Kurts Blog of Photography, minicomputers, mainframes, lightwave communications, and just whatever.

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

Building your own camera. Many people built a pinhole camera while in grade school or maybe as late as high school. It's a novelty, and the results reflect that. I built one using the carboard box a pack of 35mm film came in, cut out the end and put a piece of aluminum foil with a hole punched in. It produced an image, if you squinted just right, and the results reflected that. The project was never duplicated. Until last week. There are many forums dedicated to pinhole photography. I never looked into them. However, I was reading some text books I got on Amazon ($0.01 each, $3.99 shipping, brand new 1000 page physics texts) about light and came across a few things. This got me thinking. Seems there are certain ratios, and when followed, give reasonable focus to light when followed. In the camera world, there is a thing known as an f stop, or the amount of light allowed in by a lens.  The f stop is determined by the diameter of the lens and the distance to the film plane