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Re: Come up with a brilliant solution .......


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sent
lights
routine
is
keen
system.
If
the
truck
send
have
resistors.
by
the

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



Re: Come up with a brilliant solution .......


On Fri, 23 Sep 2005 09:14:30 GMT, Ross Herbert

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I had considered the solution proposed by Craig Hart but refrained
from suggesting it because the requirement was for a "simple" method.
Anyway, if this level of complexity is allowed, then one could easily
satisfy the safety requirement by placing a high side current sensor
within the trailer itself.

      PNP transistor
          E     C
 +V o--|---\___/-----> to RC coupled, dummy load switching transistor
       |     |
       |     R
       |     |
       |--R--|------> to LED lamp array


-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Re: Come up with a brilliant solution .......


On Sat, 24 Sep 2005 07:11:34 +1000, Franc Zabkar

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Franc (and Ken), both suggestions will work, BUT.... the "fudge"
components would have to be integrated as part of the LED lamp
assembly in order to conform to the relevant standards, I would
imagine. Not only that, if the LED lamp did go open circuit the
"fudge" components must not allow the computer to test the dummy load
and think that the LED lamp was still ok.  As I see it,any sort of
dummy load would still allow a successful lamp test when the LED lamp
itself is open circuit.  It would have to be a "fail safe" arrangement
to serve the intended purpose of the computer lamp test. I can't see
how it can be done using these methods while still providing a
meaningful test result.

Considering the reliability of incandescant bulbs I would stick to
using these in the trailer lamps. This way the automatic lamp test
will provide a meaningful test result as intended so that faulty lamps
can be replaced. After all, it is not as though a few extra watts is
going to seriously affect the alternator loading or battery capacity
on a truck.

Ross Herbert

Re: Come up with a brilliant solution .......


Quoted text here. Click to load it
sent
load
lights
dashboard.
routine
is
keen
system.
current. If
that the
truck
send
have
incandescent
resistors.
fine by
the
and

I agree - if the truck manufacturer isn't going to do a fix for their
firmware to accommodate LED lamps (and it probably isn't trivial, as you'd
have to somehow 'know' which lamps were LED and which incandescent) then any
fix is either potentially dangerous or self-defeating (ie. the globe in
parallel sorta kinda defeats the purpose of having an LED pack in the first
place).

Cheers.

Ken



Re: Come up with a brilliant solution .......



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Easy, measure the voltage drop across the led array, if it exceeds
that of the led(s), no load is switched on. If it is as expected,
switch on the load for half a second.

V+ -----+
        |
       RES
        |
        +-------Vsense_led
        |
       LED
        |
       LED
        |
       GND

If the two leds have a foward voltage of 1.2V each, then Vsense_led
should be 2.4v. If the device fails, Vsense_led will be the same as
v+, providing that the input impedance of the measuring curcuit is
reasonble high.

I would also be cautious about the dirty signal that will probably be
found on the power line. This whole circuit will no doubt need a good
dose of filtering.




Re: Come up with a brilliant solution .......


On Mon, 26 Sep 2005 17:48:29 +1000, The Real Andy


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After playing with a few circuits on paper, my conclusion is that you
will need 1 opamp or comparator with 2 transitors. It may be possible
to get away with one transistor.

Dare I say it, a 555 in monostable mode may even proved an elegant
solution.

All these parts can be had in smd packages now, so adding it to an
existing circuit should not consume much real estate.

Might have to download LT's spice and have a play.

Re: Come up with a brilliant solution .......


finger to keyboard and composed:

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How continuous? Does the computer test the lamp immediately after
switching it on and then ignore the current reading until next time?
Or does it keep testing the current during the entire time the lamp is
on?

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Re: Come up with a brilliant solution .......



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I think it would be best in the long run to solve this by the cheapest
way, and that is to lean on the computer suppliers for the manufacturer
to modify their code or hardware. Your business seems to be in the middle
of a new trailer lighting paradigm and it is obvious that the future lies
in solid state lighting. So what about more effort in debating with the
computer makers? They must be aware of the impending change, they may
even be planning engineering solutions now. If they are stone walling,
maybe point out the marketing advantage of an LED friendly system would
give them an advantage over competitors. After all, YOU are the customer
of these suppliers and they need to listen to YOU.

Re: Come up with a brilliant solution .......



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Aside from the fact that most manufacturers are based in the US/Europe
and couldn't give a flying fuck about the Aus market. From what I can
gather is that for some trucks you cant even get a program that
matches some certain australian engine-transmission combos. Why would
they care about a LED lamp on trailer?

Re: Come up with a brilliant solution .......


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OP is apparently in South Africa so there's even less chance....

Ken



Re: Come up with a brilliant solution .......



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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?

Re: Come up with a brilliant solution .......


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?


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Re: Come up with a brilliant solution .......



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Is it possible to grab a trace of the pulse on a cro? Are you using
off the shelf inicator/brake led assemblies or manufacturing your own.
Can you provide a link to the manufacturer of the assemblies if you do
not construct them yourself


Re: Come up with a brilliant solution .......


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Hello

Is this a common problem or a one-off?
You'd think the truck manufacturers would have a solution in software or
an add-on module.

It would be possible to make a simple circuit using a mosfet and a few
other small parts to apply a brief controlled load when 12/24V was first
applied. A sort of simulation of a large capacitor.
It would be convenient and more reliable if the circuit was potted into
a small module that connected in parallel with the LED lamp; preferably
at the LED lamp itself so that the wiring from the front of the truck
was still protected.
Modules could be preset (before potting) to correct for 5W, 21W etc.
Field configurable modules would probably not be long-term reliable.

To get it right you need to know the test pulse duration, the check
delay, the pass/fail window and wether the computer checks at other
times. It may just read the current a short time after the circuit is
energised.

I recall years ago we had to fake fuel injectors so that when a dual
fuel engine was running on CNG it didn't bring up the check engine light
on the dash. It was more difficult than expected because the engine
computer monitored the inductance of the injectors.

Regards
Paul
--
Regards
Paul

Re: Come up with a brilliant solution .......


finger to keyboard and composed:

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Maybe the idea requires a different approach. Just how smart is the
computer? Can you fool it into believing that the trailer is not
there? Will the computer continue to test the trailer in this case? Is
there a "trailer present" sense wire in the harness to the trailer? If
not, then how does the computer distinguish between the case where the
trailer is not present and the unlikely case where *all* lamps have
failed? Does the computer understand the difference between no current
draw and insufficient current draw?

If the trailer isn't there, will the lamps still work, ie does lamp
voltage appear at the connector? Does the computer sense the brake
switch and then supply power to a lamp, or can the brake switch
control the lamp independently of the computer? What happens if the
computer fails? Do the lights still operate? This may be a silly
question, but do the lights behind the cabin still operate when the
trailer is attached? If not, then this would indicate that the lights
are under computer control and that the trailer's presence is being
sensed.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

Re: Come up with a brilliant solution .......



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All these suggestions are a load of rubbish...
The ONLY way to fix this problem is have the manufacturer fix the
computer to correctly handle modern (LED) lamps.

If he does not want to comply then don't buy his product.

If it is a design rule requirement to do the test then he has to comply
or the OP has to stay with the original candles (incandecescent lamps)
that have to be tested because they fail often on trailers.
--
John G

Wot's Your Real Problem?



Re: Come up with a brilliant solution .......


On Sat, 24 Sep 2005 18:17:41 +1000, "John G"

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I entirely agree......

Ross Herbert

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