tree sound sensor

Discussion in 'The Projects Forum' started by Tony Elliott, Jul 20, 2015.

  1. Tony Elliott

    Thread Starter Member

    May 8, 2015
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    Hello,

    I am looking to drill a small hole and listen to the activity inside a tree. I am thinking of using a contact mic and clamping it onto a metal insert and then amplifying it, does anyone know of a ideal setup for this kind of tree probe sensor?
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Recording, listeneing, or both. It sounds like a good plan. There are a zillion little microphone amps and audio amps on ebay. Do you have a run time or battery life target?

    ak
     
  3. OBW0549

    Well-Known Member

    Mar 2, 2015
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    I'm guessing some sort of vibration sensor might do better than a microphone; perhaps one of those piezo film sensors, such as are used in guitar pickups?
     
  4. ebeowulf17

    Active Member

    Aug 12, 2014
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    I like this idea a lot because it will do a stellar job of picking up tree vibrations while picking up relatively little outside noise. In my limited experience with them, piezos seem to always have poor low frequency response, so you might want to check those specs if that would be an issue in this application.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Are you trying to prove the "if a tree falls in a forest and no one is around does it make a sound" ?
    Or attempting to spy on those darn little Keebler Elves :p
     
    wayneh, ronv, ErnieM and 2 others like this.
  6. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
    2
    Yes I have been looking into Pieto disks and LM ribbons. I am thinking of clamping it into a pointed metal probe and hearing if I get any action from the tree, but the advantage of using a mic is that you can push it into a hole so I guess ill have to try both unless there is a vibration probe out there?
    Im thinking of using small solar panels but I think I need to sort out what filter, pre amp and amp circuits that need to be powered:)
     
  7. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
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    Yes, I guess this is an issue so I have bought a LM vibration plastic film sensor to see if it is better, I might also try to use a lowpass or high pass filter to focus on the interesting frequencies:) I'm waiting for this sensor to arrive in the post.
     
  8. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
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    Yes the guitar pickup is interesting to I could try that out!
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    When I was messing about with my TL431 electret booster, I stripped an old electret capsule for the special JFET and experimented with various predominantly capacitive components.

    Certain types of capacitors were surprisingly microphonic, piezo sounder disks gave good results - but for real sensitivity and big output, you can't beat the piezo-ceramic pellet from one of those no-flint cigarette lighters.
     
  10. Tony Elliott

    Thread Starter Member

    May 8, 2015
    140
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    This is very interesting, I have a part of me feeling that your having me on and rest of me wants this to be true!! Have you got a link to one of these that is effective and how do you wire one up has it a + & - like a transducer??
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    The TL431 electret booster was published in Elektor magazine a few years ago and I've described it several times on this forum more recently.
     
  12. sirch2

    Well-Known Member

    Jan 21, 2013
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    I'm wondering if a microphone pushed into a hole is going to work. In normal circumstances a microphone relies on air pressure changes but if it is in a hole in the wood will the air pressure in the hole change very much?

    It will be interesting to find out!
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    What kind of sounds are you looking for? Growth, wind (twisting and leaves rustling), decomposition (limbs falling and cracking), ambient noises that pass into/through the tree, ... Please advise.

    Also, when you say, "hole" in the tree. Do you mean to put the microphone in there like a cork in a wine bottle, or would you have some free space for air to flow?
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    When I was messing about with the TL431 project, I converted a standard electret capsule into a vibration sensor by supergluing a "stirrup" to the diaphragm. The actual electret material is extremely fragile, I made the "stirrup" out of a short bit if insulation stripped off some hookup wire, not even a blob of superglue - just the absolute minimum it takes to stick it on.

    It was the extreme fragility of this arrangement that prompted me to experiment with the widest range I could find of other potentially piezoelectric materials.
     
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  15. ian field

    Distinguished Member

    Oct 27, 2012
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    For a first try - I'd file a flat on the side of the trunk and araldite a sounder disk on it.

    A good solid bond should eliminate the resonant frequency of the brass disk by effectively making it part of the tree.
     
    Tony Elliott likes this.
  16. wayneh

    Expert

    Sep 9, 2010
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    One thing not mentioned is signal versus noise. I assume you're not interested in ambient sounds and their propagation in the wood (noise) but rather in sounds (or at least vibrations in the audio range?)
    originating within the tree itself (the signal). You'll need some computing power and additional sensors to resolve the difference.
     
  17. ebeowulf17

    Active Member

    Aug 12, 2014
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    On a nature CD called Pulse of the Planet, they recorded tiny insects by putting a phonograph needle on the tip of a blade of grass. Don't know exactly how that would translate to your situation, but I imagine there's some potential there.

    EDIT: Here's a link to the CD, which is really cool (one of my audio engineering professors recommended it to me years ago.)
    http://www.cdbaby.com/m/cd/potpaj2
     
    Last edited: Jul 23, 2015
    OBW0549 likes this.
  18. ian field

    Distinguished Member

    Oct 27, 2012
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    A ceramic cartridge was one of the things tried on the electret capsule JFET on the TL431 mic booster, it gave a very large output.

    Unfortunately - ceramic cartridges usually contain Rochelle salt as the piezo electric material, it wouldn't even survive the first dew - let alone exposure to rain.
     
  19. ebeowulf17

    Active Member

    Aug 12, 2014
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    That's an interesting and relevant point, but the same could be said of most recording equipment and microphones. I wouldn't leave any of my recording gear out in the elements. Guess it depends a lot on whether the TS wants to leave this in place for extended, unsupervised periods or just have it in the tree for brief periods while listening and/or recording. Coming up with a waterproof mic/preamp system will be a lot more challenging than making one that's expected to stay reasonably dry.
     
  20. ian field

    Distinguished Member

    Oct 27, 2012
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    Some piezo elements are true ceramics and won't be much affected by water, those can be bonded to the wood for optimum acoustic coupling.

    The electronics aren't difficult to seal against water, or could simply be attached by connectors and taken in when it rains.

    In close contact, the sap in the wood would damage any piezo salt based element, the ceramic pellet from the spark generator in a cigarette lighter is probably the highest output and easiest to get hold of - most discount stores near me have packs of 4 lighters for £0.99p.
     
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