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Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
It's a highly anistropic beam, so first you have to correct that (with a cylinder lens or with anamorphic prisms) and then collimate the beam ... so you have to machine your own housing to mount it and the optics to do that.
As for how it's driven, you charge the internal capacitor to a manufacturer mandated level and then you pulse the internal MOSFET (with a fast MOSFET driver). Most people try to pulse diodes a lot longer than several 10s of ns, also with a lot more parasitic inductance/capacitance than this diode because of the integrated capacitor/switch.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Pinky's Brain wrote ...
It's a highly anistropic beam, so first you have to correct that (with a cylinder lens or with anamorphic prisms) and then collimate the beam ... so you have to machine your own housing to mount it and the optics to do that.
yeah i was affraid of this, thats why id rather use a laser module, like sam goldwasser reccomends.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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Some cheap lens options here
For modulating the laser: I suspect you will need exposure times in the 50uS to 500uS range, based on my experiences building IR touchscreens. So the laser driver doesn't have to be anything fancy. Someone out there probably makes a chip for driving and modulating lasers
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
2Spoons wrote ...
Some cheap lens options here
For modulating the laser: I suspect you will need exposure times in the 50uS to 500uS range, based on my experiences building IR touchscreens. So the laser driver doesn't have to be anything fancy. Someone out there probably makes a chip for driving and modulating lasers
the DLIS-2k is fast 120MHz, id odnt plan to push i that fast but still, should be good for 50-100uS, i think 1mS might be to slow. i do need quick/many sequential captures.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
2Spoons wrote ...
The max read-out rate may be 120MHz, but that doesn't mean you will get enough light in that time. Especially at longer ranges.
yes, i always plan to get less than the datasheet suggests...i also plan to pulse the laser for bright, yet eyesafe beams.
reworking the math as Pinky suggests for a 15mm FP, means i now have the farthest beam at 10m equalling 1 pixel lit (4um), and at 300mm i get about 14 pixels lit by the beam width. While traversing 625 usefull pixels in between.
As many of you know, i have a failed laptop HD, a Back injury (painful) , and math 3B finals coming up, so im pressed to the limit. On th plus side, the tricopter(which needs this lidar) is flying and i am definately going to pursue this lidar project.
The problem is now i have 5m to 10m being traversed by 88um and just 22 pixels.
im wondering, since the hypotenuse is the longest side of any triangle, can i tilit the senosr 20 degrees or more to gain distance on the pixel plane, even if it results in a slightly defocused image, since im now having to detect a 20-30 pixel wide beam anyway?
Registered Member #2901
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I think if you tilt the sensor you should tilt the lens as well ... but I also think that is equivalent to just decreasing the beam angle, which is probably easier construction wise (the sensor will shift it's centre away from the axis of the lens BTW).
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
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Pinky's Brain wrote ...
I think if you tilt the sensor you should tilt the lens as well ... but I also think that is equivalent to just decreasing the beam angle, which is probably easier construction wise (the sensor will shift it's centre away from the axis of the lens BTW).
the problem with tiliting the lens is tha that using ray tracing, only the center point matters..
EDIT: AHHHhhhh you sneaky bastard i see what you meant, changing the lens by tilt, changes its viewing angle, but keeps the center of the lens the same. I should narrow the field of view by incraseing lens FL, right?
EDIT: no appreciable chage, i think 10m is the limit for my chosen laser distance / angle.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
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YAY! parts arrived!
ive rcieved 12.7mm diameter, and 33mm FL glass, planar convex lenses. these arnt the most ideal to start with but oh well. i also have an IR filter, 2x2 inches, which will be used to hold the lens too.
once i get the math finalized enough for a first prototype, ill buy the planar cylinder lenses, as mention previously by others.
EDIT [A thought] : i wonder if a half parabola or involute curved mirror could be used to linearize the distance/pixel relation at the near and far circumstance?i just dont know how clear the image would be if i used mirror film 0.125mm thick, since this means a complex curve.
color filter and a lens...
Pinky, 2spoons, the realtion appears to vary like this... long distance between the laser and optic is better for resolution, long distance beteen the lens and focal plane even better...
my most avialable choices in cylinder lenses, appear tobe 50mm, 64mm and 80mm, im CAD-ding the geometry now. 80mm increases my near-blindess from 300mm to 1.7m!
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Optics and laser beam width, need help please.
