Come up with a brilliant solution .......

Discussion in 'Hobby Electronics' started by Geocacher, Sep 22, 2005.

  1. Geocacher

    Geocacher Guest

    I work in the trailer manufacturing business.
    We use LED tail-light clusters.
    The modern truck/tractors utilise a computer system to perform diagnostics
    on various systems within the rig. One of these is the lighting system.
    A pulse is sent to each tail light, the system monitoring the current. If
    there is current flow, it is assumed the incandescent globes are OK.

    Unfortunately, the LED lamps draw such a small amount of current that the
    computer does not see a "filament" and flags a major fault on the truck
    dashboard. In addition to the error message, the system continues to send
    curent pulss in the forlorn hope that things at the rear of the rig have
    improved. This causes the entire suite of LED lamps to flash like a
    low-class disco!

    There are ways around it. Some manufacturers have placed incandescent globes
    in parallel with the LED lamps, others have used high wattage resistors.
    Neither is acceptable for obvious reasons.

    There must be a way to "tell" the computer that the LED lamps are fine by
    emulating the current drawn by an incandescent globe, without using the
    solutions noted above.

    Do any of you outstandingly brilliant contributors have any novel and
    innovative ideas?????
    Geocacher, Sep 22, 2005
    #1
  2. Geocacher

    budgie Guest

    On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <> wrote:

    >I work in the trailer manufacturing business.
    >We use LED tail-light clusters.
    >The modern truck/tractors utilise a computer system to perform diagnostics
    >on various systems within the rig. One of these is the lighting system.
    >A pulse is sent to each tail light, the system monitoring the current. If
    >there is current flow, it is assumed the incandescent globes are OK.
    >
    >Unfortunately, the LED lamps draw such a small amount of current that the
    >computer does not see a "filament" and flags a major fault on the truck
    >dashboard. In addition to the error message, the system continues to send
    >curent pulss in the forlorn hope that things at the rear of the rig have
    >improved. This causes the entire suite of LED lamps to flash like a
    >low-class disco!
    >
    >There are ways around it. Some manufacturers have placed incandescent globes
    >in parallel with the LED lamps, others have used high wattage resistors.
    >Neither is acceptable for obvious reasons.
    >
    >There must be a way to "tell" the computer that the LED lamps are fine by
    >emulating the current drawn by an incandescent globe, without using the
    >solutions noted above.


    The only ways I can see to "emulate" current draw is to either:

    (a) actually draw it (resistor, incandescent bulb or similar, as you mention);

    (b) modify the sense circuitry for greater sensitivity; or

    (c) interpose a "box" that senses LED array current and fudges the pooter input.

    If the current sense circuitry simply senses volt drop across a sense resistor,
    you'll need to increase it. If it uses a transformer approach with an open
    toroid, wind more turns on it. This assumes that the circuitry can be modified
    (legality, access, information availability).

    >Do any of you outstandingly brilliant contributors have any novel and
    >innovative ideas?????


    Nope, only basics.
    budgie, Sep 22, 2005
    #2
  3. Geocacher wrote:
    > There must be a way to "tell" the computer that the LED lamps are fine by
    > emulating the current drawn by an incandescent globe, without using the
    > solutions noted above.


    Does the manufacturer offer an updated ROM for your model?

    Cheers,
    Nicholas Sherlock
    Nicholas Sherlock, Sep 22, 2005
    #3
  4. Geocacher

    Geocacher Guest

    No. Manufacturers of the truck/tractors offer no assistance. They will not
    permit any tinkering with their computer systems - will void the warranty -
    and have not come up with any viable solution themselves!


    "Nicholas Sherlock" <> wrote in message
    news:dgv15u$b5j$...
    > Geocacher wrote:
    >> There must be a way to "tell" the computer that the LED lamps are fine by
    >> emulating the current drawn by an incandescent globe, without using the
    >> solutions noted above.

