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Ultrasonic Sensor Help

Discussion in 'Sensors and Actuators' started by MrBretten, Jan 22, 2015.

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  1. MrBretten

    MrBretten

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    Jan 22, 2015
    I recently took an interest in ultrasonic devices and was hoping someone who understands audio would be able to offer their opinion on my circuit design.

    What I currently understand is that ultrasonic is sound that occurs outside of the human range of hearing ( >20kHz). I have created a detection circuit that can locate a device that is emitting this ultrasonic sound. I have looked at many transducers and have found that most transducers have a center frequency at around 25kHz or 40kHz (I don't entirely understand why these values have been chosen, but I've just been rolling with it and praying for the best). I would prefer receiving the entire ultrasonic frequency spectrum instead of just 40kHz (or 25kHz). The current theory I've been going off of is that if a device is emitting some random ultrasonic frequency, then there might be a 40kHz signal in there somewhere.

    So back to my ultrasonic receiver circuit now; Currently I have a 40kHz transducer that is DC filtered, amplified by a TL081 (1st stage, x2 gain), filtered through a 4th order band-pass filter with a center frequency of 40kHz and a bandwidth of 5kHz, amplified again by a TL081 (2nd stage, x100 gain), DC filtered again, and finally sent to a DSP device for signal processing (and hopefully ultrasonic sound location capabilities).

    Here's where the problems begin. Although I am able to receive a signal that is 40kHz (and with high gain too); the signal is a tad too noisy for my taste. It's most likely due to the solder-less breadboard I'm using, but I'm starting to doubt that way I've gone about receiving and analyzing the signal. Is there a better method of going about this (different op-amps?)? And is there a way to get the entire ultrasonic frequency spectrum (or at least 20kHz to 80kHz)? I was planning on just running the signal I have now through an ADC and having a raspberry pi do a spectrum analysis, but I don't know if what I'm getting is the correct signal (the transducer does respond to direction though, like if I move away from the device, amplitude decreases). Any help that you can offer would be greatly appreciated.
     
    Last edited by a moderator: Jan 22, 2015
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    have you googled for wide band ultra sonic transducers

    personally haven't heard of them but they may exist
     
  3. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hi Taylor
    Can you post a circuit diagram. It might be something in your design.
    Thanks
    Adam
     
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Dave do you think he might be better off using a microphone?
    Adam
     
  5. davenn

    davenn Moderator

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    I haven't looked specifically to what the freq response would be for a microphone would be in the 20 - 80 kHz range ?
     
  6. Arouse1973

    Arouse1973 Adam

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    I recon a bit higher, I'll have a look
    Adam
     
  7. davenn

    davenn Moderator

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    Considering mic's are designed for human voice range + plus a bit, I would be surprised if their above 20kHz is any good ... the response of several I looked at dramatically fell off even before 20 kHz
     
  8. Arouse1973

    Arouse1973 Adam

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  9. davenn

    davenn Moderator

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    that one only has a 6 kHz bandwidth centred on 80kHz ;)

    he's after a wideband sensor covering the 20 - 80kHz (100kHz) range

    as I said in post #2 Im not familiar with any wideband ones, but they possibly exist
     
  10. Arouse1973

    Arouse1973 Adam

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    Ah yes.........:rolleyes:
     
  11. BobK

    BobK

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    Your 40KHz centered transducer is probably capable of receiving signals quite a bit wider than that, but at reduced response. But then you put a 40KHz bandpass filter that will attenuate anything other than 40KHz. Lose the bandpass filter and you will get a wider response. Not sure if it will be wide enough for your purposes, but I can only improve things.

    Bob
     
    Arouse1973 likes this.
  12. MrBretten

    MrBretten

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    Jan 22, 2015
    Thanks for the responses. I have looked at high frequency range transducers, but most are WAY out of my price range. The transducer I currently have is 40 kHz with a 1 kHz BW. I did come across something interesting though; if an inductor is put in parallel with the transducer, apparently the bandwidth increases significantly. I'm still doing research into it, so I'll get back with you all on my findings. If I can increase the BW then hell, I might as well make the center frequency tunable
     
  13. Arouse1973

    Arouse1973 Adam

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    Yes used for bat detectors. It can increase it up to 60KHz. But you loose a bit lower down in frequency.
    Adam
     
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