bandpass op-amp help needed

First, thanks so much for taking the time to read this. I'm in a pickle as I don't know much about circuit design.

I'm quickly trying to build a simple circuit (well two actually) that will detect one of two signals and activate a relay. The relay can be anything from 5v to 12v actuation @ 5 amps... nothing big.

The audio signal can be anything, but it should be able to actuate two discrete relays. So, the audio output should split into a Y and then feed two different bandpass circuits, tuned to very widely different frequencies (e.g. 100Hz and 8KHz).

I've looked at the circuit design for a bandpass filter:

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Obviously, finding the values for the resistors isn't difficult.

My question(s):

1). What kind of op-amp should be used? 2). Will making a very high Q filter boost the voltage to something like 5volts or do I need a second stage of op-amp gain? 3). If I do need second stage, anybody have one in mind which would be able to actuate a 5volt relay?

thanks for any and all help you may be able to impart.

-sincerely robb kunz snipped-for-privacy@yahoo.com

Reply to
inphaseprod
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Go to

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, then to General Links, then to Spreadsheets, then open the zip file and extract bndpass1.xls ... this gives you the general idea for the opamp. For the frequencies you've chosen, almost anything will work, even the LM324 from Rat Shack.

At the output a simple two-diode "voltage doubler" rectifier, filter capacitor, and transistor driver for the relays should do the trick. Don't forget the snubber diode for the relay so that you don't destroy the transistor with a spike.

Jim

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Reply to
RST Engineering (jw)

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