How laser rangefinder or laser distance meter work and what chip can measure Time of Flight ?

[a a]

what chip, clocked at what frequency, is used to measure Time of Flight of laser light at sucjh short time intervals ?

notjhing found on the internet

https://en.wikipedia.org/wiki/Time_of_flight

https://www.fullyinstrumented.com/how-a-laser-measure-works/

https://sciencing.com/ultrasonic-sensors-work-4947693.html

[a a]

"The computer chip in the LRF uses a high-speed digital clock to calculate the time taken to hit the target.

what is an operating frequency of the clock in LRF ?

[Ed Lee]

On Friday, August 12, 2022 at 3:23:57 AM UTC-7, a a wrote:
> On Friday, 12 August 2022 at 12:18:44 UTC+2, a a wrote:
> > what chip, clocked at what frequency, is used to measure Time of Flight of laser light at sucjh short time intervals ?

GHz ASIC
3E-9 second per meter

[TTman]

FPGA...I worked on one...


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[Ricky]

On Friday, August 12, 2022 at 12:06:42 PM UTC-4, TTman wrote:
> On 12/08/2022 14:46, Ed Lee wrote:
> > On Friday, August 12, 2022 at 3:23:57 AM UTC-7, a a wrote:
> >> On Friday, 12 August 2022 at 12:18:44 UTC+2, a a wrote:
> >>> what chip, clocked at what frequency, is used to measure Time of Flight of laser light at sucjh short time intervals ?
> >
> > GHz ASIC
> > 3E-9 second per meter
> >
> >
> FPGA...I worked on one...

I have one of the laser devices. It measures to a fraction of an inch. That would be an equivalent frequency of maybe 100 GHz which is a bit difficult, even inside an FPGA. Does this require multiple inputs with varying delays to define timing to a finer resolution than the clock period?

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Rick C.

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[a a]

On Friday, 12 August 2022 at 15:46:11 UTC+2, Ed Lee wrote:
> On Friday, August 12, 2022 at 3:23:57 AM UTC-7, a a wrote:
> > On Friday, 12 August 2022 at 12:18:44 UTC+2, a a wrote:

> > > what chip, clocked at what frequency, is used to measure Time of Flight of laser light at such short time intervals ?

> GHz ASIC
> 3E-9 second per meter

c = 299 792 458 m/s > >>> c = 300 000 000 m/s

3E-9 s/m x 300 000 000 m/s = 0.9

ok
but for 1 cm resolution
we need 100 x faster clock

and for parallel analysis of point cloud 100 x 100
we need 100 x 100 faster clock

could you explain ?

[a a]

thank you Ricky
since iPhone claims Lidar in smartphone and parallel distance array calculation on-the-fly

For 1cm resolution 10 GHz single point
turns into 100 x 100 x 10 GHz clock frequency
for 100 points x 100 points array

[Ed Lee]

On Friday, August 12, 2022 at 9:06:42 AM UTC-7, TTman wrote:
> On 12/08/2022 14:46, Ed Lee wrote:
> > On Friday, August 12, 2022 at 3:23:57 AM UTC-7, a a wrote:
> >> On Friday, 12 August 2022 at 12:18:44 UTC+2, a a wrote:
> >>> what chip, clocked at what frequency, is used to measure Time of Flight of laser light at sucjh short time intervals ?
> >
> > GHz ASIC
> > 3E-9 second per meter
> >
> >
> FPGA...I worked on one...

Too slow. I have only seen a few hundred MHz FPGA.

[Ed Lee]

There is no point in measuring all 10,000 points all at once.

[a a]

so do you suggest,
what is marketed by iPhone and called Lidar in smartphone,
is a single point Laser Range Meter functionality ?

If you are correct, so why do they present 2D laser scanner functionality on images ?

Single point laser Lidar requires rotating head to work

\so some kind od mechanics is involved

[Ed Lee]

Yes, precisely, to have better relative positioning with multi-sensors. However, there is no need to measure them all within E-9 second.

