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This thread is privately moderated by Jack Crossfire, who may elect to delete unwanted replies. |
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Surprised to find the el cheapo USB video capture dongles don't use any compression. They send the full uncompressed 720x480 30fps frames through isochronous USB packets. There are still too many latency points to rely on it for monocopter synchronization.
Given the complexity of today's video codecs, it's amazing that for the entire generation which lived from 1950-2000, all their sights came down a single wire whose voltage was just the sequential scanlines of 1 frame after another. Only 1 gadget still produces a composite signal in the apartment, an ancient DSLR. Image features are visible in the waveform. The DC voltage is the luminance. -0.5V is a sync pulse. 0-1V is the luminance. The magnitude of a 3.4Mhz sine wave on top of the DC voltage is the saturation. The phase of the sine wave, relative to the color burst, is the hue. It's amazing this technology from 1953 could resolve 720x480 pixels & transported all our 1980's memories. The easiest way to overlay a monocopter synchronization code on the video is to pull up or down the voltage, but the composite output & input have very low impedences, requiring pulling enough current from the composite output to fry it. It's probably OK to pull the current for a small sync code. The right way is to use an analog multiplexer. http://electronics-home-projects.tripod.com/ uses a 74hct4052. http://garydion.com/projects/videoverlay/ gets away with directly pulling the voltage. It uses the hardware SPI to toggle the voltage. His schematic doesn't correspond to the working breadboard, but somehow the atmega's input protection diodes don't pull up the -0.5V sync pulses. Pin D7 pulls the video dark while pin B3 pulls it bright, through an adjustible resistor. The 2 pins fight each other & rely on a PNP transistor having less impedance than D7 to generate white pixels. The images on the Voyager record were encoded in a similar waveform, in a mechanical groove. What a feat if aliens manage to decode it, especially the color information. Carl Sagan obviously thought it was the simplest way to encode color photos. |
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Last edited by Jack Crossfire; Feb 08, 2013 at 06:46 AM.
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Hey, stumbled across your posts in the blogs. There is similar work going on in the FPV forums.
https://www.rcgroups.com/forums/show....php?t=1473207 https://www.rcgroups.com/forums/show....php?t=1776186 |
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