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raymondj(at)frontiernet.n
Guest

Posted: Tue Jun 17, 2014 11:36 am Post subject: LED Ghosting

How about a brighter led, so it's dimmed level will be equal to the others.



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 06/17/2014 02:06 PM, donjohnston wrote:

 	  Quote: 	
		   

 user9253 wrote:

> I suggest that you put a 1.5k resistor across the LED per the engine analyzer people.  Then replace the 390 ohm series resistor with a 330 ohm resistor.  Or experiment with different values (all less than 390) to get the desired brightness.

> Or put a pot in series with the dim LED and turn the pot until the current though the dim LED is equal to the current through one of the other LEDs.  Then substitute a fixed resistor for the pot.

> 40 years ago I could have calculated the resistor value.  Now trial and error is easier.  

> Joe

 I tried that. I ended up with no series resistor and it was still dimmer than the others.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=425032#425032

lyleapgmc

Joined: 19 Feb 2014
Posts: 57

Posted: Tue Jun 17, 2014 12:26 pm Post subject: LED Ghosting

I don't believe you will get satisfactory results       with any combination of resistors.  I think the only solution is a       driver circuit between the output and the LED.  A single transistor and a couple of resistors should       do it.  It may need a separate power source.

     

     

     On 6/17/2014 2:06 PM, donjohnston       wrote:

     

     [quote]        	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com> (don(at)velocity-xl.com)

user9253 wrote:

          	  Quote: 	
		  I suggest that you put a 1.5k resistor across the LED per the engine analyzer people.  Then replace the 390 ohm series resistor with a 330 ohm resistor.  Or experiment with different values (all less than 390) to get the desired brightness.

Or put a pot in series with the dim LED and turn the pot until the current though the dim LED is equal to the current through one of the other LEDs.  Then substitute a fixed resistor for the pot.

40 years ago I could have calculated the resistor value.  Now trial and error is easier.  

Joe

	
       



I tried that. I ended up with no series resistor and it was still dimmer than the others.





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=425032#425032



	
     -- 

Lyle



Sent from my Gateway E4610D desktop



[b]

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Tue Jun 17, 2014 1:43 pm Post subject: Re: LED Ghosting

 	  nuckolls.bob(at)aeroelect wrote: 	
		  

    Ooops, two LED's in series . . . should have asked about

    that. Okay, I suggest we pay homage to our teachers one

    of whom once opined: ". . . when you can measure what you are

    speaking about, and express it in numbers, you know something

    about it; but when you cannot measure it, when you cannot

    express it in numbers, your knowledge is of a meagre and

    unsatisfactory kind; it may be the beginning of knowledge,

    but you have scarcely in your thoughts advanced to the state

    of Science  . . ." -Lord Kelvin-



    Consider the array of sketches at:



  http://tinyurl.com/oxrwae7

	




I suggest we pay homage to our teachers one of whom once replied: "Dammit Bob, I'm a doctor, not a engineer" -Dr. Leonard McCoy- 



Unfortunately, this is a bit beyond my skillset. While the squiggly lines are not quite hieroglyphics to me, I'm not exactly sure what to do with them.



 	  Quote: 	
		  How about a brighter led, so it's dimmed level will be equal to the others. 	


That's a good idea. Except the LEDs that I'm using were the brightest that I could find. So I don't think I'll be able to find any that are brighter and have the same footprint.



 	  Quote: 	
		  I don't believe you will get satisfactory results with any combination of resistors. I think the only solution is a driver circuit between the output and the LED. A single transistor and a couple of resistors should do it. It may need a separate power source. 	


That sounds reasonable. Is this different than the MOSFET solution posted earlier?

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Tue Jun 17, 2014 3:28 pm Post subject: Re: LED Ghosting

OK, here is another idea.  Put a diode (1N4148 ?) in series with each of the bright LEDs.  If you are lucky, the voltage drop across the 1N4148 will equal the voltage drop across the oil pressure solid state switch.

Joe

_________________
Joe Gores

eschlanser

Joined: 08 Apr 2010
Posts: 60

Posted: Wed Jun 18, 2014 5:27 am Post subject: Re: LED Ghosting

 	  donjohnston wrote: 	
		   



"The engine analyzer people said it was designed for incandescent... " 	




Here's a simple solution.  Use an incandescent bulb such as this: http://tinyurl.com/kw8usxc

Dennis Johnson

Joined: 10 Jan 2006
Posts: 89
Location: N. Calif.

Posted: Wed Jun 18, 2014 5:52 am Post subject: LED Ghosting

I don't remember specifically which of your instruments has the ghosting  problem.  I'll tell you my story, which may or may not be relevant, but it  may help others with a similar situation as mine.

