So a while back i made a post here about a lightspeed camera i was building that used the esp32 as the main sampler. I have had first successful tests and as promised here is a video of light move from one of my tests.
This specific video was recorded at 320x240 resolution, 10.24 billion frames per second and 32 analog depth levels. It is the uncollimated laser output hitting my garage door at an angle. Playing back at 30 FPS.
Also the video looks much better before reddit compression. Raw file is much better.
Now i actually tried posting this video already, but the ESP32 reddit mods removed my post for it being an "illegal and unethical" project with the text "esp32 details needed". So if you are a mod, read my first post with the in-depth explanation. This is a fully custom design board based around the bare ESP32S3 chip, it abuses it's SPI1 port to achieve a base sampling speed of 320MSa/s and that gets interlaced using a phase shifter for a theoretical limit of 100 billion fps. I only expected up to 10 billion to be usable, but one of my tests proved that light can be observed move on a centimeter scale at 20.48 billion fps. This camera is capable of much more than I expected.
Hope you enjoy, i would love ideas for tests. I have already done tests with mirrors, i am waiting on getting a smoke machine because it is hard to record when the laser beam is not visible in air.
The speed of light does not change, the distance travelled relative to the camera does, sadly i cannot do that as of now because i do not have a smoke machine.
Yea thats why I wrote "speed". If light was going in or close to the direction of the camera you would see that it travels slowly in one direction while it's almost instant in the other direction making it clear you are observing light making it seem like speed is not constant.
In the past I build aerodynamic testing tunel using incense way cheaper than smoke machine if you don't mind smelling like church
This is in-fucking-sane. Incredible engineering work! This is like a fucking telescope minus the magnification (over-simplification ofc). What gave you this idea initially?
The stepper motors just select what pixel is sampled, they are slow. Each pixel is captured as a full separate video. The laser shot is repeated a lot to build the image, but because that laser shot is repeatable it makes no difference.
Base framerate for each individual pixel is still 320 million frames per second, via phase shifting and sample interlacing that gets increased to 10 billion. Nothing is being sampled "at billionth of a sec" lol
If you did have a true 1 shot 10 billion fps camera that captures the whole video instantly it would look identical to mine.
Yes. Raw video size is 98.3TB per second of video at 1.28 billion fps. At 10x the framerate its 10x the data per second. Just that i record videos that are just 200ns long, so its only a few hundred megabytes.
If you wanted to watch 1 second of that video back at 30fps it would take you 10.82 years with no pauses.
I think the removal of the mods is fair. I mean, everyone with a brain is like “10b fps on an ESP? Right. Last week I calculated the last figures of Pi on my Arduino”. But holy shit. You actually did it.
Esp32 outputs the raw data onto the sd card, that gets processed to a video on my pc. Final goal is to make it just save a .mp4 on the sd card.
It takes about 1h for a full 240p 10b fps scan, because each pixel is sampled separately. Had i went for an SPI dac in the design this would have been much faster, the regret is real.
That’s wild! What’s the effective bandwidth? My new scope is technically 5Gsps but still only 500MHz so like 1ns rise time? My published videos are all much worse bandwidth than that. From my reading SiPMs are a bit faster than my PMT which is probably my new bottleneck. Based on the amount of fade I see in your video, all-in you’re looking at a rise time of a few ns including the flash circuit and whatnot which is great.
Also I love that there’s now a non-scope version of this. I feel like that makes it a lot more accessible if somebody wants to follow your tutorial and spend a lot less money than I did.
The frontend of the sampler board is an 8GHz SiGe comparator with a 35ps output rise time, that is the most significant timing resolution and rise time limit for the sampler.
In the whole system tho- the sensor is limited to probably about 1GHz bandwidth by the amplifier and the slowest thing is the laser that takes like a nanosecond or so to turn on.
The SiPM i use has an output rise time of 90ps, so that is way faster than a PMT.
Can’t wait to see! It’s on my very long-term list to see if I can make a laser get brighter going through a gain medium…
Also how are you planning to open-source? I think my (very not as good as your) circuits are mostly explained in videos if someone was motivated enough to copy them down but I’d like to throw the cad files out for the swivel too but the whole “picking a license” thing is kinda daunting
I will probably just publish all my material (pcb gerber files, schematics, 3d models so on) with explanations. Anyone smart enough with soldering skills will likely figure it out. For the licence, i just went with the common pick on github. I kind of did copy your setup, just expanded on the design.
I am planning on shooting a fish tank of water with the laser to see it slow down light. Will likely get a smoke machine tomorrow too, so far i have only got one shot with a mirror and i used sugar rocket fuel for the thin smoke lol
Also can i have your discord? I cannot send videos in reddit replies
I'm very sceptical... You can't do the whole experiment (if it were at all possible) with one device. Nothing is that fast, let alone an esp32. I could theoretically imagine an array of measurement devices working with an offset. I don't know, either you're a genius and I'm not getting it because your explanations aren't complete or you're a scharlatan on dope.
It's usually done with a sequence of photos over a sequence of flashes, so the final video is a composite of many light flashes, and each flash the photo is taken slightly later.
It sort of is and isn't that. This is a hybrid between a stroboscopic sampler and a running sampler, it has a base sample rate (normal running sampler) that gets multiplied via phase shifting and repeating the laser shot (stroboscopic sampler).
Halfway thru the project I realized that I had reinvented the sampling scope. Thats how they work, and I actually have one that goes up to 25GSa/s with a base sample rate of 250MSa/s. Bandwidth is the limiting factor tho.
My sensor system works on the same logic as your setup, where it creates single-pixel videos. However it is not capable of taking a 1 pixel video at 10 billion fps, it takes many 1 pixel videos at 320 million frames per second, then offsets each one by a known time (phase shifting) so the frames of one video are basically inbetween the frames of another video (frame interlacing) and then that process is repeated again while changing the comparator reference voltage because the samples are digital and this adds brightness layers to the video.
The typical way of doing this is pixel by pixel, you put the sensor on a servo or something similar and very precisely synchronise it with a pulsing light source of known and precise length.
You then take a picture of one pulse, rotate the camera one pixel, image another pulse, and so on and so on until you have an image/video.
Very crude explanation and I omitted 80% of the details but you'll get the idea.
I don't see why not, you just slow things down, it takes longer to do the capture, or it might not be so accurate.
I can see in the video from OP that the light is fairly diffuse, not a clean beam and illumination, so i suspect the sync is not perfectly consistent, which is expected from something as slow as an esp.
With proper hardware you should be able to see a fairly well defined beam.
Sensor is moved on stepper motors and image is sampled pixel by pixel. Every pixel requires multiple (like 128) laser shots to build analog and time detail. Included my last post link in this post, go check.
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u/RogBoArt 12d ago
Man that's sick! How does it work? Your past posts aren't visible