Need help making switch with timed reset for gate/door alarm...

Discussion in 'The Projects Forum' started by CheeseLog, Nov 13, 2013.

  1. CheeseLog

    Thread Starter New Member

    Nov 13, 2013
    3
    0
    Hi,

    I'm totally new here and I tried to search for my answer for a bit with no luck as I'm honestly not sure what I need to look for.

    I want to build a door/gate alarm for my outside patio deck with a magnetic switch so when some one opens the gate an extremely loud siren goes off and continues to go off for 60 seconds even if they close the gate again and the magnetic switch makes contact again.

    I have looked around online to try and buy something already made that does the job but the things I have found are kind of cheesy. I want to build something beefy with some mojo that will surprise the heck out of someone opening the back deck gate

    I already know I need a magnetic door switch, a loud siren that I can mount under the deck that can be powered with batteries or maybe even solar and I need to build some type of circuit that once it gets triggered by the switch keeps the juice going to the siren for the 60 second time period then tries to reset itself. I'm thinking that if the gate is still open after the 60 seconds the siren will keep on going for another 60 second cycle until the gate/switch closes again

    I did some electronics many many years ago and with today's technology I have not clue what the easiest and or best way is to make this happen. I'm sure it is very easy for someone with knowledge of basic electronics and you can prolly buy all this stuff for not much money to make it all happen.

    Sorry if this is all too cheesy of a project for this forum but any help or advice would be greatly appreciated!

    Thanks in advance.

    G.
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    You can use an NE555 one-shot for the 60 second timer. Getting it to start when the gate opens and power the siren is for the 60 seconds is easy. Getting the siren to continue past 60 seconds if the gate is open is a little more complicated, but can be done.

    What electronic skills, tools, and parts do you have available?
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    First decide what voltage you will be using.

    What you need is a "delay off" timer".

    You can build your own with a single 555 timer driving a relay. A 12 volt power supply is needed. Or something over 5 volts. It might as well match your load. (siren)

    Or buy a packaged timer matching your supply voltage. If your not looking for an electronic project.
     
  4. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Welcome to AAC.

    I've designed a similar circuit for others and modified it here to suit your needs.

    The circuits shown will need a normally open (N.O.) switch, so if you go with a magnetic switch, make sure it is N.O., not N.C. (normally closed), otherwise we will have to add a transistor inverter.

    If you want to scare the heck out of intruders, then I strongly suggest this little nugget from RadioShack. While it says 7-14VDC, I suggest using 12VDC to get the right effect. This means eight AA batteries or a 12VDC rechargeable gel cell lead acid battery. You can find the latter at a big box hardware store for alarm systems (found in electrical aisle) - note you'll need to charge it periodically.

    When SW1 is tripped, either circuit will immediately turn on the siren for 60 seconds - you can adjust the time by adjusting VR1 (0-100 seconds with the values shown). Option A adds a resistor and capacitor so the siren goes off after 60 seconds if the switch is still tripped. Example, gate is opened, siren goes off, scares intruder, intruder runs away leaving gate open, siren goes off after 60 seconds. Siren will not go off again until gate is closed and opened again.

    Option B will keep the siren going for as long as the gate is open, but at a minimum of 60 seconds. So if gate is opened, siren goes off for 60 seconds. If gate is closed within that time, siren will go off after 60 seconds (not before). If gate is still open after 60 seconds, siren will continue to sound until gate is closed.

    If you use the siren I suggested above and a standard 555 IC, you can connect the siren directly to the 555 as shown in the circuits below. That siren requires ~150mA and a standard 555 can provide up to 200mA. If, however, you use a siren requiring more current or a 555 that puts out less current than the siren requires, you'll need to add a transistor amplifier (a transistor and a resistor). We can modify the schematic to show this if needed.

    Hope this helps. :)
     
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  5. CheeseLog

    Thread Starter New Member

    Nov 13, 2013
    3
    0

    I just found this online... it pretty much all I need + the battery and magnetic switch and the siren?
     
  6. CheeseLog

    Thread Starter New Member

    Nov 13, 2013
    3
    0
    oops...
    http://www.electronickits.com/kit/complete/timers/canck002.htm
     
  7. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Looks like it would work. You'd connect the switch in series with the battery pack so when the switch was tripped, power would be applied to the circuit and the siren would go off. The only caveat is the output current isn't much. If you like the siren I suggested, you'll need to add a transistor to increase the current output.

    This one includes a relay (no need for a transistor). I believe it works the same as the one you found, but I'm not positive.
     
  8. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Plus you will have to add a little logic when wiring. If it is an interval timer, like the description.
    The siren will need to be on with the timer "AND" the gate switch per your specs.

    Even then siren will turn off after interval with gate closure. 555 will have to be re-triggered to get another interval when gate is open past first time period.

    I would use a "time off delay" it it were me.

    http://forum.allaboutcircuits.com/showthread.php?t=71585
     
    Last edited: Nov 14, 2013
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,980
    744
    Here is timer you can make using a CD4093 cmos chip, timer is adjustable from 1 to 100 seconds, if the gate is left open it keeps buzzing, if the gate is opened then closed, the timer puts the siren on for the set value then stops until the next time the gate is opened.

    It uses a normally open reed magnet switch, so when the gate is closed the switch is closed, when the magnet is removed the siren sounds.
     
    Last edited: Nov 15, 2013
    inwo and elec_mech like this.
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