  

 When I first powered up my instrument panel, the red warning light for my  Grand Rapids EIS engine monitor glowed very dimly when the panel was powered up  but the engine monitor was turned off.  Ghosting went away when I turned  the engine monitor on.  Like you, I had replaced an incandescent light with  an LED.  On the bench, the ghosting seemed like a problem.  

  

 However, I focused on other, bigger, problems and never got around to  fixing the ghosting problem.  By the time I completed my flight test phase,  I understood that the ghosting was not a problem at all and maybe even a  benefit.

  

 I turn the engine monitor on before engine start and leave it on until  after engine shutdown.  Since ghosting only occurs when the master switch  is on and the engine monitor is off, I never see ghosting because the engine  monitor is normally on whenever the master switch is on.  I now consider  ghosting, if I ever see it, to be a warning that I've forgotten to turn the  engine monitor on.  "It's not a bug, it's a feature."

  

 Good luck,

 Dennis

  

  

  

  

  

   [quote][b]

sprocket(at)vx-aviation.c
Guest

Posted: Wed Jun 18, 2014 5:56 am Post subject: LED Ghosting

....so the relay option is looking pretty good right about now.  As I mentioned, there is the simple brute force relay method, then the more complicated 'elegant' method.... Elegance is elusive.

Vern

====================================================

Sent from my iThing. It is responsible for all gramma and typo terrors.

 	  Quote: 	
		   On Jun 18, 2014, at 6:27 AM, "eschlanser" <eschlanser(at)yahoo.com> wrote:

 donjohnston wrote:

> 

> 

> "The engine analyzer people said it was designed for incandescent... "

 Here's a simple solution.  Use an incandescent bulb such as this: http://tinyurl.com/kw8usxc

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=425076#425076

rnjcurtis(at)charter.net
Guest

Posted: Wed Jun 18, 2014 6:30 am Post subject: LED Ghosting

I submitted this a couple of days ago and it seemed  to be ignored.  Does anyone know why this very simple method would not  work??

  

         Perhaps you  could use a zener with a voltage just slitely 

         higher than  the open circuit off voltage output. Put that in 

         series with  the LED, to block the small output, and reduce 

         the series resistor to bring the  brightness up.

  

          Roger

   [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 18, 2014 6:51 am Post subject: LED Ghosting

At 09:29 AM 6/18/2014, you wrote:

  	  Quote: 	
		   I submitted this a couple of days ago and it seemed to be ignored.  Does anyone know why this very simple method would not work??

  

          Perhaps you could use a zener with a voltage just slitely 

         higher than the open circuit off voltage output. Put that in 

         series with the LED, to block the small output, and reduce 

         the series resistor to bring the brightness up. 	


    Not sure what you're suggesting . . . can

    you offer a schematic along with some

    description of where the voltage drops are

    expected and of what magnitude?



 

 

   Bob . . .    [quote][b]

sprocket(at)vx-aviation.c
Guest

Posted: Wed Jun 18, 2014 7:02 am Post subject: LED Ghosting

Dimming wouldn't work very well with an in series zener.  

Vern



====================================================Sent from my iThing. It is responsible for all gramma and typo terrors.



On Jun 18, 2014, at 7:29 AM, "Roger & Jean" <rnjcurtis(at)charter.net (rnjcurtis(at)charter.net)> wrote:

[quote]       I submitted this a couple of days ago and it seemed  to be ignored.  Does anyone know why this very simple method would not  work??

  

         Perhaps you  could use a zener with a voltage just slitely 

         higher than  the open circuit off voltage output. Put that in 

         series with  the LED, to block the small output, and reduce 

         the series resistor to bring the  brightness up.

  

          Roger

    	  Quote: 	
		  

	


[b]

rnjcurtis(at)charter.net
Guest

Posted: Wed Jun 18, 2014 7:18 am Post subject: LED Ghosting

 	  Quote: 	
		             Perhaps you    could use a zener with a voltage just slitely    

        higher than the open circuit    off voltage output. Put that in 

           series with the LED, to block the small output, and reduce    

        the series resistor to bring    the brightness up.

   

   Not sure what you're suggesting . . .    can

   you offer a schematic along with some

      description of where the voltage drops are

   expected and of    what magnitude?

    

           I am not    familiar with the device outputing the 

           signal to    the LED.  Perhaps I am all wet in 

           assuming    these outputs,  See attached.



              Roger

File1.pdf

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 18, 2014 7:51 am Post subject: LED Ghosting

At 08:52 AM 6/18/2014, you wrote:

I don't remember specifically which of your instruments has the 

ghosting problem.  I'll tell you my story, which may or may not be 

relevant, but it may help others with a similar situation as mine.



