Does anyone know how these LiDARs work?
Patrick, Fri Aug 12 2011, 04:40AMFrom my friends at the IARC, who are almost all using this device ->
(From the BNM-IT India team power point presentation.)
Im thinking of using the URG-04LX-UG01 simple one (1,200 USD), but the Michigan team was using the 6,500 USD one.
Do these devices use phase relationships to determine distance? or time of flight? If they use time of flight then the minimum useful range is 20mm, in 20mm the speed of light would mean very short emission, detection and a very fast clock.
I really think they use TDOA like the RF foxhunts with the non-moving electrically scanned radio antennas that amatures build.
Re: Does anyone know how these LiDARs work?
Bjørn, Fri Aug 12 2011, 05:59AM
A common method is to modulate the laser (often at several frequencies) and record the returning signal. From the different phase shifts at different frequencies you can calculate the distance. The webpages for URG-04LX-UG01 suggests that is what they do.
I have a $100 pocket range finder that has a resolution of 1 mm with a range of 50 m that uses that method.
Bjørn, Fri Aug 12 2011, 05:59AM
A common method is to modulate the laser (often at several frequencies) and record the returning signal. From the different phase shifts at different frequencies you can calculate the distance. The webpages for URG-04LX-UG01 suggests that is what they do.
I have a $100 pocket range finder that has a resolution of 1 mm with a range of 50 m that uses that method.
Re: Does anyone know how these LiDARs work?
Patrick, Fri Aug 12 2011, 01:12PM
We are all having problems with the data rate on the $1200 one being about 12 hertz for the $6,500 they are getting 40 Hertz, i think the electric motor is the slowest part being mechanical, 2400 rpm, so maybe i could mod a pocket one like yours.
Patrick, Fri Aug 12 2011, 01:12PM
Bjørn wrote ...
A common method is to modulate the laser (often at several frequencies) and record the returning signal. From the different phase shifts at different frequencies you can calculate the distance. The webpages for URG-04LX-UG01 suggests that is what they do.
I have a $100 pocket range finder that has a resolution of 1 mm with a range of 50 m that uses that method.
Oooo... thats just the explanation i needed. Bjorn, which lidar do you have?A common method is to modulate the laser (often at several frequencies) and record the returning signal. From the different phase shifts at different frequencies you can calculate the distance. The webpages for URG-04LX-UG01 suggests that is what they do.
I have a $100 pocket range finder that has a resolution of 1 mm with a range of 50 m that uses that method.
We are all having problems with the data rate on the $1200 one being about 12 hertz for the $6,500 they are getting 40 Hertz, i think the electric motor is the slowest part being mechanical, 2400 rpm, so maybe i could mod a pocket one like yours.
Re: Does anyone know how these LiDARs work?
Carbon_Rod, Fri Aug 12 2011, 03:40PM
SLAM + URG driver:
You can find the 1cm resolution @ 5m one for under $3500, but note they are a fragile device originally intended for use as factory light curtains.
The Kinect at $100 for both video + LADAR-like scanning is unbeatable in terms of price:
Cheers,
Carbon_Rod, Fri Aug 12 2011, 03:40PM
SLAM + URG driver:
You can find the 1cm resolution @ 5m one for under $3500, but note they are a fragile device originally intended for use as factory light curtains.
The Kinect at $100 for both video + LADAR-like scanning is unbeatable in terms of price:
Cheers,
Re: Does anyone know how these LiDARs work?
Patrick, Fri Aug 12 2011, 04:01PM
Patrick, Fri Aug 12 2011, 04:01PM
Carbon_Rod wrote ...
SLAM + URG driver:
You can find the 1cm resolution @ 5m one for under $3500, but note they are a fragile device originally intended for use as factory light curtains.
So far they've all survived really bad crashes multiple times, when the rest of the machine went to pieces. There are 6 teams using them and they've all crashed but not had a Lidar fail yet.SLAM + URG driver:
You can find the 1cm resolution @ 5m one for under $3500, but note they are a fragile device originally intended for use as factory light curtains.
Carbon_Rod wrote ...
