NI 6250 board

[nyborn]

Hi

I would to ask you. I have a program called Sound Input with FFT.vi. See attached. I don't know if you know how to use it. I tried to put a microphone on analog input and ground. I don't know how to use set those parameters. Could you please tell me how to do it if you know?

I am in an very urgent. I hope you can reply to me promply.

Message Edited by Support on 12-01-2005 02:54 PM

[alipio]

Hi nyborn

This is a quite simple program to measure armonic distortion and FFT of an input signal.

1.- The input level is set 10 ,-10, so a micro is not a good signal. Use a generator and select an adequate level.

2.- Wire a true constant to the db on input of power vi, to have a  logarithmic spectrum.

You will see spectrum, main frequency  and number of armonics of an input signal.

Hope it helps

Alipio

[nyborn]

Hi Alipio:

I would like to ask how to test my microphone. Attached are my graphs. I tired to change the max and min values from -1 to 1. I also changed my program to RSE mode. The detected frequecy changes as I varied the number of sampling rate and number of sample. It didn't seem there is a difference in having a microphone plugged into the CB68LP board or not. It still the same.

I would like to ask how to test the microphone.

[NIquist]

I haven't used the NI cards for audio testing but I don't know of many types of microphone that will put out enough power to be tested directly in that way.  You will need a good quality audio amplifier to provide a proper signal.  If your mic is a condenser type it will also need power from an internal battery or "phantom power" provided by the amp.

[nyborn]

Hi Niquist:

Could you please dercribe to me or give me a picture of the mic with an amp that I can buy it in the shop. I don't exactly have the picture right now. I know that my mic has no internal battery. Could you please send me some pictures of mic or from the web page that I can see. Thanks

Regards,

John

[nyborn]

Hi Niquist:

Could you please dercribe to me or give me a picture of the mic with an amp that I can buy it in the shop. I don't exactly have the picture right now. I know that my mic has no internal battery. Could you please send me some pictures of mic or from the web page that I can see. Thanks

Regards,

John

[nyborn]

Hi Niquist:

In this test, should I need a self-amp mic. To me, the self-amp mic with internal batteries that I have seen in the shop in general is wireless mic  with the selp-amp or self-amp with a mic plug in and then connected to speaker. Are you talking about this kind?

Could you please confirm to me.

I wonder if I buy a mic like Karoke or computer mic. Would that be OK? Attached is my graph of different type of mics. But I can afraid of differnt thinkess of wire which I cut the head of the plug and connect the black and red lead cables to CB68-LP.

Also, I am sure if the self-made mic is working. I don't know how to test it work. If I don't need to buy the self-amp, would you please tell me how to test the self-made mic working?

Regards,

John

[NIquist]

I looked at your pictures and it appears you have three simple dynamic type mics.  These are usually a diaphram attached to a tiny coil which is around a small magnet.  They are like a small speaker in reverse.  These types of mics only output very low levels and need to be amplified to get into the voltage range of you DAQ card.  NI may have signal conditioning options on other cards or perhaps a SCXI card added to yours would do. 

Other options include building your own amp.  Here is a link I found by searching "audio amplifier" on Google.  There are MANY more.

http://www.techlib.com/electronics/audioamps.html

Or you could go to an electronics store like Radio Shack, buy an amp and make the cable adapters for your various mics. 

Keep in mind that you should buy or build an amp that is better than the mics you're testing so that the quality of the amp does not limit you. 

Additionally, you will need some sound sources like sine waves, white/pink noise, etc.  You can generate these with LabView if your card has analog outputs (you'll need a speaker of course) or you can buy a CD with test tones on it and use a stereo for the source.  Again, if your source speakers are cheap you will limit the quality at which you can test the mics.

It looks like you code is good (mostly a LV example).  You don't really need to sample at 200KHz but it can't hurt if you have the PC power and memory.

Good Luck.

[nyborn]

Hi NIquist:

1) Attached is my picture of my mic. As you see, the operating voltage is 1V – 10V.

And the specification of 6250 is also +/- 10V. You said the output voltage is very small. Which one is representing output voltage in the red background diagram. Is it the -58+/-3db?  If so, the output voltage would be tenth to the negative fifty eight?

Is that right?

If it is the operating voltage, then the output is fall into the range of the specification of 6250. The source is beeper as shown in the picture. If this the case, I can use a dynamic mic, would you please correct me here?

2) If so, if I put cut the wire of this mic and put the red and black lead cable connecting to this mic. Is it OK? I am afraid the thinkness of the read and black lead cable is thinker than the mic. Do you think I can do it this way?

[nyborn]

3) If not, see attached file named speaker wire. Do you think I can connect black and red lead cable connecting the speaker cable and it will be fine?

4) The link you provided for creating amplifier http://www.techlib.com/electronics/audioamps.html

There are five examples in general, The only method to amplifier the signals is class A audio amplifiers. But Op-Amp audio amplifier seems not suitable, is that right?

The class-A audio amplifiers has three configs. There are few things I need to verify:

1)       200mV p-p, -2mV p-p, ~ 2mV p-p are all input of the mic, is that right?

2)      The output of the first config is 250mV/210mA.  

The output of the second config is 64dm, if the above question is correct?

The output of the third config  is 4.7V, is that right?