Looking for help choosing/setting up hardware for DAQ board for ultrasonic mics.

[sryabinin]

My name is Stepan I am a mechanical engineering student at  Oregon State University, currently working on a project for Garet Lahvis, a professor at Oregon Health and Science University

Dr. Lahvis is working on recording ultrasonic vocalizations in mice.  However, the mice typically only utter these vocalizations when they are in the presence of other mice.  This makes it impossible to tell which mouse is vocalizing.  To solve this problem, we plan to use a ultrasonic microphone array sending the signals through a data acquisition board and into LabView software for processing and to triangulate the source mouse.  Based on my background research, FG-3329 microphones from Knowles (see datasheet attached) have been used in several research papers on a similar topic, ultrasonic recording and localization of bat calls, quite effectively.
 
I am hoping someone at can offer some advice on setting up our equipment most optimally for this application.  At this point I am particularly in need of advice on choosing a DAQ.  I believe an NI USB-9201 will work well for our application, but am very open to other ideas.  Also, as my knowledge of microphone circuits is rather limited, I was hoping someone could give me advice on how to optimally setup the microphone circuits so that they will work with the DAQ chosen.  

Hopefully someone can help me out, thanks in advance!

Stepan

[EEsRULEtheWORLD]

Hi, Stepan.

I was looking into your FG-3329 microphone and noticed that there is no information provided on the scaling information (dB/V).  It is possible that the scaling will be different for different supply voltages.  I'm also not seeing any information on the resolution of the signal produced by the FG-3329.  If you could contact Knowles and find out the scaling information and resolution of the output signal, this would be of great value in defining your system.  

The USB-9201 may work in your application, if you're providing an external voltage source that will supply 0.9-1.6VDC.  The USB-9201 is an analog input device and will not allow you to produce the required supply voltage for the application.  Assuming that you're leaning towards the USB interface, I would suggest that you choose the USB-6211.  With this device, you'll be able to produce the 0.9-1.6VDC supply voltage through static analog output channels, as well as measure the analog signals produced by the microphone.  The USB-9201 will be able to read the analog input signal produced by the microphone, but the accuracy is much less than that of the USB-6211.  The USB-6211 has one analog input voltage range with a 12 bit resolution and therefore, will measure voltages much less accurately than that of the USB-9201 (16 bit resolution with 4 voltage ranges).  This is where the resolution and scaling of the output signal from the FG-3329 is important.

As far as the microphone circuit is concerned (assuming you are not using an external power supply):

1) Connect the Output terminal of the FG-3329 to the analog input channel of the USB data acquisition device that you choose.

2) Connect the Positive terminal of the FG-3329 to the analog output channel of the USB data acquisition device that you choose.

3) Connect the Negative terminal of the FG-3329 to GND of the USB data acquisition device that you choose.

Questions:

1.  What is the resolution of the FG-3329?

2.  Is there scaling associated with the supply voltages?

3.  What is your preference for supplying voltage to the microphone?  An external power supply or the analog output channel of a DAQ device?

I'll continue to research this issue.  I hope you're having a great day!

[sryabinin]

Thanks Sara, this was just the info I needed.

In response to some of the questions let me give a little more background info on what I intend to do.

Basically we already have a very nice ultrasonic microphone setup for actually recording any vocalizations produced by the mice.  The only thing that this microphone array needs to do is detect the ultrasonic waves and triangulate where they are coming from in the cage.  What I was planning to do is writting a program in LabView (if this is possible, I have not looked this far ahead yet) which will simply monitor the voltages at the microphones and put an accurate time stamp down when it sees ultrasonic frequencies 30kHz and higher at each microphone.  From there it shouldn't be too hard to use the time delay between microphones to see where the signal is coming from.  

Based off this I do not think voltage accuracy is as important as long as we are able to pick out when the microphone is recieving ultrasonic signals.  I believe this is something we can test once everything is setup by playing back the ultrasonic vocalizations and monitoring the voltages the DAQ is seeing.  Am I correct in these assumptions?  If not I will try to obtain this information.  Also based on my background research in the use of these microphones and after talking briefly with some people at Knowles it seems a pre-amplifier is almost always required as the as a typical microphone signal may be in the mV range.  Choosing an op amp and setting up the circuit for it was giving me some problems.

To answer your third question, I think using an analog output channel for supplying voltage to the microphone is an excellent idea.  It will definitely simplify the wiring that will have to be done. In general after looking at the comparisons between the USB-6211 and USB-9201 definitely prefer the 6211.

Hopefully that answered some of your questions.  Thanks a lot for helping me out.

Stepan

Message Edited by sryabinin on 06-10-2009 11:24 AM

[EEsRULEtheWORLD]

Hello Stepan,

After hearing a bit more about your application, it seems like it may require a bit more dynamic range and a card that can simultaneously sample on all channels.  The card that I would recommend to take a look at would be the NI 9233.  This card will enable you to take highly accuracy measurements on up to 4 microphones and calculate phase differences for triangulation.  In order to make sure that the 9233 will work for this application can you please answers the following questions:

1.  What frequency is the signal of interest?  Our devices are specified to handle only certain frequency ranges.  Anything above this range will likely be attenuated by the front end of our device or won't be properly sampled which will cause the signal to be aliased.  It sounds like you're only dealing with frequencies in the 30KHz range.  Is there any frequencies of interested much higher than this?

2.  In regards to timestamp information, would something with lower determinism in the order of seconds to milliseconds be acceptable?  The reason I ask is because our multi-function DAQ devices typically draw their initial timestamp by reading the system time.  Due to the nature of the windows operating system, this has its own level of innaccuracy.  It is also non-deterministic. 

[sryabinin]

Sara,

Sorry for the late response. 

The frequency range we are looking at is actually fairly large.  We would ideally like to scan a frequency range from 30-100 or 110 kHz. As far as the timestamp is concerned I do not think milliseconds will provide us with the resolution we need to distinguish which mouse is making the calls.  The mice are typically within a couple centimeters of eachother, with the cage itself being not much bigger than 1 ft x 1 ft.  I imagine this will need much finer time readings if I'm going to be using a timestamp method to triangulate the source.  Perhaps I need to think of a different method in this case.

I have attached a paper on bat vocalizations.  They use the same type of microphone as I intend to use and capture data using an NI DAQ.  Our application will be similar but on a smaller scale, perhaps this will provide some more information for you.

Thanks for the help

Stepan

[EEsRULEtheWORLD]

Hi, Stepan.

In order to acquire measurements for your application, you're going to need a device that will allow for simultaneous sampling and be able to detect nanosecond time changes (based off of the speed of sound).  Unfortunately, there is no portable USB solution that will meet these specifications.  You're going to need an S series that is capable of sampling at a rate of over 1MHz.  The greater the sampling rate, the better resolution of the input signal (which basically means you'll be able to detect more of your signal in smaller amounts of time).