
Open Source Time-of-Flight DIY Lidar - iliasam
https://github.com/iliasam/OpenTOFLidar
======
osamagirl69
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
Here 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
"They" can be singular.

~~~
hackonr
Is it common? I have never seen it in singular context in English grammar
textbooks.

~~~
numpad0
Actually incorrect in textbook sense, but widely accepted in recent years to
avoid specifying gender.

~~~
nicoburns
Also in less recent years. They has always been used in the singular in cases
where gender is not apparent (e.g. with babies)

~~~
regularfry
And 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

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dchichkov
The original article (in Russian) is very well written. And the author feels
like a true "full stack" engineer: high frequency and power electronics,
optics, mechanical engineering, micro-controller software development, real
time, simultaneous localization and mapping, visualization.

~~~
ragebol
These are the folks that give me impostor syndrome. Given enough time and a
project like this, I _think_ I can learn all of that stuff.

~~~
carlmr
The thing is, with Google at your fingertips, you can build almost anything.
You don't need to deep dive on all these technologies, but you can probably
gather just enough information in a short time.

However it still takes a lot of effort and most of your free time. You have to
be extremely driven to complete such a complex project.

~~~
myself248
Free time in large chunks, was the revelation for me.

I took a serious "staycation" back in December, and wrote about it here:
[https://www.reddit.com/r/Coronavirus/comments/fgvbsv/staythe...](https://www.reddit.com/r/Coronavirus/comments/fgvbsv/staythefuckhome_a_movement_to_stop_the_covid19/fk8xemy/)

During those few weeks, I made what seems like a year worth of progress on
several projects. Being able to dive in and focus, for hours at a time without
worrying that I had other stuff I should be doing, made all the difference in
the world.

Rearranging your week to have one "no-chores no-email" evening, when you just
use a single large block of time to immerse yourself in a leisure activity, is
worth a try.

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beagle3
Actually I do have a question - how safe is this for eyes (human or animal?)
and what changes are needed to make it safer?

How about measuring through translucent or transparent surfaces? Should work
as is if there is no reflection (e.g. measurement at Brewster’s angle for this
wavelength) but is it possible to TOF multiple reflections from? Or multiple
depth slices (e.g. by gating TOF to specific depth ranges? 1ns=~1ft=~30cm

~~~
iliasam
As it was answered, you could read about safety here:
[https://github.com/iliasam/OpenTOFLidar/wiki/Laser-
Safety](https://github.com/iliasam/OpenTOFLidar/wiki/Laser-Safety)

Measuring through translucent or transparent surfaces is theoretically
possible (TDC is supporting multiple measurements), but received pulse width
is too high now - it could be > 30ns after amplifier.

~~~
beagle3
Thanks! Really an awesome project and great documentation.

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iliasam
I'm surprised that there is absolutely no comments. Does that mean that this
project is really not interesting?

~~~
beagle3
I think it's very interesting, but I suspect too few people have anything to
contribute.

I know I don't have anything smart to say about this specific subject, and I
usually try to follow the old german saying "Selig sind die, sie nicht zu
sagen haben und trotzdem schweigen" (hope I got it right - I don't actually
speak german), which means "Blessed be those, who have nothing to say and
nevertheless remain silent..."

~~~
iliasam
Discussion about my previous project:
[https://news.ycombinator.com/item?id=16756901](https://news.ycombinator.com/item?id=16756901)
was much bigger in comparison with this project - this is surprising me.

~~~
AYBABTME
Probably just timing. I find it pretty cool, but I have nothing to say. I'm
impressed with the work and would like to do the same myself, but I'm not sure
immediately where I'd use this and when I'll have time. I've put it in the
section of my brain where I keep things for "when I'll need it, go look this
crazy ambitious project".

If I can provide more feedback, while looking at your project, I had the
following thoughts:

    
    
      - This is super impressive.
      - I'm thankful that people spend time making technology 
      opensource.
      - I'm sure this will grow over time and more "complex" 
      technology will become open this way.
      - I'm curious in which context the author decided to 
      dedicate that much time to this cause (probably in 
      academia? or someone with access to a lab and a lot of 
      experience in all the fields involved in this project).

~~~
iliasam
Thank you for reply!

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salty_biscuits
This is fantastic! I want to make one. Is it possible to get a cheap polygonal
mirror? Then you can get more scans per revolution.

~~~
iliasam
I think that it is possible to make own polygonal mirror (cut polygonal mirror
holder at CNC, attach flat mirrors and balance it). Also it may be found in
stationary barcode reader. But you will lose field of view with polygonal
mirror.

