Laser stuff for those interested

[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 (Parallax)]

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 [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 (Parallax)]

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 [ 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

[AIman]

Quick Question.

Instead of trying to caputre reflected light, why can't a camera be used to locate intense light?

A laser should be the brightest light source around and if the brightest spot moves then why couldn't a camera be able to translate a location based off brightest spot and velocity of the robot?

[Joe Dunfee]

AIman, I assume your question was directed at my post.

>Instead of trying to capture reflected light, why can't a camera be used to locate intense light?

Several reasons;

- Simplicity is a major goal in the design from my point of view. Aside from the obvious benefits of a simpler system (cost and effort to put it together), a simpler system is more accessible by the electronics novice.

- Video processing takes serious processor horsepower, and programming knowledge to use it.

- By modulating the light source, it is MUCH easier to eliminate false signals, and of course this GREATLY simplifies the rest of the processing.

- A retroreflective target (which reflects the modulated output from laser) is much easer to create than building multiple sources that modulate the light. We need a lot of targets, because in a house the view of the targets will often be obscured, so this is another argument against a complicated target.

- We want the Roomba to identify individual targets, so the plan is to put barcodes on the reflective targets. Multiple modulated IR LEDs would tend to create interference with each other of they were very strong at all. By the way, the Roomba manufacturer, iRobot, makes available "Virtual Walls" which put out a fairly weak modulated signal to keep the Roomba from going into another room, but there is no way to distinguish one of them from another

I am certainly open to other ideas, so here is the current plan in more detail in case you have more ideas;

The Roomba will get a laser attached onto it, along with light sensors adjacent to the laser (What these light sensors will be, is still being investigated). Then around the room some retroreflective targets will be placed. When we want accurately determine the location of the Roomba, it will spin in place, and time how long the spin takes. . When the laser hits a reflective target, the sensors detect it, and that time is logged in the Stamp for processing later.

The big benefit of the laser is it will provide a distinct on-off signal when it crosses over a target. A more diffuse light beam, such as a LED, would not.

The processor, a Stamp 2, will use the "hit logs"calculate the angles where the targets were detected. If the location of each target is already programmed in, we have the necessary information to calculate the location of the Roomba vacuum.

Of course, the next challenge is in identifying individual targets from each other. While only two targets are needed for the calculations, we think we will need many targets, because some will be obscured by things in the room. Also, we want the Roomba to be able to go from one room into another and find its way back.

The barcode idea may be implemented in a few different ways. The least demanding on the electronics is to use 1/2" wide reflective tape and put stripes representing a 0 or 1 on a piece of index card. But, I think our goal is to print barcode onto transparency and place that on a wide piece of retroreflective tape.

We've used visible lasers up to this point. The detector chips, which have internal circuitry to detect the modulated frequency and an external pin to drive the external light source, tend to be infrared (we are working with one of the few visible 650 nm detectors right now). Also, their response time seems to be a bit low for our application, which needs to detect stripes at about 8 Khz.


Joe Dunfee

[mediaprefect]

This may sound like a strange recommendation for an electronics parts source, but...

If you just want an inexpensive laser diode, you should try Walgreens drug store. Around here they have had a pen with a blue LED light and a red IIIa laser powered by three LR44 cells (included). They are selling every day for $2.99 OK, I can't resist: "But wait there's more." They also sell them two for $5. That's hard to beat for hacking and easy availability. Heck, Rshack wants $3.99 per LR44 cell on their web site (silver oxide not alkaline though). If you need new batteries for a digital caliper or stopwatch etc. the laser pointer could be considered free. You will find it hanging next to the pens and Sharpies. The SKU is 630990822001. I've heard of people buying laser pointers for a buck, but have not come across any yet.

I've had good luck experimenting with driving a laser diode (from a different hacked pointer) with an SX28 through a PN2222 and chopping at a few kHz at least. I haven't had a reason to drive it any faster yet, so don't know what the upper limit of modulation is.

At the other end of the financial spectrum, if you have the money, the top of the line Leica laser tape has Bluetooth built in (not the Stanley product). You can output measurements directly to a spreadsheet.

Good luck with your project.

Rick

[kelvin james]

This photo diode looks interesting.
www.sales.hamamatsu.com/en/products/solid-state-division/position-sensitive-detectors/two-dimensional.php

kelvin

[metron9]

Just bought 2 at the walgreens, very bright, the cats love to chase them.

Well I better get to taking one apart...

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Think Inside the box first and if that doesn't work..
Think outside the BOX!

[AIman]

In my mind the vision thing is getting way to detailed and leading to confusion.

Yes the human eye uses more things to focuse then a camera, however there are many camera's with auto focus.

A program I am working on uses a camera to navigate with a sonar as a saftey feature. The pictures allow the robot to move in any direction but if the sonar says the saftey limit is violated then the robot stops that going in that direction. In the case of using a PING its only a few inches. My point being that all you really need is a 2D camera image to use for directional findings (i.e. what direction is available to move towards) and a sonar to keep saftey limits for obsticale avoidance.

Hook the sonar up to the camera - top or bottom - and then pan the camera/sonar unit. It works much like the BOE BOT demo that used sonar to center on an object except that this uses pictures with sonar to be sure the way is clear. You· could do this with just sonar, but then if the robot was supposed to go somewhere specific you would either need a map or some other form of identifier. With this set up the robot can wander freely and not damage something or get damaged by something.

[AIman]

A thought occured to me.

What if a laser is used to point outward at a set distance or if you want a tilt device so it can change distance. The light is bounced back to a circular set of mirrors, say something small like an inch wide by an inch tall. These mirrors rotate and are not smooth but placed around the cirumfrence of thier "home" facing straight out so that each one has a gap between the mirrors to either side. In other words, cut the middle row out of a disco ball. The mirrors rotate non-stop while the laser is in use.

Shouldn't we be able to use the dead spaces between the mirrors to capture distance? For example if we cant time a flicker of light to hit a light sensor and the amount of light changes - dimmer is farther - then would it work?

Example
·················································· ··············· { outline·of dark box
······························ {==========}·············· * Light sensor
·······························{···/············· *}············· / mirror·gets light to sensor
································ <················ ·}············ Laser is the <
······························· ··· /·l···l··l· \···· }··········· Mirrors in circle /ll\
·······························{==========}··········· === top and bottom of dark

So in short the laser < fires out a pulse. The moving mirrors·/l l \ catch the reflected light and bounce it up to a stationary mirror / which sends it back to a light sensor. The box/container that everything gets mounted into is light absorbent - black painted·or some dark colored crushed velvet or foam to absorb stray light. The light sensor·won't be a need to be as fast as the laser, only as fast as the mirrors rotate. Of course a sensative light sensor would need to be used.

Would it work as a range finder?



Post Edited (AIman) : 11/17/2006 10:16:10 PM GMT

[AIman]

The diagram looked much better before it was posted...

[the_poet677]

Just a quick reply to the eye sight thing... If our eye could emit light, and then really accurately time the return, then yeah, one eye would be all we need for depth perception. The reason we have two eyes, and binocular vision, is that we, unfortunately, aren't superheroes.
I vote we work on eye-lasers next.

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And, in the end, the love you take
is equal to the love you make.
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