How to design a narrow band pass filter without DSP toolbox I've two signals X and Y. These are proximity sensors reading measuring vibrations of a rotating shaft. Now I want to plot orbit plots for these signals. I can plot unfiltered orbits with just X and Y. But since there is lot of noise in the signal I filtered it. Now there are dominant 1X frequency component and may be other sub frequency components. I want to plot the filtered orbit of 1X say 656 Hz. The sampling frequency I used is 1000000 Hz. I know band pass filter could give me only the 1X component. But I don't have DSP toolbox. Could someone help me how to design and implement narrow band pass filter without toolbox.
Any suggestion or hints or idea would be helpful.
Thanks in advance.
The steps that I would follow to handcraft a bandpass filter are these:


Figure out how wide (in Hz) you want the filter to be.
Create a low-pass filter with half the one-sided bandwidth as your desired filter bandwidth.  You can calculate the sinc function with basic functions, since $sinc(x) = \frac{sin(\pi x)}{\pi x}$.  You can adjust the bandwidth by adjusting the time scale in your sinc function.  If n is the set of all integers between -N and N, inclusive, and you make your filter taps equal to $sinc(bn)$, then the filter's normalized bandwidth will be equal to $b$.
Modulate the lowpass filter to the center frequency you want for your bandpass filter.  You do that by multiplying it, element by element, with a sine wave of that frequency.