555 Alarm

Discussion in 'The Projects Forum' started by fossy97, May 21, 2012.

  1. fossy97

    Thread Starter New Member

    May 21, 2012
    3
    0
    I have been making this Alarm Circuit using a 555 in Monostable mode, and a 555 in Astable mode. I have however come across a problem, I wanted to create a delay, in which the alarm is 'enabled'. In other words, as soon as the trigger is pressed, I would like a 5 second or more delay, before the buzzer and LED begin to flash, buzz etc. I had planned to use a capacitor, but I am not sure where to put it, or what capacitance I should use. Please can someone help me, I am a bit of a novice at this.

    I have attached an image of the circuit, with the Trigger and reset labelled.

    Thanks
    Chris
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Use another 555 as a monostable to pull pin 4 of the astable 555 low for 5 secs.
     
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  3. fossy97

    Thread Starter New Member

    May 21, 2012
    3
    0
    Thanks for the reply, I haven't been able to get on since I forgot my password, but I am back now. Now as I said before I am a bit of a novice, and am not sure where connect the next 555 to. could anybody tell me which pin will need to go where on my diagram, this is all a big help! Also, how would I 'Tune' the Monostable to pull pin 4 of the Astable for 5/10 seconds. I assume this will require something to do with timing capacitors and the like?

    Many thanks
    Chris
     
    Last edited: May 27, 2012
  4. fossy97

    Thread Starter New Member

    May 21, 2012
    3
    0
    Ok, maybe how would I incorporate a 555 Monostable into my circuit? anyone?

    Sorry If I seem impatient, I aint trying to be.
     
  5. Mike33

    AAC Fanatic!

    Feb 4, 2005
    349
    25
    I'd like to see how this works out, too. I've used 555's in either astable or monostable, but not together.

    I have a scrap PIR I'd like to use to make an alarm for my shed....10 sec delay "high" on triggering the 1st 555, and then it triggers the 2nd (astable) 555 when it goes low, to sound an alarm for "some period" (say, 2 minutes or so).

    My PIR gives out a hex signal, so it is alternating high/lo, etc. I figure the 1st pulse can be used to trigger the first 555, with the others being ignored (?).

    Anyway, hope someone comes along to enlighten us! :)

    Thx
     
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