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Re: Sound Frequenicies

Posted: Sun Mar 09, 2008 9:14 am
by Craig_Bridge
Also just to clarify, the intial RC circuit will be connected to the op amp which will filter the volts

"Brian Castelli'" gave you the initial stage break down:
1) Microphone and amplifier for picking up and boosting the signal
2) Band pass filter for blocking everything but the ring tone
3) Analog to digital to convert the level of your input signal to a 1 or 0 - on or off
4) A circuit to trigger a light, bell, or other output device.

In the advice that I've been giving you, I recommended adding an impedance matching resistor to Brian's first stage if your microphone was low impedance (say 150 ohms). I also recommended that this first stage be a unity gain buffer amplifier and recommended the voltage follower circuitry for this stage.

Brian's second stage was a band pass filter. I pointed out that because the microphone's response curve probably already falls off quickly above 20 KHz, you didn't need the low pass part of the filter to start with. I recommended a twin T high pass filter circuit for this stage tuned to something below the 17.7 KHz. This is two series capacitors with a shunt resistor to signal ground between placed between the output of the first stage Op Amp and a second stage Op Amp. You can use something like a non-inverting version with gain control (see the Bill Bowden refernce) to isolate the output of the filter from the detector.

Brian's third stage is what I've been calling a detector (blocking capacitor, diode half-wave rectifier, series resistor and RC tank) connected between the previous output and a high gain comparator (Op Amp stage without a feed back resistor).

For Brian's fourth stage, I recommended simply using an LED with a series current limiting resistor.

I've been trying not to give you a complete design while still giving you some guidance as to some basic circuits that can be made to work. I view part of this experiment is to actually playing around with the parts a bit on your own and seeing what happens. The whole purpose of having a breadboard with some parts is to be able to try some different things quickly. By your having access to a local mentor with an oscilloscope, you should be able to do a lot of experimenting and figure out how these things really work.

Re: Sound Frequenicies

Posted: Sun Mar 09, 2008 8:13 pm
by Craig_Bridge
One of the elves gave me some hints so here goes with an attempt to post a Microsoft Word document. Sorry if you don't have something that can view a Microsoft Word document with graphics. This site won't take HTML attachments with *.htm extensions.
Detector and Comparator stage
(43.5 KiB) Downloaded 406 times

Re: Sound Frequenicies

Posted: Wed Mar 19, 2008 11:34 pm
by vikdha1
Hi Mr. Bridge,

My project is due tomorrow and I just wanted to thank you for all the help you have given over the last six months. I have no doubt in my mind that if it weren't for you then I would still have no clue how to even connect the microphone tot he op amp or what a time constant. I'm not sure how I thank you enough, but, for what its worth, you were about three quarters of my acknowledgements section in my research report. I just want to thank you alot for all the help and let you know how much I appreciate it.

P.S. Don't get to angry if you see another post of mine in this forum, asking more questions about the project because I'm thinking I might actually continue to construct the device after the science fair.

Once again thank you so much,

Re: Sound Frequenicies

Posted: Thu Mar 20, 2008 1:09 am
by Craig_Bridge
I'm not sure how I thank you enough ... to thank you alot for all the help and let you know how much I appreciate it.
Glad to be of help and I appreciate your thanks. We have all had help along the way. IMO: The best way to really thank everybody who has helped you is at some future time help somebody else in a similar way.

Sorry that your project clock ran out before you were satisfied; however, learning and experimenting can continue at your own pace. As long as you want to continue getting help with this project, please just continue with this thread.

Lots of luck with your presentation. Engineering projects are like demonstration projects and often are not judged as important as scientific investigation projects.