Delayed Automatic On Relay

Discussion in 'The Projects Forum' started by epicfatigue, Feb 25, 2013.

  1. epicfatigue

    Thread Starter New Member

    Feb 22, 2013
    27
    0
    Hello everyone,

    This is my first post here,
    I drew up this circuit, i believe it is correct but before i set off on wiring it up i just wanted to double check with people that know what they are doing.

    I am attempting to create a time delay on relay, once the circuit has power then x amount of time it will close the relay and when power is gonethe relay will then open again.

    this is what i sketched up.[​IMG]
     
  2. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    your circuit will work,but it could do with a few extras......have a look at this to give an idea how to use the 555 timer and you could always download a datasheet
     
    Last edited: Feb 26, 2013
  3. epicfatigue

    Thread Starter New Member

    Feb 22, 2013
    27
    0
    thanks is that a negative or a positive trigger on that circuit. ?

    Have you tested it?
     
  4. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    yes that particular circuit has been built and tested many times and been used for quite a few different things with component changes to suit....the 555 requires a negative going trigger signal and the circuit around the bc547 etc provide an edge triggered signal for the 555
     
  5. epicfatigue

    Thread Starter New Member

    Feb 22, 2013
    27
    0
    what changes would i have to make to that circuit to make it a positive trigger or to only start when power is applied to the circuit?

    As my application requires a 5v trigger
     
  6. epicfatigue

    Thread Starter New Member

    Feb 22, 2013
    27
    0
    okay i believe i have it now, using my original circuit with a few things moved around and using a pnp instead of a npn it should work!
     
  7. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    pnp......nooooo.....as it is the trigger signal is active hi-positive-to do the same with a pnp your trigger would be active lo....the op from the 555 is active hi and the transistor switches the gnd side of the load,if using a pnp on the op that would switch the supply side to the load but the 555 op would need to be inverted.....if you wish pin 2 could be triggered as shown.....that gives you a lo going trigger which then swings hi and stays there.....
     
    Last edited: Feb 27, 2013
  8. epicfatigue

    Thread Starter New Member

    Feb 22, 2013
    27
    0
    ah thanks for your help!,

    fyi the walking dead is awesome!

    i just spent all night reading a book on the 555 and i came here to post the good news i got it working!

    [​IMG]

    this is how i did it works flawless i used the resistor from pin 2 to 8 as a fast discharge works perfectly!
     
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