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XOR at 12V and a few amps.

Discussion in 'Electronic Basics' started by George Herold, Sep 25, 2012.

  1. First off this question is of academic interest only.

    So I needed to hook up the a 4 wire trailer connector onto our Toyota
    van. (previously we had a Ford van.) My brother warned me that the
    foreign cars use a 5 wire lamp indicator system. (There are separate
    bulbs for the brake and turn signal. The trailer uses only one bulb
    for both brake and turn.)
    I first thought I could just put the two (brake, turn) lines together
    with diodes. But I then realized this wouldn’t work with both the
    brake and the turn signal on.
    What I needed was a XOR connection between the lines.
    both off, bulb off
    one on, bulb on
    both on, bulb off
    So is there a way to do this with some diodes, transistors,
    resistors?
    I’ve been unable to see the way to an answer. (I haven’t tried
    google, that’s too easy and this is more fun.)

    Any ideas?

    Oh, I solved the problem by going to carquest and buying a wiring
    harness for ~$50. But say I’m stuck on a desert island with only my
    parts box.

    George H.
     
  2. Tom Biasi

    Tom Biasi Guest

    You can make an XOR with relays. I'm not sure this is how to do your job
    though.
    I could show you a diagram but that would be the same as you going to
    Google.

    Tom
     
  3. OK thanks Tom, I'll google xor with relays. But yes I was thinking
    about power transistor. (I've got lots of them)

    George H.
     
  4. Yeah and very few roads to boot.
    (there's one in every crowd :^)

    George H.
     
  5. Thanks, I was hoping for something without relays.

    The patent looks like there is a separate 12V power line coming in to
    power the transistors. (But I didn't read it.)

    George H.
     
  6. "George Herold" <> schreef in bericht
    First off this question is of academic interest only.

    So I needed to hook up the a 4 wire trailer connector onto our Toyota
    van. (previously we had a Ford van.) My brother warned me that the
    foreign cars use a 5 wire lamp indicator system. (There are separate
    bulbs for the brake and turn signal. The trailer uses only one bulb
    for both brake and turn.)
    I first thought I could just put the two (brake, turn) lines together
    with diodes. But I then realized this wouldn’t work with both the
    brake and the turn signal on.
    What I needed was a XOR connection between the lines.
    both off, bulb off
    one on, bulb on
    both on, bulb off
    So is there a way to do this with some diodes, transistors,
    resistors?
    I’ve been unable to see the way to an answer. (I haven’t tried
    google, that’s too easy and this is more fun.)

    Any ideas?

    Oh, I solved the problem by going to carquest and buying a wiring
    harness for ~$50. But say I’m stuck on a desert island with only my
    parts box.

    George H.



    Well, guess you have right, left and brake. Assuming right and left
    blinking, for the right bulb you get:

    B R L | Rb
    ------|---
    0 0 0 | 0
    0 0 1 | 0
    0 1 0 | 1
    0 1 1 | -
    1 0 0 | 1
    1 0 1 | 1
    1 1 0 | 0
    1 1 1 | -

    If you can have both right and left on, blinking "alarm" in Europe, you get
    for both bulbs:

    B R L | Rb Lb
    ------|------
    0 0 0 | 0 0
    0 0 1 | 0 1
    0 1 0 | 1 0
    0 1 1 | 1 1
    1 0 0 | 1 1
    1 0 1 | 1 0
    1 1 0 | 0 1
    1 1 1 | 0 0

    This way you will get B xor L for the left bulb and B xor R for the other,
    just as advertised.

    So I suppose the schematic below will do the trick. Although I do not seem
    to remember I saw it before, I'm sure not to be the first one that drew it.
    Think I do not have to explain it for this public :)

    brake -->|-------------+
    Schottky |
    left -->|-------------+
    |
    right -->|-------------+
    |
    .-.
    ( X ) Lb
    '-'
    |
    +------+------------------+
    | |
    | |
    ___ |/ ___ |/
    brake--|___|-----+---| left---|___|-----+---|
    | |> | |>
    | | | |
    | | | |
    ___ |/ | ___ |/ |
    left---|___|---| | brake--|___|---| |
    |> | |> |
    | | | |
    | | | |
    | | | |
    GND-----------+-----+-------------------+-----+
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    petrus bitbyter
     
  7. Excellent! Thanks.
    Just one thing. Why do you have the right tied in at the top through
    the schottky? This doesn't seem to hurt anything.
    But doesn't help either. (that I can see.)

