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'[EE]: IR distance sensor'
2007\07\12@090442 by wouter van ooijen

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www.mcselec.com/index.php?option=com_content&task=view&id=185

This project claims to be an IR distance sensor, but my gut feeling says
microcontrollers are much to slow for that. My best guess is that he got
different readings for different distances of his object-to-be-detected
because at larger distances the signal is weaker so it takes longer for
the sensor to react. Anyy comments, am I totally wrong?

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu



2007\07\12@092900 by Ariel Rocholl

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I agree, one thing is to echo sound signals at 340m/s, a very different
thing is to do that with light at 300000km/s.
I guess what he gets is an artifact of the weak signal. (the question is
whether the artifact really works...)


2007/7/12, wouter van ooijen <spam_OUTwouterTakeThisOuTspamvoti.nl>:
{Quote hidden}

> -

2007\07\12@094720 by Jinx

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> I guess what he gets is an artifact of the weak signal. (the question
> is whether the artifact really works...)

Probably does with that particular sensor. 75mm is no time at
all for light, only about 0.25ns, so it just can't be timing. Might
not work if you had any sort of focus for the beam which kept
the intensity more uniform over distance. That would be why the
preferred method is ultrasonic. I'd say he just got lucky



2007\07\12@094823 by Mike Harrison

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On Thu, 12 Jul 2007 15:28:58 +0200, you wrote:

>I agree, one thing is to echo sound signals at 340m/s, a very different
>thing is to do that with light at 300000km/s.
>I guess what he gets is an artifact of the weak signal. (the question is
>whether the artifact really works...)
>
>
>2007/7/12, wouter van ooijen <.....wouterKILLspamspam@spam@voti.nl>:
>>
>> www.mcselec.com/index.php?option=com_content&task=view&id=185
>>
>> This project claims to be an IR distance sensor, but my gut feeling says
>> microcontrollers are much to slow for that. My best guess is that he got
>> different readings for different distances of his object-to-be-detected
>> because at larger distances the signal is weaker so it takes longer for
>> the sensor to react. Anyy comments, am I totally wrong?
>>
>> Wouter van Ooijen

I think they are relying on differing response time of a remote-control IR receiver  to different
signal strengths.
It may also be possible to get some distance info by progressively altering the width of the tx
carrier pulses and looking to see at what point the detector starts/stops receiving it.


2007\07\12@101729 by David VanHorn

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Cameras used infrared rangefinders for a while, that worked on triangulation.

A narrow IR beam was swept across the area and when it was seen
through the detector's narrow FOV, the angle was used as indication of
the distance.

So it IS optical, but not time-of-flight.

You can do TOF in analog, if you're clever.

2007\07\12@165932 by Brent Brown

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> www.mcselec.com/index.php?option=com_content&task=view&id=185
>
> This project claims to be an IR distance sensor, but my gut feeling
> says microcontrollers are much to slow for that. My best guess is that
> he got different readings for different distances of his
> object-to-be-detected because at larger distances the signal is weaker
> so it takes longer for the sensor to react. Anyy comments, am I
> totally wrong?

You can measure distance by measuring the amplitude of the reflected signal. Light
intensity is inversely proportional to the square of the distance. Variables like the
reflecting surface, angle of reflection, ambient light etc, have a great bearing on the
accuracy but it can still work very well in certain applications for short distances (a
few inches or so).

It's not immediately obvious that this is the method used in the project mentioned,
but I'm guessing it is.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  brent.brownspamKILLspamclear.net.nz


2007\07\12@173900 by Al Shinn

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David,
I would very much like to learn to be clever about analogue time of
flight ranging - any hints, clues, links etc.?? I have a FatMax laser
range finder that I have "injured" but wasn't clever enough to reverse
engineer it yet - I just know that it does not quite follow the
LEICA-GEOSYSTEMS patent in that the reference beam photo detector in the
patent is missing.

Looking forward,
Al Shinn

David VanHorn wrote
"Cameras used infrared rangefinders for a while, that worked on
triangulation.
A narrow IR beam was swept across the area and when it was seen
through the detector's narrow FOV, the angle was used as indication of
the distance.
So it IS optical, but not time-of-flight.

You can do TOF in analog, if you're clever."
--

Looking forward,
Al Shinn



2007\07\12@193515 by Jinx

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> Cameras used infrared rangefinders for a while, that worked
> on triangulation.
>
> A narrow IR beam was swept across the area and when it was
> seen through the detector's narrow FOV, the angle was used as
> indication of the distance

Sounds a bit like Dambusters

http://en.wikipedia.org/wiki/Operation_Chastise

"The second problem was to measure the aircraft's altitude (the
usual barometric altimeters lacked sufficient accuracy). Two
spotlights were mounted, one under the nose and another under
the fuselage, such that at the correct height their light beams would
converge on the surface of the water"


2007\07\12@195251 by David VanHorn

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> "The second problem was to measure the aircraft's altitude (the
> usual barometric altimeters lacked sufficient accuracy). Two
> spotlights were mounted, one under the nose and another under
> the fuselage, such that at the correct height their light beams would
> converge on the surface of the water"

That's the idea.

