Today's Message Index:
----------------------
1. 05:51 AM - Re: Re: LED Ghosting (Robert L. Nuckolls, III)
2. 05:51 AM - Re: Re: LED Ghosting (Robert L. Nuckolls, III)
3. 06:57 AM - Re: fuse link to replace fuse in low current applications? (Robert L. Nuckolls, III)
4. 10:51 AM - Re: Re: P-leads (Robert L. Nuckolls, III)
5. 11:42 AM - Re: Re: P-leads (rayj)
6. 04:35 PM - Re: LED Ghosting (donjohnston)
7. 06:04 PM - Re: Re: LED Ghosting (Charlie England)
8. 06:07 PM - Re: LED Ghosting (donjohnston)
9. 06:44 PM - Re: LED Ghosting (donjohnston)
10. 07:23 PM - Re: Re: LED Ghosting (Henador Titzoff)
Message 1
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Subject: | Re: LED Ghosting |
At 07:49 PM 6/19/2014, you wrote:
FisherPaulA(at)johndeere. wrote:
> I'm confused by this thread. Back to the original issue - why is
it important that all of the LEDs in the annunciator panel have the
same brightness?
Valid question.
The master warning panel (I should probably refer to it as an
annunicator panel) also has indicators for when the fuel pump is on
and pitot heat is on (those indicators are amber where the low oil
pressure, door unsafe, etc. are red).
So you're flying along at night and you have the pitot heat or fuel
pump on. The LEDs are rather bright so you dim the indicators. Once
you dim those LEDs to a comfortable brightness, that low oil pressure
LED will not illuminate at all.
That's another concern that we wrestle with in the TC
side of the house . . . visibility in sunlight.
Most DIY annunciators flying in OBAM aircraft would not
been welcome on the panel of a TC aircraft. That's
one of the reasons that TC annunciators are relatively
much more expensive . . . and before LEDs . . . ran HOT
due to the utilization of at least TWO, 1W lamps per
feature. Light up very many slots at the same time and the
legacy incandescent annunciator panel can become quite
warm.
Two-lamps per slot was also a hedge against
lamp failure. The loss of one lamp in an
indicator slot would be noticed during pre-flight
tests but would not KILL the annunciator's ability
to warn.
I think the modern annunciators with more than
one LED are simply concerned with sunlight visibility.
Prospects for putting another L1011 full of people into
the Everglades for lack of a light bulb are pretty much
a thing of the past.
OBAM aviation annunciators achieve sun light
visibility by mounting under a glare shield that
prevents direct exposure to sun . . . or perhaps
it's not high on the builder's list of design goals.
Hopefully tomorrow I will be able to get the voltage readings
requested. I also got the MOSFET today so I'll give that a go as well.
Great!
Bob . . .
Message 2
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Subject: | Re: LED Ghosting |
At 03:15 PM 6/19/2014, you wrote:
><FisherPaulA@johndeere.com>
>
>I'm confused by this thread. Back to the original issue - why is it
>important that all of the LEDs in the annunciator panel have the
>same brightness? Don't you just need to know if any particular one
>is on or off? Aren't they used to indicate a problem? I would hope
>that during most flights they would all be off. And if more than
>one of them was on, I certainly wouldn't be worried about one being
>brighter or dimmer than another - I'd be busy looking for a place to land!
>
>I do appreciate the electronics discussion about the physics of
>getting them to the same brightness. I just don't understand why
>that is important in this use case.
It's a 'trickle down' from legacy design goals for
most sophisticated aircraft (read - has more than one
red light right next to another on the panel).
Jobs I've had working on 6-figure airplanes catered
to customers who expected such uniformity and a
regulatory agency that expected conformity. But
you're right, the absolute functionality of the
indicator is not diluted by a difference in
purposeful illumination.
The thread was launched when it was discovered that
an engine monitor's oil pressure warning output
presented some light-off leakage that would not
have affected an incandescent lamp's OFF state.
However, still enough to excite those maddingly
efficient LED into visible light output when
they were supposed to be dark . . . again
not so big a deal in daylight but irksome
at night.
The brightness thing didn't bubble up until it
was noticed that 'fixes' for the lamp-off-leakage
also appeared to influence brightness.
That didn't make sense from the perspective of
the electronics . . . but it won't become clear
without more detailed measurements of the various
conditions I posed in the 'grand experiment'
posting . . . which is where the quest for understanding
kind of fizzled.
Bob . . .
Message 3
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Subject: | fuse link to replace fuse in low current applications? |
At 04:35 PM 6/19/2014, you wrote:
>
> > I think I'd use butt-spliced links
>
>Bob, just curious, would solder splices also be acceptable?