[a a]

-E-9 second cloc k is for 1m resolution
for 1 cm resolution
you need
E-9 * 10-2 second clock

but we still discuss a single-point operation

[Ed Lee]

With 5GHz (close to current fab cap) hardware counters, we can count pulses to the same point 100 times. If we get 25 pulses of 1 meter and 75 pulses of 1.1 meter, we can guess that the distance is close to 1.025 meters.

Give me $100,000 and i can build you the chip to prove it.

[a a]

-==c = 299 792 458 m/s > >>> c = 300 000 000 m/s

-===3E-9 s/m x 300 000 000 m/s = 0.9

300 000 000 m/s = 100 * 300 000 000 cm/s

= 30 000 000 000 cm/s

so you need 30 GHz clock x 2 to get 1 cm resolution for a single point

ok, for 1 m distant object
300 MHz x 2 clock can do the job

but if you need mobile laser range meter to scan objects on the fly, to act as 2D scanner,
1 cm counts and makes the difference

[Ed Lee]

3GHz (reasonable clock) for 10cm resolution.

> ok, for 1 m distant object
> 300 MHz x 2 clock can do the job
>
> but if you need mobile laser range meter to scan objects on the fly, to act as 2D scanner,
> 1 cm counts and makes the difference

https://en.wikipedia.org/wiki/Oversampling
for higher resolution.

[Anthony William Sloman]

On Saturday, August 13, 2022 at 9:10:07 AM UTC+10, Ed Lee wrote:
> On Friday, August 12, 2022 at 3:40:38 PM UTC-7, a a wrote:
> > On Friday, 12 August 2022 at 23:58:11 UTC+2, Ed Lee wrote:
> > > On Friday, August 12, 2022 at 2:31:31 PM UTC-7, a a wrote:
> > > > On Friday, 12 August 2022 at 22:37:28 UTC+2, Ed Lee wrote:
> > > > > On Friday, August 12, 2022 at 1:06:35 PM UTC-7, a a wrote:
> > > > > > On Friday, 12 August 2022 at 21:55:26 UTC+2, Ed Lee wrote:
> > > > > > > On Friday, August 12, 2022 at 11:45:18 AM UTC-7, a a wrote:
> > > > > > > > On Friday, 12 August 2022 at 15:46:11 UTC+2, Ed Lee wrote:
> > > > > > > > > On Friday, August 12, 2022 at 3:23:57 AM UTC-7, a a wrote:
> > > > > > > > > > On Friday, 12 August 2022 at 12:18:44 UTC+2, a a wrote:

<snipped uninformed comment>

https://en.wikipedia.org/wiki/Tellurometer

was the original wavelength-based range-finder, and it didn't send out a pulse and measure the time until it returned.

Measuring the phase shift along the path to the reflector and back is a more practical scheme.

--
Bill Sloman, Sydney

[Ed Lee]

On Friday, August 12, 2022 at 5:52:21 PM UTC-7, bill....@ieee.org wrote:
> On Saturday, August 13, 2022 at 9:10:07 AM UTC+10, Ed Lee wrote:
> > On Friday, August 12, 2022 at 3:40:38 PM UTC-7, a a wrote:
> > > On Friday, 12 August 2022 at 23:58:11 UTC+2, Ed Lee wrote:
> > > > On Friday, August 12, 2022 at 2:31:31 PM UTC-7, a a wrote:
> > > > > On Friday, 12 August 2022 at 22:37:28 UTC+2, Ed Lee wrote:
> > > > > > On Friday, August 12, 2022 at 1:06:35 PM UTC-7, a a wrote:
> > > > > > > On Friday, 12 August 2022 at 21:55:26 UTC+2, Ed Lee wrote:
> > > > > > > > On Friday, August 12, 2022 at 11:45:18 AM UTC-7, a a wrote:
> > > > > > > > > On Friday, 12 August 2022 at 15:46:11 UTC+2, Ed Lee wrote:
> > > > > > > > > > On Friday, August 12, 2022 at 3:23:57 AM UTC-7, a a wrote:
> > > > > > > > > > > On Friday, 12 August 2022 at 12:18:44 UTC+2, a a wrote:
> <snipped uninformed comment>

Yes, we should.

