Hi /diy/. I'm planing to produce some kits to make it easier

>>1196893
Few things naturally use composite anymore. Go with VGA since it goes to basically any modern computer screen and even some HDTVs, and basically every video card still has a VGA output on it.

>>1196898
The raspberry Pi and a lot of modern cameras have composite output though. I don't think I've ever seen a camera that outputs VGA directly.

Also I've looked at other video synth gear like what LZX or Dave Smith make, and they're sticking to composite.

>>1196893
How the fuck do you fit an entire video channel on a single composite lead? How is it encoded? I swear if this leads back to Fourier transforms I'll flip a tit.

>>1196929
Same way you fit an entire video channel on a single radio wave.

>>1196931
Evidently I don't know how that works either. How is X, Y, R, G, and B all encoded simultaneously?

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>>1196929
The way composite works is a huge pain in the ass, and to make matters worse all the chips that made it easy to convert to analog RGB have all been discontinued.

Black and white is pretty simple. An analog voltage sets how bright the portion of the screen being drawn is. There's synchronization pulses that tell the TV to start drawing a new line or a new frame. These are at levels below what the black and white image levels can be so it's easy to pull them out.

Colour is a nightmare because colour broadcasts had to be backwards compatible with black and white TVs and fit into the already allocated RF channels. What you do is generate a 4.43361875 MHz sin wave centered on the existing black and white waveform. This naturally gets low pass filtered out by the receivers in black and white TVs. A change in tint is represented by applying a phase shift to the wave. A change in saturation is represented by changing the amplitude of this wave. There's a reference waveform given at the start of a scanline which you need to lock an oscillator to so you can detect the tint phase shifts with a phase comparator, except most people gave up trying to do that and implemented comb filters with analog delay lines.

>>1196931
A video signal over radio is just this but with an added RF modulation.

>>1196941
So how hard is it to mess with a colour composite signal purely through analogue means?

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>>1196957
Some effects are easier than others. For example if you run the image portion of the NTSC waveform through an inverting amplifier you're both inverting the brightness and tint (180 degree rotation on the colour wheel). Dark blue areas become bright red areas and so on. There are a couple companies making Eurorack video synth modules that do these sorts of tricks.

I was wanting to take a different approach and let people work with analog R,G,B channels on a breadboard. It's easier to understand and more open to experimentation. With VGA that's easy since it's already separate RGB, but with composite it's a bitch to do the conversion then back again.

>>1196893
>It can be a lot of fun and a good way to get into analog electronics.
neither of these are true

>>1196929
>if this leads back to Fourier transforms I'll flip a tit.
you need to learn to embrace it anon. you can take an ft of pretty much anything. sometimes freq domain is very useful, especially with images! i mean image processing, not whatever this is...

How hard is it to convert between composite and VGA? VGA is a more used format for the most part, especially if you're trying to get any old yobbo with a computer monitor interested, but being able to use both would be ideal.

>>1196966
This does look fun, assuming you don't have to figure out how to build the synth from scratch.
How does a Fourier transform represent a phase shift anyways?

Speaking of video and formats, I have a VGA to Composite and S-Video cable. There's no chip on it, it's just wires.

How tf do I use it?? can I even use it??? I tried it on my TV once and it didn't work.

>>1196929
You only need one lead for binary. You send the 1's and 0's to the compositor and it converts them back into moving pictures.

>>1197003
If you perform a complex FT, it is represented by the angle (argument) of the complex numbers.
This project does not need fourier transforms, though.

http://hackaday.com/2013/03/27/color-ntsc-video-directly-from-an-avr-chip/

All about the timing. There's several projects like this out there OP.

>>1197003
>ssuming you don't have to figure out how to build the synth from scratch
i guess everyone is different lol

>>1197052
>analogue
>binary
Try again kiddo.

>>1197183
It's not like I wouldn't enjoy designing the circuit, but it would be a time consuming endeavour that would require much research and probably not be "a good way of getting into analogue electronics."

>>1197171
Going from analog R,G,B to a composite signal is pretty easy because there's still chips like the AD724 in production. What's trickier is taking in a composite signal and outputting R,G,B. This is something I really want my kit to do so people have an easy system for distorting existing signals. Chips designed for that purpose aren't made anymore; the closest thing is chips with digital outputs meant for the microcontrollers that drive LCDs. I could use one of those and go back to analog with a DAC; implement everything myself with an ADC, DAC, and microcontroller code; do it all with a very complicated analog circuit, or just forget it and use VGA.

>>1197426
https://playground.arduino.cc/Main/TVout

Dunno why you can't sample in and push it out vga

>>1197426
Maybe try looking for these integrated circuits in old TVs or VCR players? They'd be through-hole and not too uncommon, and if you have to you could probably manage to replicate the IC with a combination of existing ones, for the new buyers.

>>1197428
µCs are for hacks.

>>1197428
It's not that simple. Color in a composite video signal is done by amplifying and phase shifting a 4.43361875 MHz sin wave. You need to sample this at at least 8.8672375 MHz due to the Nyquist Shannon theorem. Arduino's ADC has a max frequency of 125 KHz and even higher end MCUs top out around 1MHz. Catching a color composite signal and converting to analog R,G,B in code requires a specialized extremely fast ADC, very fast microcontroller, and very fast DAC.

>>1197436
Nyquist is full of shit. You should be sampling about 1.2 times the Nyquist frequency at least, otherwise you might just be hitting the nodes of the wave you want to measure, especially if your frequency is too close to a multiple of the 4.43361875MHz. For this application I'd sample at 40MHz just to give the ADC a good view of the waveform, if possible.

>>1197436
You're full of shit. Lots of Micros do 80mhz easy and sampling in has been done by many. And OP can modify the signal on the fly.

>>1197434
It's called reducing the parts count you fagget.

>>1197451
I think you're confusing microcontroller clock frequency with ADC frequency. It takes a few dozen clock cycles to do an ADC conversion. If a microcontroller with a built in ADC capable of 80MHz sampling exists it's going to be a very specialized and expensive chip.

> sampling in has been done by many
I'm not sure what projects you're referring to. Sampling in black and white composite is easily achieved with a < 1MHz ADC, but not color.

>>1197451
>designs project "for people to get into analog video synthesizers" and "a good way to get into analog electronics"
>uses ADC
If you want to program your way out of every problem then go right ahead, I'll be over here taking my time putting some love into my electronic projects.