Sure . . . lap joints under heat=shrink works.
http://tinyurl.com/dgg2nb
Bob . . .
Message 4
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At 12:37 PM 3/24/2014, you wrote:
>
>The concept of a "fuse" to keep faults in a tachometer from
>disabling an ignition needs to be stamped out, it is a dangerous
>misconception. I know of at least one incident where this almost
>caused a fatal crash. It takes very little current through a P lead
>from a magneto or points wire in a Kettering ignition to disrupt
>performance of the ignition. Can you depend on this amount of
>current blowing a fuse? Is the resistor going to open if there is a
>fault? Is the engine going to keep running well if the far end of
>the resistor is shorted to ground or +12? Not unless it has been
>tested to do so.
Yes . . . these techniques have been tested many times . . .
except for the fuse . . . I don't recall seeing fuses
recommended for this application but agreed . . . they're
a bad idea.
Having said that, let us consider the use of resistors to
sample the really trashy signal that appears across the points
of either a magneto or Kettering system.
The points are already paralleled by a capacitor on the
order of .1 to .3 uF. The capacitor is necessary in
both systems to 'resonate' with the primary winding such
that rate of rise for voltage across spreading points
is slower than that level which establishes an arc
in the gap.
The source impedance of this 'ringing' energy source
is pretty low in the Kettering system . . . on the order
of 10 ohms, lower still in a magneto. Yes, the voltages
at the points can exceed 200 volts during the spark
interval . . . but the idea that a 1,000 ohms or larger
isolation resistor presents a meaningful load simply
doesn't compute.
>There are many tach designs that work without an ignition pickup.
>VDO and other companies make programmable tachs that can be set to
>take a signal from one phase of an alternator output, or an
>inductive pickup from a flywheel or magneto case. Proper design of a
>tach could also yield failsafe operation but that's still putting a
>lot of faith in something you haven't tested. The "proof by
>assertion" that I've seen from a few instrument vendors isn't really
>confidence-inspiring.
I've never heard of this being an issue. I've sampled
p-lead and Kettering points through resistive attenuators
dozens of times over the years with nary a concern
for any ill effects being reflected back to the source.
Magneto p-lead signals are really trashy, I have
found it useful to run the attenuated signal
through 4 poles of band pass filtering before squaring
it up to drive the digital interpreters.
A fuse doesn't even make sense. The signal being
observed is WAAYyyyy to big as a digital signal
source . . . attenuation on the order of 30:1
is the first thing you need to do with it.
Bob . . .
Message 5
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Please give a quick definition of the ignition designs and techniques
that are being discussed. I need some background to follow the discussion.
Thanks
Raymond Julian
Kettle River, MN
The things we admire in men, kindness and generosity, openness, honesty,
understanding and feeling are the concomitants of failure in our system.
And those traits we detest, sharpness, greed, acquisitiveness, meanness,
egotism and self-interest are the traits of success. And while men
admire the quality of the first they love the produce of the second.
-John Steinbeck, novelist, Nobel laureate (1902-1968)
On 06/20/2014 12:50 PM, Robert L. Nuckolls, III wrote:
> <nuckolls.bob@aeroelectric.com>
>
> At 12:37 PM 3/24/2014, you wrote:
>> <dlj04@josephson.com>
>>
>> The concept of a "fuse" to keep faults in a tachometer from disabling
>> an ignition needs to be stamped out, it is a dangerous misconception.
>> I know of at least one incident where this almost caused a fatal
>> crash. It takes very little current through a P lead from a magneto or
>> points wire in a Kettering ignition to disrupt performance of the
>> ignition. Can you depend on this amount of current blowing a fuse? Is
>> the resistor going to open if there is a fault? Is the engine going to
>> keep running well if the far end of the resistor is shorted to ground
>> or +12? Not unless it has been tested to do so.
>
> Yes . . . these techniques have been tested many times . . .
> except for the fuse . . . I don't recall seeing fuses
> recommended for this application but agreed . . . they're
> a bad idea.
>
> Having said that, let us consider the use of resistors to
> sample the really trashy signal that appears across the points
> of either a magneto or Kettering system.
========================== SNIP ====================================
Message 6
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Subject: | Re: LED Ghosting |
Attached are the voltage drops for the LEDs and resistors. The engine analyzer
alarm is a flashing warning so it was difficult getting a solid reading. If I
missed something, let me know and I'll get it.
Thanks,
Don
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=425178#425178
Attachments:
http://forums.matronics.com//files/led_circuit_627.pdf
Message 7
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Subject: | Re: LED Ghosting |
Weren't the LEDs in series? If so, if one fails open, you lose both.