    >
    > Does the manufacturer offer an updated ROM for your model?
    >
    > Cheers,
    > Nicholas Sherlock
    Geocacher, Sep 22, 2005
    #4
  5. Geocacher

    Franc Zabkar Guest

    On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <> put
    finger to keyboard and composed:

    >I work in the trailer manufacturing business.
    >We use LED tail-light clusters.
    >The modern truck/tractors utilise a computer system to perform diagnostics
    >on various systems within the rig. One of these is the lighting system.
    >A pulse is sent to each tail light, the system monitoring the current. If
    >there is current flow, it is assumed the incandescent globes are OK.
    >
    >Unfortunately, the LED lamps draw such a small amount of current that the
    >computer does not see a "filament" and flags a major fault on the truck
    >dashboard. In addition to the error message, the system continues to send
    >curent pulss in the forlorn hope that things at the rear of the rig have
    >improved. This causes the entire suite of LED lamps to flash like a
    >low-class disco!
    >
    >There are ways around it. Some manufacturers have placed incandescent globes
    >in parallel with the LED lamps, others have used high wattage resistors.
    >Neither is acceptable for obvious reasons.
    >
    >There must be a way to "tell" the computer that the LED lamps are fine by
    >emulating the current drawn by an incandescent globe, without using the
    >solutions noted above.
    >
    >Do any of you outstandingly brilliant contributors have any novel and
    >innovative ideas?????


    You need some way of drawing the required amount of current for the
    duration of the pulse, and zero amps thereafter. What about a simple
    circuit based around a parallel PTC resistor, ie something like what
    happens inside a TV set during automatic degaussing at switch-on?

    -- Franc Zabkar

    Please remove one 'i' from my address when replying by email.
    Franc Zabkar, Sep 22, 2005
    #5
  6. Franc Zabkar furiously typed the following on 23/09/2005 8:22 AM:
    > On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <> put
    > finger to keyboard and composed:
    >
    >
    >>I work in the trailer manufacturing business.
    >>We use LED tail-light clusters.
    >>The modern truck/tractors utilise a computer system to perform diagnostics
    >>on various systems within the rig. One of these is the lighting system.
    >>A pulse is sent to each tail light, the system monitoring the current. If
    >>there is current flow, it is assumed the incandescent globes are OK.
    >>
    >>Unfortunately, the LED lamps draw such a small amount of current that the
    >>computer does not see a "filament" and flags a major fault on the truck
    >>dashboard. In addition to the error message, the system continues to send
    >>curent pulss in the forlorn hope that things at the rear of the rig have
    >>improved. This causes the entire suite of LED lamps to flash like a
    >>low-class disco!
    >>
    >>There are ways around it. Some manufacturers have placed incandescent globes
    >>in parallel with the LED lamps, others have used high wattage resistors.
    >>Neither is acceptable for obvious reasons.
    >>
    >>There must be a way to "tell" the computer that the LED lamps are fine by
    >>emulating the current drawn by an incandescent globe, without using the
    >>solutions noted above.
    >>
    >>Do any of you outstandingly brilliant contributors have any novel and
    >>innovative ideas?????

    >
    >
    > You need some way of drawing the required amount of current for the
    > duration of the pulse, and zero amps thereafter. What about a simple
    > circuit based around a parallel PTC resistor, ie something like what
    > happens inside a TV set during automatic degaussing at switch-on?
    >
    > -- Franc Zabkar
    >
    > Please remove one 'i' from my address when replying by email.



    What about a feedback amp?
    Richard Waters, Sep 23, 2005
    #6
  7. Geocacher

    Ken Taylor Guest

    "Franc Zabkar" <> wrote in message
    news:...
    > On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <> put
    > finger to keyboard and composed:
    >
    >>I work in the trailer manufacturing business.
    >>We use LED tail-light clusters.
    >>The modern truck/tractors utilise a computer system to perform diagnostics
    >>on various systems within the rig. One of these is the lighting system.
    >>A pulse is sent to each tail light, the system monitoring the current. If
    >>there is current flow, it is assumed the incandescent globes are OK.
    >>
    >>Unfortunately, the LED lamps draw such a small amount of current that the
    >>computer does not see a "filament" and flags a major fault on the truck
    >>dashboard. In addition to the error message, the system continues to send
    >>curent pulss in the forlorn hope that things at the rear of the rig have
    >>improved. This causes the entire suite of LED lamps to flash like a
    >>low-class disco!
    >>
    >>There are ways around it. Some manufacturers have placed incandescent
    >>globes
    >>in parallel with the LED lamps, others have used high wattage resistors.
    >>Neither is acceptable for obvious reasons.
    >>
    >>There must be a way to "tell" the computer that the LED lamps are fine by
    >>emulating the current drawn by an incandescent globe, without using the
    >>solutions noted above.
    >>
    >>Do any of you outstandingly brilliant contributors have any novel and
    >>innovative ideas?????

