Hello ,

I want to make an adjustable bandpass filter for a 0-5volt audio signal.

The low-pass will be adjustable from about 30-200hz and the high pass from about 1000-5000hz.

I'm planning to do something like this

http://www.electronics-tutorials.ws/filter/filter_4.html

But i'm planning to add a unity gain op amp buffer(powered by 9v) between the two stages and on the output aswell so In total two buffers.
Two pots will be adjusting the bandpass frequencies .

I've calculated my high pass to be 100nf and 5k-50k variable resistance and for the low pass 22nf and 1k-10k variable resistance.

What do you guys think? Is it necessary to put a buffer inbetween the stages and on the output or would it be enough to have one in between.
The output is going to drive the wiper of a 50k pot which will go to a micro ADC.

 

I would buffer both of them. Then you don't need to worry about what the input to the ADC looks like.

 

Ok thanks for the advice, ronv

 

You can using CD4066 to be the AC signal switch, to select several different bandpass filters.

Also the CD4051 is another choice.

 

yes thanks that's a good idea

 

Thanks, Shagas; that's a great site to study.

 

...The output is going to drive the wiper of a 50k pot which will go to a micro ADC.

And is this ADC tied to (or integrated in) a MCU? If so, why not perform the filtering digitally? Eric007 can help you!

 

Hello,

You might want to look at some of these application notes from MAXIM:
http://www.maximintegrated.com/design/techdocs/app-notes/index.mvp/id/4#c4
I think the switched capacitor filters might interest you.

Bertus

 

Thanks, Shagas; that's a great site to study.

The ADc is an AVR adc so yes , integrated. The avr is already busy doing a load of other stuff so I didn't want to introduce digital filtering.

Thanks for the link bertus