Long range (100 m) laser rangefinders

[4by4]

Does anybody know if the laser rangefinders of the type that are used by golfers have been hacked to be able to interface them to a computer? The basic ones such as the Bushnell models are around $150. There are versions that have an RS232 interface but they cost around $600, at least as far as I could find. I could tolerate $150 but not $600.

[pomprocker]

Laser rangefinders are not cheap!

Here are some links

http://www.acroname.com/robotics/parts/R311-HOKUYO-LASER2.html


Some people use robot vision systems along with presentation laser pointers

[4by4]

The Hokuyo's are not the kind of laser rangerfinder I'm talking about. One of the Bushnell Yardage Pro models is $150 --

See http://www.opticsplanet.net/bushnell-rangefinders.html

[MaltiK]

Check out my mates writeup:

http://letsmakerobots.com/node/2989

He provided both schematics, components, and much insight, a very intelligent man.

Also, check out this one, but only works depending on your camera's resolution and the power consumtion/intensity of your laser

http://www.pages.drexel.edu/~twd25/webcam_laser_ranger.html

[4by4]

Maltik, my question is specifically about the Bushnell or golf-type rangefinders.

[ib1yysguy]

Couldn't one make a rangefinder pretty easily? If you want a long-distance one, you could use magnifying optics to enlarge the landing spot of the laser, then use a simple photoresistor tuned to the right wavelength to determine flight time to and from and object.

Am I missing something?

You could probably even use this laser:
http://www.sparkfun.com/commerce/product_info.php?products_id=8315

You might even be able to use magnifying optics and one of these http://www.sparkfun.com/commerce/product_info.php?products_id=8668 and just measure the paralax.

[chelmi]

Couldn't one make a rangefinder pretty easily? If you want a long-distance one, you could use magnifying optics to enlarge the landing spot of the laser, then use a simple photoresistor tuned to the right wavelength to determine flight time to and from and object.

Am I missing something?

I might be missing something as well, but:

Let's say you want a resolution of 1m (not that great)
The speed of light is 2,9 * 10^8 m/sec
The light travel 1 meter in 3.3 ns
This is your "time resolution", approximately 300Mhz.

The bottom line is, it's out of the range of what "common" micro-controllers (used by hobbyists).

[ib1yysguy]

Hmm. So what do they use in those hunting hand-held rangefinders? Just super fast microprocessors?

[4by4]

I believe the Bushnell rangefinders work on the principle of measuring the phase difference of the reflected wave rather than time of flight. It measures the phase of a modulation waveform imposed on the laser frequency, not the phase of the laser light itself. Usually called a continuous-wave (CW) radar. It doesn't require generating the short pulses. The circuitry is simpler than a time of flight radar.

Re the suggestions above, I think that a parallax type rangefinder could probably be built for 100 meter ranges.  You might want a laser line filter to improve signal to background ratio in daylight conditions, because you could not rely on a modulation of the beam to separate the signal from background. A 5mw laser is pretty dim at 100 meters.

However, with the Bushnell type device, all of the work is already done for you, except for the interface. I'm guessing it's hackable at the connection between the processor and the display, where you could tap into the character codes.

[4by4]

And just to add -- I think the 300 MHz estimate is probably about right. However, the processor doesn't need to handle that waveform directly. There is probably an analog RF front end with a modulator, mixer, phase comparator, etc.

[chelmi]

And just to add -- I think the 300 MHz estimate is probably about right. However, the processor doesn't need to handle that waveform directly. There is probably an analog RF front end with a modulator, mixer, phase comparator, etc.

Yes, you're right. But this does not sound like the kind of stuff you design in your garage

[4by4]

You might be surprised at some of the things the amateur radio guys used to build in their garages.

In the "old days" I once got recruited to work on a government contract that required me to get up to speed on microwave RF design very quickly. So in my spare time I got into experimenting with cheap RF gear that I found in advertised in amateur radio magazines. There was a retired microwave engineer who built & sold components for doing all the basic functions for making microwave transmitters, receivers, radars, etc., and I experimented with a lot of his stuff. So I know that you can build RF systems cheaply using box-level components connected by RF cable. What's really hard is building these systems in the miniaturized RF circuit board form factor, where you have to use microstrip design techniques.

Of course you first have to spend a lot of time learning RF stuff, e.g. read the ARRL Handbook cover to cover.

There are some sites run by amateur radio guys that deal with laser communications, and a laser radar is not too much different from a laser transceiver. A laser radar IS a laser transceiver, actually, with a special kind of modulation. You can also look up FMCW radar (FMCW = frequency-modulated continuous-wave), which is what the consumer-type laser rangefinders are.