China RGB laser modules: worth it?

[Stiffler]

Laserwave has a whole line of RGB 'bricks', which includes drivers & PSU, and uses all diodes. They are a little more than the bricks on ebay, but Laserwave makes nice stuff. I'm probably going to pick up a 3.6 watt RGB brick for a projector that I have laying around.

[metameta]

Hi all, laser noob here. I bought one of these to toy around with some ideas I have involving diffraction gratings, speakers and reflective mylar to create color patterns. http://www.ebay.com/itm/RGB-400mw-La...item19da757858

I'm intending to build a controller to modulate the colors using an arduino. I assume it will involve feeding a control voltage to those red green and blue sockets on the top of the unit, though I'll have to wait till I have a wiring diagram or schematic in front of me till I know for sure. Any tips off hand?

I plan on strictly using this to project onto a matte wall or screen. I imagine I'll enclose my "projector" in a cardboard cone to restrict the spread of the scattered beams.

That said, what goggles would you recommend with this unit and would they mainly be used when initially aligning the RGB beams? Anyone know or have strong suspicions that the green or blue diodes use frequency doubling and how does that impact the choice of goggles?

I recognize that though this cheap as hell, it's still potentially very dangerous and I will continue to poke around here and read up on laser safety before firing it up. Thanks for any pointers. No pun intended.

[Nemo222]

The red and blue are pure diodes, because you are under 500mw you most likely have 650nm red in it. The green is a DPSS and analog modulates like crap even IF you have an analog capable driver. These lasers are not really analog, even when they market them as such. Your mileage may vary. Either way you are going to modulate them with a TTL or analog signal from whatever variety of DAC you end up using. TTL is a 0V or 5V signal, on or off. Analog is 0-5V roughly corresponding to a linear brightness. Take a look at this, http://www.youtube.com/watch?v=g5N-9qTjn9o

That is an Teensy micro-controller doing color modulation attached to a simple beat detector. My laser is TTL only so my signals are just digital high and low. You cannot analog modulate with an audrino as they only support PWM output, you will need to run it through a secondary DAC to get a proper signal.

From the factory these lasers tend to come very well aligned, I never bothered to re-align mine and if you are just getting started you will probably make more of a mess of it then if you just left it alone. Your standard safety glasses in the correct wavelengths will offer good protection. You will need at least 2 pair as each will only block 2 of the 3 dangerous wavelengths of light present in a RGB module. I only have cheep goggles because none of my lasers exceed 1W and I rarely work on them out of case. The module should have an IR filter on the output so when the case is closed you should be well protected from IR. Scattered beams aren't really a concern unless you are doing this in an ice storm with an obscenely powerful laser. Reflections however are ABSOLUTELY a concern, as are stray beams which are very easy with a diffraction grating.

My blue diode recently died but otherwise I have been quite happy with this laser. It is absolutely not high quality, but for just over 100$ and almost all of the work done it is great for little projects like my squiggle generator.

[electrowiz]

Hi all, laser noob here. I bought one of these to toy around with some ideas I have involving diffraction gratings, speakers and reflective mylar to create color patterns. http://www.ebay.com/itm/RGB-400mw-La...item19da757858

I'm intending to build a controller to modulate the colors using an arduino. I assume it will involve feeding a control voltage to those red green and blue sockets on the top of the unit, though I'll have to wait till I have a wiring diagram or schematic in front of me till I know for sure. Any tips off hand?

I plan on strictly using this to project onto a matte wall or screen. I imagine I'll enclose my "projector" in a cardboard cone to restrict the spread of the scattered beams.

That said, what goggles would you recommend with this unit and would they mainly be used when initially aligning the RGB beams? Anyone know or have strong suspicions that the green or blue diodes use frequency doubling and how does that impact the choice of goggles?

I recognize that though this cheap as hell, it's still potentially very dangerous and I will continue to poke around here and read up on laser safety before firing it up. Thanks for any pointers. No pun intended.

Welcome to the forum metameta,

I hope you find a wealth of help and support here.
You are correct that the laser you have is very dangerous. The risk to you is your eyesight, which can be injured in an instant, before you even have time to blink so I would suggest the following:
Since you are new and I would guess you are using mylar on speakers to project images, get a small low power laser pointer to work out your ideas and experiments with the mylar and speakers, etc. One of the key things with laser light is always have an awareness of where the beam is coming from and pointing to, imagine it as a steel thread you don't want to cross with your face. As you work with your experiments you will learn how the beam can move, reflect, and get redirected by your project. It would be wise to do your experiments where no one else in the home can come in unexpectedly.

