Need ideas for simple geophone!

Discussion in 'General Electronics Chat' started by Mike33, Jul 14, 2010.

  1. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005
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    Hi everyone,

    Here is a potentially good discussion topic. I sometimes watch Ghost Hunters, and they have a little geophone that they place on the floor of a house that they suspect might have paranormal activity. It of course picks up vibration as from footsteps, and converts that vibration to a voltage to light a string of LEDs, with a stronger signal lighting more of them.

    I'd like to make one of these, as simple, quick & dirty as possible. I am thinking maybe a condenser mic could work to pick up the "eerie sound of footsteps" (lol), and an opamp or 2 to amplify the very small signal into something that could light up 3 or 4 LEDs. My fiancee would love this; we go into old houses quite a bit, and like to scare ourselves, ha ha.

    Does anyone have any thoughts, or even a design, on how this could be implemented?

    Thanks,

    ~Mike
     
  2. sceadwian

    New Member

    Jun 1, 2009
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    An electret mic should work quiet well, you just have to very closely bond it to the object you're trying to sense, easiest way to do that would be to glue it to a small piece of metal, you'll just want something as smooth as possible to avoid any airgaps between the mirophone and the sensing point. Eletret mics are much more common than condenser mics.
     
  3. ELECTRONERD

    Senior Member

    May 26, 2009
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    If you used a mic, it would be difficult to eliminate external audio noises. If you were to speak while walking, it might change your results and cause error. Perhaps a sensitive piezo sensor would be better. The output voltage is proportional to the stress of the viabrations detected. I would place the sensor on a wooden floor for the best detection, since wood carries viabrations better than concrete or carpet; if you can, that is.

    An op amp or two would be suitable to amplify your signal, or even an in amp. I would also program a μC to recognize the foot patterns in order to minimize error; you could have it expect viabrations at a predetermined duration for each step (for instance, have it expect a step every ~1-3 seconds).
     
  4. Mike2545

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    Mar 26, 2009
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  5. sceadwian

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    Jun 1, 2009
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    EN, I'm not sure you know what 'closely bonded' means, perhaps the poster does not either. When I recommend using an electret mic it means using glue (superglue is quiet rigid not a bad choice) or basically any other solid gap filling material to bond the electret mic against a plate that can be put against a flat surface. There should be very little to no direct coupling with the air.

    Piezo's won't pick up the low frequency vibrations the poster is looking for at all. I have never seen a piezo device used as a microphone for audio applications, not to say they aren't used for them. Even if you could use one it's neither quick simple or dirty.
     
  6. c_omalley2002

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    Mar 18, 2010
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  7. c_omalley2002

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    Mar 18, 2010
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    BTW, I'm a ghost hunters fan, myself. I used to go to supposed 'haunted' places with friends back when I was a teenager. I experienced some crazy stuff. Used to have some great pics....Sometimes I miss those days...or nights, rather. Good luck on the ghost hunting.
     
  8. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005
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    Thanks everyone! Very good links!
    I like the DIY....build amps and guitar effects, etc., so it's not foreign. I"m not sure if we're looking to specifically pick up footsteps, or just 'disturbances' of an old house, so a mic-type seems like the best bet.

    I have a CD4017 right here....Do you guys suppose that D1 thru D9 (on the .pdf link) could be hacked to be LEDs (with dropping resistors for each)? Then I could avoid the transistor and SCR, simply omitting the right side of the circuit...and could probably remove the element from a piezobuzzer from RS to use as the sensor...
     
  9. Audioguru

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    Dec 20, 2007
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    Of course it is foreign. It is from India and most circuits from that site are very old and DO NOT WORK.

    Why do you believe in Ghosts??
     
  10. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Look up automatic gain control circuits and try to build a Very High Gain with AGC microphone preamp. I think that will give you fun EVP results.

    Creating an EMF meter is pretty simple since it is a transformer antenna > diode detector > and range amplifier > that feeds a meter or stacked LED indicators. You might want to have it checking vertical lateral and linear polarities to make it fancy. If you could give it lower frequency range detecting 20Hz or lower you would have something very special.

