Help Newbie How Delay power on relay

Discussion in 'The Projects Forum' started by cfoek, Jan 17, 2010.

  1. cfoek

    Thread Starter New Member

    Jan 16, 2010
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    helo .. I need help make delay timer schematic. When i push the button then delay for 2 seconds and turn the relay on and off. i have googling but can't find what i need so can anyone help me?


    thanks guys
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    The key to this problem is two monostables, one feeding another. You need to break the problem down. You're going to find it is better to have an understanding how things work, you can build on them to create something new and original.

    You start with the basic 555 monostable (which is straight out of the data sheet).

    [​IMG]

    Then you add a transistor to drive the relay.

    [​IMG]

    And you merge them. You did not state how long you wanted the relay on for, so I assumed 1 second.

    [​IMG]


    Have you read this?

    555 Monostable

    Bill's Index

    You could use one 556 (a dual 555) instead of two 555 chips. This datasheet I drew up a while back will help with the converstions.

    [​IMG]

    BRB, drawing schematic....
     
    Last edited: Jan 17, 2010
  3. cfoek

    Thread Starter New Member

    Jan 16, 2010
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    thanks for your replay Bill Marsden

    yes 1 second will be enough i will connect the relay to other monostable (already build and work)

    so basically i need 2 monostable from fig 1 and the cap will connect from R1 to Rt then to pin2 555?
    where i put the ground from R1 or Rt ?
    where i put the push button?

    can you guide me because i'm still new to design a circuit hehehehe.....
    i have read some explanation of 555 but still confused hehehehe ....


    thanks for your replay
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Check the 3rd circuit, your schematic is drawn.

    [​IMG]
     
  5. cfoek

    Thread Starter New Member

    Jan 16, 2010
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    what for a transistor before the relay ?? can you explain to me ?? can i connect direct from R2 to relay ?
    and what q1 should i use ?
    i use a 12V

    what program that u use for drawing schematic ?

    for c1,c3,c4,c6 that's a ceramic capacitor ?

    i want to try your schematic of 2 555 because i have the parts ready

    thanks
     
    Last edited: Jan 17, 2010
  6. Wendy

    Moderator

    Mar 24, 2008
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    A 555 can handle 200ma of current, but a transistor can handle a lot more. It is to provide drive for the relay coil. Without knowing your relay I can't tell for certain what you need, but almost all high power transistors will work. Something like a TIP102 perhaps, or a 2N3055. I need more information to answer definitively.

    What the capacitor is made out of (ceramic) isn't as important as its value. If you have 0.1µF ceramic capacitors they will work.

    I use M/S Paint along with a set of template I call PaintCAD. You can download them at my blog here on AAC.

    Bill's Index

    Introduction and PaintCAD

    You didn't say how you were powering this circuit. You may need a 220µF cap to filter the power supply.
     
  7. cfoek

    Thread Starter New Member

    Jan 16, 2010
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    the relay is dc 28v 10a

    for powering i use transformer 220V - 12V 500 ma then brige dioda 2A then 1000uf 25V electrolyte then 7812 and the last one ceramic 0.1uf, what did you think ?

    if i want to change the delay from 3 second to 5 second or more what resistor and capacitor need to be change ?

    thanks
     
  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    Hi Cfoek
    You could also have done this with a small 8 pin microcontroller and a very few components. Microcontrollers have become a very useful tool for the hobbyist. And the cost of a small microcontroller is almost the same as 555 circuit.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    But the amount of work programing them is much greater, there is a significant learning curve (which I haven't climbed). Then there is the issue of programming them, a one time cost in hardware to interface with a µC, which is not included in your estimate.

    There is a reason these parts are still popular.

    That is the contact rating, I need the coil rating. How much current and voltage does it take to drive the coil? While I'm asking, what are you going to drive, a motor? What is its rating?

    That sounds fine for powering the 555. They can only take 15V max. Don't exceed it.

    If you look at the schematic I included the formula for just such a question.
     
    Last edited: Jan 17, 2010
  10. t06afre

    AAC Fanatic!

    May 11, 2009
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    I think the cost-benefit curve for say a PICKIT 2 quickly will point the correct way ;) But yes it will require some interest in learning the knowledge behind using them. And every hobbyist is free to use whatever kind of tool they are comfortable with. And build what they please
     
  11. cfoek

    Thread Starter New Member

    Jan 16, 2010
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    i use a relay for a switch by cable to other 555 monostable
    the relay is 12vdc and don't say about the current

    what i mean is the capacitor need to be change for delay 5 or more second before power on is the R2 C2 or R4 C5 ?

    @ t06afre thanks for info but i need this for door bell protection ... so it will be a waste to use a microcontroller just be a door bell protector hahahah
     
    Last edited: Jan 17, 2010
  12. t06afre

    AAC Fanatic!

    May 11, 2009
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    A microcontroller is a piece of silicon just like some 555 circuits. It is just a tool. In my toolbox it is a tool I use then I find it convenient perhaps more frequent than other tools. Other may have a toolbox with different tool(s) they like to use.
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    That and electrically µC are very simple on the outside. Simpler than two 555's by far, it's only a 8 pin package similar to a 555 package. Their complexity is writing code for them. There is a reason they exist too.

    I would recommend anyone learn these suckers, they are very open ended. They do take some serious study to learn though, but in the long run it is worth it. They are a computer in a chip, and can do some nice logic tricks.

    You wanted two delays, one is the one after the button is pushed, the second is how long the relay stays active. The first timer has the math for it included, as does the second. Without a schematic we're talking across each other.
     
  14. pilko

    Senior Member

    Dec 8, 2008
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    Picaxe microchips are very easy to learn and program ( I learned the basics in a few hours and I am getting old!!! )
     
  15. cfoek

    Thread Starter New Member

    Jan 16, 2010
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    ok thanks i will build it today and test
     
  16. cfoek

    Thread Starter New Member

    Jan 16, 2010
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    i have build it and work like a charm thanks bill marsden
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    Your welcome.
     
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