6A01.25 - Audio/Video Communications - Optical Method

Code Number:
Demo Title:
Audio/Video Communications - Optical Method
Modulation, Electromagnetic Waves
Area of Study:
Modulated Laser, Homemade Pre-amp that will operate either the LSR detector or the photovoltaic detector. LSR (Light Sensitive Resistor) Detector, Photovoltaic Cell Detector, Speaker, portable tape player, LED and batteries for portable tape player, Wave Generator, Radio Shack speaker amplifier with photocell.

Plug the LED into the portable tape player and connect the battery pack.  Then also plug the photocell into the Radio Shack speaker amplifier.  The modulated light signal given off by the tape player can be picked up with the photocell.

Plug the earphone jack of the radio or the wave generator into the modulated laser.  Caution should be observed that an amplified signal is not put into the laser as anything above 1 volt peak to peak will burn out the modulating transistors in the laser.  Also note that the laser can only be modulated to frequencies of 1 MHz. without severe distortion.  Plug either the photovoltaic cell or the LSR into the homemade pre-amp and plug the pre-amp into a speaker.  Focus the laser beam onto the detector that you have chosen.  Sound should now be transmitted via laser beam to the pre-amp/speaker assembly.

The modulated laser may be replaced with the portable tape player and the LED and battery assembly.  The batteries light the LED and by plugging into the earphone jack of the tape player you modulate the LED output.  This signal may be picked up by either the LSR or the photovoltaic cell in the same manner as the laser setup.  A fiber optics cable may be used transmit the LED signal to the photocell or LSR.

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