Post by thread:[EE]: IR distance sensor

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

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_OUTwouterTakeThisOuTvoti.nl>: {Quote hidden}> > http://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 > > > > -

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 <.....wouterKILLspam@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.

> 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.brownKILLspamclear.net.nz

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

> 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"

> "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.

On 7/12/07, David VanHorn <.....microbrixKILLspam.....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

Dave, On Thu, 12 Jul 2007 19:52:50 -0400, David VanHorn wrote: {Quote hidden}> > "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. 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

>> 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 > > > --