555 Timer Circuit. Delayed off After Power Is Removed

Discussion in 'The Projects Forum' started by Dan-O, Nov 17, 2009.

  1. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
    Me again,:D
    I'm in the middle if my pushbutton start re-design for my car (Version 3 is working great) and I decided I want to add a delayed accessory off like some luxury cars have while I'm building the project.

    I want to have a relay remain on for X amount of time, I'm thinking 8-10 minutes. I have the RC stuff figured out for around a 9 minute delay if I were able to make a 555 work, with the relay also being able to shut off if a door is opened. The reset or door open input can be high or low triggered, low being better.
    I need a little input as to what I can do. I'm assuming a 555 will fit the bill, but I just can't seem to work out the details.
    I did a search and weeded through 4 or 5 pages of results, none really hit the nail on the head.
    Thanks again for the input,
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    It seems like you need two inputs to your timer; one (ignition input) that continuously re-initializes the timing period as long as it is True, and when that input goes false, the timer times for 8 minutes and shuts OFF. The other input (door switch input) will instantly reset the timer to the OFF state, regardless of where the timer is in it's timing cycle.

    Which raises this question: What happens if you open the door with the engine running?
  3. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
    You're exactly right.
    This circuit would be a piggy back to the OEM accessory relay.
    I already have an relay in the pushbutton circuit powering the OEM unit, so it would be powering the OEM relay even if a door was opened.
    I would like the circuit to become active when the ignition is turned off.
  4. SgtWookie


    Jul 17, 2007
    OK, are you using Soeren's PushButtonStart schematic and board?
  5. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
    Nope, I don't think so.
    I'm using a 556 as a flip flop with a 555 for the delayed starter control.
    My new version is going to have a EDE2208 momentary to toggle.
    It will free up a ton of real estate on the board.

    With my current setup, you press the button and the ignition and accessories turn on, after holding the button down for 1 second the starter will engage. While the starter is engaged, the accessories shut off (just like any other car)

    To turn the car off, a momentary press is all it takes.

    This is a single button OEM like solution. I'm using a passive alarm to control whether the button is active or not. It's not RFID, just a conventional RF fob controlled remote, the only difference is when the fob is out of range the start button is disabled.
    It's completely passive and very OEM-like.

    I figured for the re-design I'd add more features like retained accessory power and lower my stand-by power consumption; It's currently 13mA.
    The EDE2208 spec sheet says it draws 13uA at rest. I can live with that!
    I also am still leaning towards still using relays instead of trying to make this solid state. It's just going to be so much simpler.
    Last edited: Nov 18, 2009