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Does anyone know how these LiDARs work?

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LAN_403

2Spoons

Wed Nov 14 2012, 01:11AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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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.

Patrick

Wed Nov 14 2012, 02:27AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

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.

Pinky's Brain

Wed Nov 14 2012, 08:58PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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I think LIDAR is a bit of a misnomer for the triangulation methods ... I'd classify it as structured lighting.

Patrick

Wed Nov 14 2012, 09:44PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

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...

Pinky's Brain

Mon Nov 19 2012, 04:22AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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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.

Patrick

Mon Nov 19 2012, 04:43AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
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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?

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.

Pinky's Brain

Mon Nov 19 2012, 04:54AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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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.

Patrick

Mon Nov 19 2012, 05:05AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i may have to buy one for 140 US$, from the Neato robotic vacuum cleaner.

1353301509 2431 FT122245 Thegoodstuffunmasked

Patrick

Mon Nov 19 2012, 09:14PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

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.)

1353360217 2431 FT1630 Sick Lms210 Backcoveroff

1353360217 2431 FT1630 Sick Lms210 Mirrorrotationassembly

1353360217 2431 FT1630 Sick Lms210 Opticalencoderassembly

Pinky's Brain

Tue Nov 20 2012, 11:17PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

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).

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