Lightwave Communications
It is possible to transmit audio (and data, video etc) across medium to long distances by modulating light with either high power LED's or lasers. Equipment made by others has effective ranges well over 100 miles. The optical portion of the equipment I made is designed for shorter ranges. The electronics portion of the above transmitter will drive any optics. For my optics I use a 3 watt red LED or 20mw red laser driven with a 20KHz pwm signal modulated by one of three sources: a front panel microphone, line-in (1/8"/3.5mm stereo jack) and an internal linux-based computer (raspberry pi zero version 2). The PWM modulator is a 12F683 PIC based microcontroller from microchip.com. Here is a youtube video showing the system described here: https://youtu.be/ujk117eTPjM The pic microcomputer has 8 pins, and is programmed in assembly. I feed in audio through an audio preamp (2N3904 transistor) which then goes to a op amp and a low pass filter at 4khz. From there it goes int