What can I do?

Discussion in 'General Electronics Chat' started by moon_df2, Aug 19, 2005.

  1. moon_df2

    Thread Starter New Member

    Aug 19, 2005
    3
    0
    I am wiring up a remote start system for a set of L.E.D's on my car. I am setting up the trunk unlatch button on my remote as the trigger to the relay. It is a (-) output but it isn't a constant power. So I am guessing I need some sort of a latching device, or relay, or even both to keep the power constant once it has beeen switched. I have no idea how to do this or get this effect, and Ive been working on it for a while. Any help would GREATLY be appreciated. And even an idea of where to find parts would help a lot. Thanks.
     
  2. Erin G.

    Senior Member

    Mar 3, 2005
    167
    1
    It sounds as though you have a momentary "trigger" source, and you want it to keep a power source on once triggered. If so, what you need is a latching relay. Any 8 pin, 12VDC relay (rated for your load) will do the job. The only drawback is that you need a seperate off button. You could overcome this by investing in a snap switch (instead of using the trunk button), which would eliminate the need for a relay.
     
  3. moon_df2

    Thread Starter New Member

    Aug 19, 2005
    3
    0
    You are right about what I am trying to do, but I was hoping I would be able to trigger the relay on and off with the same momentary (-) pulse. And any information for what a snap switch is would help a lot too. Thanks for the help!
     
  4. pebe

    AAC Fanatic!

    Oct 11, 2004
    628
    3
    Will this link help?

    http://forum.allaboutcircuits.com/index.ph...5&hl=flip++flop
     
  5. moon_df2

    Thread Starter New Member

    Aug 19, 2005
    3
    0
    Well. I thought I had found the relay I needed, well at least the person I got it from said that was it. But it was still doing the same thing, once I activate the negative it works fine until the negative pulse stops and the the power isnt staying constant. I was using a 5 pin relay and I have tried just about every wiring setup I could think of. Maybe I am missing something or I dont have the correct relay. If someone could point me to the exact relay I need (preferably cheap) and maybe a diagram of how to wire it up I could figure this thing out!! Thanks.
     
  6. Erin G.

    Senior Member

    Mar 3, 2005
    167
    1
    What JoeJester has shown is exactly the latch relay that I was talking about, but as you can see, it requires a seperate stop button. A snap switch is essentially the same thing as a toggle switch (toggles between open and closed position) but it is a push button. Push once to close, push again to open, and it makes a snap moise each time you push it. Often they have square enclosures, and they have fancy ones that have lighted buttons and what-not.
     
  7. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    Another way of doing this, although it requires more electronics, is to run the contacts of your first relay into a 74ST14 schmitt-trigger configured as a 20ms debounce circuit, which then drives the clock input of a D flip-flop. The D flip-flop should be configured as a divide-by-2 by connecting the ~Q output to the D input. Then connect the Q output to the gate of an N-MOS driver FET, with it's source to ground, and which has another relay with it's coil connected between the drain and +12V. Also, you would probably need an RC on the flip-flop reset pin to force the circuit into the "off" condition during power-up.

    Each time you click your remote the flip-flop will alternate states and the second relay will turn on and off accordingly, and will remain either "on" or "off" although the primary relay is only activated for a short time.

    The other factor of doing it this way, is that you would need a small regulator to convert the +12V down to +5V for the logic.
     
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