Sallen Key Low Pass Filter, bandpass filter

[bertus]

 

[Maglatron]

thank you, What is ca.?

 

[bertus]

Hello,

ca. is about.

Bertus

 

[Maglatron]

could you explain it a little more very greatful, it will click I'm sure

width at pass band is about centre / 4 if the center is 32 then 32/4 = 8Hz, I get that

width at stopband is about 2 X centre = 2 * 32 which is 64 this part confuses me!

input centre frequency of 32 means that that is the centre

 

[Maglatron]

is it this?

 

[bertus]

Hello,

Yes, the stopband is the width at the bottom of the graph.

Bertus

 

[Maglatron]

Hi thank you gotcha! are these perameters good for audio filtering?

 

[bertus]

Hello,

Making the passband wider will lead to more stages for filtering.
Making the stopband smaller will also lead to more stages for filtering.

Bertus

 

[Maglatron]

ok sorry for ignorance I understand that making the stopband smaller will lead to more stages for filtering.
I dont get how widening the passband will lead to more stages for filtering. surely reasoning means that there would be less stages for filtering with wider passbands

 

[bertus]

Hello,

When broadening the passband, you will need sharper edges, wich leads to more filter stages.
When narrowing the stopband, you will also need sharper edges and also more filter stages.
Just play with the numbers in the tool and see what happens.
The number of stages is given in the left bottom corner.

Bertus

 

[Maglatron]

ok I understand now I am waiting on some lined paper bumper pads and I will design the passband filters when I get them. Up untill then I'm taking it easy, thank again

I don't want the edges to be too sharp because I want the filter to gradually go from 1volt to 12v in a smooth fashon so that the lm3914 analog bar graph display driver goes from low voltage to the maximum 12volt and then when exiting the band to then go back down again, what are your thoughts on that?

 

[bertus]

Hello,

The edges I am talking about are the frequency changes.


Bertus

 

[Maglatron]

same here, so say when the "the lower edge" is approaching 32Hz in this case, I want the LED's to turn on from bottom to top of the bar graph LED and be all lit (all 10 of them) at 32Hz then receed as the you go down the "higher edge"

 

[Maglatron]

A thought just ocurred to me am I aiming for a frequency 32Hz for example that the voltage it outputs is based on theloudness thats coming through the filter ie you can have a 32Hz wave that is louder than than another 32Hz wave if you get what I'm saying and this controls the voltage out to the lm3914

 

[bertus]

Hello,

The 32 Hz filter will pass only signals in the range of 32 Hz.
The intensity (volume) is passed through the filter.
Low volume will give a low output, High volume will give a high output.

Bertus

 

[Maglatron]

what I mean is amplitude of the 32Hz wave

 

[Maglatron]

yes, I get it now, many thanks for clarification

 

[Maglatron]

The components in the chain of filters uses the op-amp LT6023, this is an smd package dual op-amp, do you know of any op-amps that do the same job in a dip chip package please with maybe more op-amps insideof them?

 

[kellys_eye]

Use any suppliers to show their op-amps via their parametric filter. Just select the parameters you want (i.e. package type, number of internal op-amps, supply voltage, bandwidth etc etc). You can narrow down the list to 'anything' that suits.

Look for the spec of the LT6023 (datasheet) to get some of the basic parameters you need.

Here's Farnell's listing - look down the left hand side for the parameters they use. RS Component, Mouser etc all do it in the same basic way.

https://uk.farnell.com/c/semiconductors-ics/amplifiers-comparators/operational-amplifiers-op-amps

 

[Maglatron]

exellent stuff!