How does a laser distance meter work? - Page 1
Forum section: electronics / general

author: Galenbo
author_rank: Super Contributor
timestamp: April 24, 2015, 07:55:53 am
content: A thing I keep asking myself, how does a laser distance meter work?Please give a scientific answer on the level of this forum, I mean, like you would give to an university engineer.Ultrasonic works with an interrupt on reflection, but how can laser do this? It measures incredibly right, on different surfaces.Speed of light is a million times faster than speed of sound, so the interrrupt based approach seems impossible?Triangulation, witch needs a multi-pixel receiver or a motorised moving receiver seems impossible, due to the price and the very small angle,this would put the results in the noise level.Am I missing something here? I'm sure.

author: AndyC_772
author_rank: Super Contributor
timestamp: April 24, 2015, 08:44:48 am
content: http://hackaday.com/2014/07/01/pew-pew-an-arduino-based-laser-rangefinder/

author: DmitryL
author_rank: Regular Contributor
timestamp: April 24, 2015, 09:00:37 am
content: Quote from: Galenbo on April 24, 2015, 07:55:53 amThose who are not banned on google may try following set of magic keywords: "laser distance meter principle phase shift"

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 24, 2015, 09:05:11 am
content: https://www.eevblog.com/forum/chat/how-does-laser-meters-work/

author: atferrari
author_rank: Frequent Contributor
timestamp: April 24, 2015, 10:10:12 am
content: Quote from: DmitryL on April 24, 2015, 09:00:37 amWho bans them?

author: wraper
author_rank: Unknown
timestamp: April 24, 2015, 10:41:30 am
content: Quote from: atferrari on April 24, 2015, 10:10:12 amThey ban themselves. Recently, in some other tread when mentioning about googling first, OP said that his majesty is too great to fall to the level of using google.

author: wraper
author_rank: Unknown
timestamp: April 24, 2015, 10:45:54 am
content: Quote from: MMDuino on April 21, 2015, 11:24:27 am

author: atferrari
author_rank: Frequent Contributor
timestamp: April 24, 2015, 11:31:44 am
content: Quote from: wraper on April 24, 2015, 10:41:30 amI see.I feel less and less inclined to "correct" people, albeit laziness is something I do not accept if they expect me to do their task. Until recently I used to enter here and post the outcome for the lazy.http://lmgtfy.comBTW, I've been many times close to your place (Sweden, Poland, Denmark) but now, I think I am not going to have any more chances to visit that part of the world. For my next life maybe...

author: Galenbo
author_rank: Super Contributor
timestamp: April 24, 2015, 12:30:18 pm
content: Thanks for the replies.In the past, I did a few searches, but the results were flooded with commercial offers, and childish explanations.I'll take a look.Edit:The link to the other EEV tread seems to contain a lot of information, glad with that.But I'm also glad all of you already know the existence of Google. Also happy that lmgtfy still exists after all those years.Please insert some numbers in the following comments, cycle time, intervals, I mean, some proof why it works in what way.And limited factors for a chosen principle. How the needed accuracy is reached,...Edit:The other tread gives some links to different articles, everything I need seems to be covered there.Thanks.

author: wraper
author_rank: Unknown
timestamp: April 24, 2015, 07:56:25 pm
content: Quote from: atferrari on April 24, 2015, 11:31:44 amTill 4 years ago I barely ever traveled outside of this small country. And felt that will barely travel ever. Turned out that now it feels that something not being right if I didn't travel 1000-8000 kilometers away from home this month. So, you never know.

author: atferrari
author_rank: Frequent Contributor
timestamp: April 25, 2015, 11:21:24 am
content: Quote from: wraper on April 24, 2015, 07:56:25 pmMay I know, doing what? Tourism?

author: SeanB
author_rank: Super Contributor
timestamp: April 25, 2015, 11:37:19 am
content: Probably works for one of the engineering firms based in Latvia, where you have a low cost of living and good education. Companies like Axia come to mind.