When I first powered up my instrument panel, the red warning light 

for my Grand Rapids EIS engine monitor glowed very dimly when the 

panel was powered up but the engine monitor was turned off.  Ghosting 

went away when I turned the engine monitor on.  Like you, I had 

replaced an incandescent light with an LED.  On the bench, the 

ghosting seemed like a problem.

    It was a legacy practice in aviation annunciator

    lamp outputs to offer some way that an annunciator

    can tell the pilot that the system driving that

    annunciator is OFF.  Using the normally closed

    contacts of a relay ALWAYS works but if they

    can be replaced at less cost, the solid state option is

    preferred.



    The output circuit depicted in the adaptation of

    LED's to the B&C LR series regulators



http://tinyurl.com/cgnwr5k



    is an exemplar approach to the task for incandescent

    annunciators common to the time. The resistor between

    the collector and base of the lamp driver causes

    a 'powered down' LR3 to drive an annunciator lamp

    into partial conduction . . .



    In later years we added a remote sense lead to the

    ov/lv detection system which causes the lv warn

    to come alive when the bus becomes hot but before

    the engine is started and irrespective of the

    position of the alternator field switch. This

    change of architecture eliminated the value of

    'powered down' conduction of the annunciator

    sorta went away.



    The 'problem' can be eliminated by snipping out

    the one-time-useful resistor. I think I'll

    suggest that B&C eliminate that resistor in

    future production and modify any regulators

    that come back for other reasons.

However, I focused on other, bigger, problems and never got around to 

fixing the ghosting problem.  By the time I completed my flight test 

phase, I understood that the ghosting was not a problem at all and 

maybe even a benefit.



    It CAN be eliminated . . . with a massaging of

    performance facts . . .

I turn the engine monitor on before engine start and leave it on 

until after engine shutdown.  Since ghosting only occurs when the 

master switch is on and the engine monitor is off, I never see 

ghosting because the engine monitor is normally on whenever the 

master switch is on.  I now consider ghosting, if I ever see it, to 

be a warning that I've forgotten to turn the engine monitor 

on.  "It's not a bug, it's a feature."



    . . . it may have been just that under

    alternative design goals. Without benefit of

    documentation or conversation with the original

    designer . . . its a WAG.

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 18, 2014 8:10 am Post subject: LED Ghosting

 	  Quote: 	
		  



 I suggest we pay homage to our teachers one of whom once replied: "Dammit Bob, I'm a doctor, not a engineer" -Dr. Leonard McCoy-



 Unfortunately, this is a bit beyond my skillset. While the squiggly lines are not quite hieroglyphics to me, I'm not exactly sure what to do with them.

   	


   Not sure how to answer this . . . analysis and

   resolution of some problems simply does not

   move forward without good data.



   Putting a resistor across the lamp/resistor

   string SHOULD have fixed your problem. But the

   narrative of your observed behavior left

   me scratching my head . . . too much is

   not yet known . . .



 [img]cid:.0[/img]



 

   Bob . . .

51d53f62.jpg

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25.35 KB

Viewed:

14826 Time(s)

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Wed Jun 18, 2014 11:53 am Post subject: Re: LED Ghosting

[quote="nuckolls.bob(at)aeroelect"] 	  Quote: 	
		  

   Not sure how to answer this . . . analysis and

   resolution of some problems simply does not

   move forward without good data.



   Putting a resistor across the lamp/resistor

   string SHOULD have fixed your problem. But the

   narrative of your observed behavior left

   me scratching my head . . . too much is

   not yet known . . .



   Bob . . . 	




Technically the resistor did fix the problem (ghosting).  But it created a new problem (dim LED).  So now I'm working on the second problem while not re-introducing the first problem.

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Wed Jun 18, 2014 12:03 pm Post subject: Re: LED Ghosting

 	  eschlanser wrote: 	
		   	  donjohnston wrote: 	
		   



"The engine analyzer people said it was designed for incandescent... " 	




Here's a simple solution.  Use an incandescent bulb such as this: http://tinyurl.com/kw8usxc 	




You are right, it is a solution. Just not very simple.  Since I would have to scrap the circuit board that the LEDs are mounted to and design a new one. And since this is a incandescent bulb, it would have to be socketed. Which means redesigning the warning panel assembly to be deep enough to accept the new light bulb. Not sure how I would handle replacing the bulb when it burns out though. 



Or I could just scrap the whole warning panel altogether. Then I'd have to fill in that rectangular hole in the panel, drill holes for the 8 warning lights. Come up with the circuit design for the new warning lights. etc., etc., etc.,

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 18, 2014 3:10 pm Post subject: LED Ghosting

 	  Quote: 	
		  

Technically the resistor did fix the problem (ghosting).  But it 

created a new problem (dim LED).  So now I'm working on the second 

problem while not re-introducing the first problem.


