Laser stuff for those interested

AIman

I have recently discovered that Jameco.com has a laser diode with about a 100 yard range that is Class IIIa (eye safe). The diode is 14.95 and the compatable driver is 7.95 - total cost 23 bucks.

The link for the laser diode
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=182932

The link for the driver
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=161736

I figured these would work good for a range finder but·haven't found a light sensor to handle the return signal yet. If I do it will get posted.

If anyone knows where to get a sensor that can detect the return light please·post the link.

Chris Savage

AIman,
·
·· A Laser Range Finder would require you to modulate the laser signal and be able to detect the modulation within a very short amount of time, so you would need a very fast reacting detector as well as circuitry which can operate at those speeds (just under speed of light).

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Chris Savage
Parallax Tech Support

metron9

About 983,581 feet per mS or about one foot per nanosecond


So a sx at 50mhz light travels about 20 feet per clock cycle

you have 5 clock cycles to measure 100 feet

not gonna happen

But I have always wanted to make a laser dector to detect breaking the beam , an invisible fence system for my back yard.

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Think outside the BOX!

crgwbr

Time based range finder-- No

Trig based range finder-- Maybe

Just a thought

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NerdMaster
For
Life

AIman

Perhaps, however all you need to know is how long a burst is put out and when. Given those two factors the details of making a range finder isn't that complex. Start the system, fire the laser, receive the signal, calculate the·length between pulses.

In other words, send a pulse every 10 or 20 ms and then calculate the time diference between recieved signals to get your distance. Doesn't need to be faster then that, just needs to be able to know when tripped. As long as the recieving end is capable of tracking at 10 to 20 ms it will work if the measurement is between the recieved times.

AIman

Found this link

http://www.eodevices.com/main_eho_1_frameset.htm

It refers to the Basic stamp.

steve_b

The basics are simple....but try and find a stable oscillator. Because, your oscillator needs to not drift from the time you've send your pulse to the time you've received it (unless of course it ends up 180deg out of phase) but any little offset will makeyour readings bad.

What kind of resolution do you want? If your pulse is long, remember that you can't start "listening" for you pulse until you've finished transmitting. You're basically blind for this time.

Anyhow, the idea is simple....but find the parts. They tend to get $$ pretty quick. Have you seen a laser range finder for less than a couple hundred $? (not up here in Canada)

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·

Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Harrison.

You don't necessarily need to measure the time between the send and receive signals.·You could look at the frequency changes as distance gets larger or smaller.· A pretty comprehensive example is shown in a student's science fair project that is posted on Parallax's main site.

Link: http://www.parallax.com/images/customer_apps/willp/Robot%20Wall%20Sensors.pdf

Harrison

Paul Baker

It seems some people are talking past each other in this thread. Many things are being discussed that don't have a direct correlation ("apples" to "oranges" comparision). IR ranging by zone is not the same as laser range finding, the first uses the bandpass frequency of the receiver to reduce the sensitivity of the receiver, the second measures the time of flight between the emitter and receiver. The two concepts are very different. There are several methods for doing TOF laser rangfinding, none of which a Basic Stamp is capable of without faster and specialized external circuitry. The link provided which has a BS2 on-board is for interfacing with another module which does the rangefinding, then sends the result via a serial connection to the BS2.

There are non-time of flight means for doing laser ranging finding, but are complex and beyond the direct capabilities of a Stamp for different reasons.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Post Edited (Paul Baker (Parallax)) : 11/1/2006 1:59:08 AM GMT

AIman

Stable oscillators and getting things to work correctly might be more difficult and somewhat pricy, however I have a hard time beliving that it will be more expensive then the robotic laser range finder at $4000 with only a 4 meter range, or the SICK laser range finders starting at 5,600.

Unless there is someone out there who makes a much cheaper laser range finder I am going to have to build my own, and so far I can get a driver and 650 nM Class IIIa laser combination for under $25.

I just need to find a way to read the return so there is useful information provided. Mouser.com has optics but so far there isn't anything discovered on a way to capture a return signal.

I don't really care if the outgoing pulse takes 1/20th of a second pause or even more. The stuff used doesn't have to be·top·notch, just useable at or below human reaction speed.

·

Paul Baker

You are correct, they can be made for far cheaper than what is commonly availible.

