So first off im not an EE, my math goes to pre-calculus, which I have a hard time recalling. Usually if I need higher level math for theory I either do a lot of research on that equation or just can something someone else has written.....
I understand first order RC/LC/RLC filtering. I just through a cap in and wrap a coil most of the time. I do not understand how to design something like a Butterworth/Sallenkey filter.... any advanced filter I just plug numbers in to a designer and use the components I am told. Im sure I could learn how to design my own 7 pole filters if I wished but I am also sure it would take me a while and wouldn't gain much from it over design software.
I have recently been thinking about DSP, I have never really gotten in to DSP thinking thats a pretty specialty area but im sure there are good functions out there on most platform to do a FIR or IIR filter. I was trying to get the basics down so I googled Arduino code LP filter, well all the post I read said to put an LC filter in front of the pin also!!!?! Why is that, if your filtering out specific bandwidths why would you need hardware on top of software? Why not just use an LC filter and call it a day?
My understanding is that digital filters dont have issues like analog do, theres no drift or precision issues, nothing degrades with age. So what is the pitfall of digital only? Secondly lets say you want to clean up a power rail, what if you just had a bunch of sot attinys around programed to do this, this is almost cheaper than a decent coil and cap? And if that is an awfull idea what about using something like a coolrunner or even a GAL to do filtering?
One reason in interested in this for regular power rail and pwm filtering etc... but what if I wanted to use this in a bigger way, what about making something like a broadband antenna pre selector for something like a 1.8ghz sdr. Is there any reason this would be a horrible idea? it seems to me like maybe a true FPGA or a ton of small micros would be a much cheaper and compact method if you wanted to maybe do a good bandpass for every 10mhz? Then what is the difference between a DSP like the blackfin and just using an fpga for DSP? Whouls a DSP chip just be much easier if your plan is to use canned code, i.e this is one of those projects where I wouldnt want to copy and paste it as much as possible because im sure it wouldn't be easy to learn and would take a lot of time awayf from learning other things... im even confident wrapping coils would be quicker than learning FPGAs and DSP math as the same time!
One last unrelated question I bought one of these, im not to sure why they just call it a common mode filter. I e-mailed the maker to ask what frequencys that acually meant and never heard back. Unfortunately the components are unreadable so I can figure it out that way. I was going to stick it across the power rails of a USB connector for sdr/radi equiptment but im not sure its needed or does much more than feright.
https://www.tindie.com/products/ivc/lc-common-mode-power-filter/there documentation mostly shows it connected to motor controllers, which if it will clean up motor noise that good, you dont want your motor noise getting in to an accelerometer.... but if anyone can give me some type of specific details on what this should be filtering It would help, as there is no specific frequency for common mode noise!