SELEM presentation topics - discussion

[buffo]

Wow! Lots of great replies so far. Keep 'em coming, folks!

Steve: The optics primer sounds like a good idea. I think it would be a fairly short topic, but it certainly would be of interest to many of our members. And your tips for building enclosures could be included at the end of that presentation.

As for measuring the modulation performance of some of the DPSS lasers at the event, that would be *very* cool, but I don't have a fast photodiode to do the measurements. Also, I'm not exactly sure how we'd go about timing it. (Oscilloscope? Plot modulation signal against photodiode response?) How would we set up the modulation pulse timing? If you've got a plan, I'm all ears...

James: Maybe you could include a brief overview of the procedure to modify a sound card when you do your LaserBoy demo...

Adam

[allthatwhichis]

James: Maybe you could include a brief overview of the procedure to modify a sound card when you do your LaserBoy demo...

Adam

Yes! This would be a great presentation in itself...

[300EVIL]

General Laser Safety
Advanced Laser Safety - Audience Scanning
Scanner Tuning
Scanner History and Theory of Operation
Using Pangolin's Showtime software
Using Pangolin's Live!Pro software
Ion Laser Alignment
Using LaserBoy software
Solid State Laser Theory
Practical Wiring for your Projector

I'd personally like to participate in seminars on all these subjects. Some of them I already have a good understanding of however, I usually find I will learn something new either way.

[mixedgas]

[QUOTE=buffo;52194]Wow! Lots of great replies so far. Keep 'em coming, folks!

Steve: The optics primer sounds like a good idea. I think it would be a fairly short topic, but it certainly would be of interest to many of our members. And your tips for building enclosures could be included at the end of that presentation.

As for measuring the modulation performance of some of the DPSS lasers at the event, that would be *very* cool, but I don't have a fast photodiode to do the measurements. Also, I'm not exactly sure how we'd go about timing it. (Oscilloscope? Plot modulation signal against photodiode response?) How would we set up the modulation pulse timing? If you've got a plan, I'm all ears...

end buffo quote

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I have a 135 mhz photodiode. in fact, correctly biased, just about any PD will do if its reverse biased and only a few mm square. you'd only need a 10 mhz scope. I wish to propose a standard circuit to do it with, and that circuit is crystal controlled. costs about 10$ to build, two TTL chips, a binary counter and a 4 bit comparitor, this outputs a variable length PWM , if you drive it at around 3 mhz, one cycle out of the counter is a single point at 30K. if you add a fet gate driver chip out of a switching power supply, we could have it swing rail to rail zero to 5V in 25 nanoseconds. so it would test either TTL or analog. if you vary the pulse width, you could simulate a image with just a little blanking, or have a fast pulse with 15 blank periods. Thats why I'm using a 4-bit magnitude comparator, a 74F85 as the PWM source, you just hook a dip switch to it and you can set 16 different states, from 1 pulse to full on to full off. simple, fast easy and partz are available anywhere in the world with no source code or programming required.

Steve

[mixedgas]

attached is proposed version zero dot one beta laser rise/fall time test circuit

and if ONE OF YOU WANTS TO BWITCH ABOUT THE DRAWING FORMAT DONE WHILE PASSING A SMALL KIDNEY STONE AND USING A LAPTOP WITH MS WINDOWS PAIN(T) YOU CAN REDRAWIT YOUR ^%$#ING SELF! we will clock it so that one complete pwm period is 16 x 1 over 30,000 OK? PLEASE NOTE THAT THIS IS not HOW I NORMALLY DRAW SCHEMATICS, ITS HOW i THINK ABOUT BUILDING CIRCUITS, AND YES, i THINK CIRCUIT DESIGN IN 3D TECHNICOLOR. i GUESS THAT MAKES ME A FREAK. oF COURSE WE COULD USE IEC/IEEE STANDARDIZED CIRCUIT SYMBOLOGY, AND NOBODY WOULD UNDERSTAND IT.

SEE ATTACHED.

Steve Roberts

[James Lehman]

yOu ShOuLd ChEcK yOuR cApsLoCk KeY eVeRy NoW aNd ThEn.

[mixedgas]

yOu ShOuLd ChEcK yOuR cApsLoCk KeY eVeRy NoW aNd ThEn.

i'M sCREAMING iN pAIN!

sTEVE

[mixedgas]

OK we add a second 7485 with B set to 0000 binary and A0-A3 coupled to 7493 Q0-Q3 and use the second 7485s A=B output to trigger the scope, that way you dont need a dual trace scope. A DT scope has some real benefits here though.

BTW, you can cascade 7485s, in 1994 or so I published a circuit using a flash A to D converter, a 8 bit counter clocked at 6X the point rate and 2 cascaded 7485s to drive a old style TTL input ON/OFF AO. This resulted in 8 bit PWM intensity control. Those who saw it and those who built it, found that PWMing the laser beam produced, at least to most eyes, a very linear fade when driven by the 0-5 from pangolin. since back then printer AOs were getting dumped by MWK for 25-50$, it made for a very nice cheap way to do intensity control. Since modern chinese yags usually use ND:Vandate and thus are inherently polarized, this should be looked at again. sadly almost no modern yag could follow a 6X pwm directly without the AO, although some US and UK companies are working on low cost green yags that can take a video luminance channel directly. Theya re NOT talking about how they do it however. Steve

[buffo]

Steve;

You are *way* over my head dude. I'll trust you on the circuit. I've got a dual trace oscilloscope (will even do X/Y plots), so I'll bring it.

As for using PWM on an AOM; I wasn't aware that they were binary state devices? Thought you could analog modulate with them just like a PCAOM? Clarification please...

James;

During your laserboy presentation, do you think you'd have time to actually do the modifications to a sound card? I can provide one for you for the demo if you wish.

Keep the ideas coming folks!

Adam

[James Lehman]

Steve;
James;

During your laserboy presentation, do you think you'd have time to actually do the modifications to a sound card? I can provide one for you for the demo if you wish.

Keep the ideas coming folks!

Adam

My thought was to bring one all done, but not in use so it can be examined and one to do, that we don't need to worry about completing. Or something like that. I have a feeling there will be other people bringing their own versions of modified sound devices.

I finally got what seems to be a real positive response out of my friend Dean. I think we might be hearing from him soon here at the PL. He just might be a little excited about the upcoming SELEM. Hopefully we can get together for enough hours before the event to really go over all of the functionality and specifications of the working LaserBoy system. He was my reality check, years ago, when I got my laser projector and really got down to the business of writing LaserBoy. He's the guy who designed the correction amp.

James.