Maker Pro
Maker Pro

Brilliant idea needed!!!

B

Boris Mohar

Jan 1, 1970
0
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


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) http://www.viatrack.ca
 
J

Jim Thompson

Jan 1, 1970
0
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) http://www.viatrack.ca

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

...Jim Thompson
 
E

ehsjr

Jan 1, 1970
0
Geocacher said:
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?????

Trigger a one-shot on the turn-on of the tail lights.
The one-shot gates a power mosfet on, which connects a properly
sized ( 10 ohms ?) resistor across the LEDs for the on period of
the one shot. Make the on period of the one-shot twice the duration
of the diagnostic pulsing period.

Ed
 
F

Fred Bloggs

Jan 1, 1970
0
Frank said:
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.

The diagnostic system checks the lights individually so it boils down to
the dual 3-way switch controlling a dummy load that exceeds the
threshold. Both lamps ON or OFF means no dummy loading, and by sizing
the current relays, CR, for the LED load, you end up with a valid
diagnostic for the truck computer with no additional power consumption
during normal mode of operation. If the lamps are tested as a single
entity, then the circuit inverts the logic by presenting a dummy load
only when one but not both LED clusters have failed, and there is no
getting around dummy loading during normal operation because the input
state during both modes, test and run, is the same. But I will not waste
my time on the obsequious and clueless non-technical types like this
particular OP.

View in a fixed-width font such as Courier.

..
..
.. L R
.. | |
.. +--|>|-----------+-----------|<|--+
.. | | -- |
.. | | | | |
.. |* DUMMY | --- * |
.. | CR | | /// CR |
.. --------- | | ---------
.. | | COM| | | |COM | |
.. | | o |-------- ---| o | |
.. | | | | | |
.. | \ NC | |NC \ |
.. | / o |-------- ----| o / |
.. | \ | | | | \ |
.. | / NO |--------|--- |NO / |
.. | | o | --------| o | |
.. | | | | | |
.. --------- ---------
.. | |
.. | |
.. | |
.. | |
.. ------- -------
.. | | | |
.. | | | <-- TAIL LIGHT --> | | |
.. | --- | CLUSTERS | --- |
.. | \ / | | \ / |
.. | --- | | --- |
.. | | | | | |
.. | | | |
.. ------ ------
.. | |
.. | |
.. --- ---
.. /// ///
..
..
..
..
.. *CR CURRENT RELAY
..
..
..
 
R

redbelly

Jan 1, 1970
0
Perhaps a Zener diode + resistor (in series) would do the trick. That
combination should be wired in parallel with the LED's.

The Zener voltage should be less than the voltage pulse, so that it
conducts only when the pulse is sent. The resistor is chosen to
provide whatever current the computer is looking for.

Mark
 
F

Fred Bloggs

Jan 1, 1970
0
A little suppression would be nice:
View in a fixed-width font such as Courier.

..
.. L -- R
.. | | | |
.. | | --- |
.. | | /// |
.. | | | **
.. +------------------------------------------PO
.. | | | | |
.. | | +------------- | |
.. | | | | | |
.. | | (-)| FWB | | |
.. | | --------------- | | |
.. | | | | | | | |
.. | +--------|-+-|<|-+-|>|-+-|-----|--+ |
.. | | AC| | | |AC | | |
.. | | | +-|>|-+-|<|-+ | | | |
.. | | | | | | | |
.. | | --------------- | | |
.. | | (+)| | | |
.. | | | -------- | |
.. | |* DUMMY | * | |
.. | | CR + | CR | |
.. | --------- PTC | --------- |
.. | | | COM| | | |COM | | |
.. | | | o |-------- ---| o | | |
.. | | | | | | | |
.. | | \ NC | |NC \ | |
.. | | / o |-------- ----| o / | |
.. | | \ | | | | \ | |
.. | | / NO |--------|--- |NO / | |
.. | | | o | --------| o | | |
.. | | | | | | | |
.. | --------- --------- |
.. | | | |
.. +-------------------------------------------+
.. | |
.. ------- -------
.. | | | |
.. | | | <-- TAIL LIGHT --> | | |
.. | --- | CLUSTERS | --- |
.. | \ / | | \ / |
.. | --- | | --- |
.. | | | | | |
.. | | | |
.. ------ ------
.. | |
.. --- ---
.. /// ///
..
..
..
..
..
..
.. *CR CURRENT RELAY
..
.. **PO POTTED OBJECT
 
F

Frank Bemelman

Jan 1, 1970
0
Fred Bloggs said:
The diagnostic system checks the lights individually so it boils down to
the dual 3-way switch controlling a dummy load that exceeds the

Don't these diagnostic systems keep checking while the lights are on?
I would expect that..
threshold. Both lamps ON or OFF means no dummy loading, and by sizing
the current relays, CR, for the LED load, you end up with a valid
diagnostic for the truck computer with no additional power consumption
during normal mode of operation. If the lamps are tested as a single
entity, then the circuit inverts the logic by presenting a dummy load
only when one but not both LED clusters have failed, and there is no
getting around dummy loading during normal operation because the input
state during both modes, test and run, is the same.

