sensor detect glass break

Discussion in 'General Electronics Chat' started by firend, Jan 15, 2015.

  1. firend

    Thread Starter Member

    Feb 18, 2012
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  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    An op-amp? Google, or vendors' sites, will find you plenty.
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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    The circuit of the linked page that it looks like too complicated as a science experiment, the circuit seems narrow to the sound of glass breaking, do you really need to do so precisely or just need a higher frequency sound detector?
     
  4. firend

    Thread Starter Member

    Feb 18, 2012
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    You are right. I want to find a chip which integrated op-pam and filter to process signal from microphone.
     
  5. #12

    Expert

    Nov 30, 2010
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    I don't think you can buy an op-amp that is limited to audio frequencies. You will have to build a circuit to limit its frequency response.
     
  6. MagicMatt

    Member

    Sep 30, 2013
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    Not sure if this info. is helpful to you or not:
    As somebody that has worked with security alarms, it may be worth knowing that most good alarm companies do not use break-glass detectors any more, because they were far too easily triggered by other factors. Also, in large retail units etc. they often now go for toughened glass panels which often don't trigger the detectors (continuity tape tends to work better because of the way the glass is designed to shatter).
     
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  7. ScottWang

    Moderator

    Aug 23, 2012
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    I think you can do as below to narrow the frequency BAND :
    Mic Amplifier → RC integrator circuit → differential circuit → op amp AC amplifier → control circuit
    You may refer to this.
     
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  8. ian field

    Distinguished Member

    Oct 27, 2012
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    You could probably get away with bonding a piezo sounder to the glass and feed it to a sensitive amplifier with suitable input filtering (mostly HPF IIRC).

    Many years ago I read about a burglary at premises protected by such a sensor. Automatic air-freshener aerosols had hit the market, and an enterprising crook had noticed that the hissing noise triggered broken glass alarms, he put one of the automatic aerosols in the guttering above the window he intended to break. As expected - the proprietor got fed up with 15 minute alerts from the security call centre and turned the alarm off.

    From time to time, I still see shops with the self adhesive conductive foil broken glass alarms - if the adhesive is top quality, even a crack in the glass will sever the circuit loop. The detector can be as simple as a small SCR (e.g. 2N5061 etc) - just add a gate pull up resistor and clamp the gate down with the conductive loop.
     
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  9. firend

    Thread Starter Member

    Feb 18, 2012
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    http://www.ti.com/lit/an/slaa351/slaa351.pdf
    I foud this link. They detect glass break sound base on frequence and frequence composition ratio. I understand algorithm calculate frequence. but I don't understand frequence composition ratio. That paper said that if frequence composition ratio from 1.75 to 7, received signal is glass break sound.
     
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