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Blinking third break light

Discussion in 'Electronic Basics' started by Bryan, Mar 14, 2005.

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  1. Bryan

    Bryan Guest

    My wife has me to build her a circuit that will make the third brake light
    blink light her friends (lucky me). Since I am rather new to electronics,
    can anyone offer any PCP designs or schematics? Thanks for any help!!

  2. Terry

    Terry Guest

    Is that legal?
    BTW yesterday driving behind car with driver side rear brake light out of
    action realized that's another advantage of the third brake light set up!
    With only two lights you may not know, when one is out of action whether the
    driver is trying to signal a turn or is tapping his brakes. The third and
    upper light tells you 'Yes it's the brakes'. (That assumes that only one
    regularly located brake bulb is out of action and the third (and usually
    upper brake light) is OK.
  3. John G

    John G Guest

    Mistaking a brake light for a turn signal has not been a problem in the
    advanced world since 1960.
    Only the flat earth society (USA) has persisted with this cheapskate
    method for so long.
  4. Wha? On my American-made truck the turn signal is orange and the brake
    light red.

  5. Once again you are full of misinformation about the US. Tail lights
    on vehicles abandonded this method a long time ago.

    Idoits spouting garbage comes to mind.
  6. Guest

    Bryan, there have been a few posts in reply to your question but other
    than to raise the quasi relevant question of legality (I've seen them
    flash on motorcycles) they're not really addressing your question.

    The good news is 1) I know how to do it, 2) I've seen and have a
    schematic for something really similar. The bad news is that I'm not
    expert so my experiences and knowledge are limited (kinda the deaf,
    dumb, and blind leading the blind. :)

    That said, I read this schematic about 5 years ago and it was for
    flashing the brake light on a motorcycle. There are two ways you can
    decide to have that light flash; continuously while the brake light
    circuit is energized or to have it flash some number of times and then
    latch on (blink - blink - blink - stay on....). Either of them will be
    simple to implement.

    Let's put into words that which is easier said than done; locate the
    wire that runs to the Elizabeth Dole light (third brake light),
    preferably somewhere inside the car instead of inside the housing (for
    space, appearance, and accessibility considerations). Bascially, just
    cut the positive wire that goes to that brake light. The raw end of
    the wire from the chassis is now your source voltage; it should have
    voltage only when the brake light circuit is energized. The other raw
    end, that goes to the Elizabeth Dole light is the output that you'll
    hook up to your circuit you're going to build.

    The circuit I use consists of basically 8 parts: one potentiometer
    (100k), one capacitor (10 micro F), one 4049 hex buffer, one 4017
    decade counter, one 680 Ohm resistors ,x number of 4148 diodes (the
    number of outputs from the 4017 you intend to use), 1 2N4401
    transistor, one more 4148 diode, and finally one relay.

    It's a really simple thing once you've played with it and seen it
    (believe me, electronics isn't my area of expertise and yet I think
    it's pretty simple). The 4017 decade counter does just what it seems
    like it would do; it counts input pulses. It sends one of 10 outputs
    high (on) depending on the number of input pulses it gets. I use the
    4049 hex buffer to generate the pulses (I have no idea how it does it,
    I just read it in the original schematic I read). I tried to use a 555
    timer to produce the pulses but could never get it to work right.
    Anyway, the capacitor is used with the 4049 hex buffer I presume as a
    filter, and the pot is used to adjust the output pulse frequency. The
    4017 receives the pulses as input and sends each of its outputs high in
    turn. You tie the output through a diode to the resistor. Then,
    finally, you tie in the transistor, final diode, and relay. I don't
    know why they used the transistor, but I suspect it's because the 4017
    might not be able to sustain the load of the relay on it's outputs.
    Here's where it gets fun.

    If you want it to blink on and off three times and then stay on you
    simply tie outputs 1, 3, 5, through diodes, to the resistor which is
    tied to the transistor. Then you tie output 7 to the resistor AND to
    the Clock Enable pin on the 4017 (tying its own output #7 to the Clock
    Enable) which "freezes" the whole thing. It'll stay locked on like
    that until the whole circuit gets reset (when the circuit loses power
    when the brake circuit de-energizes as the pedal is released). The
    output trips on the transistor which applies power (from the up-stream
    brake circuit) to the relay (any NO automotive relay that can handle
    the load (check out a horn relay for a 1998 Dodge Ram 1500 at an
    autoparts store for around 8 bucks and which has nice-sized legs for
    female blade connectors)). You use the second 4148 to kill any spike
    voltage from the coil in the relay.

    Now, I've never tried to see if one will reset when you cut power to
    it, but the original schematic that I saw worked that way, I *think*.

    Unfortunately, it's near impossible to try to describe to you what the
    connections/schematic looks like in type. This link is now dead, but
    if you could find some web archive site they might have it (I never
    looked at this site/page before so I don't know if it would do what you
    need or not):

    Here's a link to a, I think, much more complicated setup, but the
    schematic is nice and clean:

    Unfortunately I don't have a site that would be available long enough
    or reliably enough to post it in this reply. I can draw something up
    and e-mail it to you, if you'd like, just let me know and post your
    address and I'll see what I can do.

    In the meantime, here's a simple idea...if you don't mind it flashing

    Super simple, it looks.

    Anyway, hope that helps.

    Take care.

  7. Bryan

    Bryan Guest

    Thanks for the information.
    I should have been more clear on the blinking area. I did wants it for a
    duration they steady on. I have seen some vehicles with this in Arizona as
    far as the legality aspect, I have not heard of any. I do have a motorcycle
    as well and was looking to adapt the circuit to it as well as using LEDs.
    Thanks again for your help. I will look into those sites. If you have any
    other ideas as well, please feel free to let me know.

    BA Sr.
  8. HC

    HC Guest

    I have a drawing of the circuit, as an Adobe Acrobat document, and I
    could prbably hack one out in Paint (I originally used Corel Draw! to
    make the schematic, converted it to PDF and God only knows where that
    Corel Draw! file went. :-/ I hate to be an ignorant wretch, but I
    don' t know how to post a file to the 'groups. I'd be willing to send
    you my schematic as a PDF, but I'd really like to do it here in the
    'groups so others could benefit from it. Any suggestions of how I can
    "post" a PDF in a 'group posting?

    I can always send it to your e-mail address if you want to give that to
    me, but like I say, I'd really like to send it to the group to help you
    AND others.

  9. Guest

    Actually, I'm pretty sure I saw a recent model Ford that had the
    brake/turn signal use the same lighting element. Flat earth, huh?

  10. It would be interesting because Ford claims to build "International
    Designs". My neighbor bought a new full size Ford truck last year so
    I'll check when I catch her at home. I don't recall seeing any new
    vehicles without the separate light systems and it makes hauling a
    conventional trailer even more interesting with all the variations in
    wiring. On top of that, a lot of vehicles are imported from other
    countries that use separate lamps for turn and brake lights.
  11. HC

    HC Guest

    Well, that's not perfect but I guess it'll work; it's all text, it
    should propagate beyond Google (I hope) and anybody with a copy of
    Winzip can copy and paste it into a straight text file (Notepad), save
    it as blinker.uue and then open it with Winzip.

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