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Thread: Bat detector

  1. #426
    Senior Member CorBee's Avatar
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    Well the Mic is PCB mounted and thus that central pad is not something I can or will try to fiddle with ... its way to small for programmers I am used to buttons instead of a microscope

  2. #427
    Senior Member DD4WH's Avatar
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    well, then we will never know or solve the problem with the noise that you have . . .

  3. #428
    Senior Member CorBee's Avatar
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    Well we have Edwin who assembles these modules and he might have a go at trying one without the central pad connected. So never ... say never

  4. #429
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    In single ended output the -out pad is floating.

    I do have to mention the codec gain used is quite high,


    This is what I see with codec gain on 10

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    I also made a few noises....

    The spectrum of the silent part looks like this.

    Click image for larger version. 

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    When I have codec gain set to 20 I see this

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    Sorry for the different scales....

    Somehow the peak near 23Khz seems a lot larger than the rest of the noise.....

  5. #430
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    Frank,

    Maybe you could use a SD-card extender like this to be able to seperate the SD powersupply from the Teensy. On the teensy it is very hard to do that but here you can easily cut a track.


    Click image for larger version. 

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    There are also versions with white plastic ribbon cable but I think those could be a bit more difficult to solder on to.

    Edwin

  6. #431
    Senior Member DD4WH's Avatar
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    Hi Edwin,

    thanks a lot! I will think more about that!

    However, adding additional hardware for features already implemented (built-in SD card) is a bit annyoing, and I think I read that the built-in SD card is much faster, which could be important for high speed ultrasound logging.

    All the best,

    Frank

  7. #432
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    The externder was just an idea to be able to cut a power supply track and put a separate 3v3 source on the SD card to try and get the writing noise out of the teensy.



    I did some experiments again with the SGTL gain settings microphones and amplifiers. We already knew that using high gains settings on the SGTL adds a lot of noise.

    Both the ICS and SPU microphines seem to have some noise around 23Khz, with the SPU it is presented as a wider lower hump but the ICS presents a larger spike.

    The amplifiers help to suppress the low frequency sounds and enhance the high frequency sounds.

    Using these, or connecting the microphones directly seem to show the same raised levels on or around 23Khz.



    Although it seemed the noise is coming form the microphone the SGTL5000 also seems to have a big part in it.



    Of course this is not a huge problem but I just wanted to get rid of the vertical bar on the waterfall screen when I am searching for bats on high gain.
    Once one has located bats and they are closer one can reduce the gain and the bar becomes barely noticeable.



    The main problem is introduced by the user I guess, when there is no bat around, one tends to turn up the gain in the hope and hear some bats.


    If one wants great signal to noise level I guess the SGTL is not the best thing to use.

    Your stationary bat recorder is probably a lot better at recording but for running around the field using the detection modes and de graphical presentation dit approach is just great.


    Edwin

  8. #433
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    I just updated some documentation.

    I don't quite remember if I shared the link to these files before but any eBay buyer of the V0.2 board als got the link form the item description.
    The link now holds the new files.

    Anyway, if you still have to start working on the V0.2 board here are the updated files.

    The most important changes:

    Display update noise is reduced by quite a bit. (100 ohm resistors in all data lines)

    Added instructions on how to build a transistor amp on this board if you like that better.

    Beside that there was some minor parts optimization.



    The V0.2 version was designed to use a low noise rail-to-rail opamp that would give us a bigger dynamic range and less noise.
    Unfortunately the opamp als picked up some display update noise. This noise is nearly gone by using the resistors in the datalines the opamp version now is just slightly better than te transistor version. No huge differences so if you have the transistor board version keep it. The biggest improvement is in reducing the data noise, of course one can also use the resistors in the data lines with the transistor version.


    If one wants to use standard headers, it is better to use a transistor amplifier.


    Kind regards,

    Edwin


    Almost forgot, there is some extra information on LCD revisions, some versions use direct LED drive, others have a transistor on the LED pin. One can determine the difference if there is a Q1 part next to the U1. It makes a huge difference in the resistor used on the LED pin.

  9. #434
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    Quote Originally Posted by pe1pwf View Post
    I did some experiments again with the SGTL gain settings microphones and amplifiers. We already knew that using high gains settings on the SGTL adds a lot of noise.

    Both the ICS and SPU microphines seem to have some noise around 23Khz, with the SPU it is presented as a wider lower hump but the ICS presents a larger spike.

    The amplifiers help to suppress the low frequency sounds and enhance the high frequency sounds.

    Using these, or connecting the microphones directly seem to show the same raised levels on or around 23Khz.



    Although it seemed the noise is coming form the microphone the SGTL5000 also seems to have a big part in it.


    If one wants great signal to noise level I guess the SGTL is not the best thing to use.

    Your stationary bat recorder is probably a lot better at recording but for running around the field using the detection modes and de graphical presentation dit approach is just great.


    Edwin
    Edwin

    Have you tried to use the tl972 with a higher gain and using the SGTL at a lower gain?


    Alain

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