I can't figure this out!

Discussion in 'The Projects Forum' started by camobearusa, Jan 2, 2011.

  1. camobearusa

    Thread Starter New Member

    Jan 2, 2011
    4
    0
    :confused:I need to build a 12VAC circuit that uses an NE555 GP Bipolar IC that will continuously switch on and off about every 30 seconds indefinitely. It's needed to replace the original homemade circuit that was stolen from a set of gifts given to me by a departed friend. This circuit was meant to be used as a gag to repeatedly open and close a door that used a push button momentary switch to operate.


    I do have a background in Bio-Medical electronic equipment repair, although that was about 20 years ago.

    Any and all help, especially with diagrams would be greatly appreciated!!!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    We need more details about the circuit. A 555 timer can be set up to switch states every 30 seconds or so, but must use a DC supply voltage. What is the function of the 12 VAC?
     
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  3. camobearusa

    Thread Starter New Member

    Jan 2, 2011
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    That's the voltage that I have to work with to power the circuit. Building a DC rectifier won't be a problem for me.
     
  4. bearblock

    Member

    Oct 24, 2008
    18
    1
    have a look at the datasheet for the 555. you want it to continually switch on and off; that's called 'astable' mode. the on and off times are determined by two resistors and a capacitor - there's a formula that you can use to get the values.
     
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  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Do you still have the door that requires the open/close switch to operate it?
     
  6. camobearusa

    Thread Starter New Member

    Jan 2, 2011
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    SgtWookie: I still have access to the door for which it was originally built for. New manager for the business, though!!! ;-)
     
  7. soda

    Active Member

    Dec 7, 2008
    174
    13
    Hi,

    What you need is a NE555 "a stable" diagram. I upload a diagram for you.

    Just connect your door switch to the relay. If the time is too high, change the cap to a lower one like 10uF or change the pre-set. You can also use the pre-set to set the time
     
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  8. camobearusa

    Thread Starter New Member

    Jan 2, 2011
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    Does it matter what type of diode(silicon or germanium)that this circuit use? Sorry to ask, I've been away from electronics for way too many years!!!
     
  9. soda

    Active Member

    Dec 7, 2008
    174
    13
    Sorry, I forgot the say. You can use 2 "IN4002" silicon diodes. It's there to protect the ne555 from back emf.
     
  10. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Yould have quite hard time obtaining germaium ones today. I am not sure if they are even still being made.
     
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Last I heard you could still buy 1N34A diodes
     
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