Bat Detector

Discussion in 'The Projects Forum' started by GRNDPNDR, Mar 31, 2014.

  1. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    I was watching this video about rats, and how they laugh when tickled when they mentioned a device that interests me. The "bat detector" which takes sounds at high frequencies and brings them into our audible range.

    https://www.youtube.com/watch?feature=player_embedded&v=M_oKQ9Dzitc

    This looks like an old video so I assume technology has come a long way, which begs the question, how hard would it be to build one of these devices?
     
  2. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    I found a simple circuit, but the only thing I would change if it's possible, is to keep the analog part of the signal.

    This device makes it sound more like a Geiger counter, but if it's at all possible, I'd basically just like bring the actual sound within human range.

    http://pw1.netcom.com/~t-rex/BatDetector.html
     
  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The signal gets divided by 16 , this means that the 40 - 60 kHz will be outputed as 2.5 - 3.75 kHz, wich is a rather high beep.

    An other schematic uses a mixing princype:
    http://www.qsl.net/g4usp/Bat detector 3/Bat detector No3.htm
    That will keep the amplitude information as the signal is not clipped for a divider.

    Bertus
     
    Last edited: Mar 31, 2014
  4. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    That sounds like what I want, to reproduce the exact sounds being made, just in a range we can hear.

    I think that bad boy just might work.
     
  5. GRNDPNDR

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    Mar 1, 2012
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    Can't seem to find the SA612AN
     
  6. bertus

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    Hello,

    You could also look for a NE612.
    If that is not available the NE602 or SA602 could be an option.

    Bertus
     
  7. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    This can be done simply with a 555 and an op-amp! Here's how, but I can't take the time to put together a schematic:

    First, assume you have a amplified mic that captures and amplifies the ultrasound.

    Second, configure the 555 as a 50% duty cycle astable with a frequency around a khz or two (up or down) from the bats' nominal frequency. Make the frequency adjustable!

    Set up the op-amp as a +/- 1 gain, switchable by the output of the 555.

    Low pass the output of the amp (RC is fine here) for a stop band 5 to 10 khz.

    Send the signal to a set of headphones (may need a post amp to drive the headphones).

    Done.

    This configuration makes a crude superhet mixer that will down convert the ultrasound into audible frequencies. It works really well!
     
  8. GRNDPNDR

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    Mar 1, 2012
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    I only half follow the words. I'd have to see a schematic.
     
  9. joeyd999

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    Hopefully, someone here has the time to rough draft something up for you!
     
  10. bertus

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    Hello,

    I have taken the circuit from the PDF and altered it a bit.
    As the two signals from the second transistor are out of phase, you can use a 4066 as the mixer.

    [​IMG]

    Bertus
     
    Last edited: Mar 31, 2014
  11. GRNDPNDR

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    Mar 1, 2012
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    What pins on the 4066 are connected?

    I kind of follow along with the opamp idea as well.

    If I have a non-inverting amplifier setup, this amplifies the incoming signal from the mic?

    I don't know how to make the gain switchable from the 555 though.
     
  12. bertus

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    Hello,

    I have added the pin numbers on the 4066.
    The inverter can be an 4049 or similar.
    This approach will work if the duty cycle is about 50 %.
    You can change the 555 to an hysteristic oscillator for that.

    Bertus
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The schematic in post #3 is pretty much it. The 555 is running around 33 KHz, the mixer creates sum and difference frequencies, and the lpf removes the sum freqs. Joey's circuit is very similar, with a switched inverter replacing the mixer.

    The idea that switching a signal, or between signals, at some frequency creates other frequencies has been around for a while. Stereo FM is called FM multiplex because the subcarrier is not a 38 KHz carrier that is ampllitude modulated with the difference signal. The subcarrier is a consequence of switching between (multiplexing) the L and R signals at 38 KHz.

    http://transmitters.tripod.com/stereo.htm

    ak
     
  14. joeyd999

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    IIRC, this is my implementation of a mixer I designed for ultrasound down-conversion many (many!) years ago:

    [​IMG]

    Edit: IIRC, the only limitation of this circuit is that the input signal must be kept to < 0.5V pk (1 V p-p).
     
    Last edited: Mar 31, 2014
  15. AnalogKid

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    Nice mod. You can use the third section of the 4066 to invert the control signal, and eliminate the inverter.

    Also, the gain of the phase splitter matters. Rather, the difference in gain between the emitter and collector. Assuming hfe is 100, add 47 ohms in series with R108.

    ak
     
  16. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    Thanks for the input guys, I really appreciate it.

    I might have to adjust the frequencies as I'm not looking into this for bats, but for rats.

    Rats emit sound from 20Khz to 96Khz, so some changes may need to be made to hear the entire spectrum? or would this work for the entire range?

    Joey, I saw the pin numbers thanks.

    I may build one of these with the mixer, I think futurelec carries them, and then another with the inverter.

    The biggest problem is finding the parts. I can see in the schematic what I need, but when I try to make a BOM with Eagle it's full of footprints and stuff too. Also some of the parts seem old.

    edit**
    I must be using the wrong 4066 in Eagle, it doesn't have a pin 2 on the schematic, but does have 14 pins.

    It also says its an 18-bit static shift register, but the Fairchild datasheet says quad bilateral switch.

    I'm guessing I have the wrong Eagle component.
     
    Last edited: Mar 31, 2014
  17. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    Ok, I think I have the right component, but I see it has a Vss and a Vdd pin.

    Does this mean it requires a negative power supply as well, like an op-amp?
     
    Last edited: Mar 31, 2014
  18. AnalogKid

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    A 4066 will work with bipolar or unipolar supplies. For unipolar, Vss goes to ground, and the control inputs will respond to CMOS signals. But the analog signals have to be biased on a DC value of Vdd/2.

    ak
     
  19. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    so is the 4066 a direct replacement or does it need to have more done than just what joey did in his diagram?
     
  20. GRNDPNDR

    Thread Starter Member

    Mar 1, 2012
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    Here's the schematic after making some changes, like adding the 4066, a speaker and a mic.

    Would a mic even work properly? I wasn't aware they could pickup ultrasonic frequencies.
     
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