555 timer switch help

Discussion in 'The Projects Forum' started by Element1, Feb 6, 2010.

  1. Element1

    Thread Starter New Member

    Feb 6, 2010
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    Hello,
    I am working on a Hydrogen fuel cell car project that requires me to have an emergency shutoff switch on the outside of my vehicle. The problem is that the Fuel cell has a button that need to be depressed for 5 seconds to turn off. I need to figure out how i can use a momentary switch o the outside of the vehicle so that it can be pressed once and once hit activate the off circuit for the 5 seconds necessary to shut down the fuel cell.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    So why not use a relay connected to a 555 Monostable? Having trouble figuring out how to drive the relay?

    [​IMG]
     
  3. Element1

    Thread Starter New Member

    Feb 6, 2010
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    I've been thinking about this and would it be eaiser to wire the momentary switch to a flip flop circuit which directs power from the fuel cell to a relay that engages the off switch. and when the power from the fuel cell goes off so does the connection the relay makes?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    A flip flop circuit? How does that apply?

    Whatever works.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Just curious, is this a for real fuel cell, or an HHO project? We'll help with the circuits in either case, but HHO is not a favorite subject here.

    Fuel cells, on the other hand, are pretty cool stuff.
     
  6. Element1

    Thread Starter New Member

    Feb 6, 2010
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    It's for a University of Houston senior design team competing in the 2010 Shell EcoMarathon. We're using a 500 Watt PEM fuel cell to power the car.

    Also I thought a flip flop used momentary commands to direct current, so in my instance it would direct power to a relay that engages the off switch until the fuel cell is off and then the relay turns off by it self.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    So how about a simple voltage detector (minimum voltage set by your specifications, but let's say 10V for now) that turns the relay off when the voltage drops below a value?

    The set delay is also simple, but you can go either route as you choose.

    I assume you have some sort of secondary voltage for this and other circuits, otherwise you'll need a small battery to power the time delay or voltage detector.
     
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