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Digtal Stethoscope MDK sound issues

nathan meyer
Prodigy 150 points

I recently purchased the Digital Stethoscope AFE and C5515 evaluation module to start evaluating the Digital Stethoscope application.  I was able to get everything set up, code loaded and the program running.  I made a stethoscope head with a WM-64K microphone and i could only faintly pick up the noise of a heartbeat.  I creaded a second stethoscope head with a POW-1544LLWC50-B-R microphone and tried again.  i was able to get a little more sound, but still not good.  I have to have the gain turned all the way up and the volume all the way up. 

Does anyone else use this version of the MDK?  What success have you had?  I am wondering if my microphones or stethoscope head is not adequate, or if i need to make some other hardware changes on the board.  From the demo video, it looked like it should work fairly well straight out of the box.  I have tried both a diaphram and bell type heads with out much difference either.

 

Thanks,

Nathan

  • 0
    TI__Prodigy 310 points

    It is possible that your microphones are not correctly biased. The WM-64K datasheet indicates bias voltage (+Vs) from 2V to 10V. The AIC3254 bias voltage is around 1.24V.  (I could not find information about POW-1544LLWC50-B-R)

    Could you please check the following?

    1. Measure V_BIAS (+Vs) at the microphone and make sure it is around 1.24V. 
    2. Bias your microphones externally, use voltages inside the operating ranges of your microphones.

    Regards, Nel

  • 0 in reply to Nelson Vazquez
    Prodigy 150 points

    I measured the MB from the codec and it is at 1.24V.  the Voltage at the Mic is at 0.8V.  I put in an external bias that has the microphone at 2.8V now, but still i get very faint sounds and a lot of feedback hum.

    Thanks

  • 0 in reply to nathan meyer
    TI__Prodigy 310 points

    Hi,

    Were you able to figure out a solution?

    Seems like you have a huge voltage drop in your MIC (1.24V - 0.8V = 0.44V). This could mean that your MIC is going over the current limits of the AIC mic bias circuitry. Just as a suggestion, check how much current is your MIC drawing from your external power supply. Also, check that you have a nice DC voltage with low ripple from the power supply. That way you will make sure the hum/noise is not coming from the mic bias. 

    Regards, Nel

  • 0 in reply to Nelson Vazquez
    Prodigy 150 points

    Unfortunately no.  I have looked at the supply for th bias and i get a very clean signal, only about 20mV p-p noise.  I have tried other micorphones that are1.5V bais, but it is still very faint.

  • 0 in reply to nathan meyer
    TI__Prodigy 310 points

    Hi Nathan,

    Are you using the Digital Stethoscope MDK source project from the http://code.google.com/p/c5505-ezdsp/ website?

  • 0 in reply to Nelson Vazquez
    Prodigy 150 points

    Nelson,

    yes, this is the source code i have been using.

    thanks

  • 0 in reply to nathan meyer
    TI__Expert 6380 points

    Hi Nathan,

    The WM64C - has a sensitivity of -45 dbM

    a WM55D103 appears to have a -54dbM sensitivity and might work better for you. 

    What is the sensitiviy spec on that other mic you have tried?

    Also, I haven't worked with the 5515 side, but I wonder what the internal PGA of the AIC3254 is set to as default in the software.  you could try increasing and see if there is some improvement.

     

  • 0 in reply to Dave Weinzierl
    Prodigy 150 points

    Hi David,

    I have tried a CMP-5247TF-K that has a -47dB and it did work slightly better.  The MEMS module i have used has a -62dB http://www.pololu.com/catalog/product/1618 and seems to work the best out of anything i have tried.  I will look into the PGA.  you had mentioned a piezo, do you have any recomendation for that?  Have you thought of anything else for me to look into?  Thanks

  • 0 in reply to Nelson Vazquez
    Prodigy 150 points

    Nelson,

    I have gone through and deleted out what i had for code ( i had both the V_09 that may have been for the 5505 and the V_12 for the 5515)  and reloaded my code for the V_12from the above link.  Now, when i get into Code Composer and tried to build and debug the program, it tells me that there are errors because the std.h and trc.h files can not be opened.  I have looked and they are #includes for these in several subprograms, but they do not exist in the files that i down loaded.  Do you have an idea why not? 

     

    Does anyone have these files?

  • 0 in reply to nathan meyer
    TI__Mastermind 23785 points

    This should be in Bios packages\ti\bios\include. Check your Bios setup.

    Regards.

  • 0 in reply to Steve Tsang
    Prodigy 150 points

    I see them there.  I will give that a try.

    Alright, i am new to code composer and i have been using this in the debug mode hooked to my PC.  Now i want to load the program into the EVM and use it as a stand alone, but i can't figure how to program the EVM.  I have a users guide for the DS MDK, but the instructions do not match the CCS V4, so i assume that it was written for an older version.  I have gone through and tried to figure it out, but i have not been able too.  Anyone have instructions on what i need to do, or where to look for instructions?

  • 0 in reply to nathan meyer
    Prodigy 60 points

    hello nathan,

    How did you connect stethoscope to the condenser microphone. Could you please explain?? I'm working on the same. But, my board isn't picking up any signal after initialization. It shows that its 0 BPM even after connecting the stethoscope assembly.