555 Delay circuit - badly help needed

Discussion in 'The Projects Forum' started by mahmudur.rahman, Nov 5, 2010.

  1. mahmudur.rahman

    Thread Starter New Member

    Nov 5, 2010
    2
    0
    hi....
    i am trying to make a delay circuit with 555 timer that will turn on a 12V DC Load.

    i designed a monostable ckt. i attached its schematic here. here when the push button is pressed the output remains high for 30 sec. i think this is a basic monostable design.

    what i want is when the power will be turned on the output will remain off for 30 sec. then after 30 sec... my load will be turned on.

    so, my questions are...
    1. is my monostable ckt is right?
    2. what i need to do to design my requirements?
    3. do i need any relay or transistor?
    4. do i need the push button in my required circuit?

    thnx
     
  2. nerdegutta

    Moderator

    Dec 15, 2009
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  3. santos4eva

    New Member

    Oct 30, 2010
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    I need a square wave to sine wave converter. Please!!!
     
  4. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Your circuit design already do that, but its in the reverse sense. i.e. the output is ON for 30 seconds and turns OFF after that.

    You haven't told us what the load is and you now have two options.

    If the load current is about 100mA or less, then you can connect it between +12V and 555 output, as shown.

    If the current is higher than 100mA, or you have to connect one side of the load to 0V common, then you can use a PNP power transistor to do the level translation. I have chosen the MJE2955 but any power PNP transistor rated to carry two or three times your load current will also work.

    You don't need any push button if you don't want to reset the 555 timing cycle.

    [​IMG]
     
    mahmudur.rahman likes this.
  5. mahmudur.rahman

    Thread Starter New Member

    Nov 5, 2010
    2
    0
    thnx eblc1388...

    i think i got it.... here is my new schematic... i think this will do fine...:)

    tc
     
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