Color smoothing and delay circuit implementation to help prevent "jellybeaning"?

In a separate thread, Adam (Buffo) addressed the "jellybeaning" issue another PL member was having with their green laser:

http://www.photonlexicon.com/forums/...2&postcount=27

This is EXACTLY the issue I run into with my 400mw CNI green - even though it's the strongest laser in my rig, the green becomes over saturated by my dual-Maxyz red after the green has idled or required less power for any length of time. The green recovers, but the color shift is definitely noticeable (and though it's still needs some adjustment, I have run through the color palette wizard, but the temporary "underpowering" of the green still occurs).

Adam referenced a color smoothing and delay circuit discussed on the Pangolin web site (which I also discussed previously, very briefly, in an e-mail directly with Bill). I was wondering if anyone here had implemented that (or similar) circuit with their Maxyz, CNI or other Chinese import lasers, and if so, how effective was it help achieve a good, responsive color balance in their projectors?

Thanks!

I have recently been playing with the Pangolin circuit - there really isnt a lot to it but it does whats needed. I have sitting on my bench an full built 3 channel device that I just need to hook up and setup. The circuit used was breadboarded some weeks ago and tested as seen on the image below. Comparing points X on the top image and y on the lower image you can clearly see better colour alignment. In this test bed device I used two channels to slow the red and green leading edges to match the blue. The reason my built circuit has three channels is so I can speed up the falling edge of the blue because as you can see there are blue 'tails' on the image.
This circuit is to be a building block for an RGB interface I am building.

Rob

Hey Rob, may I ask which circuit you built? I think there were 3 different designs on the pangolin web site last I looked. I had started to build the "ready for anything" circuit, then got busy with other projects. I really need to revisit this, and the improvement in images above give me the encouragement to do so.

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Originally Posted by DZ

Hey Rob, may I ask which circuit you built?

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Yes, please advise... so David can get busy. ;) Mybe put itn the breakout board...

Hey boys
I did not make the ready for anything circuit - just the straight forward single op amp Sallen key. You can understand why I was very excited about it! Every frame of very show I ran looked fab!

Rob

Quote:

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Originally Posted by stanwax

Hey boys
I did not make the ready for anything circuit - just the straight forward single op amp Sallen key. You can understand why I was very excited about it! Every frame of very show I ran looked fab!

Rob

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Hi Rob,

You did the right thing. Every once in a while people contact me about that, and I tell them to do exactly what you have done. I am not sure if you ever contacted me about it, or figured it out for yourself, but I am glad that you found utility in the information we provide.

Bill

Very interesting results, Rob! I may have to build one of those delay circuits in the future...

Randy.. I had a similar problem with my projector when I first upgraded my green laser. I had a 75 mw green in there which was just right for color balance, but unfortunately it had lousy modulation characteristics. So I replaced it with a 150 mw unit. (My thought was that I'd like a little extra green in there for higher power beams.)

But when that unit blew up the moment I turned it on, I was in full-on panic mode, as SELEM was coming up and I had no green laser! In a pinch, I decided to drop a 275 mw green in there just to get by. (Thanks Aaron!) And yeah, it had analog modulation, so I figured I'd just be able to dial it way down to get my color balance back.

Well, that's where the problem started. Because I really only needed about 70 mw of green to balance my projector, I had *way* too much green. And what I found was that the green would come on *stronger* that it needed to, and then it would settle back to the power that it should have been at. This gave some shorter graphic elements a green tint, but when I went back through the color wizard, everything was fine.

The solution was to get my 150 mw green fixed and re-installed in the projector. Once I did that, everything was fine.

So yeah, running a laser well below it's rated power can cause all sorts of nonlinearities in the modulation response. (Too much in my case, not enough in yours.)

I'm rather intrigued by Dazebtwn's solution of adjusting the driver and tec circuits. If memory serves, Rob managed to do something similar on one of his DPSS lasers not to long ago. (Though I think he didn't have the advantage of the fast photodiode and oscilloscope to measure the optical pulse.) That's something I'd like to try someday. (Maybe at SELEM next year.?.)

And a big thanks to Bill for posting the initial info about the delay circuit that started this discussion!

Adam

Quote:

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Originally Posted by stanwax

I have recently been playing with the Pangolin circuit - there really isnt a lot to it but it does whats needed. I have sitting on my bench an full built 3 channel device that I just need to hook up and setup. The circuit used was breadboarded some weeks ago and tested as seen on the image below. Comparing points X on the top image and y on the lower image you can clearly see better colour alignment. In this test bed device I used two channels to slow the red and green leading edges to match the blue. The reason my built circuit has three channels is so I can speed up the falling edge of the blue because as you can see there are blue 'tails' on the image.
This circuit is to be a building block for an RGB interface I am building.

Rob

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Rob -

Thanks for posting your findings on this - I believe this may be the solution I looking for! Any chance you could post a few more specifics, i.e. - what diode and amplifier chip did you use, and perhaps a basic tutorial on how to setup and align a projector using the circuits? (Hopefully, there's a way to set this up WITHOUT the need for an oscilloscope, since that's one more expensive toy I haven't acquired yet :o)

Basic electronics I can handle - but once we start diving into the realm of theory behind filters, amplifiers, etc., I'm a bit behind the power curve! It's a shame these things aren't powered by Rolls Royce turbine engines instead of pumped diodes - THAT, I could relate to :D

It would be nice if DrLava or someone could create a board for that circuit with 3 or more channels on it. If it works well I'd stick it in my scanner. I never really understood or paid much attention to what is being talked about but I understand it now. Once my scanner is back together I am going to run some tests to see if I have that problem and to what extent.

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Originally Posted by carmangary

It would be nice if DrLava or someone could create a board for that circuit with 3 or more channels on it. If it works well I'd stick it in my scanner. I never really understood or paid much attention to what is being talked about but I understand it now. Once my scanner is back together I am going to run some tests to see if I have that problem and to what extent.

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Similar sentiments here - the more I learn, the more I realize there are things in my RGB rig that really just aren't quite right yet!

Of course, that carries over in my career as well - the more I learn, the more I REALLY wonder how they stay in the air! :D