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# I have to build a OP-AMP or 555 based project.Need an impressive project in an hour!!!Can anyone help? Answered

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it is probably a little late, but a good project that includes three OP-Amps is a band pass filter. It is the bass unit of a audio equalizer. It can also be done with one OP-Amp, but the math is a little more complex.

Can you please send me any link of the band pass filter circuit???

the circuit is great...i'll consult both ur circuit with the professor and get back to you.....thank you soo much for helping me out with this...i'll surely consult you with the math!!! Thanks again!!!

Hey i've decided on the state variable filter....can you tell me how i can demonstrate the application of this circuit in the college??? I mean, can i connect or cascade any circuit at the input and output...a CRO or something ...with which i can show the functionality of the circuit to the professors?

The easiest thing to show how this works is putting music in. The input on the schematics is for a audio signal. This can be done by just taking a 3.5mm plug and connecting it. Once this is done, you can listen to the specific range of the filter you built by grounding the output audio frequency, and then you need to place the audio out where the band pass point is. It is located immediately after the second OP-amp.

hey...but the values of the resistors and caps is'nt specified in the ckt schematic...also, is there any website or book which has more on this type of a ckt.

There is a book, but it does pretty much the same, except it explains. The only two resistors that really matter are the Rf1 and the Rf2. You can make the rest any value you want as long as they are the same. R4 is the only other one you need to worry about. I solved the two equations for R4 and Rf1. Fo is the center frequency, so if you want your range to be 100 hz at 1khz, then Q= 100/Fo. The center frequency is not exactly 1000 hz for this. It is weird, but the center frequency is actually the square root of (1050)(950). This is the part of my project that I am currently working on, so I'm not one hundred percent positive. I am fairly certain though.

See...the point is that i will be questioned thoroughly about my project by the professors....and i dunno a single word about the OP-AMP...so can u suggest any reference books...

See, i've got to submit my project to the college...so i have to let go of it forever...so i don't want something very expensive...Any suggestions??? BY THE WAY, i convinced the professor to postpone the submission of the project...so i have one week's time now...

Did you click those two links I gave you? Almost all of those should be possible for under \$20. The theremin one might be a good choice for sound, or the PWM project if you want to make an a digitally-adjustable fan.