PWM instead of analog for color control

[maxh]

I've been reading, and it seems that there are 2 main methods of modulating the lasers in a projector to create a nice spectrum of color: analog and TTL. I have some questions:

1. I'm new to electronics and lasers and don't know what TTL stands for, but it sounds like some kind of pulse width modulation (PWM). Is that correct?

2. So analog controls the current going to the laser to control the light intensity, and TTL controls the amount of time a laser is turned on/off at a some fast frequency to do the same?

3. Why do people seem to prefer analog modulation? (I'm guessing it's so they don't have to worry about their graphics looking like dotted lines if they scan fast...)

4. If I try to control color with PWM in a RGV system using the most common R and V laser diodes and a cheap green module from china, are their any predictable pitfalls? Max/min frequency? Do I need to build my own driver for the green module or can I modulate through the driver already on it? this is the one: http://o-like.com/b2b_cpinfo.asp?id=839

[Insanity]

Probably not as comprehensive an answer as others on the forum can give but in simple terms:

TTL allows you to blank the laser on and off, so if you were to combine red and green lasers you can have just red, just green or both combined to make yellow. This gives a total of 7 colours out of an RGB setup. Red, Green, Blue, Cyan, Magenta, Yellow and White.

Analogue modulation allows you to vary the intensity of the lasers as well as blanking them, this opens up a pallete of literally millions of colours...

Mark

[mixedgas]

TTL is on/off and the software only flips the color line once per point, so there are no intensity levels, its either on or off.

Analog gives you variability. TTl us on/off and slow.

As a aside, due to a fixed delay in the Nd:YAG or Nd: Vandate material in the laser, there is a limit on how fast blues and greens switch on and off. Sadly this is too slow fro true PWM, although red diodes and 403 nM violet diodes could be PWMed for dimming.

This is sad, because I once had a setup with a external modulator that I PWMed a laser with, and got what people perceived as the most linear color control I have ever seen.

Hope this helps,

Steve

[maxh]

TTL is on/off and the software only flips the color line once per point, so there are no intensity levels, its either on or off.

Analog gives you variability. TTl us on/off and slow.

As a aside, due to a fixed delay in the Nd:YAG or Nd: Vandate material in the laser, there is a limit on how fast blues and greens switch on and off. Sadly this is too slow fro true PWM, although red diodes and 403 nM violet diodes could be PWMed for dimming.

This is sad, because I once had a setup with a external modulator that I PWMed a laser with, and got what people perceived as the most linear color control I have ever seen.

Hope this helps,

Steve

Thank you for your response!

How long does it take for the green to turn on? What would be the maximum achievable frequency?

Also, I'm still curious what TTL stands for...

[mixedgas]

Thank you for your response!

How long does it take for the green to turn on? What would be the maximum achievable frequency?

Really good greens are say 10-15 khz. Perfect would be a little faster then 30 khz. In reality most color changes in laser art are slow enough that most lasers are fine. The problem is reds come on fast, followed by greens and then DPSS blues drag behind. There are a variety of software and hardware solutions to the problem.

The delay in the YAG or VANDATE materials is around 800 microseconds for green and for some reason blues are around 900-1000 uS. Diode reds have bandwidths of around 1 ghz, but most drivers are limited to 100 khz or so, You'll never see a slow red. There are some direct diode blues at 445 that are as fast as red, but they are expensive.


Also, I'm still curious what TTL stands for...

Transistor-Transistor Logic. Its a chip family that outputs .6V for a logic low and 2.4 volts for a logic high.

[buffo]

As Steve said, TTL =transistor-to-transistor logic. And while the minimums are .6 and 2.4 volts, it's generally implemented as zero volts and +5 volts (or very close to 5). But yeah, most lasers that support TTL blanking will turn on at around 2 volts or so.

As for the max frequency for PWM, forget it. Most DPSS lasers have trouble reaching the required power level for each point in the pattern. In order to do effective PWM, you'd need to be able to pulse it at least 5 to 10 x faster than the point speed. Ergo - not going to happen.

Adam

[maxh]

As Steve said, TTL =transistor-to-transistor logic. And while the minimums are .6 and 2.4 volts, it's generally implemented as zero volts and +5 volts (or very close to 5). But yeah, most lasers that support TTL blanking will turn on at around 2 volts or so.

As for the max frequency for PWM, forget it. Most DPSS lasers have trouble reaching the required power level for each point in the pattern. In order to do effective PWM, you'd need to be able to pulse it at least 5 to 10 x faster than the point speed. Ergo - not going to happen.

Adam

I'm not trying to build a projector capable of fancy graphics. Really, I'm just trying to make myself a pointer with a large, adjustable color palette. Human vision only needs 20-30 Hz for something to be perceived as fluid and not flickering. Could a green DPSS do that? Or 100 or 1000 Hz? I'm sure I could build a suitable analog driver for my laser system (with the help of my electronics guru father) but PWM seems like it would be easier.

[keeperx]

well i think you should talk to LaserJock
he built a 7 color pointer
http://akrobiz.com/laserboy/forum/in...opic,29.0.html
prety sweet...

[maxh]

well i think you should talk to LaserJock
he built a 7 color pointer
http://akrobiz.com/laserboy/forum/in...opic,29.0.html
prety sweet...

That's kind of the idea. rog8811 made one too. I want 1000's of colors, though, not just 7; hence the need for more sophisticated modulation.

[keeperx]

TTL will only get you 7

you want analog without a doubt.