>
> https://en.wikipedia.org/wiki/Tellurometer
>
> was the original wavelength-based range-finder, and it didn't send out a pulse and measure the time until it returned.
>
> Measuring the phase shift along the path to the reflector and back is a more practical scheme.

This is talking about microwave. We are talking about lightwave (laser).

[Anthony William Sloman]

Both are electromagnetic waves and phase shift works for both. HP's laser interferomenter certainly measured to small fractions of the helium-neon laser wavelength (which I used to know to ten significant digits when we were designing one in).

The bottom of the Tellurometer page offers a link to a page on laser rangefinders. I haven't clicked on it in years. Maybe you should.

--
Bill Sloman, Sydney

[Ed Lee]

The difference is the much higher frequencies of lightwave vs. microwave.

> The bottom of the Tellurometer page offers a link to a page on laser rangefinders. I haven't clicked on it in years. Maybe you should.

Yes, you should listen to your own advice:

"The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender."

https://en.wikipedia.org/wiki/Laser_rangefinder

[Anthony William Sloman]

It isn't all that accurate. The other techniques can do better, but they do tend to be more expensive, as more accurate instruments can afford to be.

"Multiple frequency phase-shift - this measures the phase shift of multiple frequencies on reflection then solves some simultaneous equations to give a final measure.

Interferometry - the most accurate and most useful technique for measuring changes in distance rather than absolute distances."

--
Bill Sloman, Sydney

[whit3rd]

On Friday, August 12, 2022 at 6:19:41 PM UTC-7, Ed Lee wrote:

> "The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in a narrow beam towards the object and measuring the time taken by the pulse to be reflected off the target and returned to the sender."
>
> https://en.wikipedia.org/wiki/Laser_rangefinder

Yeah, for rangefinding the corner-cube reflector left on Luna, that simple scheme's workable. For shorter
distances, though, modulation of an FM burst, and detection of the interference of outgoing
and incoming to generate the difference frequency, is the most practical way of doing it.

I'm pretty sure my Hot Wheels radar gun isn't "measuring the time" with a digital clock, directly.

[Ed Lee]

Yes, Bill and you are bring up all possible ways to measure distance. But OP specifically asked for digital processing of laser range-finder.

[whit3rd]

Do you have an objection? A "laser range finder" is a broad class of instruments, with no particular
'digital processing' specificity, and digital processing is not, in the general case, superior
or practical in the pulse/clock-and-count scenario, so we discuss others.

[Anthony William Sloman]

But the OP is a a, and he's time-wasting half-wit. Nobody sane is going to spend time on responding to him. You are the sucker who did.

--
Bill Sloman, Sydney

[Ed Lee]

I am just responding to OP direct question of:

[Ed Lee]

It's a rare on-topic case related to electronics and worth answering.

[Mike Monett]

I believe most short distance laser rangefinders use a simple capacitive
charging circuit with the outoing pulse as the start and the reflection as
the terminator. The capacitor voltage measures the distance. An example is
a CDN$35 unit from Amazon Canada:

https://www.amazon.ca/Distance-Handheld-Portable-Precision-
Apartment/dp/B08Y96T271/

Other methods perform interferometric distance measurements. It is the most
precise and fastest distance measurement method, but interferometric
rangefinders are expensive and susceptible to damage. This makes them
unreliable in the field.




--
MRM

[Anthony William Sloman]

Not when a a asks the question.

--
Bill Sloman, Sydney

[Ricky]

What 100 x 100 point array???

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Rick C.

