Latching Circuit that opens (stops latching) after 10 seconds (precision not important)

Discussion in 'The Projects Forum' started by live4soccer7, Jun 9, 2016.

  1. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    I've got an application where I want to take a 12v input signal to latch a 12v for just 10 seconds and then to stop and have the circuit open again until the input signal is received. I just need roughly 12v output. Really, input could be 11-15v and output can be a large range of voltage as well.

    What would be the best way to go about this?

    Thanks for any assistance, it is greatly appreciated.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    One shot.
     
  3. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    Can you elaborate?
     
  4. bushrat

    Member

    Nov 29, 2014
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  5. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    Ah.... Thank you very much. I'm reading through it now!
     
  6. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    From the page you linked:

    The output of the timer is normally low,
    if pin 2 is grounded by pressing the button,
    then the output goes high for t1 seconds.


    Is there voltage at the output when pint 2 is not grounded and t1 time as already passed?
    I might be able to make a ground signal work, however is there any way for it to do this by seeing a positive input voltage?
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Every one seems to go with a 555 for things like this, but there are other options. A CD4538 is a dual monostable/one shot chip. It unlike the 555 can be set up for either a high or low trigger signal. It uses the resistor and capacitor for timing like the 555 but gives much more options to the control and output.

    https://www.google.com/search?q=4538&ie=utf-8&oe=utf-8
     
  8. dl324

    Distinguished Member

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    Output will be LOW after OS times out.
    Use a transistor to invert the trigger signal.
     
  9. dl324

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    At least no one has suggested a microcontroller...
     
    absf and shortbus like this.
  10. crutschow

    Expert

    Mar 14, 2008
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    How much current does this pulse need to provide?
     
  11. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    Thank you for the information everyone!

    crutchchow, are you referring to the 10 second pulse or the 12v signal that feeds in to the one-shot circuit?

    I am a bit new to this, but would like to get this thing sketched up in some software for practicing and also for the modification with the transistor to allow the input signal to be positive instead of negative.

    Can someone recommend some software for building circuits, pcb design, etc....?
     
  12. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    The 12v output will feed a device that draws about .2mA from that output to turn on and stay on for the duration of that 10 seconds.
     
  13. BobTPH

    Active Member

    Jun 5, 2013
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    I will. In a 6 pin SOT-23 for the smallest size.

    Bob
     
  14. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    It looks like if I wanted to use a transistor to watch for the 12v+ signal feeding the circuit then it would be an NPN transistor. Now to figure Ic based on pin2 of the 555. Please do let me know if I'm not heading down the right path here.
     
  15. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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  16. dl324

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    Will the 12V control signal pulse duration be less than the 10 second pulse you want?

    Don't worry about the current requirement for the trigger. It's a comparator input, so very low current. The important thing is that the trigger voltage must go below 1/3Vcc to trigger the OS and needs to go above 1/3Vcc before the OS times out.

    Depending on the load you're driving, the OS output will be within a couple volts of the supply voltage (for LM555).
     
  17. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    The control signal being input in the circuit will be about 500ms at best.

    When there is no trigger signal, the voltage will be 0 or very close to it on the trigger signal input. When it is applied then it will be 12v. It should be a complete 0 or full voltage state on the signal voltage.

    The output will be just fine being a little lower. The device I'm working with it can work as low as 6v.
     
  18. dl324

    Distinguished Member

    Mar 30, 2015
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    Then a simple inverter direct coupled to the trigger input should do it.
     
  19. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    Excuse my ignorance, but can you elaborate just a little?
     
  20. live4soccer7

    Thread Starter Well-Known Member

    Jun 7, 2008
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    I feel that it may be pertinent to say that the current in the "off" state should be very low in the entire circuit as it will be an application that is in a vehicle and battery drain would be an issue if the vehicle is not being used often.
     
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