Yes, well, that's why I suggested something that draws the same
amount of current, but dumps the energy not needed by the LEDS into
the battery again, as efficient as possible. After all, the OP
wanted something brilliant and not something obvious ;)
 
F

Fred Bloggs

Jan 1, 1970
0
This one will only dim the untested lamp if the test is performed during
running operation- and it does open the possibility of bucking that CR
off to activate the dummy load by any number of means- the CR coil drop
is assumed to be 1/2 or less that of a single diode under load. This is
the last post on the subject- not going to get suckered into another
waste of time:
View in a fixed-width font such as Courier.

..
.. L -- R
.. | | | |
.. | | --- |
.. | | /// |
.. | | | **
.. -------------------------------------------PO
.. | | | | |
.. | | +------------- | |
.. | | | | | |
.. | | (-)| FWB | | |
.. | | --------------- | | |
.. | | | | | | | |
.. | +--------|-+-|<|-+-|>|-+-|-----|--+ |
.. | | AC| | | |AC | | |
.. | | | +-|>|-+-|<|-+ | | | |
.. | | | | | | | |
.. | | --------------- | | |
.. | | (+)| | | |
.. | | | | | |
.. | | | | | |
.. | | -|<|-+-|>|-- | | |
.. | | | | | | | |
.. | | | | -|------ | |
.. | |* | DUMMY | | * | |
.. | | CR | + | | CR | |
.. | --------- | PTC | | --------- |
.. | | | COM| | | | | |COM | | |
.. | | | o |--|----- -|-| o | | |
.. | | | | | | | | | |
.. | | \ NC | | | |NC \ | |
.. | | / o |--|----- --|-| o / | |
.. | | \ | | | | | | \ | |
.. | | / NO |--|-----|--- | |NO / | |
.. | | | o | | ------|-| o | | |
.. | | | | | | | | | |
.. | --------- | | --------- |
.. | | | | | |
.. | | ------------|---------+ |
.. | +----------------------- | |
.. | | | |
.. --------------------------------------------
.. | |
.. ------- -------
.. | | | |
.. | | | <-- TAIL LIGHT --> | | |
.. | --- | CLUSTERS | --- |
.. | \ / | | \ / |
.. | --- | | --- |
.. | | | | | |
.. | | | |
.. ------ ------
.. | |
.. --- ---
.. /// ///
..
..
..
.. *CR CURRENT RELAY
..
.. **PO POTTED OBJECT
..
..
 
F

Fred Bloggs

Jan 1, 1970
0
Frank said:
Don't these diagnostic systems keep checking while the lights are on?
I would expect that..

Well- does it do that by momentarily interrupting voltage to an
individual lamp?
Yes, well, that's why I suggested something that draws the same
amount of current, but dumps the energy not needed by the LEDS into
the battery again, as efficient as possible. After all, the OP
wanted something brilliant and not something obvious ;)

The LED lamps are stock standard in voltage and form factor so not a lot
you can do there.
 
F

Frank Bemelman

Jan 1, 1970
0
Fred Bloggs said:
Well- does it do that by momentarily interrupting voltage to an
individual lamp?

If it can send a pulse to an individual lamp and measure the
current, I assume it can also measure the current when it is
on continously. Unless the dahsboard switches are still hardwired
and short ciruit the diagnostic circuit. I don't know what is
common practice.
 
Y

YD

Jan 1, 1970
0
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!

You didn't mention the pulse duration, but if it's short enough you
might get away with a capacitor in parallel with the LEDs. At the
pulse edge it looks pretty much like a short so you may need to have a
low value resistor in series with it. Recall that a cold filament also
has a low resistance value. With the lights on the capacitor charges
up and doesn't draw any additional current.

- YD.
 
J

John Fields

Jan 1, 1970
0
We cannot 'play' with the computer system aboard the truck/tractor, hence
this enquiry. The solution must be attached to the trailer wiring in such a
way that the truck's system is satisfied that the lights are functional.
 