    George H.
    (
     
  8. "George Herold" <> schreef in bericht
    Excellent! Thanks.
    Just one thing. Why do you have the right tied in at the top through
    the schottky? This doesn't seem to hurt anything.
    But doesn't help either. (that I can see.)

    George H.
    (

    So you can use the "power" for the right bulb as well.

    petrus bitbyter
     
  9. Maybe. If so you can solve that problem I suppose :)

    petrus bitbyter
     
  10. Oops. That's right. No worries this gives me a circuit to start
    with.

    I think I can jsut flip the whole thing over, use pnp's and get rid of
    the
    schottky. Or p-channel Fets?

    George H.
     

  11. Suppose it depends on the age of the vehicle. Older ones may stil use
    bimetallics, newer for sure use electronics. But does it matter? Especially
    when one side of the bulb is hard-grounded the other side gets a pulsing
    voltage from the turn and a constant voltage from the brake. Originally
    meant for two different bulbs but to be combined by the circuit for one
    bulb.

    petrus bitbyter
     
  12. Thanks Jim... this is just of academic interest.... I was wondering
    how to make an XOR function out of a few parts. JF's link and
    petrus's circuit have 'shown me the way'.

    George H.
     
  13. "George Herold" <> schreef in bericht

    Oops. That's right. No worries this gives me a circuit to start
    with.

    I think I can jsut flip the whole thing over, use pnp's and get rid of
    the
    schottky. Or p-channel Fets?

    George H.
    "I think I can jsut flip the whole thing over, use pnp's and get rid of
    the schottky. Or p-channel Fets?"

    Nope. An open contact does not sink current. Right, left and brake can only
    source current.

    petrus bitbyter
     
  14. Ouch, that's right.
    'scratch, scratch'
    guess I better look at that patent circuit again.

    George H.
     
  15. "George Herold" <> schreef in bericht
    Ouch, that's right.
    'scratch, scratch'
    guess I better look at that patent circuit again.

    George H.


    Nope once more. Guess the circuit below will do the trick as well. But, as
    others stated already, the power transistor needs to be a real heavy duty
    type as the inrush current of those bulbs can easily be five to ten times
    the nominal current.

    brake -->|-------------+
    Schottky |
    left -->|-------------+
    |
    right -->|-------------+
    |
    |
    ___ |<
    +--|___|-----|
    | |\
    | |
    +-------------------+-----+ |
    | | |
    | | |
    ___ |/ ___ |/ |
    brake--|___|-----+---| left---|___|-----+---| .-.
    | |> | |> ( X )
    | | | | '-'
    | | | | |
    ___ |/ | ___ |/ | |
    left---|___|---| | brake--|___|---| | |
    |> | |> | |
    | | | | |
    | | | | |
    | | | | |
    GND-----------+-----+-------------------+-----+--------+
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    petrus bitbyter
     
  16. If you want to go for relays, you will not need a patented circuit I
    suppose. See below.

    VCC
    Left +
    | |
    | o
    _|_ \ left
    |_/_|- \
    | o \o
    | | |
    | + +
    | \ /
    === X
    GND / \
    + +
    | |
    Brake | |
    | o /o
    _|_ /
    |_/_|- / brake
    | o
    | |
    | .-.
    | ( X )Lb
    === '-'
    GND |
    |
    ===
    GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    For Vcc you can use the three Schottkys but keep in mind that they need to
    be able to handle the inrush current. Otherwise you will need a wire from
    the dashboards fuse panel.

    petrus bitbyter
     
  17. Tom Biasi

    Tom Biasi Guest

    Snip..
    Go for automotive relays. They are proven for temps and environment.
     
  18. Jasen Betts

    Jasen Betts Guest


    a couple of form b relays each wired to disconnect the other circuit...

    if you can read ascii ladder logic.

    ---|BRK|-+----( A )-------------
    |
    `----|/B|---+--(OUT)---
    |
    .----|/A|---'
    |
    ---|IND|-+----( B )-------------

    you'll want two of those, one for each side.
     
  19. Jasen Betts

    Jasen Betts Guest

    there's a simpler way if you have a +12 supply at the point where you
    want to put the circuit just one relat is enough, coil wired between
    the INDicator and BRaKe lines contacts switching +12V to the trailer.
     
  20. Jamie

    Jamie Guest

    Right, something I stated way back at the start of this tread and I
    took that from memory.

    So, it is true then, if it's on the internet it must be true
    otherwise beware of information coming elsewhere.

    Jamie
     
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