vikdha1
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Sound Frequenicies

Postby vikdha1 » Wed Sep 12, 2007 6:47 pm

Hi, I was just wondering whether anyone had invented a device that could pick up frequencies such as 17.7 khz. Perhaps a radio or some sort of receiver.

Thank You

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Re: Sound Frequenicies

Postby OneBriiguy » Thu Sep 13, 2007 8:48 am

vikdha1 wrote:Hi, I was just wondering whether anyone had invented a device that could pick up frequencies such as 17.7 khz. Perhaps a radio or some sort of receiver.

Thank You


Hello, vikdha1!

Devices exist for measuring and detecting frequencies across the electromagnetic spectrum. What is your project, and what are your goals / questions so that we can assist you?
Brian Castelli (OneBriiguy)
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vikdha1
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Sound frequencies

Postby vikdha1 » Thu Sep 13, 2007 1:29 pm

I am trying to create a receiver of some sort that pick up the mosquito ringtone. I wanted to make a cheap device teachers could use in class so all those attempting to cheat can be caught.

Thank you
Vik

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Re: Sound frequencies

Postby OneBriiguy » Thu Sep 13, 2007 1:38 pm

vikdha1 wrote:I am trying to create a receiver of some sort that pick up the mosquito ringtone. I wanted to make a cheap device teachers could use in class so all those attempting to cheat can be caught.

Thank you


Ah! So your description refers to SOUND waves, not electromagnetic waves as I had assumed. Detecting sound waves requires a different sort of technology.

Are you considering making a product out of this investigation? Are you executing a science fair project about this topic? What are your next steps and your ultimate goal?
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vikdha1
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Sound Frequenicies

Postby vikdha1 » Thu Sep 13, 2007 8:00 pm

Yes, I am planning to make a product out of my investigation. I am a scientific research student at my high school and I will be entering the Palos Verdes science fair. My next steps were, if no one's already invented it, to research the makr up of a radio and try to construct a receiver to pick up those high frequency sounds

Thank You
Vik

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Re: Sound Frequenicies

Postby OneBriiguy » Fri Sep 14, 2007 5:13 am

vikdha1 wrote:Yes, I am planning to make a product out of my investigation. I am a scientific research student at my high school and I will be entering the Palos Verdes science fair. My next steps were, if no one's already invented it, to research the makr up of a radio and try to construct a receiver to pick up those high frequency sounds

Thank You


Hello, vikdha1!

Let me make sure that I understand your project. I believe that you are interested in building a device that can detect the sound produced by the so-called mosquito ringtone - a 17 kHz ringtone that is above the hearing range of most adults. Is that right?

If so, this is not a radio-frequency signal. You can't build a radio receiver to pick it up. You must have some kind of microphone to pick up the sound waves. The microphone must drive an audio circuit that can somehow detect the frequency of interest and notify the user when it has been detected.

Your project is essentially an analog electronic circuit design exercise - it's possible to build an analog circuit that turns on a light when the sound frequency is between some values. As an alternative, you could build a circuit that digitizes the sound and processes the frequency via some kind of programmed device - a computer, a microcontroller, or a PGA. (Note that the digitizing circuitry already exists in the sound card of most PCs. An alternative to building a device would be to write some software that uses the input from a PC's microphone to accomplish your goal.)

I suggest that you focus your research on the technologies required to capture sound at your frequency of interest and the process of analyzing that sound.

To get you started, you might consider checking out Wikipedia's spectrum analyzer entry. Focus on the bandpass filter, acoustic, and spectrogram information.

Best wishes for success on your project.
Brian Castelli (OneBriiguy)

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Postby Craig_Bridge » Fri Sep 14, 2007 7:10 am

To add to what Brian's response, you proably want to do some research on the frequency spectrum of microphones. Audio engineers designing microphones for sound studios typically restrict their designs to 30Hz - 15KHz. Microphones designed for telephones are typically 300Hz - 3KHz. I suspect that many microphones associated with computers are intended for voice over IP and fall into the telephone type of range.
-Craig

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Postby OneBriiguy » Fri Sep 14, 2007 7:36 am

Craig_Bridge wrote:To add to what Brian's response, you proably want to do some research on the frequency spectrum of microphones. Audio engineers designing microphones for sound studios typically restrict their designs to 30Hz - 15KHz. Microphones designed for telephones are typically 300Hz - 3KHz. I suspect that many microphones associated with computers are intended for voice over IP and fall into the telephone type of range.


Excellent point! I hadn't thought of that. I'm glad you chimed in because a microphone that's not capable of picking up the frequency under discussion would completely prevent success! Similar frequency limitations might be built into the sound cards on our PCs. This is another area worthy of investigation.