With regard to the high power laser here is some info. Since you can have red, green, and blue you pretty much have the full spectrum of light so you would have blocked out almost all light without much left to see if you had googles that blocked all three parts of the spectrum. It is best when working with parts of a projector that you are keeping the laser power set very low, then when you are done fiddling step back to watch the projection on your screen and there you can turn the power up. Try to remove anything reflective around the edges of the screen you are projecting to - that way if the beam unexpectedly strays a bit, it would not hit something and bounce back at you. Hopefully in working with the low power laser pointer above you will know just what your projector will do and how to avoid getting into the beam.

With the laser you bought (I have one too) the input claims to be analog modulation, meaning that as voltage is applied to the three color input control pins the beam intensity should smoothly increase as you input voltage from 0vdc to 5vdc. What you will find if your beam is scanning or moving quickly is a chopping of the beam at lower powers, this is due to the way the manufacture set the laser up. Technically it is a pulse width modulated input, not true analog modulation.

What this means is that using your Arduino you can use the same technique to control each of the three beams intensities. At an output port pin of the Arduino, image a 0 to 5 volt square-wave that goes logic high breifly for 0.1 milli -second and then goes low for 0.9 milli-second and just keeps repeating this cycle - the beam will be low intensity with this signal coming in. Now as you change the ratio of high to low, making it in the high state longer, the beam will be brighter. You will discover by using different intensities on the three color inputs you can "mix" many different colors.
Happy to answer any other questions.

[metameta]

Thank You both Nemo222 and electrowiz for the insightful responses! I gathered from earlier in this thread that the "analog" on this module is not true analog. electrowiz, are you saying that I could connect a PWM directly to the analog control or to the TTL? I have seen that people on here suggest TTL only offers 7 distinct colors. But if one were to use PWM one could conceivably achieve a larger combination of colors by blending. (I am already familiar with this using RGB LEDs, both analog via potentiometers and PWM via the Arduino) Of course as soon as you start scanning the laser you will notice the pulsing that you eye would usually ignore when stationary.

Now, are they essentially taking a control voltage and feeding the laser with a PWM in their "analog" implementation? And would it make sense to put something like this http://www.instructables.com/id/Anal...WM-to-Voltage/ in between the PWM out of the Arduino and the analog in of the laser module?

Or, would it be simpler and more effective to cut out the middle man and go PWM to TTL? (I thought I saw somewhere that there's a jumper to switch between how the module interprets the input signal)

As I understand it there are 2 modes on this module: TTL and "analog" and one can fake a modulation of brightness by either of:
1. [PWM]->[TTL]
2. [control voltage]->["analog"] which in my case with the arduino would equate to [PWM]->[DAC]->["analog"]

If my assumptions are correct, I wonder which mode offers the highest dynamic range.


Nemo, nice project. From most angles that case looks like a serious piece of equipment. What is it a gutted tape deck? My project will likely be very similar: laser module feeding into some magic box.

[Nemo222]

TTL does only offer 7 colors (2^3=8 and includes off). non diode lasers, especially cheep DPSS greens do not PWM well since the transient rise time of the laser is too slow to PWM at high frequencies. With the advent of low cost, pure diode projectors we may be able to start PWMing at Mhz frequencies, but even then once the beam is moving fast enough it will still be visible. Since these cheep bricks do not PWM at high frequencies as soon as you scan the beam you will have a fan pattern of the different colors you are trying to achieve. This may generate a very interesting effect and if that's what you are looking for then by all means, go hard. I do not know how PWM on the TTL line would work. I haven't tried it but will definitely experiment when I get my new laser.

That simple converter may work, but I would be curious about how much voltage drop you get across it which would reduce your maxium brightness, and the delay in the signal caused by that capacitor. It would be a problem for projectors, but squiggle generators and visualizers would likely be more tolerant of those issues. Also, since it is just smoothing the signal and is not actually a DAC there will be jitter, if you set the pwm frequency very high it likely wont be noticeable. Since there are no schematics on the drivers for these lasers its hard to tell how they interpret an incoming analog signal, its possible the signal processing done by the driver is very similar to what that little converter does, in which case you would just be doubling it. I would try feeding a 50% pwm signal directly to the laser on the analog line and see if it responds differently than to a 2.5V signal.

