VGA Feedback Loop

Thread Starter

Eskapist

Joined Jan 4, 2012
5
Hey AAC.

I think this is my first post here (I'll see in a while. Hehe)

A friend and I are making a VGA Video "Synthesizer" with an Arduino Uno. Things work great but we need to get a feedback loop running on each of the RGB channels in order to make some nice "glitch". Is there a way to do this? It does not have to be perfect sync or color.

- Eskapist.
 

Thread Starter

Eskapist

Joined Jan 4, 2012
5
Hey AnalogKid.

Sorry for the confusion. I've made a picture - Hopefully it will explain it better.
Basically we create graphics using some simple code on the arduino. We then manipulate each channel with analog effects like filters. We are trying to come up with a way for the signal to be fed back into itself, with a delay, creating a feedback effect on the output.

Untitled-1.jpg
 

AnalogKid

Joined Aug 1, 2013
10,987
A video delay line is a relatively complex circuit, but the innergoogle has some. A fractional-line delay probably will producee mush; a full line delay will give some synchronized effects. But for the really cool effects you need a full frame delay (or a graphics card with a CPU behind it thumping away).

The innergoogle also has products: http://www.ovation.co.uk/DelayLine/DelayLine.html

ak
 

Brownout

Joined Jan 10, 2012
2,390
Hey AnalogKid.

Sorry for the confusion. I've made a picture - Hopefully it will explain it better.
Basically we create graphics using some simple code on the arduino. We then manipulate each channel with analog effects like filters. We are trying to come up with a way for the signal to be fed back into itself, with a delay, creating a feedback effect on the output.

View attachment 91611
In days of yore, one could produce "reverberation" effects with a device called a "Bucket Brigade." It's essentially an anlalog shift register. With feedback taps, it can produce multiple, diminishing copies of the original signal to add to the original for the kind of effect you want. I've never seen it used on video before, but I see no reason why it wouldn't work. One show-stopper might be low clock frequency of ~1.5Mhz, however. A possible work-around might be 3 strings in parallel and a 3-phase clock for 4.5Mhz operation.
 
Last edited:

AnalogKid

Joined Aug 1, 2013
10,987
BBD's were barely acceptable to the golden-eared audio crowd, and never fast enough for video (NTSC needed at least 10.8 MHz). Similar to acoustic delay lines made with springs, Anderson and others made glass "ultrasonic" video delay lines. A 1-line delay (approx 63 us) was about 4" long. Ultrasonic in this case was a 20 MHz carrier. When computer memory expanded beyond 1024 bits per chip (!) and TRW popped out its 8-bit video-speed A/D and D/A, analog delay tech faded rapidly. One six-foot equipment rack was the perfect size to hold one frame of video.

ak
 

Brownout

Joined Jan 10, 2012
2,390
I offered a work around to the "never fast enough" issue. Required frequency actually depends on several factors, like image size, refresh rate, etc.
I assume the OP knows about computer memory size and has a reason he doens't what to do this in software. I never claimed it is a perfect solution, but one that might be worth a look.
 
Last edited:
Top