	


   That's the fact that does not make sense. The barefoot

   string of two LEDS and a resistor function with a

   current level on the order of 15 to 20 milliamps.

   (First sketch in the document I published). This

   is much lower than the typical incandescent lamp

   at 80+ milliamps. Adding the resistor (second sketch)

   adds another 12 to 14 milliamps for a total of

   27 to 34 milliamps . . . much LOWER than the incandescent

   lamp being replaced.



   We can continue to flog this topic with all

   manner of cut, paste, try, suppose, wish and

   propose . . . with poor prospects for fixing

   it and poorer prospects for understanding

   root cause for the symptoms you've observed.



   The second sketch 'fix' should have NO effect

   on lamp intensity . . . the fact that it does

   have an effect says we don't know squat about

   what we're doing  . . . yet.



   Hence, the 'dim LED' is a mystery that

   cannot be resolved without knowing the reason

   for what appears to be a reduction of available

   voltage. The experiments I asked you to conduct

   went toward resolving the mystery.

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Thu Jun 19, 2014 9:47 am Post subject: Re: LED Ghosting

Resistors can make the oil pressure LED the same brightness as the others under one set of conditions.  But when the conditions change (reduced dimmer voltage) the brightness of all LEDs will no longer be the same.

The only way for all LEDs to have the same brightness under all conditions is if each circuit has the same components.  A relay can be used to switch the oil pressure LED to make that circuit the same as the other LEDs that use mechanical contacts.  Here are possible relays to use:  http://tinyurl.com/pt9yd6v or http://tinyurl.com/o3g77dc or http://tinyurl.com/q28mku6

Another option is to modify the other LED circuits to match the oil pressure circuit.  Adding a diode to those other circuits might do the trick.  The only way to find out is to try it.

  The relay is a sure thing but costs more and is harder to install and is less reliable then a solid state solution.  Diodes may or may not work but are very inexpensive and easy to install.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 19, 2014 11:02 am Post subject: LED Ghosting

At 12:47 PM 6/19/2014, you wrote:




Resistors can make the oil pressure LED the same brightness as the 

others under one set of conditions.  But when the conditions change 

(reduced dimmer voltage) the brightness of all LEDs will no longer be the same.

   Quite true. Stings of led's driven in parallel from a common dimmer

   will vistually track each other only when all the strings are

   identical. From a pure physics perspective, LED light output is

   proportional to the current in the device . . . for values at or

   below the device's rated operating point.



The only way for all LEDs to have the same brightness under all 

conditions is if each circuit has the same components.  A relay can 

be used to switch the oil pressure LED to make that circuit the same 

as the other LEDs that use mechanical contacts.  Here are possible 

relays to use:  http://tinyurl.com/pt9yd6v or 

http://tinyurl.com/o3g77dc or http://tinyurl.com/q28mku6



    The quest for intensity tracking between the various

    indicators is purely a matter of average current through the

    devices. Suppose the annunciator panel featured in the

    start of this thread had two LEDs in some slots, and

    single LEDs in others. It's entirely possible that they

    could be made to appear identical at some level of illumination

    by juggling their series resistors . . . but a bit

    of pencil whipping of the numbers will show that as

    supply voltage is reduced, the current through a series

    string of 2 LEDs will fall off faster than for a single

    LED.



    The use of a relay to energize an LED string to

    emulate the performance of an oil pressure

    switch isn't the issue. For all practical

    purposes, hard contacts and transistors produce

    the same behavior when turned ON for any given

    level of 'balanced' illumination. The variances

    of configuration don't come into play until the

    illumination is adjusted to some new value.



    This is why duty cycle switched dimming works so well

    for mixed configurations of LED illumination. When you duty-cycle

    switch the LED, peak light output remains constant while

    the eye integrates a reduced average energy into a perceived

    level of brightness that will be more uniform across mixed

    configurations.



    I wrote the spec for a mix illumination dimmer control

    for the Gates Piaggio GP-180 program where the design

    goal was to dim 5v incandescent, 28v incandescent and

    and 115vac electro-luminescent from a single knob.



    Nobody stood up and offered a proposal for that

    spec (about 1985). With micro-controllers and lookup

    table driven power supplies, it could be done today

    but not easily back then.



    Joe is right, unless the constellation of illumination

    sources have the same configuration, they will not

    track each other well with simple adjustment of applied

    voltage.

   Bob . . .

FisherPaulA(at)johndeere.
Guest

Posted: Thu Jun 19, 2014 12:16 pm Post subject: LED Ghosting

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.



Paul A. Fisher 

RV7A N18PF



--

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Thu Jun 19, 2014 4:49 pm Post subject: Re: LED Ghosting

 	  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?  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.



Paul A. Fisher 

RV7A N18PF



-- 	




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. 



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.

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