In both cases the color range you could expect would be roughly comparable when the beam is stationary. Persistence of vision will smooth out the pulsing of the laser and all will be well. Once scanning I have no idea how they would look. You are definitely not going to be achieving smooth gradients and depending on how fast you are scanning the color perceived may not be even remotely similar to what it would be if the beam were stationary.

My squiggle generator in that video is an old micro high-fi system that has been re-purposed. It normally has a 100mw green laser pen laser in it but I wanted to see how the RGB would look so I took out the green, cut a hole in the back and fired the other laser in through it. the RGB laser will be going in a different stereo box which is currently being assembled. The BIG box its sitting on is a laser cutter.
I made a post about it recently here. http://www.photonlexicon.com/forums/...e-Generator-V2
That has most of the information about it.

[electrowiz]

Thank You both Nemo222 and electrowiz for the insightful responses! I gathered from earlier in this thread that the "analog" on this module is not true analog. electrowiz, are you saying that I could connect a PWM directly to the analog control or to the TTL? I have seen that people on here suggest TTL only offers 7 distinct colors. But if one were to use PWM one could conceivably achieve a larger combination of colors by blending. (I am already familiar with this using RGB LEDs, both analog via potentiometers and PWM via the Arduino) Of course as soon as you start scanning the laser you will notice the pulsing that you eye would usually ignore when stationary.

Now, are they essentially taking a control voltage and feeding the laser with a PWM in their "analog" implementation? And would it make sense to put something like this http://www.instructables.com/id/Anal...WM-to-Voltage/ in between the PWM out of the Arduino and the analog in of the laser module?

Or, would it be simpler and more effective to cut out the middle man and go PWM to TTL? (I thought I saw somewhere that there's a jumper to switch between how the module interprets the input signal)

As I understand it there are 2 modes on this module: TTL and "analog" and one can fake a modulation of brightness by either of:
1. [PWM]->[TTL]
2. [control voltage]->["analog"] which in my case with the arduino would equate to [PWM]->[DAC]->["analog"]

If my assumptions are correct, I wonder which mode offers the highest dynamic range.


Nemo, nice project. From most angles that case looks like a serious piece of equipment. What is it a gutted tape deck? My project will likely be very similar: laser module feeding into some magic box.

metameta,

I just left the laser in the mode it was shipped in for "Analog Modulation", in my tests I found with +5 volts in to the color control inputs it was pretty near maximum output and with 0 volts in, the beam was off. So what will limit the way you use your Arduino will be the resolution you have in creating a PWM signal. In my system each color input on the laser has an 8 bit resolution for 256 steps. If your Arduino has a PWM control that would allow for 256 steps of PWM into each of the three color control inputs you should be able to do the same colors I have in my system. I am able to create the following distinct colors: RED, ORANGE, YELLOW, LIGHT GREEN, GREEN, BLUE GREEN, AQUA, BLUE, FUSCHIA , PURPLE, WHITE, PINK.
You don't need the interface circuit you mentioned. Really TTL just means a system where 5v is considered a high, or "1" and 0v is low or "0". The answer is on these inputs they act like both TTL steps 0v =off to 5v= full on, as well as voltage steps("analog") between 0 to 5V.

Good luck, be safe

[paulckruger]

I just got the W800 to tinker with. Out of the box I have what seems to be a pretty well aligned beam that is white light. ( all three set full I assume )
I am looking for a simple circuit to control the analog plugs in order to vary each color by way of a pot to change the output beam color.

If some one has done this already I would rather not re-invent the wheel.

Anyone have the circuit they used for this? Voltage range to the three plugs?

Thanks for any feedback.

[Nemo222]

I received a w400 a few days ago but haven't got a chance to play with it yet. I have powered it on and I.m a little underwhelmed with the beam. the green is VERY fat but I should be able to fix that, and everything needs a big of alignment.

If you got an analog capable board its expecting 0-5V signals on the input lines roughly corresponding to a linear brightness response. If you do not have an analog laser it is expecting a 0/5V logic signaling corresponding to off and on. A 5V supply with three pots wired into the input lines will probably work for testing purposes but are not very good for modulation in an application.

[paulckruger]

Mine has a good strong beam and appears well aligned. Beam is very white, just a tinge of blue. The cost of the W800 was not enough more than the W400 so I went the higher output.