microphone,pitch calculations
stamptrol
Posts: 1,731
Hi folks,
A client has a machine to analyze the materials used in making his product. It basically hits the material sample with a small hammer and listens for the resulting "ring". The sound is analyzed by a PC and the fundamental frequency is used to sort the material.
I suspect the PC is needed to do an analysis in software.
Any thoughts on how this analysis can be tackled Stamp or Prop-wise? The frequencies observed are right around 440 Hz +/- 30%.
Thanks,
A client has a machine to analyze the materials used in making his product. It basically hits the material sample with a small hammer and listens for the resulting "ring". The sound is analyzed by a PC and the fundamental frequency is used to sort the material.
I suspect the PC is needed to do an analysis in software.
Any thoughts on how this analysis can be tackled Stamp or Prop-wise? The frequencies observed are right around 440 Hz +/- 30%.
Thanks,
Comments
Probably possible on the Prop. Depending on what kind of accuracy you want.
What you need is a Fast Fourier Transform to tell what frequencies are present in your signal.
There is one here : http://propeller.wikispaces.com/FFT
Or my FFT is here : http://forums.parallax.com/showthread.php/128292-Heater-s-Fast-Fourier-Transform.
There are a few similar transforms you can use. Check out this nice Propeller Sound analyser demo video: http://www.youtube.com/watch?v=qvjG2j6uh94
You may need a steep low pass filter to get this working nicely.
frequency. Or equivalently a narrow band-pass filter.
-Phil
BTW) you could do this with a Stamp and obviously a Propeller if you knew the >> exact << frequency that you were looking for.
Good observation. To build upon that, I would say the 2 harmonics, and one prime frequency.(need to review my physics book, :frown:)
Where you hold it, may shorten or lengthen the frequency depending on the attributes of the hammer, relative to the oscillating arm. The energy imparted to the hammer when struck, is
energy converted to Moment around the point where you are holding it. I would suggest doing a "Free Body Diagram" of the hammer/material model,
Maybe the movement of the hammer (oscillations) could be measured to produce a result of the frequency. If the oscillation could be observed, then
maybe an infrared light source could help in discerning the frequency, which the basic stamp can be used in.:cool:
Alternatively:
A derivative of this would be to use acoustic resonance mechanical propagation delay through the object. Essentially a speaker at one end of the object, and a microphone on the other end of the object creating a mechanical feedback loop with the object under detection in the middle. By measuring the frequency (at this point the frequency would easily be a digital signal) and just counting the number of pulses over a determined amount of time you can determine the resonant frequency.
Phil, Because it does not work.
Back in uni some guys were trying to measure the frequency of a good old fashioned brass bell that way. What with all the noise of striking it and all the harmonics going on it's impossible.
Im asking because it sounds like the application is using the latter- a force hammer for finding deadblow frequencies.
-Phil
I could be wrong, as usual, but I always understood that if you want to look at any signals in the digital domain you are going to have to filter out the high frequencies that you are not interested in before you digitise it. Reason being that anything above the Nyquist frequency will get aliased to a lower frequency. That rather implies you cannot do that low pass filtering digitally but have to have an analogue filter.
With that in place, yes I think your scheme would work. But isn't it rather hard to make such a steep analogue filter?
CuriousOne,
I suspect that a crystal that operated in the 440Hz range would be huge. Certainly I have never heard of one.
But your idea is good. In the old days they would measure the frequency of the mains power by having a row of tuning forks of slightly varying lengths excited by coils driven from the mains. A different tuning fork would resonate as the mains frequency changed. Accurate to 1Hz or so.
Jim
Thanks for all the discussion.
The hammer is a machined rod which dropped from a fixed distance. Picture a solenoid that lets the rod drop straight down then retracts it. A microphone picks up the resulting ring.
The sample material under test rests on two supports that are acoustically isolated from the sample. The samples all get placed in exactly the same position by the transfer mechanism.
The machine at present takes about 10 seconds to weigh, freq check, imprint a label and bin sort each material sample. The overall aim is to get the cycle down to 4 seconds or so.
I'm meeting with the client next week so should have more details then.