The Kinect at $100 for both video + LADAR-like scanning is unbeatable in terms of price:
Cheers,
But so far the Dubai and USC teams have the most experience with the Kinect and they say it cant see or generate useful data past 30 inches or so (for navigation, LiDAR), dont know what you all think, but thats what they said. The Dubai team was going to use both, but wanted to use the kinect only if possible.The Kinect at $100 for both video + LADAR-like scanning is unbeatable in terms of price:
Cheers,
Re: Does anyone know how these LiDARs work?
PSCG, Fri Aug 12 2011, 06:05PM
If you want more information about Lidars, check Sam's Laser Faq - Laser Insruments and Applications. He has put a lot of work about them (and it seems that isn't difficult to construct something like this ether).
PSCG, Fri Aug 12 2011, 06:05PM
If you want more information about Lidars, check Sam's Laser Faq - Laser Insruments and Applications. He has put a lot of work about them (and it seems that isn't difficult to construct something like this ether).
Re: Does anyone know how these LiDARs work?
Patrick, Fri Aug 12 2011, 08:20PM
Patrick, Fri Aug 12 2011, 08:20PM
PSCG wrote ...
If you want more information about Lidars, check Sam's Laser Faq - Laser Insruments and Applications. He has put a lot of work about them (and it seems that isn't difficult to construct something like this ether).
TY PSCG, i really need a more optimal solution, so ill look at sams stuff.If you want more information about Lidars, check Sam's Laser Faq - Laser Insruments and Applications. He has put a lot of work about them (and it seems that isn't difficult to construct something like this ether).
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Fri Aug 12 2011, 08:31PM
If you just record the returning signal you still have the problem of needing to detect minute time of flight for high resolution (~3 ps for 1 mm resolution). The modulation only helps with aliasing.
Pinky's Brain, Fri Aug 12 2011, 08:31PM
wrote ...
A common method is to modulate the laser (often at several frequencies) and record the returning signal.
I assume you mean record the interference of the returning light with the (attenuated) original?A common method is to modulate the laser (often at several frequencies) and record the returning signal.
If you just record the returning signal you still have the problem of needing to detect minute time of flight for high resolution (~3 ps for 1 mm resolution). The modulation only helps with aliasing.
Re: Does anyone know how these LiDARs work?
Patrick, Fri Aug 12 2011, 10:05PM
I think I wil use the one called phase difference or some such name they call it.
Patrick, Fri Aug 12 2011, 10:05PM
Pinky's Brain wrote ...
If you just record the returning signal you still have the problem of needing to detect minute time of flight for high resolution (~3 ps for 1 mm resolution). The modulation only helps with aliasing.
wrote ...
A common method is to modulate the laser (often at several frequencies) and record the returning signal.
I assume you mean record the interference of the returning light with the (attenuated) original?A common method is to modulate the laser (often at several frequencies) and record the returning signal.
If you just record the returning signal you still have the problem of needing to detect minute time of flight for high resolution (~3 ps for 1 mm resolution). The modulation only helps with aliasing.
I think I wil use the one called phase difference or some such name they call it.
Re: Does anyone know how these LiDARs work?
Bjørn, Fri Aug 12 2011, 10:24PM
Yes, it is the phase difference that is recorded.
I have one of the Bosch units and it is very accurate but the refreshrate is about 3 Hz so it would be very slow for this use.
Bjørn, Fri Aug 12 2011, 10:24PM
Yes, it is the phase difference that is recorded.
I have one of the Bosch units and it is very accurate but the refreshrate is about 3 Hz so it would be very slow for this use.
Re: Does anyone know how these LiDARs work?
Patrick, Fri Aug 12 2011, 10:37PM
Patrick, Fri Aug 12 2011, 10:37PM
Bjørn wrote ...
Yes, it is the phase difference that is recorded.
I have one of the Bosch units and it is very accurate but the refreshrate is about 3 Hz so it would be very slow for this use.
Yes this is the problem for our flying machines, the refresh rate (even at 40 Hertz) is just to slow. We also need them to weigh about 200 grams or less. The Dubai team also said they were signal noisy at they're devices quoted 10-12 hertz rate. (They only averaged in the real-world flight environment 6-8 hertz of useful signal. )Yes, it is the phase difference that is recorded.
I have one of the Bosch units and it is very accurate but the refreshrate is about 3 Hz so it would be very slow for this use.
