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. :confused:

[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]

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.asp?CATEGORY=LASER+MEASURING&TYPE=PRODUCT&PARTNUMBER=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]

Have you looked at the Stanley 77-910 - TLM 100 FatMax™ Tru-Laser™ Distance Measurer: http://www.stanleytools.com/default.asp?CATEGORY=LASER+MEASURING&TYPE=PRODUCT&PARTNUMBER=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]

Have you looked at the Stanley 77-910 - TLM 100 FatMax™ Tru-Laser™ Distance Measurer: http://www.stanleytools.com/default.asp?CATEGORY=LASER+MEASURING&TYPE=PRODUCT&PARTNUMBER=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]

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]

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/default.aspx?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]

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]

I understand. Hacking the Stanley may not be an option anyway: http://forums.parallax.com/forums/default.aspx?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]

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]

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]

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$.