08-10-2010, 10:45 AM
[attachment=5383]
LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER full report
Using this circuit you can communicate
with your neighbours
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
metres. 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 potmeter 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
LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER full report
Using this circuit you can communicate
with your neighbours
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
metres. 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 potmeter 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
