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Sound Impact Sesnor sensitivity — Parallax Forums

Sound Impact Sesnor sensitivity

r.daneelr.daneel Posts: 96
edited 2014-02-27 11:54 in Accessories
I just knocked-up a DIY sound impact sensor according to the schematic provided by Parallax. I can only get it to detect a hand-clap from less than about 2 metres. I know the electret mic I am using picks up sounds at least 3-4 metres away. Any suggestions for making the sound impact sensor more sensitive? I've tried adjusting the 1k pot - no help there. A better amp maybe? I was kind-of hoping I could use the sound impact sensors off-the-shelf, but I need a better range than 2 metres.

Comments

  • kwinnkwinn Posts: 8,697
    edited 2014-02-17 11:24
    An amplifier would probably help with that. Could use an op amp or a single transistor for that.
  • r.daneelr.daneel Posts: 96
    edited 2014-02-17 12:31
    kwinn wrote: »
    An amplifier would probably help with that. Could use an op amp or a single transistor for that.

    The sound impact sensor schematic shows a transistor already - is that not an amplifier? Would an op amp give me that much better amplification? I suppose it depends on the transistor and op amp. I tried both 2N3904 and 2n2222 transistor with similar results.
  • r.daneelr.daneel Posts: 96
    edited 2014-02-17 15:15
    I Googled and played... This seems to work for me:

    SoundSensor.jpg



    I get about 100x gain from the amp, and a ~10ms pulse out of the 555 (the 555 datasheet says the pulse duration will be 1.1xR8xC5). Detects hand claps from at least 5 metres.

    If I change R3 to a 100k trimmer pot will that allow me to adjust the sensitivity? (I don't have one, otherwise I'd just try it...)
    SoundSensor.jpg
    1024 x 419 - 75K
  • kwinnkwinn Posts: 8,697
    edited 2014-02-18 21:37
    Changing R3 would change the sensitivity (probably for the worse) but it would also affect the DC bias of the circuit which is not a good thing.

    Do you want more range or just a longer output pulse?
  • kwinnkwinn Posts: 8,697
    edited 2014-02-18 21:43
    BTW, this is the type of circuit used in some "glass break" detectors in security systems.
  • r.daneelr.daneel Posts: 96
    edited 2014-02-18 22:43
    kwinn wrote: »
    Changing R3 would change the sensitivity (probably for the worse) but it would also affect the DC bias of the circuit which is not a good thing.

    Do you want more range or just a longer output pulse?

    I was looking for the best sensitivity. Maybe I'll just leave R3 at 22k.

    I varied the pulse length by reducing R8 to 1k. My reading of the 555 datasheet is that the pulse length is given by 1.1 x R8 x C5.
  • kwinnkwinn Posts: 8,697
    edited 2014-02-26 21:18
    r.daneel wrote: »
    I was looking for the best sensitivity. Maybe I'll just leave R3 at 22k.

    I varied the pulse length by reducing R8 to 1k. My reading of the 555 datasheet is that the pulse length is given by 1.1 x R8 x C5.

    Increasing R1 might increase the sensitivity, and varying the value of R3 will change the sensitivity. You could try replacing both with potentiometers so you can find the optimum resistance values for maximum sensitivity.
  • r.daneelr.daneel Posts: 96
    edited 2014-02-27 11:54
    kwinn wrote: »
    Increasing R1 might increase the sensitivity, and varying the value of R3 will change the sensitivity. You could try replacing both with potentiometers so you can find the optimum resistance values for maximum sensitivity.

    Thanks - I'll give that a try.
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