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

Started by August 12, 2022
```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:
> > > > > > 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 ?
> > There is no point in measuring all 10,000 points all at once.
> 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

Yes, precisely, to have better relative positioning with multi-sensors.  However, there is no need to measure them all within E-9 second.
```
```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:
> > > > > > > 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 ?
> > > There is no point in measuring all 10,000 points all at once.
> > 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
> Yes, precisely, to have better relative positioning with multi-sensors. However, there is no need to measure them all within E-9 second.
-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
```
```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:
> > > > > > > > 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 ?
> > > > There is no point in measuring all 10,000 points all at once.
> > > 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
> > Yes, precisely, to have better relative positioning with multi-sensors. However, there is no need to measure them all within E-9 second.
> -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

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.
```
```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:
> > > > > > > > > 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 ?
> > > > > There is no point in measuring all 10,000 points all at once.
> > > > 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
> > > Yes, precisely, to have better relative positioning with multi-sensors. However, there is no need to measure them all within E-9 second.
> > -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
> 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.
-==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
```
```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:
> > > > > > > > > > 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 ?
> > > > > > There is no point in measuring all 10,000 points all at once.
> > > > > 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
> > > > Yes, precisely, to have better relative positioning with multi-sensors. However, there is no need to measure them all within E-9 second.
> > > -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
> > 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.
> -==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

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.
```
```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
```
```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.

```
```On Saturday, August 13, 2022 at 11:00:46 AM UTC+10, Ed Lee wrote:
> 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).

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
```
```On Friday, August 12, 2022 at 6:12:58 PM UTC-7, bill....@ieee.org wrote:
> On Saturday, August 13, 2022 at 11:00:46 AM UTC+10, Ed Lee wrote:
> > 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).
> 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 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.

"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
```
```On Saturday, August 13, 2022 at 11:19:41 AM UTC+10, Ed Lee wrote:
> On Friday, August 12, 2022 at 6:12:58 PM UTC-7, bill....@ieee.org wrote:
> > On Saturday, August 13, 2022 at 11:00:46 AM UTC+10, Ed Lee wrote:
> > > 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).
> > 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 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.
>
>
> "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

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
```