Proving the Speed of Sound - 5th grade science fair project
Beau Schwabe
Posts: 6,566
Proving the Speed of Sound
By: Paxton Shorow
Date: Friday, May 14, 2010
Teacher: Mrs. Henry - 5th Grade Science fair project
Theory of operation:
Most of us can go to Google and search for the speed of sound and we find a number somewhere in the ballpark of 1125 feet per second. We take that number, use it and take it for granted to calculate a distance. Keep in mind that there are several factors that can affect the actual speed of sound, such as altitude, humidity, temperature, etc. which introduce errors to our ‘fixed’ value we obtained. But what if we wanted to prove what the speed of sound was instead of using some number we were able to find on-line?
The idea with this experiment is basically the same as sonar, except we are doing it with audible sounds instead. The idea is straight forward, you send a signal out and wait for an echo. The 'time' in-between when you send the signal verses receiving the signal
can be calculated as the object distance. Since the Propeller controls all aspects of the timing, the procedure is relatively simple.
1) Make noise (a loud pop) on an external speaker (a PING) and start a counter
2) Wait for the microphone to pickup the signal (an ECHO) and stop a counter
3) Send the value of the counter to a visual display and clear the counter
4) Repeat step 1
From this basic information and a couple of tests it is possible to measure the actual value for the speed of sound. In my tests, I setup 3 positions at 1 foot, 2 foot, and 3 foot positions with the distance measured from the microphone.
At each distance I placed the speaker and measured, rounding to the nearest 1000, after the average value settled.
My test measurements:
1 foot = 171,000
2 feet = 243,000
3 feet = 315,000
Knowing that the Propeller, running at 80 MHz, is capable of counting up to 80,000,000 in one second and that the value returned is the difference in time or the number of counts between the transmitter (The Speaker) and the receiver (The microphone), the speed of sound can be calculated by dividing 80,000,000 by the difference of the 2 foot reading
and the 1 foot reading. (or the 3 foot reading and the 2 foot reading)
80,000,000 / (243,000 - 171,000) = 1111 feet per second
OR
80,000,000 / (315,000 - 243,000) = 1111 feet per second
Another way to look at this....
'Counts per second' is what your processor is capable of... in this case 80,000,000
'Counts per foot' is what you are measuring ... in my test case 72,000
'feet per second' an acceptable unit to represent the speed of sound
...The above equation can be re-written as...
...Where 'Counts' cancels out and you are left with 'feet per second'
A question you might ask... If there are 72,000 ticks per foot, then why in the first foot do we get a reading of 171,000? This is due to propagation delays within the system. i.e. how quickly the microphone responds, and general program overhead from the Propeller. This value would be a calibration factor you could just subtract off 99,000 in software, but in order to find that number, you would have needed to run this program in it's un-calibrated form in the first place to make that determination.
At this point though, the reason that we take the difference of two known distances is to ensure that the propagation delay, whatever it may be, is equally presented to both test locations. This has a way of canceling out any kind of a bias in delay that could be introduced to the test.
Experimenting further:
Once you determine or prove what the speed of sound is relative to you and your surroundings...
1) ...set the speaker at an unknown distance and try to calculate how far away it is.
2) ...or predict how many counts you would get at another known distance based on previously measured data
TX Schematic:
RX Schematic:
(For the RX Schematic) refer to the Microphone connection to the Propeller Demo Board
www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropDemoDschem.pdf
One thing to note and it took me awhile to figure out what was going on, the speaker and the microphone should be facing each other, otherwise you can get a 'reflection' or echo off of the ceiling causing your numbers to be higher than you would expect.
Propeller Program Screen shot
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 5/16/2010 3:22:18 AM GMT
By: Paxton Shorow
Date: Friday, May 14, 2010
Teacher: Mrs. Henry - 5th Grade Science fair project
Theory of operation:
Most of us can go to Google and search for the speed of sound and we find a number somewhere in the ballpark of 1125 feet per second. We take that number, use it and take it for granted to calculate a distance. Keep in mind that there are several factors that can affect the actual speed of sound, such as altitude, humidity, temperature, etc. which introduce errors to our ‘fixed’ value we obtained. But what if we wanted to prove what the speed of sound was instead of using some number we were able to find on-line?