    For your Geophone I wonder how a MEMS accelerometer would do as a sensing element.
     
  11. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Ouch! Be careful because you made it sound like the circuits don't work because they are from India. I am not sure if that is what you meant to say.

    Why do people believe in anything.

    Try asking people why they believe in God.

    Ask them if they believe this world is real.

    Ask them why they believe that there might be life out there around other stars.

    Ask them if they believe in love.

    It is possible that people have been in contact with spirits from the past, or some parallel dimension that is off our real worlds table. It is possible they only had a freaky experience with natural phenomenon that they have interpreted as something unnatural.

    It is easy to take the strangest moments of your life and put them in the wrong box. But which is the wrong box.

    Tell people that the Presidents Energy Adviser would use his spare time to finish and publish a paper in a Nature showing a way to possibly use optical microscopes to look at atoms and you would think that it was the stuff that could only happen in science fiction right? The world of the possible is pretty much unlimited except in our minds.
     
  12. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005
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    Well said, Potato Pudding.
    The answer is - who said I believe in ghosts? I do believe in scaring yourself, and watching zombie movies, tho! :)

    Plus, isn't it easy to hack a geophone circuit into one that will alert you if someone is breaking in your house (or other place, since it's portable)? Walking up the stairs....

    I like devices that are interesting like that. The motion detector devices of the Alien movies are one of my favorite gadgets which currently are in their infancy but will eventually be mass-marketed.
     
  13. Audioguru

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    Dec 20, 2007
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    I wouldn't use a geophone in my home to detect a burglar.
    My home is solid, a geophone would not detect somebody walking but it would detect a big truck outside driving past or maybe even a noisy motocycle or lawnmower.

    Most jet airplanes are fairly quiet now but I have recently seen, heard and felt the vibrations from an old one flying past.

    People who live in a dangerous neighbourhood have steel doors and thick metal bars over all windows. They don't need useless burglar alarms.
     
  14. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Ghosts?

    Maybe if you bonded your sensor to a guitar, Elvis might play it for you?

    Otherwise you'd still have a useful electric guitar.
     
  15. Mike33

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    Feb 4, 2005
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    Actually, I have about 6 guitars, Studiot. Elvis can stop by and jam a little any time he wants, but I think I'd have more fun with Hendrix!!

    I don't live in a dangerous neighborhood; I live in a rural area. My neighbors use Smith & Wesson home security, lol. I am merely curious about yet another circuit that I could build if I chose to. After 10 yrs. of building 'stuff', it gets hard to find new things to catch your interest sometimes. Then you see something on TV, and the Mrs. says "Honey, build that for me!", and away you go! :)
    Maybe I should not have used the word "ghost"?
     
  16. sceadwian

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    Jun 1, 2009
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    omally, if you want to study some crazy stuff you should learn the psychology behind it =) Even the most intelligent human being on the planet is still susceptible to the deeper portions of our brains deepest nearly subconscious drives.

    There is no reality behind it, the experience however makes it a real emotional moment which will imprint in our memory sometimes orders of magnitude beyond the actual experience's validity outside of the emotional response.
     
  17. retched

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    Dec 5, 2009
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    And sometimes it is swamp gas. ;)
     
  18. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    You can make a cheap geophone by gluing a few penneys to the voice coll of a small speaker, pref. a high z, something like audio 34 from BGMicro[ best bet is the seismometer ]. Output around 2-5 mV. last time used fed into a comparator,[ 2&3/4" Calrad .1 W, 8Ω with 3 coins ] but that only gives presence of impulse- not amplitude. might feed it into OP amp then bar graph IC. From far left field: 'remember the havock the B 36 made with a string of 24 seismometers- shut down operations for a smoke break.
     
  19. Mike33

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    Feb 4, 2005
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    So, pennies as dampers, cool idea :eek:) Could do something with that, I think. Or the piezo element.
     
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