I was pleased to see a cool laser rangefinding project on Kickstarter- I hope this project gets fully funded (and I'm a backer). I've actually been experimenting myself with structured light and laser rangefinding using our ArduEye hardware and thought I'd share it here.
The setup is very simple- An Arduino Pro Mini serves as the computing backbone of the device. Via a 2N2222 transistor (I know I know...) the Arduino can on and off a red laser module. The Arduino is connected to an ArduEye breakout board with one of Centeye's Stonyman image sensor chips and a cell-phone camera lens. The whole setup (excluding the red FTDI thing) weighs about 10.9 grams. I think we can reduce that to maybe 4 or 5 grams- the laser module weighs 1.9 grams and is the limiting factor.
The principle of operation is straight forward- the laser is mounted horizontally from the image sensor by a known baseline distance. The Arduino first turns off the laser and then grabs a small image (3 rows of 32 pixels in this implementation). Then the Arduino turns the laser on and grabs the same pixels. The Arduino then determines which pixel experienced the greatest increase in light level due to the laser- that "winning point" is the detected location of the laser in the image. Using this location, the baseline distance, the lens focal length, the pitch between pixels on the image sensor, and basic trigonometry, we can then estimate the detected distance. I haven't yet implemented this final distance calculation- my main interest was seeing if the laser could be detected. The above video shows the system in operation.
In practice, I've been able to pick up the laser point at a distance of up to about 40 feet- not bad for a 2 mW laser. In brighter lights you can put an optical bandpass filter that lets through only laser light- with this the system works at distances of say 10 feet even in 1 klux environments e.g. a sunlit room. If you are using this for close ranges, you can turn up the pulse rate and grab distances at up to 200Hz. How does an Arduino grab and process images at 200Hz? Easy- at 3x32 it is only grabbing 96 pixels!
Comments
This is a really cool application and something that I can really use. I am curious about a few things: What is the Sparkfun piece that is connected to the bottom? Is it a USB adapter of some sort? Also, would you be willing to share the code for this device?
Thanks
Darren
Geoffery, Which laser were you using in the photo? When measuring from 0" to 40" what resolution do you think you might be able to obtain (2mm increaments)?
@Monroe- I've never tinkered with LIDAR itself since it would involve accurate timing that I've never put into our chips. (I *could* do that, just *haven't* gone that direction yet.) But it is an interesting idea.
On the other hand, I've a few ideas for some low light sensors using SPADs (single photon detectors)...
@Marko- actually that is in the code and it works but I didn't report it here. I took the winning pixel, it's two neighbors, constructed a LaGrange polynomial with them, and computed the max. The only cost is that it works better if you blur the image slightly, which reduces the range and/or max light level the device can operate. Also the pixels have a log response so a different interpolation method might be better.
@Lefebvre- agreed. I think though with more tinkering I can prob get it working outside, certainly with a different image sensor or laser.
This is pretty neat, but IMO, severely limited if it can't work outside.
Very interesting! Do you interpolate between pixels, or does it detect at most 32 depth levels (i.e. number of horizontal pixels)?
Marko
Wow, this looks quite promising.
I would think one could do filtering of the data to deal with any texture-induced noise... ?
200hz isn't quite enough to do a fast updating, high resolution XV-11 style LIDAR but it's way, way better than nothing. :)
@Jack,
Good question- with my limited experiments it did fine, probably because the delta-intensity (laser on vs. laser off) was stronger than the background texture. But it might not work as well if the laser spot is near a bright light. Also when you crank up the speed to 200+ Hz you have to move it pretty fast for that type of interference to matter.
@Travis,
Thanks for the link! I did not know about that but I am not surprised. The concept is very simple. Did that laser rangefinder ever get turned into a proper product?
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