F

Fred Bloggs

Jan 1, 1970
0
Frank said:
If it can send a pulse to an individual lamp and measure the current,
I assume it can also measure the current when it is on continously.
Unless the dahsboard switches are still hardwired and short ciruit
the diagnostic circuit. I don't know what is common practice.
That's a good point and as far as I can find out the current is measured
continuously- the pulsing the OP talked about must have been an artifact
of the controller flashing a dashboard lamp when it read the whole
circuit dead. In the US it is a seven "circuit" SAE standard from the
tractor to the trailer with six light circuits and a common chassis
ground- no VBATT is available- and these are big circuits 20, 30, and
100 amps. There is nothing the OP can do except load it down.
 
R

Ross Herbert

Jan 1, 1970
0
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?????

Everybody seems to forget that the lamp test must correctly detect an
open circuit LED lamp. A dummy load which allows the computer to
record a successful test must actually include the LED lamp in a fail
safe manner. In other words, assume the dummy load is in place and the
LED lamp was not connected in parallel. The computer would still carry
out a successful test I would imagine. Now how meaningful would this
result be?
 
R

Ross Herbert

Jan 1, 1970
0
It wouldn't, but it would get the truck to start. Let's face it - LEDs
are so reliable that they'll probably outlive the computer anyway. The
point of this exercise was to spoof the obsolete computer in the first
place, wasn't it?

If, in successfully fooling the computer, the relevant vehicle design
standards were being ignored or breached, then I do not agree that the
proposed solution is effective or wise.

One can stay within the design standards and satisfy the vehicle
computer by simply reverting to incandescant bulbs, which, to my
recollection, have proved remarkably reliable for many decades. In my
own vehicle (a '93 Mazda 626 V6) I have not yet had cause to replace a
single incandescant bulb of any type. Of course, I realise that rough
roads and severe vibration can lead to the early demise of bulbs so
perhaps there would be some argument for replacing them with LEDs in
some circumstances, but I wouldn't do it if I were in the OP's
position.

The real solution is to pressure the vehicle computer manufacturer to
design a system to cater for modern, high reliability LED lamps.
Eventually, these will be so popular they will have to do something
anyway.
 
K

keith

Jan 1, 1970
0
If, in successfully fooling the computer, the relevant vehicle design
standards were being ignored or breached, then I do not agree that the
proposed solution is effective or wise.

The OP is designing trailer lights, not ones for the vehicle itself.
There is no modification of the vehicle. LEDs make a *lot* of sense
here (and are often used in new vehicles).
One can stay within the design standards and satisfy the vehicle
computer by simply reverting to incandescant bulbs, which, to my
recollection, have proved remarkably reliable for many decades. In my
own vehicle (a '93 Mazda 626 V6) I have not yet had cause to replace a
single incandescant bulb of any type. Of course, I realise that rough
roads and severe vibration can lead to the early demise of bulbs so
perhaps there would be some argument for replacing them with LEDs in
some circumstances, but I wouldn't do it if I were in the OP's position.

I've replaced *many* bulbs. The last safety inspection caught a blown
"cyclops" on my 2001 pickup. I'd replace the thing with an LED unit, were
there one in the same configuration. I don't like driving around with
lights out.
The real solution is to pressure the vehicle computer manufacturer to
design a system to cater for modern, high reliability LED lamps.
Eventually, these will be so popular they will have to do something
anyway.

The OP is trying to match a trailer to existing tractors. Newer tractors
likely do accept LEDs (they're not at all unusual). Given the reliability
and redundancy inherent in LEDs, replacing single filament lamps is a
*good* idea.
 
R

Ross Herbert

Jan 1, 1970
0
The OP is designing trailer lights, not ones for the vehicle itself.
There is no modification of the vehicle. LEDs make a *lot* of sense
here (and are often used in new vehicles).

I fully realise that he is designing a trailer lighting system. Where
I come from that exercise also comes under vehicle design standards.
The fact that the existing tractor electronics is unable to cater for
the additional LED trailer lighting without some sort of additional
method of fooling the vehicle computer means that the modified trailer
wiring would also possibly contravene vehicle design standards where
the OP is located.
I've replaced *many* bulbs. The last safety inspection caught a blown
"cyclops" on my 2001 pickup. I'd replace the thing with an LED unit, were
there one in the same configuration. I don't like driving around with
lights out.

Yes, I dare say you have replaced many bulbs. It may depend on the
roads you regularly drive on, to some extent, and the quality of the
bulbs used. In the case of tractors there may be some added vibration
which might lead to early incandescant lamp failure but unless the
tractor is used on public roads (many aren't) the requirement for high
reliability LED lamps would not be so great. It is fairly easy to find
out when an incandescant bulb is not working by simply walking around
the vehicle - brake lights do need an extra person however. An
automated lamp test does remove that requirement and saves some time,
but surely people are not so time poor or lazy that they can't do
simple safety checks when going on public roads. Truckies driving road
trains have to do it regularly, and they do have big rigs.

http://outbacktowing.tripod.com/
The OP is trying to match a trailer to existing tractors. Newer tractors
likely do accept LEDs (they're not at all unusual). Given the reliability
and redundancy inherent in LEDs, replacing single filament lamps is a
*good* idea.