Cheers,
If such crystals are hard to get, there's workaround. go get two IF crystals from AM radios, 455 and 465khz (dirt cheap, available everywhere). Buld a FCO (frequency controlled oscillator), tuned at 450khz. also quite simple, can be done using 1 transistor, and use your mic output as frequency shifter for that FCO. Remaining is same as written above. There's no need to make things too complicated.
The International Crystal Manufacturing Company lists low frequency crystals only down to 10KHz.
http://www.icmfg.com/crystal_hc51u.html
Do you have a circuit of that Frequency Controlled Oscillator? I have also never heard of such a thing. Google is not helping.
Yes. Follow that You Tube link I posted above.
Everyone has put in excellent ideas. I would like to give an overall suggestion. If the goal is to identify A frequency with the object, then a very simple approach is required, as
noted by others with ambient noise, which may inject error into your project. Measuring the oscillations of the hammer by infrared, magnetic, or other means will be simple,
cheap, and cut down of software/memory demands. IF, that is your goal.
IF you goal is to use the frequency & harmonics to provide an "audio signature" of the target material, then, by all means, a spectrum/frequency analyzer is needed.
Your target goal will determine the software, hardware, money, and logistics of were you want to be.
If you are trying an "audio signature" approach, then more information will be needed. Knowledge of target materials & hammer will be needed, depending
on the quality of the level of results you are trying to "drill" down to. Good Luck!
http://f-page.ru/fp/8a56fa7b9f184ca48a2cdaeedafd4646
I had similar designed 1khz one. The quartz was formed in shape of rod, with about 5x5mm sides and length about 20mm.
For my 443hz one, I will have look in my junk box, to find that crystal again, I've aquired it more than 30 years ago.
FCO is modification of VCO with added lowpass or highpass filter, so change of input (low) frequency results change in frequency of high output frequency signal.
Still don't get the FCO idea.
I was wondering. What is the material we are examining here?
Is it metallic?
Perhaps there are other ways to excite it's resonances than hitting it with a hammer.
:nerd: Brilliant suggestion. These factors suggested can affect the results you may be looking for.
May I take the time, and humbly suggest, investing time in the HP 50g calculator to basic stamp
project? Your project is an example of why I started the 50g project. You will have projects in the
future, and need the processing power to solve/analyze. I plan to use th 50g/basic stamp combo
for a Rapid Math Model Integrator, for this purpose. Just a thought. I appreciate your time.
software, in which there are many.(consumes time and money) The HP/stamp combo can get you the point
of invention creation for profit or ?.
HPCalc.org has programs already written that may help you. Take the basic stamp input from the transducer,
put into the specfic variable table in the program in the calc, and Volia!
You have a spicy "Audio hammer" Parallax sandwich! Just a thought.
kalimba on Youtube:
http://www.youtube.com/watch?v=4XD02oMHC5E
Project details:
http://petehemery.github.io/Final-Year-Project/Dissertation.pdf
Discussion and source code(FFT powered scrolling musical note representation:):
http://forums.parallax.com/showthread.php/140777-Audio-Signal-Processing-on-the-Propeller-Demo-Board?p=1105502#post1105502
There used to be a video available for his project but the link doesn't work anymore. However, I have a copy downloaded.
That is quite close to what I'm expecting will be needed. Thanks for the links.
The materials being tested are various wood blanks and it is the resonance of the blanks that is being measured.
Cheers,
Interesting discussion
@Bob thanks for the interest, I'll be editing the video and reposting it soon (when I have a machine capable of editing HD videos)
Cheers,
Pete
Nothing of substance yet as the client struggles with financing for the upgrade. Will report in as things progress.
Tom
Hi Heater,
Sorry you missed it first time. Thanks for your message, you gave me the kick I needed to get my editing hat on
Here you are:
http://www.youtube.com/watch?v=xQUO_jfl8SE
Can a wooden instrument (guitar?) "tuning fork" be of any help ?
-Phil
Ok thanks! I'll have a look. I have a copy of the unedited version that I could upload should you ever get out of line LOL Actually, I don't know why you are editing because the first version was fine.