Re: Does anyone know how these LiDARs work?
Carbon_Rod, Sat Aug 13 2011, 04:15AM
@Patrick
Hokuyo URGs:
* I seem to recall the scan rates can be set higher (see open driver for more details)
* A spinning prism & lenses sit on top of the sensor internally, but they are still unreliable outdoors
* Power consumption after spin-up is under a few hundred milliamps
* The surface being scanned can create "noise" (mirrors/glass etc. are fun), but the system noted above has some very nice filtering algorithms.
* IIRC they are not eye-safe at close proximity
Unlike several other manufacturers, Hokuyo will not support university student research initiatives.
You may have to get funding for your team with the help of your institution's faculty members.
Additionally, you may want to get someone to contact these people for you:
Cheers,
Carbon_Rod, Sat Aug 13 2011, 04:15AM
@Patrick
Hokuyo URGs:
* I seem to recall the scan rates can be set higher (see open driver for more details)
* A spinning prism & lenses sit on top of the sensor internally, but they are still unreliable outdoors
* Power consumption after spin-up is under a few hundred milliamps
* The surface being scanned can create "noise" (mirrors/glass etc. are fun), but the system noted above has some very nice filtering algorithms.
* IIRC they are not eye-safe at close proximity
Unlike several other manufacturers, Hokuyo will not support university student research initiatives.
You may have to get funding for your team with the help of your institution's faculty members.
Additionally, you may want to get someone to contact these people for you:
Cheers,
Re: Does anyone know how these LiDARs work?
Patrick, Sat Aug 13 2011, 09:34AM
We were all standing at close range, so thats kinda scary.
its good to know about my college staff/hokuyo.
Patrick, Sat Aug 13 2011, 09:34AM
Carbon_Rod wrote ...
@Patrick
Hokuyo URGs:
* I seem to recall the scan rates can be set higher (see open driver for more details)
* A spinning prism & lenses sit on top of the sensor internally, but they are still unreliable outdoors
* Power consumption after spin-up is under a few hundred milliamps
* The surface being scanned can create "noise" (mirrors/glass etc. are fun), but the system noted above has some very nice filtering algorithms.
* IIRC they are not eye-safe at close proximity
Unlike several other manufacturers, Hokuyo will not support university student research initiatives.
You may have to get funding for your team with the help of your institution's faculty members.
Additionally, you may want to get someone to contact these people for you:
Cheers,
we arnt outdoors, were in a arena with roof. about the noise, the staff of Iarc used foil tape and foil foam board to give us so difficulty.@Patrick
Hokuyo URGs:
* I seem to recall the scan rates can be set higher (see open driver for more details)
* A spinning prism & lenses sit on top of the sensor internally, but they are still unreliable outdoors
* Power consumption after spin-up is under a few hundred milliamps
* The surface being scanned can create "noise" (mirrors/glass etc. are fun), but the system noted above has some very nice filtering algorithms.
* IIRC they are not eye-safe at close proximity
Unlike several other manufacturers, Hokuyo will not support university student research initiatives.
You may have to get funding for your team with the help of your institution's faculty members.
Additionally, you may want to get someone to contact these people for you:
Cheers,
We were all standing at close range, so thats kinda scary.
its good to know about my college staff/hokuyo.
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Sat Aug 13 2011, 04:23PM
Just to be clear ... what you do is modulate the laser with say white noise (or a frequency swept signal) and then just correlate the received signal with the original to determine the phase difference of the modulating signal? (Rather than of the light itself, which becomes unmeasurable without some very high coherence length laser.)
Pinky's Brain, Sat Aug 13 2011, 04:23PM
Just to be clear ... what you do is modulate the laser with say white noise (or a frequency swept signal) and then just correlate the received signal with the original to determine the phase difference of the modulating signal? (Rather than of the light itself, which becomes unmeasurable without some very high coherence length laser.)
Re: Does anyone know how these LiDARs work?
Patrick, Sat Aug 13 2011, 07:11PM
Patrick, Sat Aug 13 2011, 07:11PM
Pinky's Brain wrote ...
Just to be clear ... what you do is modulate the laser with say white noise (or a frequency swept signal) and then just correlate the received signal with the original to determine the phase difference of the modulating signal? (Rather than of the light itself, which becomes unmeasurable without some very high coherence length laser.)