I do understand the OP's problem. His trailers can probably be used on
tractors of all ages, with or without computers. Older tractor
computers may only cater for incandescant's and newer ones may handle
LED's, but he can't determine who is going to use his trailers.
However, if he is forced to fudge a fix to enable older tractors to
work with the LED's, he may be in breach of vehicle design standards.
It would be far simpler, imo, to offer both incandescant and LED
options to cater for both types depending on the customer
requirements. In this case, one size doesn't fit all.
 
E

ehsjr

Jan 1, 1970
0
Ross said:
Everybody seems to forget that the lamp test must correctly detect an
open circuit LED lamp. A dummy load which allows the computer to
record a successful test must actually include the LED lamp in a fail
safe manner. In other words, assume the dummy load is in place and the
LED lamp was not connected in parallel. The computer would still carry
out a successful test I would imagine. Now how meaningful would this
result be?


Would this make you happy, or would it still violate
some design standard?

----+--------------[Rload]-------------+
| |
[R] |
| /
+-----[comparator]---[oneshot]---|
| | \
[LED] Vref |
| Gnd
Gnd

Comparator triggers one-shot when it sees Vfled.

I'm clueless as to how the testing is done by the computer -
I don't know if it is a one time test at turn on, or if it
is continuous. If it is continuous, remove the oneshot.
Ed
 
T

The Cheese Machine

Jan 1, 1970
0
Geocacher said:
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?????

Use a current sense R in the LED array. Amplify the voltage drop, use this
to drive a current shunt across the supply to the array.

If the measurement is indeed a pulse measurement, use AC coupling.
 
R

Ross Herbert

Jan 1, 1970
0
Ross said:
Everybody seems to forget that the lamp test must correctly detect an
open circuit LED lamp. A dummy load which allows the computer to
record a successful test must actually include the LED lamp in a fail
safe manner. In other words, assume the dummy load is in place and the
LED lamp was not connected in parallel. The computer would still carry
out a successful test I would imagine. Now how meaningful would this
result be?


Would this make you happy, or would it still violate
some design standard?

----+--------------[Rload]-------------+
| |
[R] |
| /
+-----[comparator]---[oneshot]---|
| | \
[LED] Vref |
| Gnd
Gnd

Comparator triggers one-shot when it sees Vfled.

I'm clueless as to how the testing is done by the computer -
I don't know if it is a one time test at turn on, or if it
is continuous. If it is continuous, remove the oneshot.
Ed

Ed,

Your arrangement would appear to trick the vehicle computer into
providing a fail safe test result, however the cost of including this
custom modification into each LED lamp assembly would imo make it
uneconomical compared to simply using incandescent lamps.

I would imagine that the additional components would also need to be
integral to the LED lamp itself so that it formed a complete unit in
order to meet the relevant vehicle design standards (for Sth. Africa
in this case). I would also ssurmise that the design standards for the
trailer would specify the type of lighting fixtures, wiring,
connectors etc, but additional circuitry to make LED lighting
agreeable to an existing vehicle computer would not be covered. Since
the modified lamp assembly as proposed by your suggested circuit is
not a standard product then it would need to be approved under the
design standards before being allowed to be installed.

On the subject of LED automotive lights I did some further research;

When attempting to use LED lighting in high reliability, long life and
efficient operation, it appears that some type of regulated driver
circuitry is required which preferably incorporates diagnostics.
Including LED lamps to work with existing vehicle computers is bound
to create some difficulties particularly where the computer only
caters for incandescent lamps which are standard on the vehicle
itself. Trying to mix incandescants and LED's on the same vehicle
appears to be a no-go situation.

A search for LED drivers for automotive applications revealed that
using LED's is not as simple as just wiring a series of LEDs into an
array and connecting them to the vehicle power supply. Some sort of
control module may be needed.

Melexis make an IC specific to this application. However, to include a
diagnostic function seems to be relatively complex.
http://www.melexis.com/relinfofiles/applicationnotemlx1080103.pdf

ST Microelectronics have an IC which does includes a diagnostic
function http://www.st.com/stonline/products/literature/an/8414.pdf

Analog Devices have the AD8240
http://www.analog.com/en/prod/0,2877,AD8240,00.html

This recent EDN article sheds a little light (pardon the pun) on the
subject of automotive LED lighting and some considerations
http://www.edn.com/article/CA490413.html
 
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