i would appreciate if anybody could help me with a circuit design for an Equalizer. i should realize the board for a connection with STM32F411 Discovery (it would be a second part of task).

It is an example for a study. Recently i received this project to realize, original text is in German but there are details:

3 Channel Equalizer:

Bandpass for frequencies 100Hz, 1kHz, 10 kHz
those frequencies should be gained trough potentiometer from +12dB to -12dB
Band-passes should be min 4th order
as an input source should be used BNC-socket
output signal to be transmitted to an existing AD channel
simulation in Multisim or Spice

i added a picture of an expected gain graph (potentiometer should limit gain between +12dB and -12dB)

Thanks for help
i guess that the way of circuit design is not as much complicated for someone who already has experience with this tasks

 

There are several free programs that will help you design such filters such as FilterPro from TI or Filterlab Filter Design Software from Microchip Technology Inc.
I suggest you download one of those and then, if you have questions, get back with us

 

you can use your micro controller (STM32F411) as a digital filter you can build a FIR filter as a firmware, ARM based micro controller can deal with math calculations easily, you have a DSP_Lib which is built by ARM and there are many examples for FIR filter

 

Thanks. I just want to add it is an active filter and i have many examples how to realize it. Bandwidth is an optional in this task. Calculating is also not such a big problem. But I lost myself in realizing gain +12 to -12dB.
How to add a potentiometer in this circuit (uploaded file) to control a gain but not with additional op amps.
This would be 1 Channel example. Gain is missing... positive to negative... it should not be complicated but i am not thinking in the right direction

but thank you both for a good tips!

 

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This would be 1 Channel example. Gain is missing... positive to negative... it should not be complicated but i am not thinking in the right direction
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You cannot readily change gain in your posted circuit without changing the frequency response but you could add a potentiometer to the output of the second filter.