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Help with simple circuit

Discussion in 'Electronic Design' 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. Robert Baer

    Robert Baer Guest

    First, one needs TWO wires for a complete circuit for those lamps....
  3. Sean,

    You're confusing us as well. FAIK most wings have two tips so I guess you
    have one light for each tip. Furthermore all lights I'm aware off have two
    connections. So if you want to use one wire, what to connect to the other
    connection? Relais don't work with one wire either. Think you have to
    explain more clearly what you want to achieve. So what do you have, what do
    you want to add and what limitations or constrains do you see.

    petrus bitbyter
  4. Perhaps the frame is the return wire (aka ground)? I know nothing about
    this application so this may or may not be the case.

  5. Deefoo

    Deefoo Guest

    It can be done with one wire if there is a conducting frame. (Think about
    old-school bicycle lights.)

    Or if you cut the wire somewhere, put the light at the cut and use the two
    remaining ends to make a closed circuit ;o)

    If the OP uses the word wire for cable then he might even be talking about a
    multi-conductor cable...

  6. These - and other - assumptions crossed my mind too. But to give a usefull
    answer I need to *know*.

    petrus bitbyter
  7. john coates

    john coates Guest

    Hello Sean,

    I think the following circuit should do what you want.
    Switch on: Nav lights are on
    Capacitor was empty and charging but the lower MOSFET is conducting
    because its gate is drawn to 12V immediatly, thus keeping the other
    MOSFET non-conductive.

    Now switch off and On again.
    The capacitor will not be discharged when the voltage returns, so the
    top FET is in conduction, now keeping the lower FET out of conduction
    while keeping the strobe light on.

    You can play around with the 1M or 10uF to shorten or lenghten the
    max. time period between the two 'on' cycles of the switch.
    The FETS should be N-channel MOSFETS, select based on required lamp

    Need further help? Let me know...


    John Coates
    Gent, Belgium

    | | |
    | diode | |
    V | |
    - 10k .-. |
    | ___ ( X ) strobe |
    o--|___|--o------| '-' |
    | | .-. | |
    | | | |1M o---' |
    .-. |+ | | | | |
    | | === '-' ||-+ | .-.
    1M | | 10u=== | ||<- | ( X )
    '-' | '---o--||-+ | '-'
    | | | | | |Nav
    | | | | | |
    | | ||-+ | | |
    | | ||<- | | |
    | | .--||-+ | | |
    | | | | | | |
    | | | | | | |
    | | '-----)-----)---' |
    | | | | |
    | | | | |

    (created by AACircuit v1.28.6 beta 04/19/05
  8. MacGyver

    MacGyver Guest

    first off, thanks for the reply... I have been racking my simple brain
    on this for too long.

    I am only talking about one wing in this scenario.

    right now there is 1 positive wire that runs through the wing to the
    green light & the wing itself acts as a ground.

    The strobe piggybacks off of it & one wire goes to ground & the other
    goes to the same positive wire.

    Now the switch controls both the strobe & the light at the same time.

    Problem is: I want to be able to flip the switch once & have the
    green light come on. then turn off & on the switch again (within a
    second or two) and have bot the strobe & the light on.

    I am thinking that a relay possibly a latching relay with some sort of
    capacitor out at the wingtip could keep the line charged for the coil
    on the relay just for the 2 seconds it takes to flip the switch.

    If I leave the switch off, the capacitor just runs out & resets.

    Hope this helps. I don't know how to post diagrams here but if you
    e-mail me at: I will send you diagrams that explain
    this even better.

    Thanks again!

    Sean Gallagher
  9. Ken Smith

    Ken Smith Guest

    Perhaps the frame is the return wire (aka ground)? I know nothing about
    this application so this may or may not be the case.[/QUOTE]

    If the wing is made of metal, it is the return path. Its a lot like what
    is done in cars.
  10. Rich Grise

    Rich Grise Guest

    I know exactly what this guy wants to accomplish. On one wing tip, he
    wants to mount two lights - the running light, and the strobe. He has
    one switched power wire, and the frame of the craft is the ground
    return. He wants circuitry at the tip end of the wing such that
    when he turns the switch "on", the main running light comes on.
    If, while the main running light is on, he turns the switch to
    "off" and then back to "on" again within two seconds, the
    main running light (which will have gone dark while the switch
    is off) will come back on _and in addition_, the strobe will come
    on, having been triggered by the 1 ms < x < 2 sec interruption of
    power, so that they'll BOTH be on now.

