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Lights problem

Discussion in 'Electronic Basics' started by Ed, Jul 25, 2006.

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  1. Ed

    Ed Guest

    I am trying to design a warning sign with several bulbs which a section of
    the bulbs turn on while the other section just stay off. Then the section
    that just turned on would turn off and the other section will turn on. Can
    anyone give some help what to do to get that project finished. Thanks in
  2. Jamie

    Jamie Guest

    use a 555 timer for the duration pulse.. have it
    drive a DT (double throw relay)..
    the main power goes the Center pole of the
    the outer legs will connect to one set of lights.
  3. jasen

    jasen Guest

    first you need to figure out what sort of lights to use.
  4. Chris

    Chris Guest

    Hi, Ed. If you're using a DPDT relay and you've got a 12VDC supply
    available (you can always use a wall wart), this may be the easiest way
    to do this (view in fixed font or M$ Notepad):

    | CRY1B
    | o---o NO
    | .--o--__
    | | o---o NC
    | |
    |VCC VCC '----------o C
    | + +
    | | NC |
    | '---o ___ |/ NPN Darlington
    | __--o-|___|--o---|
    | .---o C R | |>
    | | NO +| |
    | | C --- |
    | | --- C|
    | | | C|RY1
    | | | C|
    | | | |
    |=== === ===
    (created by AACircuit v1.28.6 beta 04/19/05

    Look for a 12VDC relay with a 400mW coil. You can use just about any
    NPN darlington in a TO-220 package. With a 1000uF cap and a 1K
    resistor for R, you should have a total cycle time of around a second.

    The idea behind this circuit starts with the fact that a 12V relay will
    typically turn on at about 9V or so. Once it's on, the voltage across
    the coil typically has to drop to about 4V for the relay to open up.

    When power is applied, the cap is at 0V, so the relay will be off. The
    normally closed (NC) contact starts charging cap C up to about 10.4V,
    which will put about 9V at the coil, turning the relay on. The contact
    changes over, and the resistor R is then connected to GND, discharging
    the resistor until the cap voltage gets down to about 5.4V, which means
    there's less than 4V across the coil. This makes the relay turn off,
    which repeats the process.

    Hook up your lights to the N.O. and N.C. contacts of the other pole of
    the relay.

    There are a couple of limitations to this circuit. First, the duty
    cycle (% time on) is pretty much fixed at a little less than 50% (it
    takes a little longer to charge up than discharge, because the base of
    the darlington is stealing a little current from the cap). You can
    provide some control over total cycle time over a limited range by
    putting a pot (say, 2K to 5K) in series with the R. This will give you
    up to several seconds cycle time. Timing on this circuit is
    susceptible to change with mechanical vibration. Also, this circuit
    won't work very well at lower voltages (although it will work well at

    If this doesn't do it, possibly you could provide a little more
    information (like what voltages you have to work with, what kind of
    timing cycle you want, and what kind of precision you need in your
    cycle time).

    Good luck
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