In analogue to digital conversion ,it is often that sampling frequency should be greater than twice the maximum frequency contained in the original signal.How to choose a an analogue to digital conveter if we have no idea about the frequency content of the signal to be conveterd to digital.
Quite right. A quick & dirty method is to look at the signal on a 'scope and eyball the frequency content (it's a knack!) If you have the equipment, sample it at a "high enough" frequency and do a Fourier transform to see what's in it, i.e. get the power spectrum. Figure out what you want to capture for your application what you have to filter out. Design a steep low-pass cut-off filter to select what you want. Always use an anti-aliasing filter before sampling and always respect Nyquist! Cheers, Roger