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[TTman]

On 12/08/2022 17:48, Ricky wrote:
> On Friday, August 12, 2022 at 12:06:42 PM UTC-4, TTman wrote:
>> On 12/08/2022 14:46, Ed Lee wrote:
>>> On Friday, August 12, 2022 at 3:23:57 AM UTC-7, a a wrote:
>>>> On Friday, 12 August 2022 at 12:18:44 UTC+2, a a wrote:
>>>>> what chip, clocked at what frequency, is used to measure Time of Flight of laser light at sucjh short time intervals ?
>>>
>>> GHz ASIC
>>> 3E-9 second per meter
>>>
>>>
>> FPGA...I worked on one...
>
> I have one of the laser devices. It measures to a fraction of an inch. That would be an equivalent frequency of maybe 100 GHz which is a bit difficult, even inside an FPGA. Does this require multiple inputs with varying delays to define timing to a finer resolution than the clock period?
>

How much did you pay for it?


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[TTman]

Enough to get time of flight... My test gear used Atmel running at 20MHz
to get +/- 50nS resolution, checking the FPGA output and my test gear
simulating the return pulse and seeing the answer in the test kit,
provided by the FPGA. Test pulse was designed to simulate 10Km out and back.

[Ricky]

I don't recall exactly, but it was under $50 or I wouldn't have bought it.

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[Cydrome Leader]

Love all this retarded math and units.

Here's the short story. Light travels about 1 foot per nanosecond. If you're measuring reflections the
distance traveled is twice between you and the target, so this in essense doubles your resolution. A 1GHz
clock should be fine for measuring in increments of fractions of a foot.

[Cydrome Leader]

Is it 10 millionths of an in per "ring" on a optical flat with the blue/krypton light when measuring
surface flatness? It's pretty amazing you can actually see such levels of interference. Autocollimators are
pretty fascinating devices too.

[Cydrome Leader]

LM555

[John Larkin]

Fast clocks are power hogs. There are better ways to measure
nanoseconds.

[a a]

Very cheap unique wavelength light for using with Optical Flats... Using a 532nm. 50mw LED laser
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Pierre's Garage
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In this video, I’ll be showing as a proof of concept how to make a real cheap, but, quite reliable light source using a 50 mw. LED pointer with a fixed wavelength in order to use with Optical Flats.
A Xenon or any laboratory type fixed wavelength is quite out of reach for any hobbyist or small shop owner, this option of using a LED with a known wavelength isn’t pretending to be as precise as a multi thousand of dollars instrument, but, will allow for reasonably accurate measurements in non-critical situations.
The fixed wavelength allows the Optical Flats to create a pattern by reflection and diffraction on a polished surface, the goal is to measure the flatness of that surface, and, knowing the wavelength we’re being able to quantify the amount of irregularity if there is any.

Please take note that I'm using the term laser for the light emitting diodes, in fact a real laser is a very different technology, it's a bad habit to call a LED a laser diode...

https://youtu.be/xSYl7q6yKPU

[Ricky]

How about fractions of an inch, like a tenth?

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[Phil Hobbs]

The usual method is a time-to-amplitude converter.

Cheers

Phil Hobbs

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Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[Cydrome Leader]

You better ask the trillion of centimeters per second folks to do the math for you in that.

[Michael Kellett]

On 13/08/2022 18:42, Phil Hobbs wrote:

>
> The usual method is a time-to-amplitude converter.
>
> Cheers
>
> Phil Hobbs
>

TI make some nice chips, you can even buy them:

TDC7201, TDC7200

Resolution: 55 ps
• Standard Deviation: 35 ps
• Measurement Range:
– Mode 1: 12 ns to 500 ns
– Mode 2: 250 ns to 8 ms

It needs a 16MHz input clock, work it out before you look at the data sheet.

MK

[jla...@highlandsniptechnology.com]

One way is to use a simple analog time stretcher and a
modest-frequency counter.

[a a]

just watched video

kinect - sensor IR projection

https://youtu.be/MlTf0yYQjSg?t=43

let me know if the projected IR points cloud is made of static preset points
and what is a role of the pattern ?

Can theory behing Kinect be turned into large scale indoor 3D scanner,
replacing lenses in ca,meras,
moving IR projector far from VGA camera to read depth at large distance ?

Can IR pattern projected be replaced by another, higher IR power/ higher resolution pattern ?

[Ed Lee]

Nobody's talking, so i will.