    >
    > You need some way of drawing the required amount of current for the
    > duration of the pulse, and zero amps thereafter. What about a simple
    > circuit based around a parallel PTC resistor, ie something like what
    > happens inside a TV set during automatic degaussing at switch-on?
    >
    > -- Franc Zabkar
    >

    That would work for the pulse but would it work when the light was switched
    on (as in tail lights - the PTC would go high resistance and the computer
    would no longer detect enough current)? I think just a parallel resistor is
    going to be required. Certainly the least complexity solution. Or maybe,
    dare I say it, the light bulb.....

    Ken
    Ken Taylor, Sep 23, 2005
    #7
  8. Geocacher

    Craig Hart Guest

    how about, you make a circuit that AC-couples (use a capacitor) the brake
    line to a transistor that switches in a low impedance load (resistor) for a
    short time (e.g. 50ms). each time the brake line pulses high, the pulse
    turns on the transistor for a moment.

    the constant "on" signal of the brakes won't trigger the circuit due to the
    AC coupling.

    such a short on-time won't effect brakelight performance any, but will be
    long enough to allow the computer to 'sense' the higher load.






    " Geocacher" <> wrote in message
    news:dgu6hc$g0q$...
    > I work in the trailer manufacturing business.
    > We use LED tail-light clusters.
    > The modern truck/tractors utilise a computer system to perform diagnostics
    > on various systems within the rig. One of these is the lighting system.
    > A pulse is sent to each tail light, the system monitoring the current. If
    > there is current flow, it is assumed the incandescent globes are OK.
    >
    > Unfortunately, the LED lamps draw such a small amount of current that the
    > computer does not see a "filament" and flags a major fault on the truck
    > dashboard. In addition to the error message, the system continues to send
    > curent pulss in the forlorn hope that things at the rear of the rig have
    > improved. This causes the entire suite of LED lamps to flash like a
    > low-class disco!
    >
    > There are ways around it. Some manufacturers have placed incandescent

    globes
    > in parallel with the LED lamps, others have used high wattage resistors.
    > Neither is acceptable for obvious reasons.
    >
    > There must be a way to "tell" the computer that the LED lamps are fine by
    > emulating the current drawn by an incandescent globe, without using the
    > solutions noted above.
    >
    > Do any of you outstandingly brilliant contributors have any novel and
    > innovative ideas?????
    >
    >
    Craig Hart, Sep 23, 2005
    #8
  9. Franc Zabkar wrote:
    > On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <>
    >>A pulse is sent to each tail light, the system monitoring the current.

    > You need some way of drawing the required amount of current for the
    > duration of the pulse, and zero amps thereafter. What about a simple
    > circuit based around a parallel PTC resistor, ie something like what
    > happens inside a TV set during automatic degaussing at switch-on?


    Surely the obvious solution is an electrolytic capacitor with large
    valued parallel discharge resister and smaller series resister. When
    the current pulse is sent, the series resister determines the initial
    current draw. The parallel resister enables the cap to discharge for
    another cycle.

    How big a capacitor you need is determined by the required current
    draw and the amount of time after switch-on that the current is sensed.
    The idea will only be feasible of the time is very short. Normal
    V=I*C*T rule applies.

