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Thread: Bat detector

  1. #451
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    Quote Originally Posted by CorBee View Post
    Hi,

    The amplitude will be depending on the distance from the key-ring to your detector, the loudness of your ring (intensity), the gain for the one-transistor amplifier (which design ?) and the mic_gain setting of the teensy_batdetector .

    One thing you can try to get a bit better understanding of the sensitivity is listening to for instance a constant high frequent signal coming from many devices with clocks inside. I have for instance an audio-player that emits this signal and I can pick it up about a meter away or so ... depending on the gain I use. Or a programmable timer (to switch appliances) will also. When you have a good and reliable source you can start recording/testing your device settings against that.

    Cor

    EDIT: this is my current 1-transistor amplifier (BC547=BC550c)
    Attachment 17298
    I use almost the same
    Click image for larger version. 

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    /bengt

  2. #452
    Senior Member CorBee's Avatar
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    Quote Originally Posted by benlenkar View Post
    I use almost the same
    Click image for larger version. 

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    /bengt
    I think Edwin has removed C2 from his design later on. But the simulation with LT-spice does show this is probably not going to change the amplification

  3. #453
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    Quote Originally Posted by CorBee View Post
    I think Edwin has removed C2 from his design later on. But the simulation with LT-spice does show this is probably not going to change the amplification
    Yes I removed C2, it was supposed to "short" RF signals to ground.
    Working with the opamp amplifier it just seemed to pick up display update noise so I chose not to place it.

    Also C1 can be changed, If you want to attenuate lower frequency sounds you can lower the value of C1. I guess you should not bring it below 220pF
    I do like 220pF myself but you can notice a bit less gain on 20Khz which is not a big problem because the microphones alleady have stronger signals on lower frequencies.

    For the microphone, if you have it inside the box, create a seal between the microphone and the box.
    Do not use it inside the box just behind a small hole.


    I use a cone that I can screw into the box. The cone is because it seems like the microphone behind a "long" audio channel does not work best. The cone also provide some amplification.



    I added a picture.

    On the left the construction I use,
    the second is a microphone behind a hole in the box. I do not recommend that.
    The third is a microhone in the box but with a seal, If you can construct that it, it is fine. (do not use a thick seal)
    The fourth picture is what I would suggest of the box wall is quite thick
    picture number five is just keeping the microphone outside the box.


    Click image for larger version. 

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    I do not have any commercial detector so I can not compare.
    I was on a bat excursion two days ago, at some moments it seemed my own build picked up earlier, at other times the 300 euro commercial device picked up better.
    We were a few meters apart so maybe that also made some difference.

    Edwin

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