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Thread: Bat detector

  1. #651
    Senior Member CorBee's Avatar
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    Hi,

    Edwin reported this morning that the code to prevent the counter resetting to 0 during autorecord has worked. Some more testing will be done and after that I will probably update the code and hex.

    regards
    Cor

  2. #652
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    I discovered this issue Cor described when I wanted to have some recordings comparing the FG element I recently bought and the SPU element that I have been using up to this point.

    Some times the recording seemed to stop during the night but the last one was file number 1 from the early morning when I pressed the stop button and the recorder indicated #400+ where I only had 80 recordings or so.
    Cor made a nice log function that showed suddenly overwriting of file 1.


    Anyway, for all you curious about my experiments with the FG elements, here are some findings.

    I altered a few values in the opamp circuit. The FG element needs quite a bit more gain to produce the same voltgage levels. This is where a low noise design proves to be more important.
    (R2 4k7, R4 68k, C1 1nF, C3 3.3nF)

    The images below are a recording of the same sounds recorded in my garden.
    The top one is the SPU, the bottom the FG

    I used the same simple amplifier construction that reduces the low frequencies. People may think that this could cause issues but I had no problems and it gives a much better live experience. If you also amplify the lows quite a bit turning and pressing the controls and walking around become nasty noises. If you use this a as recorder outdoors the whole night without any man made noises in the area you will be fine with an unfiltered amplifier. Specially near roads with car traffic filtering the low sounds is very pleasant. I also did try other filtering but this simple circuit seems te so better than the others I tried.


    SPU element

    Click image for larger version. 

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    FG element

    Click image for larger version. 

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    One can see there is a bit of difference between high and low frequencies. But there is not a huge difference. The big benefit of the stronger output of the SPU can probably be seen in the noise of the FG. Since we only have low amplification with the SPU and much more gain on the FG the noise also seems to become a little stronger on the FG recording.

    Since these are two different devices, I guess I should swap the mics and amplifier circuits to be sure there is no hardware difference, but I used the one with FG element with an SPU before and had very similar results as with the other SPU equipped unit.

    As far as I can see we do not gain a lot with the FG element, of we should build an extremely low noise amplifier and stay away from low frequency noise sources.

    Edwin

  3. #653
    Senior Member CorBee's Avatar
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    Hi,

    To get rid of the issues with possible overwrites of files-numbers etc I have changed the code for filenames. This is still a feature that needs some testing but my initial tests look fine.

    The files will be saved as a hexencoded datetime using 8 characters, this allows us to always have unique filenames. These filenames however would not look very interesting inside the detector as you cannot see the datetime itself but only an 8byte hexcode. When you want to replay them it would be difficult to find a specific file back. So I changed the code that displays the filename to convert a unique-hexcoded date of the file into a readable timestamp. Normal filenames will be shown as they are still.

    If anybody has been using our system and has created a workflow (eg. in audacity) that is based on the current naming style of the files (BXXX_XXX) this change might introduce some problems. But for the long run this is a sustainable setup. Files can be saved and if you move them to a PC (or other permanent storage) you can automatically change the filenames into something readable for storage. This option will only be available when saving in WAV files, WAV files have allready the samplerate encoded inside the file. For RAW files we could use the same naming setup but without any clear information on the samplerate this would not be very helpfull.

    Which makes me come to the next question: anybody in favour of keeping RAW recordings ? There is no difference between RAW and WAV in terms of the recorded data so I am planning to remove this option unless some people have very clear demands to keep it available. Than RAW will be still using the old number convention when saving a filename.

    regards
    Cor

    regards
    Cor

  4. #654
    Senior Member CorBee's Avatar
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    Hi,

    For those interested, I have just uploaded (https://github.com/CorBer/teensy_bat...e_compiled_hex ) a hex version of the new update (firmwaredev_20200925). In this update (I will push the source out later today) recordings of WAV files will use a hexadecimal encoded filename. The 8 hexbytes of the filename are thus unique for each recording and represent the number of seconds passed since 1 jan 1970 (unix time) this solves issues with wrong filenumbers during recording.
    Recordings in RAW are still possible and will be using the old filenumbering system.

    kind regards
    Cor
    PS. Source code can be found on github under /src/update20200925
    Last edited by CorBee; 09-25-2020 at 05:55 AM.

  5. #655
    Senior Member CorBee's Avatar
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    Hi all,

    The previous code was working ... but not completely as planned. You could record data but not play them on the device (at least WAV formatted). This has been repaired in https://github.com/CorBer/teensy_bat...v_20201006.hex and the sourcefile is also updated (https://github.com/CorBer/teensy_bat...update20200925).

    As the bat-season is more or less ending in my area I think development will for some time be at a lower pace (or in full hibernation). I still encourage anybody with requests/problems etc to forward them in this forum.

    regards
    Cor

  6. #656
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    Hi Ivano, Are you still reading this tread? I guess so.

    I have been playing around with your schematic, it actually looks like something I tried before. And I mean the active filtering in te second opamp stage.
    I never had any luck working with them, that is why I stuck to one simple stage doing te amplifying and applying just some simple filtering.
    The active filtering always seemed to start oscillating or give some bad side effects. Yes I know the op-amp I use is different and I also use lower value resistors since these should produce less noise (or I was badly informed). Or maybe those have something to do with my bad results.

    I just wondered how you were doing and if there was any progress made already.

    I was playing around with an ALC4040 USB adapter myself because that is quite affordable and allows a sample rate of 192kHz enough for the pips here in the garden.

    Using a non inverting single stage op-amp with simple filtering like in the Teensybat detector I got these results.

    Click image for larger version. 

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    You can see although I am filtering out low frequencies, there still is a bit more noise on 23kHz. We also did see similar effects on the Teensybat detector. Some people did blame the electronics in the Teensybat detector but it seems it comes down to the SPU microphone element.

    Kind regards,

    Edwin

  7. #657
    Junior Member Dodotronic's Avatar
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    Hi Edwin

    I started to work on the preamp but I always go slowly to to other project running that must be completed.
    However the first test seems to be good even if the signal level is quite low. I used the OPA1642 with a preampli and a second stage with a low pass filter.
    I hope to have better results this week.
    Ivano

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