    Clifford Heath.
    Clifford Heath, Sep 23, 2005
    #9
  10. " Geocacher" <> wrote in message
    news:dgu6hc$g0q$...
    > I work in the trailer manufacturing business.
    > We use LED tail-light clusters.
    > The modern truck/tractors utilise a computer system to perform diagnostics
    > on various systems within the rig. One of these is the lighting system.
    > A pulse is sent to each tail light, the system monitoring the current. If
    > there is current flow, it is assumed the incandescent globes are OK.
    >
    > Unfortunately, the LED lamps draw such a small amount of current that the
    > computer does not see a "filament" and flags a major fault on the truck
    > dashboard. In addition to the error message, the system continues to send
    > curent pulss in the forlorn hope that things at the rear of the rig have
    > improved. This causes the entire suite of LED lamps to flash like a
    > low-class disco!
    >
    > There are ways around it. Some manufacturers have placed incandescent

    globes
    > in parallel with the LED lamps, others have used high wattage resistors.
    > Neither is acceptable for obvious reasons.
    >
    > There must be a way to "tell" the computer that the LED lamps are fine by
    > emulating the current drawn by an incandescent globe, without using the
    > solutions noted above.
    >
    > Do any of you outstandingly brilliant contributors have any novel and
    > innovative ideas?????
    >


    Is the current only checked during the pulse?

    Ross
    Ross Marchant, Sep 23, 2005
    #10
  11. "Clifford Heath" <> wrote in message
    news:43334683$0$15030$...
    > Franc Zabkar wrote:
    > > On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <>
    > >>A pulse is sent to each tail light, the system monitoring the current.

    > > You need some way of drawing the required amount of current for the
    > > duration of the pulse, and zero amps thereafter. What about a simple
    > > circuit based around a parallel PTC resistor, ie something like what
    > > happens inside a TV set during automatic degaussing at switch-on?

    >
    > Surely the obvious solution is an electrolytic capacitor with large
    > valued parallel discharge resister and smaller series resister. When
    > the current pulse is sent, the series resister determines the initial
    > current draw. The parallel resister enables the cap to discharge for
    > another cycle.
    >
    > How big a capacitor you need is determined by the required current
    > draw and the amount of time after switch-on that the current is sensed.
    > The idea will only be feasible of the time is very short. Normal
    > V=I*C*T rule applies.
    >
    > Clifford Heath.


    Or use the charge time of the cap to turn off a PNP power transistor which
    would allow the use of very much smaller values.
    Ross Marchant, Sep 23, 2005
    #11
  12. Geocacher

    Geocacher Guest

    As far as we've been able to check this mess, yes, the current pulse is sent
    when the ignition is switched on, and will keep on pulsing until the load
    sense is satisfied. Vehicle diagnostics are performed (obviously, the lights
    are only one of the tests) and any errors are indicated on the dashboard.
    However - it would appear that the system has a continuous checking routine
    to determine whether a lamp has failed during the run.
    Sorry I sound so hazy over this, but trying to get a truck to play with is
    not easy. Suppliers are not too interested, and the operators are not keen
    on taking a truck out of service for us to investigate further.
    Sometimes, I hate my job!!!!!


    "Ross Marchant" <> wrote in message
    news:43334c72$...
    >" Geocacher" <> wrote in message
    > news:dgu6hc$g0q$...
    >> I work in the trailer manufacturing business.
    >> We use LED tail-light clusters.
    >> The modern truck/tractors utilise a computer system to perform
    >> diagnostics
    >> on various systems within the rig. One of these is the lighting system.
    >> A pulse is sent to each tail light, the system monitoring the current. If
    >> there is current flow, it is assumed the incandescent globes are OK.
    >>
    >> Unfortunately, the LED lamps draw such a small amount of current that the
    >> computer does not see a "filament" and flags a major fault on the truck
    >> dashboard. In addition to the error message, the system continues to send
    >> curent pulss in the forlorn hope that things at the rear of the rig have
    >> improved. This causes the entire suite of LED lamps to flash like a
    >> low-class disco!
    >>
    >> There are ways around it. Some manufacturers have placed incandescent

