Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

Buy Site Supporter Role (remove some ads) | LPF Donations

Links below open in new window

FrozenGate by Avery

White laser *now with host* :)






First off, hat's off to you ROG8811!!!!!!! Simply beautiful, completely pro job. Brought me and a few friends to LPF.

I just ordered a broken PS3 drive from eBay and can't wait to get it. The loading mechanism is broken, I hope the blue ray LED is working. The optics on the sled will be nice in any event. I have red 5mw red lasers, and just ordered the green you recommended - by the way, thanks for the great links to the various sources. (Doh! just got email that green lasers won't ship until after Chinese new year, Feb 01 - Gung Hay Fat Choy!)

I built a PC controlled, home made galvo, laser light show in 1996 when red pen pointers were new (and $70) and wrote the software for it myself but it's been collecting dust for years. I hope to restart it in full color!!!

Which brings me to why I'm posting now - why PWM to get color from the lasers? I've used PWM for LED colors in a lot of projects but they always leave dashed "trails on your retina" as you look around because LED's can switch on and off so fast. I expect this dotted line would be completely unacceptable for the laser light show so I've been thinking about outputting n bits of intensity from a PIC to an R-2R ladder (look up "resistor ladder" on wikipedia, I'm to new to post links.) which is a current source that can drive a simple 1 transistor NPN common emitter amplifier that would drive the current through the diode. That should give brightness control without dashed lines. I know the brightness curves aren't linear but they are continuous. Has anyone done this?

I generated a color composit NTSC TV signal from 8 digital outputs of an FPGA and 16 resistors - it was amazingly rock solid and beautiful. The R-2R circuit is the cheapest, best digital to analog I have ever played with.

Since I'm new to the forums, here's some boring bio.
I'm a professional software engineer - video games actually, including PS3 (and Xbox 360, Wii, PS2, PSP, PC, .....) which makes this little project like 1000x more cool - as if it needed it.
I'm an advanced hobbyist electrical engineer. I program PICs, PLDs, FPGA's and design a lot of circuits. I've done just about everything radio controlled, and am working on a couple home brew CNC tables now. Too bad I don't have a lathe :)

Scott
 
Spot1984 said
Lots.....  ;)
Click to expand...

It is nice to hear I have inspired you! I would be very interested in other forms of drive circuit, I would need chapter and verse on building it though. I am no electronics expert, all my builds tend to be hard wired mechanical switching as I can understand that :)
Though drive circuits are a breeze these days, having soaked up the expertise on LPF, programing chips and writing code is a complete mystery.........

Should you perfect your control  for this application please post the info as the mk2 white is underway and I like added value :).

Regards rog8811
 
No promises but what voltages and current ranges would you like for each LED.

And/OR post some links to laser diode data sheets and I will think about it.

Are you driving the LED's yourself or letting the driver board regulate the current (power)?
 
No promises but what voltages and current ranges would you like for each LED.
The green laser has a built in driver which no doubt would need to be replaced, It drives an IR laser diode, approx values 2.5v @ 200 to 300ma
Blu ray 4.5v @ 90 to 110ma
Red is 3v @ 100 to 200ma
These values are all a bit "suck it and see" as the white beam, on my build, is all based around the "fixed output" of the green laser and max safe output of the Blu ray, the red was just adjusted until the white looked right.

And/OR post some links to laser diode data sheets and I will think about it.
The senKat reds have data sheets somewhere around the forum, Blu ray...not that I recall and for the green not likely as we don't build them

Are you driving the LED's yourself or letting the driver board regulate the current (power)?
The circuits we use are constant current, the voltage takes care of itself

Regards rog8811
 
PWM works well without dashed lines, as long as you are outputting it at 5kHz or faster. I hooked up a cheap 5mw red to an arduino and had its brightness controlled by a potentiometer.

I only tested to see if the line was continuous by quickly moving the dot across a wall, but I was probably getting 10-20m/sec at the end of the laser. (If one does the math, 20m / 5000Hz / 2 (One cycle is both on and off) = 2mm dashes, probably less than beam diameter. On a spiro the dot may be hitting higher speeds, I'm not sure just how fast software pwm on a pic can go.


The only problem that I can see with regulating current is that as well as output not varying linearly, apparent brightness does not vary linearly with the mW outputted by the diode either. Even with my PWM scaling linearly the high end of the pot was virtually indistinguishable while the lower 20% or so had major stepping and went from looking 50% to 0% brightness very quickly.
 
Agreed.

But...

Laser diodes have built in photodiodes. They aren't meant to be operated at constant current, instead they use the photodiode as feedback to get constant power output. I had forgotten that when I wrote my previous post. Anyway, you should be able to mix an analog signal from a PIC with the feedback voltage to regulate the current through the laser diode. The response of the photodiode is probably nonlinear as well, but nonlinearity can be compensated for by a lookup table in the PIC program.

Re PWM times: On a 4Mhz Microchip PIC, each instruction takes 4 clocks or 1us to execute. I've done PWM for motor controllers in the 16Khz range and a dedicated tiny loop can more than double that. Most PICs can be run up to 20Mhz or 5x the speed. Some PICs also have one or two PWM outputs.

I really don't have a preference - if the built in regulator is fast enough to turn the beam off and on to blank the beam during drawing and if it can use PWM without degrading line quality, then it's a perfectly valid way to go.

My interest in what has become making my own mixing regulator is now academic. :)

Interestign sites...
www<dot>geocities.com/lemagicien_2000/elecpage/chlaser/chlaser.html
www<dot>roithner-laser.com/Drivers.htm
www<dot>repairfaq.org/sam/laserdps.htm
 
^Not all laser diodes have a built-in photodiodes in their can. The ones in the optical drives often use a separate photodiode for controling the power output (like the one that is detecting the signal coming off the disc and has to be there anyway).
 
Oh. I didn't know they didn't all have optical feedback. Several other pages and datasheets make a big deal about the power output varying with temperature.

this article is pretty informative, especially the circuit diagram...
electronicdesign<dot>com/Articles/Index.cfm?AD=1&ArticleID=6316
electronicdesign<dot>com/Files/29/6316/Figure_01.gif

the MOD input can gate the laser output
IC2 is a serial 10 bit d to a, and the pic output can replace it.

I also think if you are already using a simple LM317 current regulator like

In +-------+ Out R1
(+) o-----+---| LM317 |--------/\/\-----+-----+------o LD anode
| +-------+ 18 ohms* | |
C1 _|_ + | Adjust | _|_ C2 __|__
22uF --- +---------------------+ --- 1uF _\_/_
| = | |
| |
(-) o-----+-----------------------------------+------o LD cathode

or

In +-------+ Out R1 1 ohm,2 W
(+) o-----+---| LM317 |--------/\/\-----+-----+------o LD anode
| +-------+ | |
C1 | | Adjust R2 1K | |
22uF _|_+ +------------/\/\-----+ +_|_ C2 __|__
Tant- --- | R3 R4 500 --- 1uF _\_/_
alum | - +---/\/\----/\/\----+ - | |
| 560 ^ | |
| | | |
(-) o-----+--------------------+------+-------+------o LD cathode



You could mix the analog out from the pic r-2r ladder onto the adjust line of the 317. I'm sure care must be taken to mix the control signal with the feedback to reduce the output current and not amplify it :)
 
You must log in or register to reply here.





Back
Top