The nazis had a similar system using radio "beams" that crossed over the target.
My intuition says that this was probably pretty "fuzzy", and I know
that the british discovered this, and worked on hacking the system
such that bomb loads were released over open fields rather than
cities.

2007\07\12@210009 by Xiaofan Chen

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On 7/12/07, David VanHorn <.....microbrixKILLspamspam.....gmail.com> wrote:
> Cameras used infrared rangefinders for a while, that worked on triangulation.
>

Simple diffusive or retro-reflective photoelectric sensor can be
used as a simple distance measurement device if the requirement is
not high by correlating the signal strength with the distance.

Many "background Suppression" photoelectric sensors use
triangulation using PSD device or photo diode array.

More precised optic distance measurement sensors can
be a bit more complicated. Some of them offer 4-20mA output
and some of them even have network connection.

Regards,
Xiaofan

2007\07\30@054450 by Howard Winter

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Dave,

On Thu, 12 Jul 2007 19:52:50 -0400, David VanHorn wrote:

{Quote hidden}

Yes, I believe the aircraft flew along one beam, and the bombs were released when they crossed the other one.  They called it "X-equipment", which
rather gave the game away as to how it worked!  Another system was called "Wotan", after the norse one-eyed god... guess how many beams that
used?  :-)

Watching the television series "The secret war" with Dr.R.V.Jones many years ago, it was amazing how much was learned just from german
code-names.

I believe that the Instrument Landing System (ILS) still used today in commercial flying was developed from the two-beam bomber guidance idea.

Cheers,


Howard Winter
St.Albans, England


2007\07\30@063955 by Russell McMahon

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>> The nazis had a similar system using radio "beams" that crossed
>> over the target.
>> My intuition says that this was probably pretty "fuzzy", and I know
>> that the british discovered this, and worked on hacking the system
>> such that bomb loads were released over open fields rather than
>> cities.

>
> Yes, I believe the aircraft flew along one beam, and the bombs were
> released when they crossed the other one.  They called it
> "X-equipment", which
> rather gave the game away as to how it worked!  Another system was
> called "Wotan", after the norse one-eyed god... guess how many beams
> that
> used?  :-)

The British two beam system (which AFAIR they developed before the
German one) was named Oboe and a similar 3 beam system was named Gee
(actually a series of timed pulses from 3 transmitters).

> Watching the television series "The secret war" with Dr.R.V.Jones
> many years ago, it was amazing how much was learned just from german
> code-names.

Reading Dr Jones material it is surprising how much he could learn
from almost anything the enemy did or said or even didn't do. Send a
signal of any sort and he could learn something from it. FWIW he was
also the 1st person to correctly identify V2's at Peenemunde for what
they were using aerial photos- after others had looked at them and
missed them.

If there was no suitable enemy signal to analyse he was not above
getting them to make him one. Want to find new radar? Send an aircraft
to fly a multi leg course then receive their subsequent report,
translate it, plot the route they report and then fit the report to a
map to see where it was made from. Then, in that case, send commandos
to carry off the whole station.

Receive an Enigma report that two new (then still very rare and
secret) radars are being sent to the Baltic coast. Measure coastline,
work out Pulse repetition rate of signals that would cover half that
(1/4 there and back) as stations would ideally be place at 25% and 75%
points for most linear cover, then look for signals of that PRF at
about the frequencies suspected until voila. Send bombers ... .

Jones' book "Most Secret War" (renamed for the US market as "The
Wizard War" :-( ) is utterly compelling reading.
530 pages of fun and games and practical jokes while doing much to
assist the allied war effort.


> I believe that the Instrument Landing System (ILS) still used today
> in commercial flying was developed from the two-beam bomber guidance
> idea.

Loran was developed directly from Oboe.


       Russell

       http://en.wikipedia.org/wiki/Oboe_%28navigation%29

       http://en.wikipedia.org/wiki/GEE_%28navigation%29


>
> Cheers,
>
>
> Howard Winter
> St.Albans, England
>
>
> --

2007\07\30@090815 by David VanHorn

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>
> Watching the television series "The secret war" with Dr.R.V.Jones many years ago, it was amazing how much was learned just from german
> code-names.

I'd like to see that one!  This subject has always been a fascination for me.

> I believe that the Instrument Landing System (ILS) still used today in commercial flying was developed from the two-beam bomber guidance idea.

As it happens, I'm re-reading "Glide Path" by Arthur C Clarke.
:)

2007\07\30@101724 by Marcel Duchamp

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David VanHorn wrote:
>> Watching the television series "The secret war" with Dr.R.V.Jones many years ago,

Say, wasn't Dr. Jones Indies father?

2007\07\30@102847 by Luis.Moreira

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Funny enough I am at the moment reading is book, Most Secret War.
Is absolutely brilliant reading.
Best regards
               Luis



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