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Old 06-12-2011, 08:47 PM #1
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Default Noobie looking for advice on range finder project

Ok so I'm currently an electronics engineering technology major, junior level. I'm working on a personal project that involves creating a laser based range finder. I'm planning on using a camera and triangulation to do this. Right now I'm trying to figure out the components I need to get this done, on the laser emitter side that is.

I'm sorry if these are really basic questions and I appreciate if anyone is willing to help answer them anyway. I've been reading and searching for the last couple days and just want to get a couple questions ironed out for sure.

1. What items are required to run a laser diode? From what I can tell I need a driver and housing (with adjustable lens). From what I can gather, relatively simple constant current/voltage circuits are sufficient for a basic red laser diode, but other wavelengths require more complex circuitry. Is this correct? However if I bought a module, I would just need a source to power it?

2. This range finding "system" needs to be usable outdoors in full daylight at a range of up to around 15ft. Based on these requirements would it be dangerous if pointed at something reflective like a bare piece of metal?

edit: just wanted to end by saying this is a pretty cool board. Now that I'm looking into lasers more I think I might make them a hobby. Pretty cool stuff here.



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Old 06-13-2011, 02:11 AM #2
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Default Re: Noobie looking for advice on range finder project

I think probably nobody has or will want to respond to this thread because of how noobish the questions are. After more reading it looks like I'd need a 500mW+ 532nm laser for it to be visible in broad daylight. So basically laser isn't an option.
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Old 06-13-2011, 03:23 AM #3
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Default Re: Noobie looking for advice on range finder project

Do you need the beam to be visible or the dot? cuz a little wee 5mw red pointer will have a visible dot in broad daylight...

If you do need a clearly visible beam in broad daylight, then you are indeed looking at a lot of money.
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Old 06-13-2011, 04:44 AM #4
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Default Re: Noobie looking for advice on range finder project

No just the dot. I'm gonna be using a camera to calculate distance to the object the dot hits. I read a few threads about this and they said you need 500mW or more. I'm guessing they were talking about the beam and not the dot.

If just a 5mW would work then that would be great.
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Old 06-13-2011, 12:26 PM #5
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Default Re: Noobie looking for advice on range finder project

Laser rangefinders don't need 500mW lasers. If you can see the laser dot, a camera can see the laser dot. Get some color light filters and use that to make the dot viewing easier. The cheapest method is to get red filters and use a red laser.

Also look into OpenCV to do image filtering, etc. for projects like yours.
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Old 06-13-2011, 05:18 PM #6
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Default Re: Noobie looking for advice on range finder project

Most laser range finders use time of flight or phase shift measurements to determine range. This requires very fast sampling frequencies which makes it expensive when made on a small scale. The main issue with triangulation is that you'll want the dot to be the brightest set of pixels to make it easy to track. I'm trying to build this into an RC car that you can drive around with a phone (via bluetooth). I want the user to be able to drive it using an onboard camera, so I'm hoping to incorporate the laser into that. That would make a red filter a problem. I've also considered using a line scanner (meaning a camera with a single column of pixels) in addition to the normal camera, but hoping to avoid that for now. I've also been looking into the OpenCV libraries to see if I can port some of it for use on a microcontroller, specifically ARM K-60.

Thanks for the input so far!
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Old 06-13-2011, 11:39 PM #7
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Default Re: Noobie looking for advice on range finder project

I'm not sure I understand.

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Old 06-14-2011, 12:05 AM #8
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Default Re: Noobie looking for advice on range finder project

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Originally Posted by nillocsivad View Post
Most laser range finders use time of flight or phase shift measurements to determine range. This requires very fast sampling frequencies which makes it expensive when made on a small scale. The main issue with triangulation is that you'll want the dot to be the brightest set of pixels to make it easy to track. I'm trying to build this into an RC car that you can drive around with a phone (via bluetooth). I want the user to be able to drive it using an onboard camera, so I'm hoping to incorporate the laser into that. That would make a red filter a problem. I've also considered using a line scanner (meaning a camera with a single column of pixels) in addition to the normal camera, but hoping to avoid that for now. I've also been looking into the OpenCV libraries to see if I can port some of it for use on a microcontroller, specifically ARM K-60.

Thanks for the input so far!

I dont know what your plans are for building this into an RC Car but phidgets.com has some cool stuff. I build an rc car with their single board computer that runs linux, motor controller, and I added a GPS. The SBC also has digital outputs that can be hooked up to a MOSFET to turn the laser on and off.
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Old 06-15-2011, 05:42 AM #9
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Default Re: Noobie looking for advice on range finder project

Well, you could try sending out a beam with a specific intensity waveform, and then measure the intensity detected at the surface using a receiver. Then you sum the two values and depending on DC value of the resulting waveform caused by the constructive/destructive interference of the two signals, you could measure the distance. It effectively computes the distance using the phase difference of a long wavelength signal.
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Old 06-16-2011, 02:13 AM #10
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Default Re: Noobie looking for advice on range finder project

Hum, time of flight ranging cards for diode lasers start at around 200$ for a kit.
They have came way down in cost. However ranges less then a few meters are phase, not time of flight based, and are not easy. Here is a phase based ranger done by a friend. It would not be cheap to copy:

http://www.electrooptical.net/www/isicl/isiclAO.pdf



The classic thing to do is to use a x-y diffraction grating (two linear gratings in series) to create a grid of dots and look at the displacement of the dots with a camera. This is very accurate, much more then one would think.

Narrow bandpass filters exist for laser light and show up surplus for cheap.
You can get a filter 5 to 20 nanometers wide. They are all over the place for bar code scanners.

If you do some digging for 3D scanners on Youtube, you will find lots of folks who have placed objects on rotation stages and used a line scan from a camera to make a 3D scanning imager. The laser projection used is a flat scan or line from a cylindrical lens.
This is not rocket science if you can do math and have a decent processor. Lots of freeware frame grabbers that interface to microcontrollers for college level image work have been published.

Another technique would be to use two X-Y galvanometer scanner pairs and overlap the dots, a 2D variation of the classic "co-incidence" rangefinder.

If you can pull this off, this project will get you hired. Ranging is a skill that is in demand

"Cordic" is your friend.

If it gets you a job or a paper published, you can send me your first paycheck. (Just kidding)



Steve

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Old 06-16-2011, 02:29 AM #11
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Default Re: Noobie looking for advice on range finder project

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Originally Posted by Bionic-Badger View Post
Well, you could try sending out a beam with a specific intensity waveform, and then measure the intensity detected at the surface using a receiver. Then you sum the two values and depending on DC value of the resulting waveform caused by the constructive/destructive interference of the two signals, you could measure the distance. It effectively computes the distance using the phase difference of a long wavelength signal.
Close.


What you really do is amplitude modulate 2 or 3 carrier frequencies onto the beam and look at their phase when they return.

Dr Trevor Wadley made a fortune and changed the world doing this:

http://www.fig.net/pub/fig2008/paper...right_2833.pdf

NOAA 200th: Collections - Distance Measurement Tools: Tellurometer Model M/RA 1

Aka a Tellurometer (Can be done with light or RF)

I love Barlow-Wadley loop shortwave receivers (his other invention)

Steve

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