Subject:
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Re: laser distance sensor
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Wed, 4 Aug 2004 15:42:02 GMT
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Viewed:
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3794 times
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In lugnet.robotics.rcx, Andreas Jurk wrote:
> Hi
>
> I'd like to build a laser distance sensor for my mindstorms robot.
> Does anyone know if any plans of circuits of such sensors exists?
This is an interesting subject and one which generates some interest every so
often. The conventional assumption would be that you are talking about LIDAR.
The thing is, even if simple plans where available, would you be able to use
them to construct and build such a device?
The speed of light is really really fast. To be useful at Lego robot scales of
say one inch resolution, you'd need to be able to measure light pulse timings to
about 1/10 nanosecond. Laser diodes, photo-sensors and electronic parts that
work up to 10GHz are available. They are not exactly cheap and they are not easy
to assemble and have them actually work as expected, let alone diagnose when
they don't.
On a much cruder, more Mindstorms-esque and practical level, I have wondered,
but never got as far as testing, the possibility of using a laser pointer as an
illuminator in a triangulation/trilateration based range finder. You simply put
a tube (or lens) on the front of your Lego light sensor and block its LED (with
a short piece of black heat shrink tube slipped over it). You place this more
directional sensor on a scanning mechanism made with a motor and rotation
sensor. Similarly, you can do the same thing with the laser pointer. Now, you
can scan the sensor and the source beams, and measure their relative angles. I
assume you'd know the distance between them - you get to build the assembly. So
you have the baseline and the two beam angles - you're all set.
The trick is that in your software you're looking for the "spot" created by the
laser on an object at an unknown distance. So you set your laser to point in
some direction of interest and slowly scan the sensor looking for the spot. I
would power the laser pointer from a motor port - paying attention to voltage
and polarity issues - so you can switch it on and off. In the software, you'll
see all sorts of different values coming in from the light sensor as it scans
based on the scene. However, blinking the laser on and off and checking for a
synchronous change in reading from the light sensor allows you to know when you
are looking at the spot.
I have done a similar thing with an IR LED, but I cheated and used a rotating
mirror instead of mounting it on a rotating mount. Its a lot of work getting
such a system going, but you'll have fun and learn a lot.
JB
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Message is in Reply To:
 | | laser distance sensor
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| Hi I'd like to build a laser distance sensor for my mindstorms robot. Does anyone know if any plans of circuits of such sensors exists? Andreas (20 years ago, 4-Aug-04, to lugnet.robotics.rcx)
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