On Fri, Jun 20, 2014 at 7:49 AM, Robert L. Nuckolls, III <
nuckolls.bob@aeroelectric.com> wrote:
> nuckolls.bob@aeroelectric.com>
>
> At 07:49 PM 6/19/2014, you wrote:
> don@velocity-xl.com>
>
>
> FisherPaulA(at)johndeere. wrote:
> > I'm confused by this thread. Back to the original issue - why is it
> important that all of the LEDs in the annunciator panel have the same
> brightness?
>
> Valid question.
>
> The master warning panel (I should probably refer to it as an annunicator
> panel) also has indicators for when the fuel pump is on and pitot heat is
> on (those indicators are amber where the low oil pressure, door unsafe,
> etc. are red).
>
> So you're flying along at night and you have the pitot heat or fuel pump
> on. The LEDs are rather bright so you dim the indicators. Once you dim
> those LEDs to a comfortable brightness, that low oil pressure LED will not
> illuminate at all.
>
> That's another concern that we wrestle with in the TC
> side of the house . . . visibility in sunlight.
> Most DIY annunciators flying in OBAM aircraft would not
> been welcome on the panel of a TC aircraft. That's
> one of the reasons that TC annunciators are relatively
> much more expensive . . . and before LEDs . . . ran HOT
> due to the utilization of at least TWO, 1W lamps per
> feature. Light up very many slots at the same time and the
> legacy incandescent annunciator panel can become quite
> warm.
>
> Two-lamps per slot was also a hedge against
> lamp failure. The loss of one lamp in an
> indicator slot would be noticed during pre-flight
> tests but would not KILL the annunciator's ability
> to warn.
>
> I think the modern annunciators with more than
> one LED are simply concerned with sunlight visibility.
> Prospects for putting another L1011 full of people into
> the Everglades for lack of a light bulb are pretty much
> a thing of the past.
>
> OBAM aviation annunciators achieve sun light
> visibility by mounting under a glare shield that
> prevents direct exposure to sun . . . or perhaps
> it's not high on the builder's list of design goals.
>
> Hopefully tomorrow I will be able to get the voltage readings requested. I
> also got the MOSFET today so I'll give that a go as well.
>
> Great!
>
>
> Bob . . .
>
>
Message 8
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Subject: | Re: LED Ghosting |
That one string that had different drops was bothering me. :(
I checked it again but on a different string and got the attached. I'm guessing
that one of the LEDs in the first test is a little out of spec.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=425183#425183
Attachments:
http://forums.matronics.com//files/led_circuit_2_904.pdf
Message 9
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Subject: | Re: LED Ghosting |
ceengland7(at)gmail.com wrote:
> Weren't the LEDs in series? If so, if one fails open, you lose both.
I think that assumes incandescent bulbs. The failure rate with LEDs isn't anywhere
near what you have with incandescent bulbs.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=425185#425185
Message 10
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Subject: | Re: LED Ghosting |
Actually, he's correct, Don.- Two LEDs in series will give you a failure
rate of Pr1 + Pr2.- The only reason I can think of to use two LEDs in ser
ies is to get twice the illumination while minimizing resistors.- If you
put two LEDs in parallel, each one has to have its own resistor to balance
(control) the current flow through each one.=0A=0AIf they are in parallel a
nd one LED fails, then at least you'll have half the original illumination
to indicate a failed LED.- If you accept Pr1 + Pr2 as your failure rate,
then it's your choice.=0A=0A-=0AHenador Titzoff=0A=0A=0A=0A=0A=0A=0A>____
____________________________=0A> From: donjohnston <don@velocity-xl.com>=0A
>To: aeroelectric-list@matronics.com =0A>Sent: Friday, June 20, 2014 9:43 P
M=0A>Subject: AeroElectric-List: Re: LED Ghosting=0A> =0A>=0A>--> AeroElect
ric-List message posted by: "donjohnston" <don@velocity-xl.com>=0A>=0A>=0A>
ceengland7(at)gmail.com wrote:=0A>> Weren't the LEDs in series? If so, if o
ne fails open, you lose both. =0A>=0A>=0A>I think that assumes incandescent
bulbs. The failure rate with LEDs isn't anywhere near what you have with i
ncandescent bulbs.=0A>=0A>=0A>=0A>=0A>Read this topic online here:=0A>=0A>h
ttp://forums.matronics.com/viewtopic.php?p=425185#425185=0A>=0A>=0A>=0A>
- - - - - - - -=0A - - - - - -Matt Dralle, List
=========0A>=0A>=0A>=0A>=0A>=0A>
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