Video demonstration: https://www.youtube.com/watch?v=F98WkdnYbrQ&ab_channel=GauravDuggal
Example output of a spectrogram while looking at a rotating fan:
Hypothesis -> 18 peaks in 1.2 seconds -> 15 peaks in 1 second -> 5 revolution per second (divide by 3 fan blades) -> 900 rpm which is approximately how fast a ceiling fan rotates at full speed.
1). Connect the Arduino Pin A0 to the Doppler radar signal out (i.e. pin 12 of RCWL-0516) refer to https://github.com/jdesbonnet/RCWL-0516/ 2). Burn the Doppler_radar.ino to the Arduino, I used an AMTEGA 328P based Arduino UNO. 3). Put the appropriate port settings in settings.txt in eg "port": "COM4" 4). Run main.py
The console should read:
FILE SETTINGS*********************** N: 4096 clk 16000000.0 prescaler 256.0 baudrate: 115200 port: COM4 xlim: [0.0, 5.0] ylim: [-0.5, 15.0]
Sampling frequency of ADC: 1563.5 Sampleing time of ADC: 0.0006395906619763352 Wavelength: 0.09674298613350532 m Hamming window used Sampling duration: 2.619763351455069 Doppler frequency resolution: 0.3817138671875 Hz Doppler velocity resolution: 0.018464069680143504 m/s max detectable velocity: 37.79595063525375 m/s
The file settings contain user editable and independent parameters:
1). Arduino Parameters: The Arduino runs timer0 at 1563 Hz and the ADC is sampled each time the Interrupt Service Routine is called (ISR).The sampling frequency is given by:
fs = (clk)/(prescaler*trip) + 1
the xlim and ylim set the axis limits in the fourier plot generated so we can see clearly the Doppler shifts
2). Radar Parameters: a). The sampling frequency controls the maximum doppler frequency that we can measure which is given by fs/2 according to the nyquist theorem b). The Dwell time (T) is given by N*(1/fs) and this controls the width of the Doppler Frequency bin or Doppler frequency resolution (del_f). Doppler frequency resolution is given by the inverse of the Dwell time.
del_f = 1/T
c). The Doppler shift velocity resolution (del_v) given by:
del_v = del_f*lambda/2
where lambda is the wavelength of the passband radar signal i.e. in our case
lambda = c/f_c where f_c = 3.101 GHz