Brilliant idea needed!!!

Eventually the computer manufacturers will get off their duffs and correct _their_ problem. Call them up, tell them LED tail lights have been on the market for years, and ask them which one of their competitors does the job right.

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Tim Wescott
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The computer doesn't send the pulse, it instructs the "system" to send the pulse and measure the response.

Change your algorithm, so the response is meaningful... maybe trickle

100uA and measure the voltage... LED's ARE junction devices, you know?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

How about a diode in series with the cap to isolate the LEDs? Maybe a resistor across the cap to discharge it since the LEDs won't.

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  Keith
Reply to
Keith Williams

Geocacher wrote in sci.electronics.design:

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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Anno Siegel

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?????

Reply to
Geocacher

Not clear what you mean. Is "pulse" a VOLTAGE pulse and you measure the current?

CURRENT pulse?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Jim Thompson

Easily and obviously fixed but how much do you want to pay for the answer????

Reply to
Fred Bloggs

The first thing that comes to mind is to place a lage capacitor (1000uF?) across the LEDS, to draw a high current pulse during the test, providing the test is short enough. But I suspect this will flash the lights as well since the cap is discharged through the LED's.

Meindert

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Meindert Sprang

" Geocacher" a écrit dans le message de news:dgu6ht$g24$ snipped-for-privacy@ctb-nnrp2.saix.net...

globes

You can have the information in about 50ms if you pay me the right price.

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Fred Bartoli

The payment you request would be adequately supplied by the outright admiration of your peers on this forum. They (me included) would bow our heads in honour of the man who could fix the problem in 50mS!

"Fred Bartoli" wrote in message news:4332d190$0$21208$ snipped-for-privacy@news.free.fr...

Reply to
Geocacher

Give each LED in the array its own dropping resistor, and run all of those LED/R strings in parallel. Use enough of them, at enough current, so the total current is over the threshold. LEDs _do_ take _some_ current, you know. ;-)

Good Luck! Rich

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Rich Grise

" Geocacher" a écrit dans le message de news:dguk7a$b53$ snipped-for-privacy@ctb-nnrp2.saix.net...

The answer was in the answer. Just find it :-)

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Fred Bartoli

[...]

Get rid of the computer. It's probably less reliable than the LEDs anyway.

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Adrian Tuddenham

With a trickle current they will have a measurable forward drop, yet not emit significant light.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Jim Thompson

When exposed to light, LED will act as a photo diode. LED's ARE junction devices, you know? ;)

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

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Boris Mohar

Do you know what the old tail lights current draw is vs. the new LED ones? Is it 12VDC?

Reply to
Thomas Magma

Reply to
Geocacher

OK here is my "brilliant idea" of the day. A resistor that is in series with a polyfuse and then both in parallel with the LED lamp. This will shunt the appropriate amount of current to fool the computer into thinking it's drawing the right amount of current, then the polyfuse will trip before the resistor has time to heat up. The polyfuse will stay open until the voltage is removed. So you could probably get away with a small and cheap half watt resistor.

Here is a link to polyfuses:

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Good luck. Thomas

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Thomas Magma

"Fred Bloggs" schreef in bericht news: snipped-for-privacy@nospam.com...

by

I don't know. Can the current sensor (resistor?) be replaced, does the fix only fix the disco behaviour, or does it also fix the annoying error message?

Perhaps a switcher could be used to make the LED units work at a much lower voltage, drawing a higher current. The remaining voltage could run a step-up switcher to dump that energy back into the battery.

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Reply to
Frank Bemelman

Look up CAN bus, seems to be the indusrty standard. You need a micro in the LED array, that can talk to the vehicle

martin

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martin griffith

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