    > globes
    >> in parallel with the LED lamps, others have used high wattage resistors.
    >> Neither is acceptable for obvious reasons.
    >>
    >> There must be a way to "tell" the computer that the LED lamps are fine by
    >> emulating the current drawn by an incandescent globe, without using the
    >> solutions noted above.
    >>
    >> Do any of you outstandingly brilliant contributors have any novel and
    >> innovative ideas?????
    >>

    >
    > Is the current only checked during the pulse?
    >
    > Ross
    >
    >
    Geocacher, Sep 23, 2005
    #12
  13. On Fri, 23 Sep 2005 05:10:34 +0200, " Geocacher" <> wrote:

    >As far as we've been able to check this mess, yes, the current pulse is sent
    >when the ignition is switched on, and will keep on pulsing until the load
    >sense is satisfied. Vehicle diagnostics are performed (obviously, the lights
    >are only one of the tests) and any errors are indicated on the dashboard.
    >However - it would appear that the system has a continuous checking routine
    >to determine whether a lamp has failed during the run.
    >Sorry I sound so hazy over this, but trying to get a truck to play with is
    >not easy. Suppliers are not too interested, and the operators are not keen
    >on taking a truck out of service for us to investigate further.
    >Sometimes, I hate my job!!!!!
    >


    How long is the pulse? Is is a consistant duration? I would go for a
    somple circuit that switches in a load for a breaif period, perhaps
    half a second, then switches off.


    >
    >"Ross Marchant" <> wrote in message
    >news:43334c72$...
    >>" Geocacher" <> wrote in message
    >> news:dgu6hc$g0q$...
    >>> I work in the trailer manufacturing business.
    >>> We use LED tail-light clusters.
    >>> The modern truck/tractors utilise a computer system to perform
    >>> diagnostics
    >>> on various systems within the rig. One of these is the lighting system.
    >>> A pulse is sent to each tail light, the system monitoring the current. If
    >>> there is current flow, it is assumed the incandescent globes are OK.
    >>>
    >>> Unfortunately, the LED lamps draw such a small amount of current that the
    >>> computer does not see a "filament" and flags a major fault on the truck
    >>> dashboard. In addition to the error message, the system continues to send
    >>> curent pulss in the forlorn hope that things at the rear of the rig have
    >>> improved. This causes the entire suite of LED lamps to flash like a
    >>> low-class disco!
    >>>
    >>> There are ways around it. Some manufacturers have placed incandescent

    >> globes
    >>> in parallel with the LED lamps, others have used high wattage resistors.
    >>> Neither is acceptable for obvious reasons.
    >>>
    >>> There must be a way to "tell" the computer that the LED lamps are fine by
    >>> emulating the current drawn by an incandescent globe, without using the
    >>> solutions noted above.
    >>>
    >>> Do any of you outstandingly brilliant contributors have any novel and
    >>> innovative ideas?????
    >>>

    >>
    >> Is the current only checked during the pulse?
    >>
    >> Ross
    >>
    >>

    >
    The Real Andy, Sep 23, 2005
    #13
  14. Geocacher

    swanny Guest

    Geocacher wrote:

    > I work in the trailer manufacturing business.
    > We use LED tail-light clusters.
    > The modern truck/tractors utilise a computer system to perform diagnostics
    > on various systems within the rig. One of these is the lighting system.
    > A pulse is sent to each tail light, the system monitoring the current. If
    > there is current flow, it is assumed the incandescent globes are OK.
    >
    > Unfortunately, the LED lamps draw such a small amount of current that the
    > computer does not see a "filament" and flags a major fault on the truck
    > dashboard. In addition to the error message, the system continues to send
    > curent pulss in the forlorn hope that things at the rear of the rig have
    > improved. This causes the entire suite of LED lamps to flash like a
    > low-class disco!
    >
    > There are ways around it. Some manufacturers have placed incandescent globes
    > in parallel with the LED lamps, others have used high wattage resistors.
    > Neither is acceptable for obvious reasons.
    >
    > There must be a way to "tell" the computer that the LED lamps are fine by
    > emulating the current drawn by an incandescent globe, without using the
    > solutions noted above.
    >
    > Do any of you outstandingly brilliant contributors have any novel and
    > innovative ideas?????
    >
    >


    This was a problem with LED traffic lights and the traffic controllers
    which sense failed lights.

