Laser Rangefinders

[DavidGitz]

Actually there are two ways of doing it without using triangulation. You can measure the time delay, assuming the processor is fast enough. The speed of light is 3*10^8 meter/second. If you have a 80MHz clock on your processor (Propellor with an external clock), that means your step distance is 3.75 meters per cycle (and a minimum distance of 3.75 meters too), plenty close for me, since I will be using UltraSonic's for close distances that work up to 6 meters. The other method is to modulate the laser with a frequency, then you can determine the distance using the properties of the Doppler effect, as long as you're relatively moving

[EHaskins]

Originally Posted by DavidGitz

Actually there are two ways of doing it without using triangulation. You can measure the time delay, assuming the processor is fast enough. The speed of light is 3*10^8 meter/second. If you have a 80MHz clock on your processor (Propellor with an external clock), that means your step distance is 3.75 meters per cycle (and a minimum distance of 3.75 meters too), plenty close for me, since I will be using UltraSonic's for close distances that work up to 6 meters. The other method is to modulate the laser with a frequency, then you can determine the distance using the properties of the Doppler effect, as long as you're relatively moving

You would need a much faster processor than that. You couldn't possibly process the signal every cycle.

I'm just curious what are you building?

[Alan Anderson]

Originally Posted by EHaskins

You would need a much faster processor than that. You couldn't possibly process the signal every cycle.

The CPU doesn't have to do all the work. I know of a system having a 2 MHz processor that still manages to do time-domain reflectometry with better than 2 meter resolution. A separate 75 MHz clock drives a fast counter which controls the pulse generation and detection circuitry.

[Eldarion]

Originally Posted by DavidGitz

Actually there are two ways of doing it without using triangulation. You can measure the time delay, assuming the processor is fast enough. The speed of light is 3*10^8 meter/second. If you have a 80MHz clock on your processor (Propellor with an external clock), that means your step distance is 3.75 meters per cycle (and a minimum distance of 3.75 meters too), plenty close for me, since I will be using UltraSonic's for close distances that work up to 6 meters. The other method is to modulate the laser with a frequency, then you can determine the distance using the properties of the Doppler effect, as long as you're relatively moving

Can't you use interferometry?

[DavidGitz]

Originally Posted by Eldarion

Can't you use interferometry?

I assume you mean using more than one laser to triangulate your position. I didn't really want to do that, since my goal is to have 4 lasers on the robot, at 90 degree intervals. Using 8 for triangulation would be a bit too much I think

[Eldarion]

Originally Posted by DavidGitz

I assume you mean using more than one laser to triangulate your position. I didn't really want to do that, since my goal is to have 4 lasers on the robot, at 90 degree intervals. Using 8 for triangulation would be a bit too much I think

One of these, near the bottom of the page:
http://www.williamson-labs.com/laser-mic.htm

It's pretty complicated though. i think a device of this type *might* be what the surveyors use?

Do a Google search for laser interferometry distance measuring and you might be able to find something better.

[Gdeaver]

Try looking looking on Globalspec for time of flight sensors. Even raw moduals will cost over 100$.