True, but in radar applications where you're looking at the doppler shift of the returned signals, you end up dealing with a much more manageable signal - as evidenced by the fact that you can buy a (basic) working radar speed gun as a children's toy for about $30. With LIDAR (aka LADAR, to the military), you're stuck with much more difficult timing tasks.3iMaJ said:Its the speed of light applies to a radar as well.
Marks256 said:I guess lidar would work too, but i would like to stick with LADAR for now...
I guess you could say that it is just pure curiosity. Maybe make a few projects with it, but nothing major.
I would like to stay away from radar, because it uses radio, and i need to find the distance of an EXACT point. It really doesn't have to be all that accurate, maybe within a 1/2" (~1.27cm) or so...
Really i would just like to see if i could make one... I saw one going on ebay for $5000usd, and almost fainted....
Marks256 said:I guess lidar would work too, but i would like to stick with LADAR for now...
I guess you could say that it is just pure curiosity. Maybe make a few projects with it, but nothing major.
I would like to stay away from radar, because it uses radio, and i need to find the distance of an EXACT point. It really doesn't have to be all that accurate, maybe within a 1/2" (~1.27cm) or so...
Really i would just like to see if i could make one... I saw one going on ebay for $5000usd, and almost fainted....
So, they're talking about range resolution of 25 cm (20 times worse than the 1.27cm which you considered "not that accurate") and they're dealing with a frequency range that is hundreds of MHz. Needless to say, such a system is not exactly going to be practical for a hobbyist to build, especially one without at LEAST an undergraduate college education in EE under their belt...This paper treats a practical adaptation of frequency modulation (FM) radar ranging principles to an incoherent laser radar (ladar). In the simplest sense, the ladar's laser transmitter output is amplitude modulated with a radio-frequency subcarrier which itself is linearly frequency modulated. The subcarrier signal may have a start frequency in the tens to low hundreds of megahertz and stop frequency in the hundreds of megahertz to low gigahertz. The difference between the start and stop frequency, (Delta) F, is chosen to establish the desired range resolution,(Delta) R, according to usual equation from FM radar theory, (Delta) R equals c/(2(Delta) F), where c is the velocity of light. The target-reflected light is incoherently detected with a photodiode and converted into a voltage waveform. This waveform is then mixed with an undelayed sample of the original modulation waveform. The output of the mixer is processed to remove `self-clutter' that is commonly generated in FM ranging systems and obscures the true target signals. The clutter-free waveform is then processed coherently using the discrete Fourier transform to recover target amplitude and range. A breadboard of the ladar architecture was developed around a 30-mW GaAlAs diode laser operating at 830 nm. Imagery and range responses obtained show that the theoretical range resolution of 0.25 m was attained for a (Delta) F of 600 MHz. Embodiments of this ladar are likely to be practical and economical for both military and commercial applications because low-cost continuous wave laser diodes are used, coherent optical mixing is not required, and the post- mixing processor bandwidth is low.
NIgel said:Perhaps you were planning using a Z80 to do the timing?
evandude said:you seem to have some VERY unrealistic goals...
Marks256 said:I would like to stay away from radar, because it uses radio, and i need to find the distance of an EXACT point. It really doesn't have to be all that accurate, maybe within a 1/2" (~1.27cm) or so...
Marks256 said:What else is there that can be used to find the distance of ONE point. I don't want any of this "[hardware sending robot data] Hey, guess what? There is an object about 20cm from this position! Wanna guess where it is so we don't hit it?"...
plenty of people have made plenty of good robots without being able to measure every distance at every possible angle with 1/2" accuracy. Even if you could do it, your robot would never get anywhere, it would spend all its time scanning everything in front of it.
Well it is a lot easier to explain why things are too complicated than to explain how to build complicated things! If it could be explained on here then it wouldn't be complicated.
(If you want accuracy you should still go with the Sharp IR since it's accurate to 1cm and dirt cheap. The LADAR you are planning would be far harder and expensive and only an accuracy of 10cm)
Marks256 said:You can't tell me that talking about making expensive, complicated, and downright stupid projects isn't fun. I would think any geeky person would jump on that!
Marks256 said:But i don't think that a ir sensor could detect object upto 40 feet away in the blairing sun now, can it?
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