In a laser communication system, the information signal such as sound or music is transmits through a laser beam. the intensity of the laser beam changes with respect to amplitude of the laser beam which is the modulation process. In the receiver circuit a solar panel is used to reproduce the desired voltage level. The voltage variation on the solar panel is amplified by a low-voltage audio power amplifier LM386 which has a volatge gain of 20 to 200 and reproduced by a speaker.
This Laser communication system has main two parts:
1. Laser transmitter Circuit
2. Laser receiver circuit
Both the transmitter and the receiver are built around IC LM386, powered by a 9V battery. In transmitter circuit, a laser diode (LD1) with maximum operating voltage of around 2.6V DC and maximum operating current of 45 mA is used to transmit the audio signal. The voltage divider network formed by R2, R3 and VR3 keeps the voltage as well as the current for the laser diode in the safe region. A laser pointer can also be used in place of a laser diode.
Potentiometer VR1 (10-kilo-ohm) is used to change the level of the input audio signal. The audio input (Vin) is taken from the preamplifier output of the music system (CD player, DVD player, etc). Capacitor C2 and preset VR2 are used to vary the gain of the LM386.
The receiver circuit is shown in the figure. The audio signal transmitted by the laser diode (LD1) is received by the calculator’s solar panel and amplified by IC2. The gain of the amplifier is fixed by capacitor C7. Preset VR4 is used to change the signal level from the solar panel. This signal is fed to input pin 3 of IC2 through coupling capacitor C5 so that the DC value from the solar panel can be eliminated. The amplified output from IC2 is fed to the speaker, which plays the music from the CD player connected at the input (Vin) of IC1.
Two seperate PCBs can be used to assemble transmitter and receiver circuit and enclose in two cabinets. Make an arrangement such as the laserbeam from diode falls directly on the solar panel.