    Have you any idea how much current is required for the sensing circuit
    to be happy with the load? What kind of power rating is the normal truck
    incandescent globe?

    Found any decent caches recently?
    swanny, Sep 23, 2005
    #14
  15. Geocacher

    Geocacher Guest

    The Brake and Indicator lamps are 24V 21W, the Park lights are 5W

    Yes I have found some good caches. Placed some too!!!
    Are you also a geocacher?


    "swanny" <> wrote in message
    news:vgNYe.10676$...
    > Geocacher wrote:
    >
    >> I work in the trailer manufacturing business.
    >> We use LED tail-light clusters.
    >> The modern truck/tractors utilise a computer system to perform
    >> diagnostics on various systems within the rig. One of these is the
    >> lighting system.
    >> A pulse is sent to each tail light, the system monitoring the current. If
    >> there is current flow, it is assumed the incandescent globes are OK.
    >>
    >> Unfortunately, the LED lamps draw such a small amount of current that the
    >> computer does not see a "filament" and flags a major fault on the truck
    >> dashboard. In addition to the error message, the system continues to send
    >> curent pulss in the forlorn hope that things at the rear of the rig have
    >> improved. This causes the entire suite of LED lamps to flash like a
    >> low-class disco!
    >>
    >> There are ways around it. Some manufacturers have placed incandescent
    >> globes in parallel with the LED lamps, others have used high wattage
    >> resistors. Neither is acceptable for obvious reasons.
    >>
    >> There must be a way to "tell" the computer that the LED lamps are fine by
    >> emulating the current drawn by an incandescent globe, without using the
    >> solutions noted above.
    >>
    >> Do any of you outstandingly brilliant contributors have any novel and
    >> innovative ideas?????

    >
    > This was a problem with LED traffic lights and the traffic controllers
    > which sense failed lights.
    >
    > Have you any idea how much current is required for the sensing circuit to
    > be happy with the load? What kind of power rating is the normal truck
    > incandescent globe?
    >
    > Found any decent caches recently?
    Geocacher, Sep 23, 2005
    #15
  16. Geocacher

    quietguy Guest

    Maybe I am missing something here - it seems simple. Power transistor thru
    resister from active side of tail lamp supply to earth - resistor set so
    required current is drawn when transistor is biased on - transister base fed
    thru zener so conducts when pulse arrives. Pulse sent, transistor conducts,
    computer thinks happy thoughts.

    David - or is this just too easy (and cheap - $5 worth of bits at the most)

    Nicholas Sherlock wrote:

    > Geocacher wrote:
    > > There must be a way to "tell" the computer that the LED lamps are fine by
    > > emulating the current drawn by an incandescent globe, without using the
    > > solutions noted above.

    >
    > Does the manufacturer offer an updated ROM for your model?
    >
    > Cheers,
    > Nicholas Sherlock
    quietguy, Sep 23, 2005
    #16
  17. Geocacher

    Ross Herbert Guest

    On Fri, 23 Sep 2005 05:10:34 +0200, " Geocacher" <> wrote:

    >As far as we've been able to check this mess, yes, the current pulse is sent
    >when the ignition is switched on, and will keep on pulsing until the load
    >sense is satisfied. Vehicle diagnostics are performed (obviously, the lights
    >are only one of the tests) and any errors are indicated on the dashboard.
    >However - it would appear that the system has a continuous checking routine
    >to determine whether a lamp has failed during the run.
    >Sorry I sound so hazy over this, but trying to get a truck to play with is
    >not easy. Suppliers are not too interested, and the operators are not keen
    >on taking a truck out of service for us to investigate further.
    >Sometimes, I hate my job!!!!!
    >
    >
    >"Ross Marchant" <> wrote in message
    >news:43334c72$...
    >>" Geocacher" <> wrote in message
    >> news:dgu6hc$g0q$...
    >>> I work in the trailer manufacturing business.
    >>> We use LED tail-light clusters.
    >>> The modern truck/tractors utilise a computer system to perform
    >>> diagnostics
    >>> on various systems within the rig. One of these is the lighting system.
    >>> A pulse is sent to each tail light, the system monitoring the current. If
    >>> there is current flow, it is assumed the incandescent globes are OK.
    >>>
    >>> Unfortunately, the LED lamps draw such a small amount of current that the
    >>> computer does not see a "filament" and flags a major fault on the truck
    >>> dashboard. In addition to the error message, the system continues to send
    >>> curent pulss in the forlorn hope that things at the rear of the rig have
    >>> improved. This causes the entire suite of LED lamps to flash like a
    >>> low-class disco!
    >>>
    >>> There are ways around it. Some manufacturers have placed incandescent

