude is taken as input from condenser mic.
Condenser mic is directly followed by the transistor amplifier stage consist of BC548. Transistor BC548 is connected in common emitter configuration.
Resistor R1 is the source resistor, which is directly connected to the power-supply.
R2, R3 and capacitor C1 are acting as self-biasing circuits, which is used for the biasing transistor. These circuit arrangements provide or establish a stable operating point. The biasing voltage is obtaining by R2 and R3 resistors network. Self-bias is used for obtaining entire audio signal as input.
Capacitor C1 is the coupling capacitor, since audio input signal is having a non-sinusoidal waveform of different amplitude and frequency, coupling capacitor is used to reject some of the dc noise/line as well as level from audio input signal.
The self-biased circuit is connected with the BC548 in CE configuration. It is transistor amplifier stage, where the low amplitude audio signal is amplified to the desired voltage.
The output is taken from the collector terminal; so inverted audio input signal is obtained.
Transistor pre-amplifier stage is coupled with op-amp stage built by ua741. C2 is the blocking capacitor while R4 is the op-amp stage resistor. Op-amp ua741 is easily available general-purpose operational amplifier.
Pin configuration of UA741 is shown in the glossary. Here pin no. 1 and 5 are not connected in order to nullify input-offset voltage. Pin no. 7 and 4 are VCC as well as –VEE supply voltage. Pin no. 3 is non-inverting input while pin no. 2 is inverting input. Between pin no. 2 and 6, 1 mega-ohm potmeter is connected as voltage series negative feedback, which control the infinite gain of the op-amp.
Resistors R5 and R6 of it value acts as a voltage-divider network, thus it gives a fixed voltage at the non-inverting pin.
Input inverted audio signal is applied to the inverting pin. Op-amp works on the differences into the applied two input voltage and provide a output at pin no. 6. Since, input is applied to the inverting pin the output is also an inverting one. Thus, again we get in phase high power and high amplitude level audio signal.
Capacitors C3, C4 and resistor R7 are acting as diffusion capacitors and feedback resistor respectively. These diffusion capacitors stored the carriers like holes and electrons in the base and thus provide self-biasing of the transistor.
Power dissipation rate of UA741 is very high, which is not practical for driving other electronics devices, so heat sink power transistor BD139 is used.
LASER TORCH-BASED VOICE
TRANSMITTER AND RECEIVER
TRANSMITTER AND RECEIVER
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 pomp stage built around μA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm potmeter VR1.The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, inturn, 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 ofBD139 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. The reflected sunlight, however, does not cause any problem. But the sensor should not directly face the sun.
A BRIEF DISCRIPTION OF LASER TORCH BASED
TRANSMITTER AND RECEIVER
PROJECT DESCRIPTION
(a) A. LASER BASED VOICE TRANSMITTER
The circuit is based upon the principle of LIGHT MODULATION where instead of radio frequency signals; light from a laser torch is used as the carrier in the circuit.
Here, the transmitter uses 9V power supply.
Audio signal or voice is taken as input from the condenser mic, which is, followed transistor amplifier BC548 along with op-amp stage built around UA741.
The gain of the op-amp can be controlled with the help of 1 mega ohms potmeter.
The AF output from op-amp UA741 is coupled to the base of the power transistor BD139, which in turn, modulates the laser.
However, the three volts laser torch can be directly connected to the emitter of BD139 and the spring loaded lead protruding from inside the torch to the ground.
In the transmitter circuit, audio signal of the non-sinusoidal waveform and having a few mV of amplitude is taken as input from condenser mic.
Condenser mic is directly followed by the transistor amplifier stage consist of BC548. Transistor BC548 is connected in common emitter configuration.
Resistor R1 is the source resistor, which is directly connected to the power-supply.
R2, R3 and capacitor C1 are acting as self-biasing circuits, which is used for the biasing transistor. These circuit arrangements provide or establish a stable operating point. The biasing voltage is obtaining by R2 and R3 resistors network. Self-bias is used for obtaining entire audio signal as input.
Capacitor C1 is the coupling capacitor, since audio input signal is having a non-sinusoidal waveform of different amplitude and frequency, coupling capacitor is used to reject some of the dc noise/line as well as level from audio input signal.
The self-biased circuit is connected with the BC548 in CE configuration. It is transistor amplifier stage, where the low amplitude audio signal is amplified to the desired voltage.
The output is taken from the collector terminal; so inverted audio input signal is obtained.
Transistor pre-amplifier stage is coupled with op-amp stage built by ua741. C2 is the blocking capacitor while R4 is the op-amp stage resistor. Op-amp ua741 is easily available general-purpose operational amplifier.
Pin configuration of UA741 is shown in the glossary. Here pin no. 1 and 5 are not connected in order to nullify input-offset voltage. Pin no. 7 and 4 are VCC as well as –VEE supply voltage. Pin no. 3 is non-inverting input while pin no. 2 is inverting input. Between pin no. 2 and 6, 1 mega-ohm potmeter is connected as voltage series negative feedback, which control the infinite gain of the op-amp.
Resistors R5 and R6 of it value acts as a voltage-divider network, thus it gives a fixed voltage at the non-inverting pin.
Input inverted audio signal is applied to the inverting pin. Op-amp works on the differences into the applied two input voltage and provide a output at pin no. 6. Since, input is applied to the inverting pin the output is also an inverting one. Thus, again we get in phase high power and high amplitude level audio signal.
Capacitors C3, C4 and resistor R7 are acting as diffusion capacitors and feedback resistor respectively. These diffusion capacitors stored the carriers like holes and electrons in the base and thus provide self-biasing of the transistor.
Power dissipation rate of UA741 is very high, which is not practical for driving other electronics devices, so heat sink power transistor BD139 is used.
