Help with laptop alarm

Discussion in 'The Projects Forum' started by c0de3, Aug 22, 2012.

  1. c0de3

    Thread Starter Active Member

    May 1, 2009
    50
    1
    Hi all,

    I hope this is the correct area. I'm not sure as it is a strange request.

    I'm building a custom project that is going to be remote running from a laptop. There will be no AC power, only the power of the laptop battery.

    I need a loud alarm or siren that I can trigger from the laptop. I am familiar with programming and have already written the software I need. the problem is the built in amp/speakers doesn't get anywhere near loud enough. Can anyone think of something clever I can either plug into the sound out jack or even a usb based device that would be a loud alarm?

    I thought of perhaps a speaker powered by a simple 9v battery amp (I think they are called C Moy?) but I wasn't sure how loud that would get. I'd like to be able to hear the alarm from a couple hundred feet away. But that is in a quiet area. I also thought of some sort of horrible loud piezo buzzer, but wasn't sure how to drive that.

    Let me know any thoughts suggestions! Thanks all!
     
  2. Austin Clark

    Member

    Dec 28, 2011
    409
    44
    So, will the circuit be plugging into the laptop, or controlled via the internet?

    Either way, your main problem would probably be getting enough power out of your battery without making major modifications to the battery pack itself. The USB is a source of power, but not an incredible amount nor at very high voltage, limiting it's usability. If you CAN get plenty of power, consider using an audio amp, there are circuits and ICs that do this without too much sophistication involved. Piezos, if you can get one that you find loud enough, would be the best option I think. They require little power and can take simple DC. All you'd need is a transistor to switch it on and off from your PC.
     
  3. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    Look into Piezo buzzers (the ones that are internally driven), you can get some that run on 5 volts (USB power compatible) with an output frequency of around 4khz..... use a USB to Serial dongle, and use the DTR line of the RS232 end to switch the buzzer on or off (if you have already written the software, it should not be too hard for you to add a comm object to access the port :) ).... something like this buzzer >>> http://www.digikey.com/product-detail/en/MSS5M1/458-1118-ND/1949386
     
  4. c0de3

    Thread Starter Active Member

    May 1, 2009
    50
    1
    Thanks BMorse. The code for the port shouldn't be too bad. I've done serial work before, although it was in the late 90s!! :eek:


    How do I control the "volume" of a piezo buzzer?
     
  5. Austin Clark

    Member

    Dec 28, 2011
    409
    44
    I can only answer from my own experience, which is that voltage WILL change the volume, but not by much, and the frequency also changes with voltage. Piezos aren't very dynamic in either of those regards.
     
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