Will a 555 do this?

Discussion in 'The Projects Forum' started by roadey_carl, Mar 6, 2015.

  1. roadey_carl

    Thread Starter Active Member

    Jun 5, 2009
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    Hi,

    I need to build a Delay On circuit but my understanding of the Delay On schematics available with a 555 on the internet don't quite match what I am trying to achieve....

    I need to have a latching switch input , delay of 2 seconds then the output goes high until the switch input is turned off, then the sequence starts again.

    is this something I am able to achieve with a 555?


    Thanks for your time,

    Carl
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I am not sure exactly what you are wanting, but maybe the circuit below will help.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I am confused about your switch description. Is it like a toggle switch that stays in the ON position or could it be?

    Delaying the application of power to something down stream if the switch stays on is trivial. Then everything (including the delay circuit) can be shut off when the switch is turned off.
     
  4. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    Could be done with a transistor, capacitor and a few resistors.

    Basically you discharge the capacitor on the base with a resistor, then charge it with another through the switch.
    The capacitor will delay the transistor turning on.
    But you need a fairly large capacitor. You could also use a digital MOSFET and increase the resistors.
    Since the required gate voltage is even higher, the capacitor can become even smaller.

    Disadvantage it wont turn on fully immediately. For many kinds of loads it will not be noticeable, but the transistor will work in the linear region means will dissipate power.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    A bit confusing , but here is a 555 timer delayed output goes high after 2 seconds when the switch is opened.the timer goes low when the switch is closed.

    555.png
     
    roadey_carl likes this.
  6. roadey_carl

    Thread Starter Active Member

    Jun 5, 2009
    116
    5
    It's actually a momentary switch held in but you might as well think of it as a toggle switch that stays in the ON position.

    As the switch is turned on, one motor will run. 2 seconds after that switch was turned on, another motor will run. So its like .....

    - Input high ( switch closed)
    - Delay Output High for 2 seconds,
    -Output High

    Dodgydave - That's close to what I'm after, but when the switch is closed I need pin 3 to come High after 2 seconds.
     
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    OK here is the modified version, the timer goes high after 2 seconds when the switch is closed, it goes low when the switch is opened. Set the delay with R,C



    555.png
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Missing info:
    Supply voltage?
    Operating current for "another" motor?

    Here is a hack without knowing the above. I assumed the supply voltage is 12V, and that the motors draw 1A each...

    Motor 1 runs whenever V(sw) = 12V. Motor 2 runs ~2sec after V(sw) goes high. NFET switches up to several Amps.

    168.gif
     
    Last edited: Mar 6, 2015
  9. roadey_carl

    Thread Starter Active Member

    Jun 5, 2009
    116
    5
    Dodgydave That has done the job perfectly. Thank you very much.

    MikeML Thanks for your time, I appreciate what you have done.


    Thanks to everybody else also!


    Carl
     
    Dodgydave likes this.
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