author: atferrari
author_rank: Frequent Contributor
timestamp: April 25, 2015, 11:44:02 am
content: Quote from: Galenbo on April 24, 2015, 07:55:53 amI have no idea what an answer like that looks.Time ago, under a friendly NDA agreement, I was allowed to peek into a service manual of an instrument produced in Switzerland.The principle was a microprocessor triggering two synchronized actions:a) a modulated laser emision going to the target (reflector located at the point of interest) and then hitting a sensor after bouncing back.b) a super stable internal optical system where an emission run continuously along a path until stopped when the reflected emission hit the in sensor. Path's length is accurately known.TOF/2 (half of the time it takes to go and back) was compared (divided) by the runs' equivalent time. I recall an exterior air's temperature correction being applied somewhere to make it valid.I cannot recall precision or repeatablity but stringent requiriments for people servicing them.To me it seemed extremely convoluted but I was not given the chance to ask for details. Just like why not simply measuring time. Is suspect I didn't grasp some important basic details.

author: Marco
author_rank: Super Contributor
timestamp: April 25, 2015, 02:21:25 pm
content: Detecting an amplitude modulated wave and doing phase comparison with a reference wave is much easier to do to a high precision than measuring the ToF of a single pulse. Only if you need very fast measurements will you use direct time of flight.I ran into what was basically a design study for a commercial distance meter a while back, but I can't find the page any more :/

author: atferrari
author_rank: Frequent Contributor
timestamp: April 25, 2015, 04:36:11 pm
content: Quote from: Marco on April 25, 2015, 02:21:25 pmThanks for the clarification. It makes sense then.

author: Dago
author_rank: Frequent Contributor
timestamp: April 26, 2015, 06:45:02 am
content: They are a type of an interferometerhttp://en.wikipedia.org/wiki/Interferometry

author: helius
author_rank: Super Contributor
timestamp: April 26, 2015, 10:41:01 pm
content: This type of optical setup can also be used as a gyroscope:http://en.wikipedia.org/wiki/Sagnac_effect

author: wraper
author_rank: Unknown
timestamp: April 27, 2015, 12:29:16 pm
content: Quote from: atferrari on April 25, 2015, 11:21:24 amFreaking damn job

author: Marco
author_rank: Super Contributor
timestamp: April 27, 2015, 03:14:42 pm
content: Maybe once we need to measure the size of our rooms in nm they'll start using interferometry.

author: Galenbo
author_rank: Super Contributor
timestamp: April 27, 2015, 04:11:33 pm
content: Really nice answers here.What surprised me a lot the last years, it that such things are sold now very cheap for the given precision.And it works. All the time.

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 28, 2015, 09:13:19 am
content: Quote from: mojo-chan on April 28, 2015, 09:02:17 amMy car has what's called "Adaptive cruise control", it measures the distance to the car in front and lowers the speed if it comes too close (Settable in 0.5 seconds steps, minimum 1 second). I guess it is based on normal radar, but it is a bit hard to measure on the highway

author: DmitryL
author_rank: Regular Contributor
timestamp: April 28, 2015, 11:25:59 am
content: Quote from: mojo-chan on April 28, 2015, 09:02:17 amWhy ? What's wrong with a cheapish ultrasound sensors ? Does you parking require a millimeter precision and accuracy? And you'll probably need some scanning system, because these laser meters produce a beam ~1mm in diameter.Ah, btw, how do you talk with such sensor ? It has a proprietary ASIC.I attaching lasers to sharks works better!

author: Dago
author_rank: Frequent Contributor
timestamp: April 28, 2015, 12:02:59 pm
content: Quote from: DmitryL on April 28, 2015, 11:25:59 amAFAIK most of the parking sensors on new cars are radar based and not ultrasound based. Apparently getting the ultrasonic sensors to work reliably when they are covered with snow/mud/water is pretty hard.The radar ones are mostly on the 24 GHz band but the newest ones are starting to use the 77 GHz band.

author: VK5RC
author_rank: Unknown
timestamp: May 01, 2015, 12:30:43 am
content: Is there a typical radar frequency used by police? I had in mind approx 2GHz???

author: BAhmad
author_rank: Newbie
timestamp: May 01, 2015, 12:35:45 am
content: Quote from: VK5RC on May 01, 2015, 12:30:43 ami think they use relatively higher frequency round about 24 GHz or so older low range units may be at 10.6 GHz