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

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?????

On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <(E-Mail Removed)> 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.

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

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" <(E-Mail Removed)> wrote in message
news:dgv15u$b5j$(E-Mail Removed)...
> 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

On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <(E-Mail Removed)> 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 furiously typed the following on 23/09/2005 8:22 AM:
> On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <(E-Mail Removed)> 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?

"Franc Zabkar" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <(E-Mail Removed)> 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

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" <(E-Mail Removed)> wrote in message
news:dgu6hc$g0q$(E-Mail Removed)...
> 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?????
>
>

Franc Zabkar wrote:
> On Thu, 22 Sep 2005 14:02:39 +0200, " Geocacher" <(E-Mail Removed)>
>>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.

" Geocacher" <(E-Mail Removed)> wrote in message
news:dgu6hc$g0q$(E-Mail Removed)...
> 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