Filter topology and cuttof guess

MrAl said:

Hi audioguru,

Thanks for mentioning that. I do have to wonder however, why you
want to choose that filter response when it sounds like he wants to
filter the dc from a low frequency noisy input mixed with dc.
I could have misunderstood the application, but it seems to be that
we would want to reject all frequencies above dc as
well as possible and not attenuate any if possible. Forcing the
response to be -3db at the cutoff doesnt seem to have any useful
purpose for this app, again unless i misunderstood something.
He also didnt mention what kind of time profile he needed so i
didnt think that was important either.

BTW, there is another approach we have not talked about yet and
that is going totally digital (well almost). The implementation of
such would reduce the hardware requirement to one resistor and
one capacitor, regardless of the type of characteristic response
required.
This kind of implementation might require a bit more program code
memory but probably not a huge amount. A few calculations have
to be performed, usually done as part of the micro controller program.

Click to expand...

MrAl said:

Hi again,


Oh ok, so i guess the actual sensor here puts out dc. That changes the game a bit and so you want a smooth output hopefully even in the event of some noise.

We then have to know what is the fastest change in actual signal you have to measure? In other words, do you have to measure every 1 second or every 10 seconds or every 100 seconds etc.?
This changes the way the filter can be set up.

Also, what kind of control do you have over the actual program that the
(presumably) micro controller will have programmed into it?

Click to expand...