Can anyone show a gragh or picture of how this is done? Im trying to wrap my mind around it, but this is hard to get. (Other websites seem to show "cartoonish" explanations of TOF only.)Just to be clear ... what you do is modulate the laser with say white noise (or a frequency swept signal) and then just correlate the received signal with the original to determine the phase difference of the modulating signal? (Rather than of the light itself, which becomes unmeasurable without some very high coherence length laser.)
Re: Does anyone know how these LiDARs work?
Mattski, Sat Aug 13 2011, 07:54PM
Hope that makes sense.
Mattski, Sat Aug 13 2011, 07:54PM
Patrick wrote ...
This is more or less what's going on in such a system. The original signal could be truly random or it could be a pseudo-random signal which has been chosen so that its self-correlation is very small when it is offset a small amount, and very large when it lines up exactly with itself.Pinky's Brain wrote ...
Just to be clear ... what you do is modulate the laser with say white noise (or a frequency swept signal) and then just correlate the received signal with the original to determine the phase difference of the modulating signal? (Rather than of the light itself, which becomes unmeasurable without some very high coherence length laser.)
Can anyone show a gragh or picture of how this is done? Im trying to wrap my mind around it, but this is hard to get. (Other websites seem to show "cartoonish" explanations of TOF only.)Just to be clear ... what you do is modulate the laser with say white noise (or a frequency swept signal) and then just correlate the received signal with the original to determine the phase difference of the modulating signal? (Rather than of the light itself, which becomes unmeasurable without some very high coherence length laser.)
Hope that makes sense.
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Sat Aug 13 2011, 08:19PM
They do it with a sweep, although personally I'd just use a repeated block of white noise and FFT based correlation followed by interpolation around the peak to get subsample accurate delay.
TOF usually refers to the use of really fast shutters to cut off pulses to determine distance by how much of a returned pulse arrives at a CCD before it cuts off by the shutter (it's compared against the received light from pulse not cut off by the shutter at all to compensate for surface reflectance). A very interesting method, but not really doable on a budget because of the shutter.
Pinky's Brain, Sat Aug 13 2011, 08:19PM
They do it with a sweep, although personally I'd just use a repeated block of white noise and FFT based correlation followed by interpolation around the peak to get subsample accurate delay.
TOF usually refers to the use of really fast shutters to cut off pulses to determine distance by how much of a returned pulse arrives at a CCD before it cuts off by the shutter (it's compared against the received light from pulse not cut off by the shutter at all to compensate for surface reflectance). A very interesting method, but not really doable on a budget because of the shutter.
Re: Does anyone know how these LiDARs work?
Patrick, Tue Nov 13 2012, 06:16AM
this site explains it well: ->
i wonder if a primative lidar could be made using a CD/DVD head... those have a laser, beam splitter and matched detector all in the same device, though the lens would probably need to be removed.
I presume that this is only good for 2pi or less of the beat frequency, or else it repeats on intervals.
here is the Neato XV-11 one -> (it uses triangulation)
Patrick, Tue Nov 13 2012, 06:16AM
this site explains it well: ->
The sensor measures the phase shift between the transmitted and reflected signals. The picture shows how this technique can be used to measure distance. The wavelength of the modulating signal obeys the equation:
c = f ∙ τ
where c is the speed of light and f the modulating frequency and Ï„ the known modulating wavelength.
The total distance D' covered by the emitted light is:
D' = B + 2A = B + (θ * τ) / 2π[not sure what "n" is though?]
where A is the measured distance. B is the distance from the phase measurement unit. The required distance D, between the beam splitter and the target, is therefore given by
D = τ * θ / 4π
where θ is the electronically measured phase difference between the transmitted and reflected light beams.
It can be shown that the range is inversely proportional to the square of the received signal amplitude, directly affecting the sensor’s accuracy.
i wonder if a primative lidar could be made using a CD/DVD head... those have a laser, beam splitter and matched detector all in the same device, though the lens would probably need to be removed.
I presume that this is only good for 2pi or less of the beat frequency, or else it repeats on intervals.
here is the Neato XV-11 one ->
(it uses triangulation)Re: Does anyone know how these LiDARs work?