Here is a link you should find interesting and informative: http://www.philohome.com/sensors/lasersensor.htm

(edit: dagnabit·I just realized the above link is useless, it is like the default IR detector configuration, it only provides an "Object/No Object" output only for·much further distances. There was an article posted that was true rangefinding, I'll go look for it)

The important measure isn't the length of time the laser is on for, its how long it takes to hit the target and bounce back. To achieve resolution of 1 foot, you need to be measuring the round trip with a·500 MHz detection unit. A·250 MHz detection unit gives a resolution of 2 feet (ie is it 2,4,6,8,... feet away). And a 100 MHz detection unit can only measure in 5ft increments, and it only gets worse from there. Measuring the signal directly from stamp speeds, and your talking about 50s of miles (is it 50, 100, 150, ... miles away, not very practical).

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Post Edited (Paul Baker (Parallax)) : 11/1/2006 5:03:41 AM GMT

Paul Baker

OK I found it, its an old N&V article posted in the same thread: http://nutsvolts.texterity.com/nutsvolts/200504/

Its the article "Measuring the speed of light".

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

kelvin james

Aye, i can relate to this. I have been looking at this for a long time, and there are so many variables involved, it hardly seems worth the effort to attempt a diy. A lot of the problem leans to the resolution factor, you may be able to read some distance, but if it is off by a large factor, it won't do much good. Acam makes a chip called the GP1 that is specifically designed for this, it measures at 3 nanoseconds, does the calulation and the output at around 17 us. It will do a few hits, and then do an average comparison to improve the resolution. But then you have to have a trigger unit, then the laser stuff, beam spitter and good optics, and that makes things complicated. F.I.Y. Stanley tools have joined up with Leica to make a consumer range finder starting at around 100 bucks. It is good to 100 ft. with a 1/4 in. resolution. I am going to be getting the next model up that has continuous measure, and see if it can be hacked for output to micro use. So far, this seems like the most logical alternative. If anyone is interested, Acroname is selling a scanner for a measily $2700, at least cheaper than a Sick, but nowhere near the range.

kelvin

p.s. Any laser can still hurt the eyes on continuous exposure.

Paul Baker

Thanks for the the info Kelvin, those chips look very promising some of thier units approach possible resolution into the millimeter range.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

steve_b

That Stanley tools price is about as cheap as you'll find.
I was going to mention the Bushmills laser ranging binoculars as cheap, but at over $500 you've got them beat.

Interested to see a hacked version for sure!

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·

Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

kelvin james

Paul, i was seriously looking into getting the Acam tdc, but when i started looking at the complexity of putting the whole thing together, it got a little overwhelming. Just don't have the time to deal with it now, although i may still pursue it in the near future. The Gp2 looks a little easier to deal with, has spi and a trigger, but lacks some of the options. Hopefully with the Parallax resources, and your knowledge, you can put something together for the hobbiest.

kelvin

Tom Walker

I would see this as more of a peripheral for the Stamp than a Stamp based project. Something that would, upon receiving a "start", fire the laser (modulated however you like) and start a high-speed counter at the same time and latch the count on receiving the bounce. This type of design would offload the speed requirements from the target processor and should be able to support some scalability. Conceptually, it sounds do-able, but I haven't really looked at the details...so if it isn't as easy as it seems to me, then blame it on my ignorance.

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Truly Understand the Fundamentals and the Path will be so much easier...

AIman

I looked up the Nuts and Volts link and started tracking down parts but discovered the part number for the Sharp reciever is invalid. The search took me to Jameco, Mouser, Sharp and then finally Digikey. Digikey has not yet responded however no one has that part number.

Mouser, Jameco and Sharp Microelectronics all have Lasers and/or drivers but so far no one has a reciever.

kelvin james

This company has some laser stuff worth looking at for the d.i.y. people. The upcoming kits might be promising, but again, these are not cheap.

kelvin

www.eodevices.com/main_eodmain_frameset.htm

Paul Baker

AIman,

You may best be served by using the trigonometric method of laser rangefinding. It is a much simpler method of of performing distance finding. This is where a laser is placed in line and a slight angle with a linear array sensor (TAOS makes such sensors). A lens is used and placed so the linear sensor is at its focal length, the laser spot will be reflected back onto a different spot on the sensor. Here's a crude diagram of the setup:



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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Paul Baker

Here's some stuff Beau has done to illustrate the trig method of laser range finding.

Remove the .txt file extension to view the video.

His diagram talks about using the light to frequency meter (he drafted it for use with Parallax parts, but the TSL3301 will provide a higher resolution result (which is a 102 pixel 8 bit intensity serial output linear sensor)).

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Post Edited (Paul Baker (Parallax)) : 11/2/2006 11:51:46 PM GMT

AIman

Thanks for the data. My intent is to use a couple of different lasers to scan the distance in incrememts instead of trying to use one to do everything. KISS method...