The idea with this experiment is basically the same as sonar, except we are doing it with audible sounds instead. The idea is straight forward, you send a signal out and wait for an echo. The 'time' in-between when you send the signal verses receiving the signal
can be calculated as the object distance. Since the Propeller controls all aspects of the timing, the procedure is relatively simple.
1) Make noise (a loud pop) on an external speaker (a PING) and start a counter
2) Wait for the microphone to pickup the signal (an ECHO) and stop a counter
3) Send the value of the counter to a visual display and clear the counter
4) Repeat step 1
From this basic information and a couple of tests it is possible to measure the actual value for the speed of sound. In my tests, I setup 3 positions at 1 foot, 2 foot, and 3 foot positions with the distance measured from the microphone.
At each distance I placed the speaker and measured, rounding to the nearest 1000, after the average value settled.
My test measurements:
1 foot = 171,000
2 feet = 243,000
3 feet = 315,000
Knowing that the Propeller, running at 80 MHz, is capable of counting up to 80,000,000 in one second and that the value returned is the difference in time or the number of counts between the transmitter (The Speaker) and the receiver (The microphone), the speed of sound can be calculated by dividing 80,000,000 by the difference of the 2 foot reading
and the 1 foot reading. (or the 3 foot reading and the 2 foot reading)
80,000,000 / (243,000 - 171,000) = 1111 feet per second
OR
80,000,000 / (315,000 - 243,000) = 1111 feet per second
Another way to look at this....
Counts Counts feet -------- / -------- = -------- second foot second
'Counts per second' is what your processor is capable of... in this case 80,000,000
'Counts per foot' is what you are measuring ... in my test case 72,000
'feet per second' an acceptable unit to represent the speed of sound
...The above equation can be re-written as...
Counts foot feet -------- X -------- = -------- second Counts second
...Where 'Counts' cancels out and you are left with 'feet per second'
A question you might ask... If there are 72,000 ticks per foot, then why in the first foot do we get a reading of 171,000? This is due to propagation delays within the system. i.e. how quickly the microphone responds, and general program overhead from the Propeller. This value would be a calibration factor you could just subtract off 99,000 in software, but in order to find that number, you would have needed to run this program in it's un-calibrated form in the first place to make that determination.
At this point though, the reason that we take the difference of two known distances is to ensure that the propagation delay, whatever it may be, is equally presented to both test locations. This has a way of canceling out any kind of a bias in delay that could be introduced to the test.
Experimenting further:
Once you determine or prove what the speed of sound is relative to you and your surroundings...
1) ...set the speaker at an unknown distance and try to calculate how far away it is.
2) ...or predict how many counts you would get at another known distance based on previously measured data
TX Schematic:
RX Schematic:
(For the RX Schematic) refer to the Microphone connection to the Propeller Demo Board
www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropDemoDschem.pdf
One thing to note and it took me awhile to figure out what was going on, the speaker and the microphone should be facing each other, otherwise you can get a 'reflection' or echo off of the ceiling causing your numbers to be higher than you would expect.
Propeller Program Screen shot
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 5/16/2010 3:22:18 AM GMT
837 x 471 - 82K
423 x 203 - 13K
800 x 600 - 109K
Comments
Cool demonstration.
Do you think it would work with just two microphone placed a set distance apart. And then use a hand clap or finger snap and measure time between when the closer microphone detects it and the further micrphone detect it ?
Bean
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Use BASIC on the Propeller with the speed of assembly language.
PropBASIC thread http://forums.parallax.com/showthread.php?p=867134
March 2010 Nuts and Volts article·http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp5.pdf
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There are two rules in life:
· 1) Never divulge all information
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If you choose not to decide, you still have made a choice. [noparse][[/noparse]RUSH - Freewill]
Absolutely!, with modification to the code of course to detect two mic's.
