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Help with a simple circuit:

Discussion in 'Electronic Basics' started by MacGyver, Oct 4, 2005.

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  1. MacGyver

    MacGyver Guest

    At least I think it is simple...

    I have 2 12v wingtip lights that I need to be able to control with
    one switch and one wire running through a wing in an airplane.
    This is for just one wing. That's the gist of it.

    I just bought piggyback strobes for the wingtips, but I don't want to
    have them on all the time that I have the navigation lights on.

    I was thinking of a relay that has a remote control, or has a signal
    run through the positive wire or could possibly have a low & high
    setting and if we send 12 volts to the relay it trips, but it won't
    trip at say 10 volts.

    Also was thinking about if I turn the switch on once just the light
    comes on. Flip the switch off & on again in under 2 seconds and the
    lights & strobes come on. Leave the switch off & everything turns off.

    I was thinking about relays with a capacitor to keep the line live for
    2 seconds to be able to flip another relay... but now I am confusing
    myself again.

    Any Ideas???

    Seems like it should not be too difficult.
    Thanks so much for any advise!!!

    Sean Gallagher
    Pheonix, AZ
  2. ehsjr

    ehsjr Guest

    Since you want relay logic: 2 relays, 2 diodes and a cap plus
    a spdt switch will do it. All the parts are available at
    Allelectronics. (url included below)

    N/C o o----------------+---[RY2]---+
    Ry1\ | |
    Off o----------o o---------+-----|<----+
    / Ry2/ |
    +12-------o Sw1 N/C o o N/O +-----|<----+
    | | |
    On o-------------------+--------+---[RY1]---+
    | |
    Gnd -------------------------------------------------+

    Turn the switch on and the navigation lights turn on.
    Flip it off, then back on within ~ 2 seconds, and both
    the navigation lights and the strobe lights come on.

    How it works: Switch1 is off, RY1 and RY2 are de-energized.
    RY2 cannot energize through the switch because RY1 contact
    is in the closed (de-energized) position. Flip the switch to
    on. RY1 energizes and Capacitor C1 charges. Flip the switch off,
    and C1 holds RY1 energized for a brief time. The RY1 N/O (normally
    open) contact is now connected to the off position of the switch,
    so RY2 is energized. Flip the switch on again within the brief
    time, and both relays are energized and will stay that way until
    you turn the switch off.

    The brief time delay of about 1-2 seconds is achieved with a 2,200 uf
    cap and a DPDT relay, part # RLY-622 from Allelectronics
    The relay has a coil resistance of 720 ohms, and the contacts can
    carry up to 2 amps for your lights. The diodes are 1N400x. The
    second set of contacts on RY1 control the nav lights, and the
    second set on ry2 control the strobe lights.

  3. Jasen Betts

    Jasen Betts Guest

    well it meats the criteria if you mount the switch inside the wing...
    not the most convenient location :)
    So current flows through the ry1 contacts and ry2 contacts and continues to
    energise ry1.

    Flip the switch on again within the brief
    And forever.... I think you need a diode between the ry2 contacts and ry2.

    but it's a start...

    | |
    | +-----------+ |
    | |nc ry1 | ry2 |
    to | +---0-_ | o-_ |
    switch | D1 ~-o | D2 ~-o-+
    <-----+-------+-+->|--o . | +-|<-+-o .
    | | no | | |no
    | +---+ . | | +-------------+
    /~\ nav | | | . |
    | |light | . | +----+ |
    | | | | |. /~\
    \_/ |. C1 | | | |strobe
    | ### ----- ### | |light
    | ry1 ### ----- ### \_/
    | ### | ### |
    | ### | ### ry2 |
    chassis | | | | |
    <-----+--- - - -----+------+-------+--- - - -----+
    ground | | |
    --+-- --+-- --+--
    ///// ///// /////
    (is it still ground while airbourne:)

    when initially turned on the nav light illuminates and ry1 energises
    current flows through D1 and the RY1 contacts to charge C1

    when turned off the light goes out and D1 blocks the current from the
    capacitor so RY1 releases and current flows from the capacitor to energise
    RY2 which closes, D2 also blocks the current from the capacitor.
    so all the current from the capacitor flows to RY2 which closes and remains
    closed momentarily.

    if the power is reapplied before the voltage in the capacitor drops below
    about 6-8V current flows through the RY2 contacts and D2 to maintaing RY2
    in the energised state and also powers the strobe light. ry1 also switches
    and recharges C1

    if turned off for longer than the discharge time for the capacitor RY2 will
    release and when turned back on only the nav light (and RY1) will operate,

    RY1 can be any 12V spdt relay, use the cheapest one, RY2 shoulf have
    contacts rated to pass the strobe light current (but as they don't need to
    switch the current the contacts in a DPST or DPDT relay could be paralleled
    to increase the current capacity)

    assuming a 400ohm coil on RY2 4700 uF would be a good size for C1
    lower for a faster let-go higer for longer.
    D1 shoud be

  4. ehsjr

    ehsjr Guest

    The *circuit* is mounted near the light inside the wing.
    (You need 2 complete circuits - one in each wing near the
    lights.) The switch is in the cockpit. Why do you think the
    circuit requires the switch to be in the wing?

    With single wire, it physically looks like this:
    Wing Wing
    ======== | ========
    | | |
    | | |
    Good pickup - you're right.
    The strobe doesn't draw full current at turn on?
    Nice. Add diodes across the relay coils.
  5. ehsjr

    ehsjr Guest

    ehsjr wrote:

    Corrected diagram - Jasen noted a missing diode:

    N/C o o----------------+---[RY2]---+
    Ry1\ | |
    Off o----------o o---------+-----|<----+
    / Ry2/ |
    +12-------o Sw1 N/C o o N/O +-----|<----+
    | | |
    On o-------------------+--->|---+---[RY1]---+
    ^^ | |
    Gnd -------------------------------------------------+
  6. Jasen Betts

    Jasen Betts Guest

    the most stress on relay contacts is when they are moving and current is
    being switched, the relay 2 contacts only move when the power is turned off.
    so they don't need to interrupt the strobe current etc...
    ry1 is in parallel with the nav light, (and the nav light in the other wing),
    that'll absorb any backlash, but yead a diode across ry2 could extend its
    life a little.

  7. Jasen Betts

    Jasen Betts Guest

    you have one wire running into the switch and two wires running out of it.
    to satisfy the "one wire running into the wing" requirement the switch would
    need to be located in the wing :)

  8. ehsjr

    ehsjr Guest

    Thanks! You would need a 3rd relay in the wing. Hard to
    envision a switch in the wing - and a pilot with arms
    lone enough to reach it from the cockpit!

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