This IR stuff has nothing to do with measuring distance, unless you have to do it in the dark. If you are asking about 3D distance mapping, you have to enable it one at a time, even if you have a 100x100 laser matrix.

As someone pointed out, you can buy existing chips. But if you are integrating it into laser matrix, you might have to build your own hardware counters and routing circuits. 5GHz counters can handle at least an inch or couple cm resolution, before oversampling. You can turn off most of the circuit except for fraction of a second, in order to save power.

[a a]

thank you
I need to learn more about laser IR projector in Kinect

"The Kinect infrared sensor sees the sofa as a large number of tiny dots. The Kinect sensor constantly projects these dots over the area in its view. If you want to view the dots yourself, it’s actually very easy; all you need is a video camera or camcorder that has a night vision mode. A camera in night vision mode is sensitive to the infrared light spectrum that the Kinect distance sensor uses.

Figure 1-6, for example, was taken in complete darkness, with the sofa lit only by the Kinect. The infrared sensor in the Kinect is fitted with a filter that keeps out ordinary light, which is how it can see just the infrared dots, even in a brightly lit room. The dots are arranged in a pseudo-random pattern that is hardwired into the sensor. You can see some of the pattern in Figure 1-7.


https://www.microsoftpressstore.com/articles/article.aspx?p=2201646

I need to know how pseudo-random pattern of dots is generated by IR laser projector
Resolution is not low

https://www.microsoftpressstore.com/content/images/chap1_9780735663961/elementLinks/httpatomoreillycomsourcemspimages1239382.jpg

dots are not lined up so it seems to me some laser optics / lens is involved

- single laser diode + lens with drilled pattern ?

"pseudo-random pattern that is hardwired into the sensor.

not sure what they mean, since to have pseudo-random[pattern hardwired into the sensor
you need to get (x,y) coordinates for every single point

I recall another algorithm to generate 3D depth images by moving camera, based on blur effect,
since closer objects move faster in the plane perpendicular to the camera axis
so if we stack a number of images/frames together, we get blur effect for the closer objects to intensify.

----
Kinect`s infrared projector in action
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Vladimir Seregin
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Video recorded with an regular webcam without IR filter on it.
https://www.youtube.com/watch?v=brnIty7mh2Q

since every single dot is clearly visible in regular HD webcam
so a number of dots projected must be below HD resolution

--
there is a number of web links but they refer to IR camera resolution only

640 x 480
The Kinect sensor returns 16 bits perpixel infrared data with a resolution of 640 x 480as an color image format, and it supports up to30 FPS. Following are the couple of images ( taken in a complete dark room) that captures from IR stream data.
Get the IR Stream and control the IR Emitter – Kinect for Windows SDK ...
abhijitjana.net/2013/01/11/get-the-ir-stream-and-control-the-ir-emitter-kinect-for-windows-sdk/
abhijitjana.net/2013/01/11/get-the-ir-stream-and-control-the-ir-emitter-kinect-for …


Get the IR Stream and control the IR Emitter – Kinect for Windows SDK

https://abhijitjana.net/2013/01/11/get-the-ir-stream-and-control-the-ir-emitter-kinect-for-windows-sdk/#:~:text=The%20Kinect%20sensor%20returns%2016%20bits%20perpixel%20infrared,dark%20room%29%20that%20captures%20from%20IR%20stream%20data.

[a a]

from
https://www.dfki.de/fileadmin/user_upload/import/8767_wasenmuller2016comparison.pdf

The Kinect v1 measures the depth with the Pattern Projection principle, where
a known infrared pattern is projected into the scene and out of its distortion
the depth is computed. The Kinect v2 contains a Time-of-Flight (ToF) camera
and determines the depth by measuring the time emitted light takes from the
camera to the object and back. Therefore, it constantly emits infrared light with
modulated waves and detects the shifted phase of the returning light [17, 18]. In
the following, we refer to both cameras (Pattern Projection and ToF) as depth
camera

not sure how ToF can be live implemented into 2D image analysis