    >> globes
    >>> in parallel with the LED lamps, others have used high wattage resistors.
    >>> Neither is acceptable for obvious reasons.
    >>>
    >>> There must be a way to "tell" the computer that the LED lamps are fine by
    >>> emulating the current drawn by an incandescent globe, without using the
    >>> solutions noted above.
    >>>
    >>> Do any of you outstandingly brilliant contributors have any novel and
    >>> innovative ideas?????
    >>>

    >>
    >> Is the current only checked during the pulse?
    >>
    >> Ross
    >>
    >>

    >



    I don't think there is any legitimate way around this, for the
    following reason.

    The whole idea of the computer check for blown lamps is to alert the
    operator to a safety issue.

    If you use ANY system which "fudges" the computer into thinking that
    the led tail-lights are in fact incandescants (such as dummy loading,
    transistor current loads etc) then what happens if somebody actually
    disconnects the led lamps (try it out using a parallel incandescant
    bulb)? With the dummy load in place the computer will think the led
    tail lights are connected when in fact they are not. Such work-arounds
    are potentially hazardous and should not be contemplated. Either the
    manufacturer of the truck computer modifies his program to cater for
    led lamps or you should stick to using incandescant bulbs.

    Ross
    Ross Herbert, Sep 23, 2005
    #17
  18. Geocacher

    Ken Taylor Guest

    "Ross Herbert" <> wrote in message
    news:...
    > On Fri, 23 Sep 2005 05:10:34 +0200, " Geocacher" <> wrote:
    >
    > >As far as we've been able to check this mess, yes, the current pulse is

    sent
    > >when the ignition is switched on, and will keep on pulsing until the load
    > >sense is satisfied. Vehicle diagnostics are performed (obviously, the

    lights
    > >are only one of the tests) and any errors are indicated on the dashboard.
    > >However - it would appear that the system has a continuous checking

    routine
    > >to determine whether a lamp has failed during the run.
    > >Sorry I sound so hazy over this, but trying to get a truck to play with

    is
    > >not easy. Suppliers are not too interested, and the operators are not

    keen
    > >on taking a truck out of service for us to investigate further.
    > >Sometimes, I hate my job!!!!!
    > >
    > >
    > >"Ross Marchant" <> wrote in message
    > >news:43334c72$...
    > >>" Geocacher" <> wrote in message
    > >> news:dgu6hc$g0q$...
    > >>> I work in the trailer manufacturing business.
    > >>> We use LED tail-light clusters.
    > >>> The modern truck/tractors utilise a computer system to perform
    > >>> diagnostics
    > >>> on various systems within the rig. One of these is the lighting

    system.
    > >>> A pulse is sent to each tail light, the system monitoring the current.

    If
    > >>> there is current flow, it is assumed the incandescent globes are OK.
    > >>>
    > >>> Unfortunately, the LED lamps draw such a small amount of current that

    the
    > >>> computer does not see a "filament" and flags a major fault on the

    truck
    > >>> dashboard. In addition to the error message, the system continues to

    send
    > >>> curent pulss in the forlorn hope that things at the rear of the rig

    have
    > >>> improved. This causes the entire suite of LED lamps to flash like a
    > >>> low-class disco!
    > >>>
    > >>> There are ways around it. Some manufacturers have placed incandescent
    > >> globes
    > >>> in parallel with the LED lamps, others have used high wattage

    resistors.
    > >>> Neither is acceptable for obvious reasons.
    > >>>
    > >>> There must be a way to "tell" the computer that the LED lamps are fine

    by
    > >>> emulating the current drawn by an incandescent globe, without using

    the
    > >>> solutions noted above.
    > >>>
    > >>> Do any of you outstandingly brilliant contributors have any novel and
    > >>> innovative ideas?????
    > >>>
    > >>
    > >> Is the current only checked during the pulse?
    > >>
    > >> Ross
    > >>
    > >>

