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

[Geocacher]

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?????

 

[budgie]

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.

 

[Nicholas Sherlock]

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]

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!

 

[Franc Zabkar]

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.

 

[Richard Waters]

Franc Zabkar furiously typed the following on 23/09/2005 8:22 AM:

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?

 

[Ken Taylor]

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

 

[Craig Hart]

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.

 

[Clifford Heath]

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.

 

[Ross Marchant]

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]

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.

 

[Geocacher]

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!!!!!

 

[The Real Andy]

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.

 

[swanny]

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]

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?

 

[quietguy]

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)

 

[Ross Herbert]

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!!!!!

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

 

[Ken Taylor]

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

 

[Franc Zabkar]

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]

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.