Re: Brilliant idea needed!!!

Geocacher <gps@xxxxxxxx> wrote in sci.electronics.design:
> 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 test you describe is applicable while the tail-lights are off. Does
the diagnostic system permanently monitor the current when they are
switched on? If so, I don't see a simple solution except re-calibrating
the current the diagnostic system expects.

For the test you describe you could use the parallel resistor, but switch
it off after a second or so of power. The duration must be long enough
to cover the test pulse and short enough not to cause excess power
consumption in the long run. A more sophisticated solution would check
if the LED array draws the expected current and only add the parallel
resistor if it does.

Anno
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