Paul Baker

Let us know how it works out for you.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

AIman

Will Do.

metron9

Hey Paul thats cool. Now a question.

I am aware that judging distance using your eyes is performed similarly except it takes two eyes for the brain to make the distance calculation. I know because I am almost blind in one eye. The question then is, if my brain can not judge distance using only one eye how can a micro controller? I see the dot moves across the page given the distance variation but with two eyes the distance is calculated from the difference between the two images on the retinas. I would think you would need two laser spots with a known distance between them to calculate distance in this manner.

Remember I have no clue about this and I am just trying to fit the two seemingly opposing ideas into a logical container.

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Think outside the BOX!

PAR

metron9 said...

I am aware that judging distance using your eyes is performed similarly except it takes two eyes for the brain to make the distance calculation. ... The question then is, if my brain can not judge distance using only one eye how can a micro controller? ...

They're probably not very similar at all. A person('s vision system, even one-eyed cases) uses many types of visual·cues (sometimes including other biosensory systems, e.g. audio)·and stored information (memory, experience)·about the natural/built world to _estimate_ location and relative/absolute distance.

PAR

Beau Schwabe

metron9,

You are correct, without both eyes your depth perception is severely impacted.

With binocular vision, humans measure depth by comparing the two slightly different
2D images from each eye.· If you think about it this is a remarkable ability, the
brain is capable of taking two images, filtering out the noise, and producing a
smooth rendition of the 3D world around us.

...Back to the laser distance question.· Its actually very much the same thing.
Your eyes work by sending the signals to your brain and then your brain takes this
information, converges the signals and interprets the difference.

Suppose you had one eye that was "fixed".· You could see just fine, but you couldn't
move it left, right, up, or down without moving your entire head around... it would
probably be a pain in the &^*&$! but eventually you would learn to adapt, because
your brain would "know where it is" relative to the position of your other eye.· Over
time your brain would adapt and learn to filter out any noise and eventually provide
a smooth rendition.· Now consider the laser as the "fixed" eye.· We know where the
laser is mathematically because of the angle the laser has been set to in our design
and the distance of the laser relative to the sensor in our design.· The "sensor" that
is detecting the position of the laser point would essentially be your "other" eye.
Now by reading the sensor we can calculate the depth based on the convergence of the
known angle of the laser, the distance from the laser to the sensor, and the position
of the laser point that the sensor is providing.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 11/4/2006 6:46:13 AM GMT

PAR

Beau Schwabe (Parallax) said...
metron9,

You are correct, without both eyes your depth perception is severely impacted.

...Back to the laser distance question.· Its actually very much the same thing.
...

Semantics is getting in the way of the meaning(s) of "...judging distance using your eyes is performed similarly...", and "...if [noparse][[/noparse]a] brain can not judge distance using only one eye how can a micro controller?"

Sure, both systems have a sort of "binocularity", and both "calculate" distance to target. So, in that sense, they're "much the same thing".

But, people with one-eyed vision can move there heads to provide an alternative sort of binocular cues, and both two-eyed and one-eyed persons' brains·use·much more and different information than simple trigonometry to estimate depth and relative and absolute·distance.

It is in this more detailed sense (of human experiences,·perceptions and brainpower) that I suggest that the two systems of estimating distances are quite dissimilar.

PAR

·

Beau Schwabe

PAR,

Agreed, however people with one-eyed vision moving there heads to provide an alternative monocular view, still provide the brain with two images to compare. I do not doubt that there
are many more things at work than simple trigonometry when it comes to how we interpret distance. What I was trying to give was an explanation that was more along the line of apples to apples
in reference to the trig-laser method of determining distance.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Chris Savage

Metron,
·
·· The laser is firing its beam straight out and it is being reflected back onto a linear optical array.· Depending on the distance from the object the laser beam will be striking a different section of the array and that is how the distance is determined.· So basically where the array is, the beam will hit a different part of it based on the distance from the object.· Take care.

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Chris Savage
Parallax Tech Support

Joe Dunfee

I was looking at this process for the Roomba Vacuum project I am working on. I had read about the Sharp distance sensors such as the GP2D02 [noparse][[/noparse] http://www.junun.org/MarkIII/datasheets/sharp-app-note.pdf ]

It uses the parallax method, but I was disapointed to find that it only used an IR LED, not a laser.

I am currently working on a method for a laser scanner to detect reflective targets covered with a barcode. So, I am looking for similar sensors, but don't need the linear array of sensors.

Joe Dunfee