I have posted before about using a Maxim 281 Low pass Bessel filter. I need to be able to switch cutoff frequencies between three different values. I'm using an external clock oscillator to set my cutoff frequencies. It's cascaded with a couple of flip flops used as divide by twos to halve the frequency twice. I know how to wire a manual switch to choose between these three values to send to the Maxim chip.
However.
The Maxim requires an external resistor and capacitor to operate as part of a feedback loop and as one pole of the filter. They have to be computed as 1/(2*pi*R*C)=fc * 1.1579, or performance degrades. I can use the same resistor value and have 3 different capacitor values.
So in order to change the cutoff, I need to change not only the clock frequency, but also a capacitor value
I want to use another manual switch (my clock is on a different board, so it can't be the same switch) to switch between 3 capacitor values. Is this possible? I've just never seen it done.
The cutoffs will probably be around 600, 1200, and 2400 Hz and capacitor values around 4, 8,and 16 nF.
Thanks for any tips, concerns, suggestions for types of switches, caveats, etc.
Amanda