Thank you for pointing out this crucial requirement.
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Postby Louise » Fri Sep 14, 2007 8:44 am

Another variation on this theme is to explore the idea that this frequency cannot be heard by people over 30 and can be heard by people under thirty. That is, you could test a large number of people of various ages, and see if they can hear the ringtone (you could even change test different volumes too). I know some "old" people can hear the ring tone, and I'm sure some teenagers cannot, so it might be very interesting to explore the distrubution of hearing abilities by age.

This experiment will also require a bunch of research to determine how to effective design this experiment, and how to determine the validity of the results (statistical analysis). It may require additional approval from your school (since it involves human subjects).

Louise

vikdha1
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Sound Frequenicies

Postby vikdha1 » Fri Sep 14, 2007 11:14 pm

Thanks for the information about the receiver not being possible. The idea of inventing a software sounds interesting but I am not very good at computers and that kind of stuff. But I was very interested in the light bulb invention that would turn on between certain frequencies. However I'm not sure how to do that. What would I use in place of a microphone. And for the light bulb invention would i require a computer or anything?

Thank You
Vik

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Re: Sound Frequenicies

Postby OneBriiguy » Mon Sep 17, 2007 5:43 am

vikdha1 wrote:Thanks for the information about the receiver not being possible. The idea of inventing a software sounds interesting but I am not very good at computers and that kind of stuff. But I was very interested in the light bulb invention that would turn on between certain frequencies. However I'm not sure how to do that. What would I use in place of a microphone. And for the light bulb invention would i require a computer or anything?

Thank You


Hello, vikdha1!

For the light-bulb experiment you would not need a computer. You would need a microphone or similar device to convert the sound waves into electrical impulses. These impulses would need to be amplified and fed into something like a band-pass filter. A band-pass filter allows signals within a specific frequency range to pass while attenuating frequencies outside of the range. A little circuit logic on the output of the bandpass filter would turn the light on when the signal strength exceeded some threshold indicating that the ringtone was present.

You would be desiging and building an electronic circuit. I suggest that you research analog circuit design, especially band-pass filters. There are many ways to build such a circuit, and part of your project may be to weigh the pros and cons of the different approaches.

Best wishes for success with your project!
Brian Castelli (OneBriiguy)

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vikdha1
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Postby vikdha1 » Sun Sep 30, 2007 9:25 pm

Hi,

I have researched the analog circuit and band pass filters which I will require to create my device. However, I was wondering whether a sophmore in high school would be able to create something like this. I just wanted to know if I would require some extra help or need to obtain more extenisive knowledge about a subject to conduct the experiment. I am only asking because I do not want to attempt something that I do not have a chance of succeeding at.

Thank You so much.
Vik

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Postby OneBriiguy » Mon Oct 01, 2007 4:56 am

vikdha1 wrote:Hi,

I have researched the analog circuit and band pass filters which I will require to create my device. However, I was wondering whether a sophmore in high school would be able to create something like this. I just wanted to know if I would require some extra help or need to obtain more extenisive knowledge about a subject to conduct the experiment. I am only asking because I do not want to attempt something that I do not have a chance of succeeding at.

Thank You so much.


Hello, vikdha1!

In my opinion, a high school sophomore is capable of doing this work. When I was a sophomore, I had an electronics class in which I built a simple AM radio. Sure, you will need some guidance. We all do.

I think the biggest challenge you will have is in assembling the components. To make it simpler, and to avoid soldering and circuit board fabrication, I would use a breadboard kit available from places like Radio Shack. A breadboard kit will allow you to make connections by plugging components into a grid and making connections with colored wires.
Brian Castelli (OneBriiguy)

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vikdha1
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Postby vikdha1 » Mon Oct 01, 2007 5:17 pm

Hi,

Thank you so much for the advice about the breadboard kit. I will make sure that I get that soon. However, I researched the bandpass filters and the microphones and all the other components and all the online prices seem very expensive and I just wanted to know whether the prices I had researched were correct. For example, the bandpass filters I saw were no less than $160.00
Vik

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Postby OneBriiguy » Tue Oct 02, 2007 4:29 am

vikdha1 wrote:Hi,

Thank you so much for the advice about the breadboard kit. I will make sure that I get that soon. However, I researched the bandpass filters and the microphones and all the other components and all the online prices seem very expensive and I just wanted to know whether the prices I had researched were correct. For example, the bandpass filters I saw were no less than $160.00


Hi, vikdha1!

Wow! I couldn't afford to build a science fair project using $160 filters!

What you spend on your project is up to you. When we started discussing this project, however, I assumed that you would be building a band-pass filter out of component parts - resistors, capacitors and inductors. I just looked at an online catalog from Digi-Key (http://www.digikey.com) and I saw individual component parts from $0.25 to $1.00. My estimate is that you could build a bandpass filter for under $10 using individual pieces.

The key here is to design the circuit so that you can specify the appropriate component values. If you do a search on "band pass" you will find web sites that describe hwo to do the design such that the center frequency of your filter is at the same frequency as the mosquito ring tone.
Brian Castelli (OneBriiguy)

Engineering Specialist


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