Aligning The Laser Beam - A Nub's Question

[ElektroFreak]

Not everyone is intending to use the same laser in different projectors. TTL is fine for a green-only system if you don't intend to upgrade it. You can still control the brightness and do fades by controlling the pulse width.

I have several TTL green-only systems that I have no intention of upgrading to RGB. They will always remain green only systems. TTL works great for these, plus it allows me to keep to a good budget and still have multiple projectors.

A huge concern for me concerning TTL is the fact that many Chinese imports are normally on with no signal on the TTL inputs. It would be better IMO if they were off until a signal is applied, but this is a safety issue that also applies to many Chinese analog lasers..

If you can afford to go analog from the start, go that route. If (like me) you find a bunch of TTL lasers for a good deal, I wouldn't pass them up solely because they're TTL not analog. As long as the pump diode doesn't require much more than 5A or so, you can use a flexmod to power any smaller laser and provide analog modulation instead of the original TTL driver. TEC cooling complicates things a bit, but it's not impossible.

[FourDee]

I believe PWM does not exactly work when you are scanning the beam ...

[buffo]

Pulse-width modulation on a TTL-only DPSS laser is dicey at best for intensity control. In order to get decent intensity variation, you really need to be able to vary the duty cycle on a point-by-point basis. That means your pulse rate will have to be even higher than your point speed, and that puts you beyond the modulation frequency response of most DPSS designs.

True, DPSS lasers don't modulate well even under the best of circumstances (even analog modulatable units suffer from problems), but slower modulation works better than fast. And at least for green lasers, adding analog modulation capability doesn't add a lot to the price.

I do agree that for a beams-only projector, TTL is fine.

Adam

[XysteR]

I use the word 'Personally' in my last post

Going off this build i'm assuming he's looking to add more colours in the future? My advice as little as its worth is always pay the extra and buy analog.

Looking back, even if i was gonna stick to a green only system i would have still chose analog modulation. TTL is like a light switch on/off thats all you get. Analog modulation is effectively like a dimmer light switch, so my reckoning of this, and the conclusion i came to when i look back, is that i would be far happier with analog both visually, and when making my own shows etc. When i only had the green analog in my projector i remember so vividly how much i loved the subtle brightness blends on wide fan effects, it just looks awesome! I can't see how TTL can emulate this effect you get from analog.

TTL has its place and is very nice indeedy, just not as nice as analog. I just know personally i'd never buy TTL a modulated laser. I'd instanly regret and wish i payed more for analog.


I was just thinking. Years ago when i was a kid i got my first synthersizer, great sounds, no touch sensitivity - Great for basic stuff. When i got my first touch sensitive keyboard it was creatively in a different world and opened up one thing my playing lacked, expression.

[ElektroFreak]

"Personally" is key here. I have many lasers, both analog and TTL, cheap and expensive, and I never "instantly regretted" buying any of them. I also have lasers that can't be directly modulated at all.. I don't regret buying them either.

It seems that the OP has already bought a green unit for his system. Rather than tell someone that they need to upgrade to something different (thus adding to the cost) I have found it is better to help them make the best of what they already have. This way we're not just assuming the person has the financial means to do so. In this case the OP probably does have the means, but I won't assume that he does.

Building laser projectors is cost prohibitive to many, many people. I believe in helping people to get the best value for their money and in helping them make the most of what they may already have acquired. For this reason, I won't ever say that TTL lasers don't have their place. I have seen many TTL projectors that would absolutely make someone's day if they were to build one. To automatically discount them without ever having seen one isn't the proper response IMO.

@ the OP: For the record, though, if you should decide to add more colors to this projector, adding analog modulation would be a very good idea. Fortunately, your module would work perfectly with a flexmod driver for analog modulation, especially since it seems like it is not TEC stabilized.

[XysteR]

Yup, thats exactly my point. If more colours are going in then analog for this build mefinks. If its only gonna be green then TTL is fine but if you can financially make the small push to analog then personally i'd recommend he does.

I just noticed he's looking into buying an FB3. That seals it for me. Its gotta be analog!



Gil, the FB3 is what i own, you will not be dissapointed! It really is awesome, and with QuickShow out now its even better. It'd be criminal in my opinion to use TTL modulated lasers with an FB3 and your 30k scanners.

[ElektroFreak]

Why on earth does the DAC matter? ANY DAC will provide analog outputs, regardless of what brand or model it is.. even a homemade DAC will do this.

gilv 58: Analog modulation is very good, and if you want to improve your existing module by adding analog modulation to it, I would be glad to help you do just that. I can't in good conscience recommend that you go out and buy a whole new laser just to get analog modulation, especially when you based your choice of lasers on the advice of one of our most respected members. Steve didn't steer you wrong. An inexpensive 100mW TTL laser is an excellent starting point.

[Doc]

Why on earth does the DAC matter? ANY DAC will provide analog outputs, regardless of what brand or model it is..

Except those "only good as a heatsink/coaster for over hot drinks" Ishow DACs TTL only

[ElektroFreak]

yeah.. I have a tendency to overlook ishow DACs completely. They are worthless..

Regarding the comparison between TTL and analog, it is well known that analog modulation provides a possible 16.7 million color hues. In the real world, however, DPSS lasers (green and most blue) do not respond to analog modulation in a linear fashion. One of my CNIs is so nonlinear that it nearly may as well be TTL. At 0V I have no output. At 1V I have no output. At 2V, no output. At 3V VERY dim output. At 4V FULL output. At 5V full output. So between 3V and 4V the power ramps up very quickly. While this is a worst case example, ALL DPSS lasers respond somewhat similarly to analog modulaton. Therefore you will never see anywhere near the maxmum color palette when using DPSS lasers. You might get a few hundred colors in the best cases. The real exception to this is projectors which utilize a PCAOM rather than direct modulation. Then you'll get some real color spread.

[XysteR]

Why on earth does the DAC matter? ANY DAC will provide analog outputs, regardless of what brand or model it is.. even a homemade DAC will do this.

The DAC matters, the software used to run the DAC matters the FB3 is simply awesome, he's making the right choice, and has obviously been well informed and advised to buy an FB3.

I just feel a FB3 controlled colour projector with good 30k scanners really needs to be analog, personally TTL wouldn't even cross my mind for such a projector