The engineer likes to communicate with their mates but radio wave is too easily to intercept but using light with morse code is tricky. Here is a project Laser Voice Transmitter uses a laser beam to transmit the voice.
Circuit Description of Laser Voice Transmitter:-
All most all communication system comprised of two parts, the project laser voice transmitter also comprised of two parts i.e. the transmitter circuit and the receiver circuit.
Transmitter circuit of Laser Voice Transmitter:-
The transmitter circuit is build using microphone, audio amplifier, laser diode and few passive components. A microphone is used here as sound sensor which detect sound and change it into electrical signal. The signal coming from the microphone is very small to alter the power of laser light, so it needs further amplification. To amplify the signal we used here CMOS operational amplifier IC (7611).
The operational amplifier is used here in non-inverting mode. The output electrical signal is connected to the positive amplifier input. This input is basically held halfway between GND(0V) and the supply voltage of 9V by resistor R2 and R3; however it will fluctuate from this by influenced of the microphone.
A feed-back network determines the gain of the circuit and is connected to the negative terminal (inverting terminal) of operational amplifier. The formula for calculation the gain of circuit is
Gain = (R4 + R5)/R5
And in this case it will (47+1)/1 = 40.
Therefore, the signal at output is multiplied of input signal by factor of 48.
This amplification provides sufficient amplitude or voltage to the signal and is given to the base of transistor T1 is used as laser diode driver circuit where resistor R7 is worked as current limiter.
Receiver Circuit of Laser Voice Transmitter:
The receiver circuit is build around a signal audio amplifier IC (TDA 7205). A photo transistor detects light from the transmitter and allows it to conduct. The more light on phototransistor, the more it conduct and vice versa. The output from photo transistor is given to the pin 3 of amplifier IC through capacitor C3. Where capacitor C3 is AC coupling capacitor which block DC bias. The amplifier output is given to the loudspeaker directly.
The sensitivity of the circuit is determined by the resistor R8, the more value of resistor increase the sensitivity and less value of resistor decrease the sensitivity.
PARTS LIST OF LASER VOICE TRANSMITTER
|Resistor (all ¼-watt, ± 5% Carbon)|
|R1 = 10 KΩ|
R2 – R4 = 47 KΩ
R5, R6 = 1 KΩ
R7 = 47 Ω
R8 = 10 KΩ, 0.5W metal film resistor
|C1 – C3 = 1 µF (Electrolytic Capacitor)|
|IC1 = 7611 (CMOS Operational Amplifier)|
IC2 = TDA7205 1-Watt amplifier IC
T1 = BC458 (NPN transistor)
T2 = Photo transistor
D1 = 5mW red laser diode module
|SW1 = Toggle Switch|
LS1 = Loud Speaker
MIC1 = Condenser Microphone
Complete Build Circuit of Laser Voice Transmitter
Fig: Transmitter Circuit
Fig: Receiver Circuit