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Delayed Trigger - siren to go off a few seconds after trigger

Discussion in 'General Electronics Discussion' started by shockuk, Mar 10, 2011.

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  1. shockuk


    Jul 25, 2010
    Hi all,

    Wondering if anyone could help me with the following problem?

    Basically, I have a speaker in a bellbox which "turns on" when the "trigger line" is reduced to 0v. While the trigger is above 4v, the speaker stays quiet.

    The line is usually at 12v, until I want to make a noise, when the line is dropped to 0v.

    I would like to set a "delay", so that the speaker is only "turned on" when the trigger line has dropped below 4v for a five seconds.

    I was thinking an inline capacitor would be the way to do this (so that the line remains above 4v for five seconds) - however i'm really not sure if this is the best way, or what capacitor to get.

    Please see images to aid my description:
    Uploaded with

    Would anyone be able to help me out with this? Is it the best way to achieve such a "delay"? What capacitor do I need?

    Thanks very much for your help :)

  2. shockuk


    Jul 25, 2010

    The bellbox'es rated load current when operating is 260mA.

    Whilst quiet, the bellbox uses 20mA.

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