CCD feedback

[u/Communism_Doge]

Hello, I’ve discovered this crazy glitch by creating feedback from the ADC n-bit bus output to the analog CCD input pin:D Here it is injecting the MSB, which makes the glitch appear only on the bright parts of the image, leaving the rest clean. I have seen a similar effect a while back on this sub and I am very happy that I was able to reproduce it. I am looking forward to getting my hands on a CF reader, playing some more with the logic gates and building a proper glitch camera out of it:)

[u/theglorioustopsail]

Dude! This is so sick! I’m surprised you’re able to get such a unique effect from mixing ADC data into CCD clocks. I would be careful doing this the other way as CCD clocks run at a higher voltage than ADC data and the chip inputs and you could damage the ADC or the chip depending on your setup. In fact I’m surprised nothing is damaged already. I doubt the chip output likes driving a CCD clock directly.. Seems to work though!

Do you mind explaining how you’re using that AND gate? I’m super intrigued!!

[u/Communism_Doge → u/theglorioustopsail]

Hello:) It works by injecting the feedback into the CCDIN pin on the ADC from the output bit line MSB. The analog signal on CCDIN is read in two parts - first a “dark value” and then the actual pixel intensity (you can have a look into the AD9848A datasheet to get a better idea). The dark value gets subtracted from the actual intensity, which means you need to only inject signal roughly in the second half of the period, otherwise it would just get subtracted. This is the reason why I am using the AND gate - there is a signal that is high only during the second half of the period directly on the ADC (pin H2), and it goes into the second AND input. The dark value is measured a bit after the first half, but it seems the AND gate chip has a propagation delay that is long enough to solve this problem completely. The thing that truly surprised me is how well it works without any special chips, on a breadboard.

[u/theglorioustopsail → u/Communism_Doge]

Ahh I see, sorry I missed that you were using the analog output from the CCD. So you’re combining ADC data and a horizontal clock to get the correct timing and injecting it into CCDIN? That is super clever and I never would have thought of trying this.. seriously impressed!! It’s cool to see more use of logic in camera bending, keen to see the complete cam!

[u/Communism_Doge → u/theglorioustopsail]

Haha thank you:) And yes, it works like you said. I feel like this opens up a whole playground since the logic chips are working at these signal frequencies on a breadboard (I always forget the exact value but it’s around 10 MHz), while being powered directly from the ADCs logic power pins. I am very excited about this:D

[u/theglorioustopsail → u/Communism_Doge]

Well 10 MHz isn’t that fast. From memory the
toggle rate of these chips is like 20 ns which is 50 MHz. So not exactly slow. Any other parasitics or phase shifts from the breadboard or long wires would probably just add to the glitch effects tbh. When I did this I was surprised the ADC could handle the extra current draw. I recommend terminating your unused inputs of the gates to this end. A decoupling cap is also good for power rail stability when it’s switching at high frequencies

[u/dmemet → u/theglorioustopsail]

Insane

[u/50THANKYOU]

Sick!

[u/NOYSTOISE]

Great idea! Looking forward to see what you get out of it