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Current Sensors

Discussion in 'General Electronics' started by Inspar8r, Jan 27, 2005.

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  1. Inspar8r

    Inspar8r Guest

    I have a question about a design problem i need to address.

    I designed and built a set of LED taillights for my car. Obviously,
    the LEDs draw significantly less than a standard bulb.

    The problem is, there is a circuit that is designed to monitor the
    bulbs, and illuminates a light in the cluster when the bulb fails.
    Right now, it thinks my LEDs are failed bulbs.

    I am not satisfied or comfortable with wiring up parallel 6© 10W
    resistors for the taillights and 47© 25W resistors for the brake
    light circuits just to mimick the standard bulb (as well as dissipate
    almost 1A of current as heat every time the brakes are applied).
    Removing the bulb is not an option either. Most have told me that b/c
    they are LEDs, i don't need to monitor the circuit, but i'd like to
    anyway (you never know)...

    The failure sensor is a CURRENT sensing device, and according to the
    schematic, uses an OR-gate that signals a npn transistor that powers
    the warning light. The OR-gate is fed by 2 unidentified "boxes" (i'm
    guessing IC's). I think the OR-gate is there to allow the failure
    sensor to monitor the tails both when the car is in ACC and when

    My question is, where can i find schematics on IC current sensors that
    i can tailor to my needs to build my own sensor and just bypass the
    stock sensor?

    If I knew what those unknown boxes where, i would modify the stock box
    to "look" for less current.

    Any ideas...
    Posted at:
  2. Robert Baer

    Robert Baer Guest

  3. Inspar8r

    Inspar8r Guest

    Thanks for the info...

    Here's a cutout of the box i'm looking at..

    Pin 3 is the power coming from the car in ACC/ON mode
    Pin 8 is the power coming from the car when STARTED
    Pin 11 is ground
    Pin 7 goes to my taillights.

    Is that lone resistor the one setting up the current for the sensor?

    Or do you really need to know what those to little boxes are (i'm
    guessing ICs)??

    Thanks for the help so far..
    Posted at:
  4. SCADA

    SCADA Guest

  5. beast

    beast Guest

    Since LED's don't burn out, why not just neutralise the sensors?

    Or that IC is probably a low voltage box, why not wire the output of
    the LED directly into the box?
    Posted at:
  6. SteveB

    SteveB Guest

    There's also the problem that a failed LED doesn't necessarily take a lower
    or zero current, it may even take more when it fails.
  7. beast

    beast Guest

    I got it!

    Glue a 1V photocell on the lens, the back ofthe light probably will
    do, and run the signal to the pin.
    Posted at:
  8. Yukio

    Yukio Guest

    A: I have seen circuits that just use a couple of turns of wire over a
    REED switch to sense DC currents in the milli-amp/amps. range with
    virtually no voltage drop ! for greater sensitivity just add more turns, for
    more capacity use heavier wire !
    B: On several automobiles , I know that the Tail-lights are fed off the
    same circuit as the Dash-board fuse, ie, if the tail-light fuse fails, the
    dash-light will not turn on !

    Yukio YANO
  9. Inspar8r

    Inspar8r Guest

    Here's the schematics I drew up..


    The IC a drew is the way it would look if you were looking AT THE

    The harness connector is the pin asignments as if you were looking

    The harness PLUG is the pin assignments as if you were looking
    DIRECTLY AT THE PLUG. Try no to get confused. The best way to
    remember is to match up the "X's", since they denote a terminal that
    is UNUSED.

    Hopefully you can understand my notes...

    Oh and C1, C2, C3 are all .047µf Ceramic Discs. I forgot to ge tthe
    values of C4 and C5, but i don't think it matters much. schematic.jpg
    Posted at:
  10. Inspar8r

    Inspar8r Guest

  11. beast

    beast Guest

    The pin that indicates "lights on" should be 3V to 5V if it's a
    standard digital voltage, then the pin that triggers the dash light
    should be hot. So you run the 3V photocell to the sensor array,
    whichever one it is.

    I think your unknown boxes are sensor arrays.
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