Laser Rangefinders

[DavidGitz]

Does anyone have a source for a laser rangefinder? I'm looking to either make one or buy one, for under $100 each. I've only been able to find two types online, home-made ones that use a webcam as a receiver or using a photodiode ic, but the only ic's i can find only tell if it detects a laser beam or not, they don't give an actual distance.
What I am looking to do is measure distances up to around 100 feet with a laser that operates similar to a UltraSonic, you send a trigger pulse out from your controller and then you count the number of cycles before you get a response, which will give the distance (of course, you have to divide by 2). I don't really care if the one I get works that way or not though, just as long as I can somehow get a distance reading.

[Jeremiah Johnson]

Wouldn't you have to calculate it using the speed of light? Therefore, please correct me if I'm wrong, but it's not possible?

[EHaskins]

Originally Posted by Budda648

Wouldn't you have to calculate it using the speed of light? Therefore, please correct me if I'm wrong, but it's not possible?

I believe most laser range finders work based on the angle the beam is received at, not the time difference.

[ChuckDickerson]

Have you looked at the Stanley 77-910 - TLM 100 FatMax™ Tru-Laser™ Distance Measurer: http://www.stanleytools.com/default....TNUMBER=77-910

It sounds like what you are looking for and they sell for $100 just about anywhere online. It is a true laser measuring device not an ultarsonic with a laser pointer.

Are you just wanting something to buy to measure distance or something to use as a sensor on a robot or something? Maybe you can hack this Stanley unit?

[EHaskins]

Originally Posted by DeepWater

Have you looked at the Stanley 77-910 - TLM 100 FatMax™ Tru-Laser™ Distance Measurer: http://www.stanleytools.com/default....TNUMBER=77-910

It sounds like what you are looking for and they sell for $100 just about anywhere online. It is a true laser measuring device not an ultarsonic with a laser pointer.

Are you just wanting something to buy to measure distance or something to use as a sensor on a robot or something? Maybe you can hack this Stanley unit?

I'd google that unit. I'm sure if its possible to hack it somebody already has.

[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

[DavidGitz]

Originally Posted by DeepWater

Have you looked at the Stanley 77-910 - TLM 100 FatMax™ Tru-Laser™ Distance Measurer: http://www.stanleytools.com/default....TNUMBER=77-910

That's funny, actually I was just looking up that out of desperation. Plan B is to hack another one, but as this robot is actually for production-design, I would like something not so hack-ish.

[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?

[ChuckDickerson]

Originally Posted by DavidGitz

That's funny, actually I was just looking up that out of desperation. Plan B is to hack another one, but as this robot is actually for production-design, I would like something not so hack-ish.

I understand. Hacking the Stanley may not be an option anyway: http://forums.parallax.com/forums/de...?f=15&m=174249

I think you may be asking for a tall order to get what you want under $100. If you find something let us know. I have several uses for such a device if it can be interfaced to a microcontroller.

[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.

[DavidGitz]

Originally Posted by DeepWater

I understand. Hacking the Stanley may not be an option anyway: http://forums.parallax.com/forums/de...?f=15&m=174249

I think you may be asking for a tall order to get what you want under $100. If you find something let us know. I have several uses for such a device if it can be interfaced to a microcontroller.

Yeah it seems like not many people are having luck, at least with a fairly inexpensive module. I'm sure I could get something to work if I could just find a detector IC that is sensitive to around 690 nm for a red laser pen (cheap emitter As I said before, I found a detector but it only returns either a detected or not-detected value:
http://www.junun.org/MarkIII/Info.jsp?item=79

[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$.