Edit:
To get dead on accuracy, you will probably nee to interdigitate the ADC function so that the mic's are read within a few clocks of each other... even so, at 80MHz (20MHz instruction), one inch resolution should still be about 1480 instruction counts.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 5/16/2010 7:39:37 PM GMT
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"WOAH! that wasn't supposed to happen!"
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Whit+
"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
The 5th grader takes Advanced science and math courses at the local high school. He approached me with the idea based on something that they were doing in school, and I basically programed a timer for him that would do the job. He took it from there for use in his his presentation.
Whit,
Thanks! ... it was fun!
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
This would be a good science fair item for middle or even high school. Excellent!
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Tom Talbot
New Market, MD, USA
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Never force anything - Always get a bigger hammer.
Meanwhile, here in Oklahoma, they're cutting teachers and instituting two elective Bible courses in public schools, Old and New Testaments, I kid you not.
It's a cryin' shame. So many young minds wasted.
Where in Oklahoma? ... just for the record Paxton and myself live in Oklahoma.
I don't think that the cutting of teachers is isolated to Oklahoma. I think what you see is more of a sign of the current economy AND the broken education system can be seen just about everywhere you go.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Here in PA the govenor has raised education spending from 6.9 billion in 2003 to 12.3 billion in the 2010-11 budget.
The schools STILL are complaining that they don't have enough money (they will NEVER have enough money) and the students are no better off.
The school doesn't even provide pencils or tablets to the students. They haven't for years... But they build indoor swimming pools and get astro-turf for the fields, stadium lighting. etc...
50% of students in the large cities do not even graduate.
To make matters worse, the taxpayers will have to "make-up" the teachers pension fund in 2012-2013 because of the downturn in the stock market. The only way this is possible is with more and more taxes.
It's a terrible situation, and it's gonna take a MAJOR reform to fix it.
See there you go... You had to get me started on it.
Bean.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Use BASIC on the Propeller with the speed of assembly language.
PropBASIC thread http://forums.parallax.com/showthread.php?p=867134
March 2010 Nuts and Volts article·http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp5.pdf
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There are two rules in life:
· 1) Never divulge all information
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
If you choose not to decide, you still have made a choice. [noparse][[/noparse]RUSH - Freewill]
I'm in South Tulsa/Bixby, where the high school football and basketball stadiums rival some of the colleges, but math, computer, and science labs remain unfunded. Oklahoma is a perennial bottom-dweller when it comes to public education ratings. Part of the problem is the poverty, another is political graft, kickbacks, and party politicking, while a third is the strong influence of the anti-science religious right who successfully lobbied for the elective Bible classes to be added to an abbreviated curriculum.
One of the reasons it was so nice to read about Paxton's project, was seeing proof that SOMEBODY out there hasn't dropped the ball for bright kids like Paxton. I only hope the same opportunities present themselves for him to further his education through middle school and senior high. He's off to a great start!
Still, I think that Oklahoma is not an isolated situation. If you point a finger you must point it at everyone ... you see this sort of thing everywhere you go. It doesn't even need to pertain to anything technically related for that matter. Perhaps it's just me getting old(er), but I see much of this poor mentality and attitude in business as well, however that could be a direct filtration from the education system or lack there of. Point is, it's on the East coast just as prevalent as it is on the West coast, and everywhere in between. I don't know how to fix it any better than the next guy, but if I can show somebody how to do something that makes sense and it is something that they can benefit from, then in some way I hope that I have made a good difference.
Anyway, yes, I agree ... Paxton really gets excited about this stuff, and I hope that he can have the proper tools at his disposal in the future to excel in whatever path he chooses to entertain.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
·I don't know how to fix it any better than the next guy, but if I can show somebody how to do something that makes sense and it is something that they can benefit from, then in some way I hope that I have made a good difference.
I would like to thank you for taking the time for our kids and there learning some thing that will be useful in the years to come
That is so cool and very nice project and write up about it
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·Now wanting to learn Spin· Thanks for any·
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Sam
·That is why when·I hear or see·some one taking the time with our kids trying to make a difference· I have some hope that thing may get better
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·Now wanting to learn Spin· Thanks for any·
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Sam
Post Edited (sam_sam_sam) : 6/18/2010 1:36:15 AM GMT