    I've seen this switching logic function in a standard PIR porch
    light, only the "Strobe too" function would be exchanged with "turn
    porch light on unconditionally".

    The circuit should be triviaL. The question is, how severely does the
    OP want to start hacking into his airplane? ;-)

    Good Luck!
  11. Jim Thompson

    Jim Thompson Guest

    If the wing is made of metal, it is the return path. Its a lot like what
    is done in cars.


    I don't think that is legitimate in aircraft. I think the OP is
    heading for problems with the FAA, unless his craft is "experimental".

    ...Jim Thompson
  12. Ken Smith

    Ken Smith Guest

    With relays:

    From switch --+----+------------+------------------------ Green light
    ! ! !
    \ ! !
    R1 / ! ----------
    \ ! ! NC ! !
    / ! ! O- ! - ! ------------------- Strobe
    ! !NC ! <-- !
    D1 V O ! O------
    --- <----+-- NO
    ! O !
    ! NO )
    +---- )
    ! ) ) K2
    C1 --- )K1 )
    --- ) !
    ! ) GND

    I think this is right. It uses two normal relays that should be easy to
    get. C1 has to be quite big. The coil resistance times C1 has to be a
    few seconds so you'd be best off with a small relay that has a highish
    coil resistance.

    R1 is some small fraction of K1's coil resistance and serves to limit the
    charging current on C1 to something that D1 can handle.

    You may be better off with some semiconductors beyond just D1 in the
  13. Ken Smith

    Ken Smith Guest

    ! ! ^ 15V ! ! !
    ! ! ! ! ! !
    The power in an aircraft is about as bad as in a car. Adding the 1K
    resitor and 15V zener protects the MOSFET from the high voltage spikes.
  14. Ken Smith

    Ken Smith Guest

    Lots of aircraft have lots of currents flowing in the skin. If the
    factory made it that way, getting rid of the current in the skin will get
    the FAA spun up.
  15. The hacking should be relatively trivial with the exception of very old
    aircraft. The wingtip is generally removable with lebenty-dozen screws, and
    the last outboard rib is the first thing you see. The electronics is
    generally bolted to the outboard rib and the nav light is pigtailed through
    an inexpensive connector to the electronics so that the whole wingtip can
    come off without removing the nav light.

    You simply do your electronics in a box that will fit the surface of the rib
    and you are home free.

  16. Jim ...

    I'll make you a deal. You don't guess at airplane answers and I won't guess
    at IC internal design, since it is obvious that neither one of us has
    expertise in the other's field.

    The OP can legitimize such an installation without a lot of hassle...and
    should be relatively simple to design and approve.

    Google on "FAA Form 337" and "FAA Field Approval" if you want more
    information than you really need. I would argue that such a modification
    comes under the heading of "minor modification" and is a simple logbook
    entry, but the installing mechanic can go the 337 / Field Approval route if
    (s)he wishes.

    Airframe and Powerplant Mechanic
    Inspection Authorization
  17. You actually have four functions that are necessary:

    Nav Light On
    Strobe On
    Nav Light and Strobe On.

    Think about it.

    Off is obvious

    Nav Light On when flying in darkness in cloud. Strobes induce vertigo when
    you are in IMC, but the nav lights by law have to be on at night.

    Strobe On would be daytime use when you want to be seen but not keep a $5
    lamp burning for no good reason.

    Nav Light and Strobe On for VMC at night when you need not only nav lights,
    but to be seen at a distance as well.

    NOW the problem complexes itself up, but shouldn't be a problem with a few
    well chosen capacitors and a simple counter.

  18. MacGyver

    MacGyver Guest

    This is exactly what I want, thanks for the great description! With
    this circuit, I won't have to hack the plane at all. That's why I want
    to build it.
    It can fit in the fiberglass wingtip in a small enclosed box no
    It is for an experimental aircraft, so no worries there with the FAA!
    Thanks so much for all of your posts.
  19. MacGyver

    MacGyver Guest

    Not too worried about having just the strobes on without the Nav
    I don't think I would ever use the strobes without the Nav lights.

    I just want to be able to have a way to turn off the strobes so I don't
    piss off other pilots while taxiing...
  20. Guest


    Even if the FAA OKs this mod, the OP should be made aware that this mod
    can affect other systems in the aircraft, particularly heading compass
    that uses magnetic sensing (flux valve).

    It's good practice to use two wires (signal and return). They should be
    twisted wires to reduce magnetic effects on the compass system.

    Of course, none of this matters if you don't care if you arrive at your
    intended destination...

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