Timeline for Motion detection with FMCW radar
Current License: CC BY-SA 4.0
15 events
| when toggle format | what | by | license | comment | |
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| Sep 7, 2021 at 10:32 | comment | added | Marcus Müller | that is the beat frequency while the frequency is rising. As I tried to explain, there's different beat frequencies at different times in your cycle. You can't just say "that's the beat frequency", you need to look at the moment. That's why the figures I've added have a time axis, and that's why I said a single FFT itself doesn't give you the information you need. | |
| Sep 6, 2021 at 15:34 | comment | added | red15530 | I just thought and did not understand one point: in 1ms I will have a whole period, that is, 43MHz / ms = 4.3e10. At a distance of 1m, the signal will need to travel twice the distance at the speed of light, that is, 2m / 300000000 = 6.7e-9. 4.3e10 * 6.7e-9 = 288.1. Correct me if something is wrong. If i understood everything correctly, then this is the beat frequency at a distance of 1m. And if the object moves, then to this frequency I will get another Doppler shift. | |
| Sep 6, 2021 at 8:49 | comment | added | red15530 | I added the signal spectra when the rangefinder is aimed at empty space and when arriving at a distance of 0-3.5m. During the passage, it is seen that a signal appears diverging in both directions from 1 kHz. If you walk at a distance of 3.5-7m, you can see the same thing in the 2kHz region. | |
| Sep 5, 2021 at 12:10 | comment | added | Marcus Müller | The FFT screenshots won't tell me anything: I have literally no idea what the signal is you're visualizing there. I also don't think a single FFT is going to help you here | |
| Sep 5, 2021 at 12:07 | comment | added | red15530 | Yes, I am sure! Because as long as there is no movement there is no signal. There is a constant component at only 1kHz, 2kHz, 3kHz, etc. But if there is movement in the corresponding subzone, then I see a signal diverging in both directions from frequencies of 1 kHz, 2 kHz, 3 kHz, etc. Tomorrow I can show you the FFT screenshots. | |
| Sep 5, 2021 at 10:23 | comment | added | Marcus Müller | are you sure you see the Doppler and not a consistent beat frequency shift due to changed distance? | |
| Sep 5, 2021 at 9:48 | comment | added | red15530 | Maybe I'm wrong, but it can be seen that there is a constant component at frequencies of 1 kHz, 2 kHz, etc. if the radar is pointing into empty space. And if the object is moving, I see the Doppler shift diverging in both directions from these frequencies (if at a distance of 0-3.5 m, then the signal diverges from 1 kHz, etc.). I forgot to clarify (perhaps this is important) that after the notch at 1kHz and the BP filter 500-1500Hz, I use a detector and then I build the envelope by passing 5Hz through the low-pass filter and so I see the signal from the movement. | |
| Sep 5, 2021 at 9:48 | comment | added | red15530 | Yes, I will study the site radartutorial. I'm just confused ... Tomorrow I can take screenshots of the FFT signal from the I output of the microwave module. | |
| Sep 4, 2021 at 21:16 | comment | added | Marcus Müller | The mixer doesn't give you a sum, but a product filtered such that you only observe the beat frequency signal! In a multiple-target scenario, well, you need to find the multiple frequency components of your beat frequency signal. If this is news to you, you honestly might do well refreshing your radar basics - the site I've linked to is quite OK. | |
| Sep 4, 2021 at 21:02 | comment | added | red15530 | I'm completely confused ... You gave an example of how to determine the distance and Doppler shift from the transmitted signal and the reflected one. But in reality I do not see these signals, but I already see their sum after the mixer, which I receive at the output of the I microwave module. Also, I do not understand what to do if there are several moving ones? My task is only to move the object at a certain distance. Its exact speed is not important to me. | |
| Sep 4, 2021 at 16:52 | comment | added | Marcus Müller | @red15530 re:triangle: read the complete answer. | |
| Sep 4, 2021 at 16:27 | comment | added | red15530 | As I wrote, I tried to isolate this signal with 500-1500Hz and 1500-2500Hz bandpass filters for frequencies of 1kHz and 2kHz, respectively. I don't understand then what I saw ... | |
| Sep 4, 2021 at 16:27 | comment | added | red15530 | As I wrote above, I made an FFT of the signal from the I output of the microwave module and when directed into empty space, I see the amplitude at frequencies of 1 kHz, 2 kHz, etc. I just tried to get rid of them with notch filters. Then I stayed to make passes at a distance of 0-3.5 and saw a signal in the region of 1 kHz diverging in both directions. How much it diverges depended on the speed of movement. If I walk at a distance of 3.5-7m, then I see the same thing in the 2kHz region. | |
| Sep 4, 2021 at 16:01 | history | edited | Marcus Müller | CC BY-SA 4.0 |
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| Sep 4, 2021 at 15:37 | history | answered | Marcus Müller | CC BY-SA 4.0 |