Pinky's Brain, Tue Nov 13 2012, 07:43PM
I don't see the need for the beam splitter ... easier to just measure the return pulse slightly off axis. Here is a nice page showing how probably most the range finders work (hell of a lot cheaper than using an ADC) :
Pinky's Brain, Tue Nov 13 2012, 07:43PM
I don't see the need for the beam splitter ... easier to just measure the return pulse slightly off axis. Here is a nice page showing how probably most the range finders work (hell of a lot cheaper than using an ADC) :
Re: Does anyone know how these LiDARs work?
Patrick, Tue Nov 13 2012, 11:37PM
ive been told that the XV-11 neato lidar (wich uses a pixel PSD, and line laser) use slip rings to conduct the signals from the rotating head to the stationary base.
Panavision 2048 pixel sensor...
Patrick, Tue Nov 13 2012, 11:37PM
Pinky's Brain wrote ...
I don't see the need for the beam splitter ...
i think the splitter and emitter are meant to move so the rest doesnt have to.I don't see the need for the beam splitter ...
ive been told that the XV-11 neato lidar (wich uses a pixel PSD, and line laser) use slip rings to conduct the signals from the rotating head to the stationary base.
Panavision 2048 pixel sensor...
Re: Does anyone know how these LiDARs work?
2Spoons, Wed Nov 14 2012, 01:11AM
Another method modulates the laser with a chirp (frequency sweep). The transmit and receive frequencies are mixed in a multiplier and the difference frequency gives you a measure of the round trip time, based on the sweep rate.
2Spoons, Wed Nov 14 2012, 01:11AM
Another method modulates the laser with a chirp (frequency sweep). The transmit and receive frequencies are mixed in a multiplier and the difference frequency gives you a measure of the round trip time, based on the sweep rate.
Re: Does anyone know how these LiDARs work?
Patrick, Wed Nov 14 2012, 02:27AM
there would be so much demand for the neato type lidar, if somebody could figure out how to make it, supposedly it costs only $30 now, but they refuse to sell them, even as spare parts...
when i contacted Neato corp, they scofffed at me i copped a piss poor attitude, then quipped: " they come fully integrated from china in the vacuum cleaner itself..."
the color filter, panavision sensor, and optic lens are probably highly inetgrated, and thus could not just be thrown together with apparlently similar parts found on the web, i bet with my luck.
Patrick, Wed Nov 14 2012, 02:27AM
there would be so much demand for the neato type lidar, if somebody could figure out how to make it, supposedly it costs only $30 now, but they refuse to sell them, even as spare parts...
when i contacted Neato corp, they scofffed at me i copped a piss poor attitude, then quipped: " they come fully integrated from china in the vacuum cleaner itself..."
the color filter, panavision sensor, and optic lens are probably highly inetgrated, and thus could not just be thrown together with apparlently similar parts found on the web, i bet with my luck.
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Wed Nov 14 2012, 08:58PM
I think LIDAR is a bit of a misnomer for the triangulation methods ... I'd classify it as structured lighting.
Pinky's Brain, Wed Nov 14 2012, 08:58PM
I think LIDAR is a bit of a misnomer for the triangulation methods ... I'd classify it as structured lighting.
Re: Does anyone know how these LiDARs work?
Patrick, Wed Nov 14 2012, 09:44PM
Patrick, Wed Nov 14 2012, 09:44PM
Pinky's Brain wrote ...
I think LIDAR is a bit of a misnomer for the triangulation methods ... I'd classify it as structured lighting.
yes as would I...I think LIDAR is a bit of a misnomer for the triangulation methods ... I'd classify it as structured lighting.
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Mon Nov 19 2012, 04:22AM
I think you could build a high update rate laser range finder with an electronic component cost of around 30 bucks ... the single most expensive component being a PECL AND gate.
Pinky's Brain, Mon Nov 19 2012, 04:22AM
I think you could build a high update rate laser range finder with an electronic component cost of around 30 bucks ... the single most expensive component being a PECL AND gate.
Re: Does anyone know how these LiDARs work?
Patrick, Mon Nov 19 2012, 04:43AM
second, as you said the "structured light solution" is nice, it involves high speed, and no calculating burden.
third, the phase type SICK and URGs are slow (the 6,500US$ one is 30Hz, 270Degrees) the cheaper ones are 12 hertz of which about 6 hertz are usful signal.
