5 ms·
This is a very neat project, I really wish I could read Russian to understand some of the details in his writeup. The overall architecture is pretty standard fo
by osamagirl69 7y ago
This is a very neat project, I really wish I could read Russian to understand some of the details in his writeup. The overall architecture is pretty standard for a LIDAR setup.
For the source they are using an osram SPL PL90_3 laser diode which provides 75W peak output at 900nm, with pulse duration roughly 10ns and costs $10.
For the detector they are using a MTAPD-07-013 avalanche photodiode, which has a quantum efficiency of about 80% and an internal avalanche gain of 100 and 0.6ns rise time. Also costs about $10.
For the time measurement they are using a TDC-GP21 time to digital converter with 22ps resolution, although the author has it configured for 90ps counts. Costs a bit over $5.
It is really a testament to the amount of development work that has gone into the lidar and related field, that for under $100 you can build a full lidar system out of parts from digikey including custom pcb's and scan mirror. When I was in grad school we paid $7500 for our avalanche photodiode, $25k for our pulsed laser, and used a $50k oscilloscope to read it out.
- iliasam 7y agoHere is a link to the video: https://youtu.be/lTPH_Xa9yCk https://youtu.be/lTPH_Xa9yCk with short Lidar description. What kind of details do you want to know? Why did you write "they are using"? Thre was no team, it's my own project.
- regularfry 7y ago"They" can be singular.
- iliasam 7y agoThanks, I have never heard about it.
- regularfry 7y agoNot a problem. Every so often this otherwise unremarkable grammatical point becomes somewhat contentious, but it's easy to see how it can be confusing if English isn't your first language. There's more here: http://itre.cis.upenn.edu/~myl/languagelog/archives/002748.html http://itre.cis.upenn.edu/~myl/languagelog/archives/002748.h...
- C1sc0cat 7y agoI just love the line "This use of they isn't ungrammatical, it isn't a mistake, it's a feature of ordinary English syntax that for some reason attracts the ire of particularly puristic pusillanimous pontificators, and we don't buy what they're selling."
- hackonr 7y agoIs it common? I have never seen it in singular context in English grammar textbooks.
- numpad0 7y agoActually incorrect in textbook sense, but widely accepted in recent years to avoid specifying gender.
- C1sc0cat 7y agoFor example "they must have forgotten to add the catch all redirect in the .htaccess file"
- nicoburns 7y agoAlso in less recent years. They has always been used in the singular in cases where gender is not apparent (e.g. with babies)
- regularfry 7y agoAnd also where it is: There's not a man I meet but doth salute me As if I were their well-acquainted friend - A Comedy of Errors, Act IV, Scene 3
- deleted 7y ago[deleted]
- regularfry 7y agoWidely accepted back at least as far as Shakespeare. The objection that it's incorrect is what's recent.
- Bjartr 7y agoEnglish grammar textbooks started excluding it because doing so made the language more like Latin and this was considered a good thing.
- gsich 7y agoIt's misused for that. It's not correct grammatically and leads to confusion for non-native english speakers.
- jbms 7y agoThe video is impressive. I liked seeing the speed it spins at, and I liked the demo of how an AGV can explore and build a map of its surroundings.
- michaelt 7y agoGreat project, thanks for posting it! > What kind of details do you want to know? What is the limiting factor on the precision - is it just the specs of the TDC-GP21 or something else? How did you calculate the appropriate laser lens and standoff? Is the CS mount lens's focal length important, or is there no need for a sharp image at all distances? Why use one CS-mount lens and one M12 lens, rather than two M12 lenses? Do you need any sort of dynamic gain or optical filtering on the received signal? Is it vulnerable to getting washed out by bright sunlight? Did you need much fancy $$$$ test equipment to get the design working, or did you achieve it with tools mere mortals can afford?
- iliasam 7y ago> "What is the limiting factor on the precision" Precision in this project is limited by rise time of the received signal. Meanwhile, this time is limited by rise time of laser's current. It is too long now - 10 ns. Theoretical TDC resolution is ~13mm per BIN. You could see real results here: https://github.com/iliasam/OpenTOFLidar/wiki/Resolution-of-the-LIDAR https://github.com/iliasam/OpenTOFLidar/wiki/Resolution-of-t... > "How did you calculate the appropriate laser lens and standoff" I can't say that there was too much calculations. The is some information here: http://www.ti.com/lit/ug/tiduc73b/tiduc73b.pdf http://www.ti.com/lit/ug/tiduc73b/tiduc73b.pdf (part 2.3.5) and here: http://www.ti.com/lit/ug/tiducm1b/tiducm1b.pdf http://www.ti.com/lit/ug/tiducm1b/tiducm1b.pdf (part 2.3.2) Laser's lens should have maximum possible focal length, but it must not crop light beam from the diode. Photodiode's lens should have maximum Entrance pupil > "Is the CS mount lens's focal length important, or is there no need for a sharp image at all distances?" You need to have sharp image at big distances. At short distances it is not important - light signal is high enough. > "Why use one CS-mount lens and one M12 lens, rather than two M12 lenses?" I think that it is easier to find lens with big "Entrance pupil" with CS mount that with M12 mount. Bigger mount - bigger lens diameter, bigger "Entrance pupil". > "Do you need any sort of dynamic gain" I don't have any kind of electrical gain control. There is an ability to change APD gain, but I don't use it. > "optical filtering on the received signal" I don't have filter in my LIDAR, but it is necessary to have it if you are going to run LIDAR at sunlight. I give links to a several interference filters in "LidarTotalBOM.xlsx". > "Did you need much fancy $$$$ test equipment to get the design working". All that I have is Tektronix TDS540D oscilloscope (bought at the Ebay for $300) and multimeter.
- regularfry 7y agoIs it worth trying to do spread spectrum with this? Or do you need a different amplifier setup?
- namibj 7y agoAverage power vs. SNR favours very short pulses. Peak power vs. SNR favours pseudorandom sequences with a peaky autocorrelation function. In practice, an LFSR is typical, but if you use e.g. AES-CTR, you can get quite a lot of resilience against (intentional) jamming and be potentially undetectable as long as the sensor doesn't move directly into the beam.
- regularfry 7y agoYeah, I'm just not clear on how to go from that theory to practice in this case. Like, could you do it with this specific photoamplifier, or would you need something very different? Are we immediately into FPGA territory to get enough processing speed, or is there something you can do with the delay lines to have the same effect?
- namibj 7y agoYou basically do AM of the laser, and then otherwise normal baseband radar processing. You don't need much bandwidth, but more bandwidth needs less SNR, as you can do superresolution if you have sufficient SNR. There is no need for an FPGA, but you will rather quickly throw FFT correlation processing at it. This would not use any delay lines. You'd just need to lock the sampling of your ADC to the signal generation, because 2ns jitter are 30cm/1ft jitter in distance.