Any CCD Sensor guru in the house? is my CCD damaged? - Page 1
Forum section: electronics / projects

author: pieroc91
author_rank: Contributor
timestamp: February 05, 2023, 06:28:24 pm
content: Hi everyone, I'm on the project of resurrecting one specimen of the very first DSLR, I got to the point of reading something but I'm a little bit concerned of what I'm reading, ignore the skew, that's a problem of the logic analyzer ignoring my clock signal, also, i've set my FPGA to output white pixels when is doing V1 and black pixels when is doing V2, those are the bars on the left.The concerning problems are the vertical artifacting all over the image and the white bloom on the left. The sensor readout starts at the thin black line.Thanks!

author: wykasz
author_rank: Contributor
timestamp: February 05, 2023, 07:40:36 pm
content: HiI have no experience with ccd, but i had some experience with proceesing images and working with camera module so i'll share.What can you tell us about your pipeline?Is this raw data prom CCD or was it altered in any way before converting to image we see?How do you convert binary data to image?Is there anything you can tell us about gain control and other ccd parameters? Are those available to you?Also, from my shot adventure with astrophotography i remember, that with CCD you always need two shots.First would be with closed iris, second would be the "main" shot, with the same parameters. The you need to substract first from the second to correct for noise introduced by amplifier.That noise look like a gradient starting with gray color in a corner of the shot and changing towards black at the opposite side. It was very repeatable.But it was not as regular as yours. For me it looks more like a mistake or a missing step in processing or configuring ccd.Good luck!

author: pieroc91
author_rank: Contributor
timestamp: February 05, 2023, 09:00:59 pm
content: Hey, thanks for your reply.It is totally raw data from the ADC, it tunnels thru an FPGA but just tunnels, no processing whatsoever, none of the analog parameters are available to me.My only controls are HGATE, which turns on the clock signal for the shift register, then V1 and V2 that do exactly what they are named,I go next line by-V1 on V2 off-V1 off V2 on-V1 on V2 off-V1 off V2 offat first I was only leaving 2.7uS for every V pulse resulting in a melting image, now i'm quite good at 11.42uS as a safe measure but the results are the same with 6uS.There is no datasheet for my sensor but a similar one expects at least 5 uS.http://www.astrosurf.com/audine/pdf/kaf1600.pdfi'm doing the dual shot thing to flush my sensor but since i'm using a logic analyzer to read my data I got both images, and the first one is completely white.Is it possible that some surrounding electronics are inducing that white glow?

author: pieroc91
author_rank: Contributor
timestamp: February 05, 2023, 09:16:41 pm
content: I removed the CCD entirely to discard any amplifier noise and bumping the gain a little got thisIt is on point the starting from grayish to black in a very subtle manner but not even close as the blooming or the black level not being black at all that I get from the sensor

author: berke
author_rank: Frequent Contributor
timestamp: February 05, 2023, 09:20:48 pm
content: Are you sampling the CCD output at the right time?What is the impedance of the CCD output compared to your ADC's input?

author: pieroc91
author_rank: Contributor
timestamp: February 05, 2023, 09:44:43 pm
content: It is a commercial product, i can only access the ADC output, ADC and CCD are correctly matched since well, it is (was) a commercial product.I guess i'm sampling it correctly since i've tested modifying it a lot and the problems are there no matter what, some times I got worse artifacting but that artifacting looks different, and the blooming is there all the time.

author: wykasz
author_rank: Contributor
timestamp: February 05, 2023, 10:17:28 pm
content: That vertical pattern is very consistent. Looks like on average every 8th row is affected. Maybe ADC is somehow sensitive to timing and you have some kind of slight delay every 8 bits?Also there are (more gentle) horizontal stripes - barely visible differences in brightness. I wander if it's property of the ccd and should be corrected i postprocessing?Could you post a single shot with ccd connected but completely covered (so no light could be catched by ccd) ?Regards

author: pieroc91
author_rank: Contributor
timestamp: February 05, 2023, 11:44:20 pm
content: Sure, this is the complete reading from power on of it, and just let it run. i've also taken another shot and the artifacting is completely gone, could be a lousy connection that got fixed when i took it out to get the shot without the sensor... the blooming is still there

author: pieroc91
author_rank: Contributor
timestamp: February 05, 2023, 11:51:30 pm
content: btw, that artifacting still present i'm 100% sure is a problem of how i'm reading the data since is an artifact smaller than a pixel, my logic analyzer is completely ignoring my clock so that kind of artifacts are because of it.And i'm also thinking that the blooming can also be a problem of how i'm accessing the CCD, reviewing my code i found that for each line i'm sending an "all reset" command that turns everything off but immediately i'm turning back all on again, I've tried removing this reset command but I only get to stop reading the ADC and just got a return of the last command I sent (the ADC and the command share the same bus and the direction is handled by another pin).I guess i could try to put a huge capacitor on the sensor and ADC VCC lines so they won't turn on that fast... and then deal with the code of course.

author: pieroc91
author_rank: Contributor
timestamp: February 06, 2023, 02:09:38 am
content: Well adding caps did absolutely nothing, i'm still blaming that reset for the failure... gonna keep smashing my head with code