Ive seen the fastest ones populate a real-time screen graphic, it was scary slow! considering they had a flying bot moving about needing real-time guidance.
Patrick, Mon Nov 19 2012, 04:43AM
Pinky's Brain wrote ...
I think you could build a high update rate laser range finder with an electronic component cost of around 30 bucks ... the single most expensive component being a PECL AND gate.
first, not sure what you mean ,Positive emitter couple logic gate?I think you could build a high update rate laser range finder with an electronic component cost of around 30 bucks ... the single most expensive component being a PECL AND gate.
second, as you said the "structured light solution" is nice, it involves high speed, and no calculating burden.
third, the phase type SICK and URGs are slow (the 6,500US$ one is 30Hz, 270Degrees) the cheaper ones are 12 hertz of which about 6 hertz are usful signal.
Ive seen the fastest ones populate a real-time screen graphic, it was scary slow! considering they had a flying bot moving about needing real-time guidance.
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Mon Nov 19 2012, 04:54AM
Ya, that PECL ... it's for determining the phase delay of a pulse train compared to a reference clock (together with an integrator).
In the end I think the phase delay measurement is too cheap component wise to bother with structured light ... both would require significant engineering effort any way.
Pinky's Brain, Mon Nov 19 2012, 04:54AM
Ya, that PECL ... it's for determining the phase delay of a pulse train compared to a reference clock (together with an integrator).
In the end I think the phase delay measurement is too cheap component wise to bother with structured light ... both would require significant engineering effort any way.
Re: Does anyone know how these LiDARs work?
Patrick, Mon Nov 19 2012, 05:05AM
i may have to buy one for 140 US$, from the Neato robotic vacuum cleaner.
Patrick, Mon Nov 19 2012, 05:05AM
i may have to buy one for 140 US$, from the Neato robotic vacuum cleaner.
Re: Does anyone know how these LiDARs work?
Patrick, Mon Nov 19 2012, 09:14PM
if i were to make my own "Neato killing lidar", i would need:
[structured light not TOF, and open source of course.]
--- color filter, blocks all but the wavelength emitted by the laser.
--- lens/mirror (have no idea how this is to be done, Edmund Scientific?)
--- red laser line generator (no idea where to get one should be 3-5 degrees wide or so.)
--- DLIS-2k Panavision sensor, 2048 pixel (easy to get)
--- Serial and or parallel out via a PIC/STM32 or other MCU, no USB! (USB is evil)
++everything else i can figure out.
the problem with the neato lidar is that it has 4 slip rings that conduct the serial TTL signals back from the rotating parts to the static ones, and this creates a speed limit (due to signal noise) i guess around 115kbps @ 360 pulses in 0.1 sec...
And another guys attempt! -> (WiiDAR)
Even better WiiDAR ->
if i were to invest time and money building this device it would follow the SICK model:
(a single rotating mirror and encoder, with all other components being static.)
Patrick, Mon Nov 19 2012, 09:14PM
if i were to make my own "Neato killing lidar", i would need:
[structured light not TOF, and open source of course.]
--- color filter, blocks all but the wavelength emitted by the laser.
--- lens/mirror (have no idea how this is to be done, Edmund Scientific?)
--- red laser line generator (no idea where to get one should be 3-5 degrees wide or so.)
--- DLIS-2k Panavision sensor, 2048 pixel (easy to get)
--- Serial and or parallel out via a PIC/STM32 or other MCU, no USB! (USB is evil)
++everything else i can figure out.
the problem with the neato lidar is that it has 4 slip rings that conduct the serial TTL signals back from the rotating parts to the static ones, and this creates a speed limit (due to signal noise) i guess around 115kbps @ 360 pulses in 0.1 sec...
And another guys attempt! ->
(WiiDAR)Even better WiiDAR ->
if i were to invest time and money building this device it would follow the SICK model:
(a single rotating mirror and encoder, with all other components being static.)
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Tue Nov 20 2012, 11:17PM
What's wrong with USB? It's the only high speed I/O with explicit DMA support available on most micros ... serial I/O is slow, GPIO most likely won't work with DMA (can forget it outright on the Pi given the lousy documentation).
