Low Pass Filter design

[HWguru]

Hi All,

I am trying to design and build a Low Pass Filter ( Active Filter with opamps ) . This will be the front end pre-amplifier as well as filter connected to a coil that will pick up 22hz to 32hz pulses from a Magnetic coil placed 10 feet away . I have used Filter Wiz Lite and Filter LAB2.0 , but both tools suggest using opamp of either TI or Microchip . What i need is a tool or tutorial that help design one using opamp 741 . Any suggestions ???

Thanks

HWguru

 

[KlausST]

Hi,

Just use 741. The values of R anc C don't change.

What opamp to use depend on other parameters like noise, input curren, offset voltage, gain....

From your description, i think you should try the 741.
For sure there are opamps with better performance.

Klaus

 

[Surendhar Murugan]

Use the IC741 or try to find the opamps from the manufacturer whomever you want with the same spec of opamp which has been used in your tool.

 

[HWguru]

Basically i need to amplify signal picked up from a Rx coil . The pick up coil has the impedance of 2.4Kohm and its a AWG #44 wire wound air core coil . Actually i do need a pre-amp IC with AGC so that if the TX coil is near or far the gain is controlled . What other opamp or circuit would you suggest , i need a gain x5 or x10 or ideally adjustable

 

[KlausST]

Hi,

2k4 source impedance .. is in a range wher a bjt or a fet opamp can be used. I'd prefer a low noise bipolar opamp.

Variable gain. You could look for automatic gain control, often made with OTAs, (compressor)
Or you could manually adjust it wit pot. Or control it with microcontroller, e-pot, multiplying DAC, or special opamp with built in gain control.

Klaus

 

[HWguru]

Yes i think a p-channel MOSFET should do the job