    > >

    >
    >
    > I don't think there is any legitimate way around this, for the
    > following reason.
    >
    > The whole idea of the computer check for blown lamps is to alert the
    > operator to a safety issue.
    >
    > If you use ANY system which "fudges" the computer into thinking that
    > the led tail-lights are in fact incandescants (such as dummy loading,
    > transistor current loads etc) then what happens if somebody actually
    > disconnects the led lamps (try it out using a parallel incandescant
    > bulb)? With the dummy load in place the computer will think the led
    > tail lights are connected when in fact they are not. Such work-arounds
    > are potentially hazardous and should not be contemplated. Either the
    > manufacturer of the truck computer modifies his program to cater for
    > led lamps or you should stick to using incandescant bulbs.
    >
    > Ross


    Well I'm glad that someone thought of this at last! :) The simple resistor
    is probably the only method that would permit 'proper' operation of the
    sensor if you selected it to 'trick' the processor only when the LED lights
    were working. It'd be a trial-by-error job of selection, though.

    Ken
    Ken Taylor, Sep 23, 2005
    #18
  19. Geocacher

    Franc Zabkar Guest

    On Fri, 23 Sep 2005 10:04:18 +1000, Clifford Heath
    <> put finger to keyboard and composed:

    >Franc Zabkar wrote:
    >> On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <>
    >>>A pulse is sent to each tail light, the system monitoring the current.

    >> You need some way of drawing the required amount of current for the
    >> duration of the pulse, and zero amps thereafter. What about a simple
    >> circuit based around a parallel PTC resistor, ie something like what
    >> happens inside a TV set during automatic degaussing at switch-on?

    >
    >Surely the obvious solution is an electrolytic capacitor with large
    >valued parallel discharge resister and smaller series resister. When
    >the current pulse is sent, the series resister determines the initial
    >current draw. The parallel resister enables the cap to discharge for
    >another cycle.


    The LED array may itself provide an appropriate discharge time
    constant.

    >How big a capacitor you need is determined by the required current
    >draw and the amount of time after switch-on that the current is sensed.
    >The idea will only be feasible of the time is very short. Normal
    >V=I*C*T rule applies.


    That should be dV = I * dT / C

    or C = I * dT / dV

    >Clifford Heath.


    -- Franc Zabkar

    Please remove one 'i' from my address when replying by email.
    Franc Zabkar, Sep 23, 2005
    #19
  20. Geocacher

    Franc Zabkar Guest

    On Fri, 23 Sep 2005 00:01:07 GMT, "Craig Hart" <> put
    finger to keyboard and composed:

    >how about, you make a circuit that AC-couples (use a capacitor) the brake
    >line to a transistor that switches in a low impedance load (resistor) for a
    >short time (e.g. 50ms). each time the brake line pulses high, the pulse
    >turns on the transistor for a moment.
    >
    >the constant "on" signal of the brakes won't trigger the circuit due to the
    >AC coupling.
    >
    >such a short on-time won't effect brakelight performance any, but will be
    >long enough to allow the computer to 'sense' the higher load.


    I had the same idea but declined to suggest it because the OP
    specified a "simple" solution. I was thinking of something like this:


    |---------------------|
    | dummy R R = 50 ohm ???
    | |
    | Z |/ Z = 6V zener
    o--|--C--|--|<|--|---R--| Q npn
    | | | |\
    low R D hi R | D = diode (grounded anode)
    |_____|_______|__ ____|
    _|_
    =

    -- Franc Zabkar

    Please remove one 'i' from my address when replying by email.
    Franc Zabkar, Sep 23, 2005
    #20

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