Pinky's Brain, Tue Nov 20 2012, 11:17PM
What's wrong with USB? It's the only high speed I/O with explicit DMA support available on most micros ... serial I/O is slow, GPIO most likely won't work with DMA (can forget it outright on the Pi given the lousy documentation).
Re: Does anyone know how these LiDARs work?
2Spoons, Wed Nov 21 2012, 12:08AM
USB is OK if there are pre-written libraries for the MCU code. Writing your own usb drivers is very painful. Took two of us three months to get USB working on a small MCU - and that was working with Windows built-in HID class driver, not writing a windows driver. Our first code attempt put the PC into an endless reboot cycle - which i didn't think would be possible for a USB device to do!
2Spoons, Wed Nov 21 2012, 12:08AM
USB is OK if there are pre-written libraries for the MCU code. Writing your own usb drivers is very painful. Took two of us three months to get USB working on a small MCU - and that was working with Windows built-in HID class driver, not writing a windows driver. Our first code attempt put the PC into an endless reboot cycle - which i didn't think would be possible for a USB device to do!
Re: Does anyone know how these LiDARs work?
Patrick, Wed Nov 21 2012, 12:58AM
[quote]
USB is OK if there are pre-written libraries for the MCU code....
...Writing your own usb drivers is very painful....
...Took two of us three months to get USB working on a small MCU
[/quote1353459535]
BINGO !!!
Patrick, Wed Nov 21 2012, 12:58AM
[quote]
USB is OK if there are pre-written libraries for the MCU code....
...Writing your own usb drivers is very painful....
...Took two of us three months to get USB working on a small MCU
[/quote1353459535]
BINGO !!!
Re: Does anyone know how these LiDARs work?
Carbon_Rod, Wed Nov 21 2012, 05:56AM
Ah yes, the old rs422 based protocol with dynamic baudrate changes and proprietary binary packet formats... with password login...
LOL... emulated serial ports also allow the system terminal to actually handle the 500KBs+ rates (unlike a buggy adapter). However, the high end units typically use 100/1000base Ethernet these days which is better for many reasons.
You must be Mechanical or Physics majors....
Carbon_Rod, Wed Nov 21 2012, 05:56AM
Ah yes, the old rs422 based protocol with dynamic baudrate changes and proprietary binary packet formats... with password login...
LOL... emulated serial ports also allow the system terminal to actually handle the 500KBs+ rates (unlike a buggy adapter). However, the high end units typically use 100/1000base Ethernet these days which is better for many reasons.
You must be Mechanical or Physics majors....
Re: Does anyone know how these LiDARs work?
Patrick, Wed Nov 21 2012, 05:38PM
i need to get the bits out of the lidar in polar form, distance and rotation, then to another MCU through something without overhead, and without the technological terror of USB driver writing...
Patrick, Wed Nov 21 2012, 05:38PM
i need to get the bits out of the lidar in polar form, distance and rotation, then to another MCU through something without overhead, and without the technological terror of USB driver writing...
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Fri Nov 30 2012, 04:40PM
I'm kinda interested in trying out the time of flight based LIDAR ... although having no experience in high frequency circuits I don't rate my chance of success very high.
First things first, a ns range laser pulser ... simply use a fast opamp with a MOSFET or BJT as a voltage to current converter? Or buy a dedicated driver IC?
Pinky's Brain, Fri Nov 30 2012, 04:40PM
I'm kinda interested in trying out the time of flight based LIDAR ... although having no experience in high frequency circuits I don't rate my chance of success very high.
First things first, a ns range laser pulser ... simply use a fast opamp with a MOSFET or BJT as a voltage to current converter? Or buy a dedicated driver IC?
Re: Does anyone know how these LiDARs work?
Pinky's Brain, Sat Dec 08 2012, 05:00PM
Oh hey, you can get time to digital converters for ~10 bucks with 22 ps precision ... that takes a whole lot of problems out of the construction of a laser range finder.
Pinky's Brain, Sat Dec 08 2012, 05:00PM
Oh hey, you can get time to digital converters for ~10 bucks with 22 ps precision ... that takes a whole lot of problems out of the construction of a laser range finder.
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