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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0
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
20,772
2,540
So why not use a relay connected to a 555 Monostable? Having trouble figuring out how to drive the relay?

3. Element1 Thread Starter New Member

Feb 6, 2010
8
0
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
20,772
2,540
A flip flop circuit? How does that apply?

Whatever works.

5. Wendy Moderator

Mar 24, 2008
20,772
2,540
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
8
0
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
20,772
2,540
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.