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LED Ghosting
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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jun 20, 2014 4:51 am Post subject: 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 . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jun 20, 2014 4:51 am Post subject: LED Ghosting

At 03:15 PM 6/19/2014, you wrote:

 	  Quote: 	
		  

<FisherPaulA(at)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 . . .

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Fri Jun 20, 2014 3:34 pm Post 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

LED circuit.pdf

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ceengland7(at)gmail.com
Guest

Posted: Fri Jun 20, 2014 5:04 pm Post subject: 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(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 [quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

  



 At 07:49 PM 6/19/2014, you wrote:

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

 

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

  -

 ric-List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

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

 MS -

 k">http://forums.matronics.com

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

 e -

           -Matt Dralle, List Admin.

 t="_blank">http://www.matronics.com/contribution

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

 

 

 

 



[b]

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Fri Jun 20, 2014 5:05 pm Post 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.

LED circuit 2.pdf

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donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Fri Jun 20, 2014 5:43 pm Post 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.

henador_titzoff(at)yahoo.
Guest

Posted: Fri Jun 20, 2014 6:23 pm Post subject: 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 series 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.



If they are in parallel and 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.

 

Henador Titzoff





 	  Quote: 	
		          From: donjohnston <don(at)velocity-xl.com> To: aeroelectric-list(at)matronics.com  Sent: Friday, June 20, 2014 9:43 PM Subject: Re: LED Ghosting  

 --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com (don(at)velocity-xl.com)>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#425185http://www.matronics.com/Navigator?AeroElectric-Listhttp://www.matro=

 

 

 	




   



 [quote][b]

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Sat Jun 21, 2014 3:42 am Post subject: Re: LED Ghosting

 	  henador_titzoff(at)yahoo. wrote: 	
		  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 series 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.



If they are in parallel and 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.

 

Henador Titzoff



	




I'm using two LEDs for brightness and reducing the resistor. I am well aware that a failure of one LED will result in a failure of indication.



Thank you.

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Sat Jun 21, 2014 4:37 am Post subject: Re: LED Ghosting

Attached is my plan for implementing the MOSFET.  I have a feeling (given the voltage at S is going to be pretty much non-existent) that the 12v connection to G is going to be needed.

MOSFET.pdf

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user9253

Joined: 28 Mar 2008
Posts: 1940
Location: Riley TWP Michigan

Posted: Sat Jun 21, 2014 5:42 am Post subject: Re: LED Ghosting

The the brightness problem will likely be solved by the MOSFET transistor as long as it does not drop much voltage.  If it doesn't work out and it is desired not to use a relay, then another option is to make the other LED circuits drop the same same voltage as the Engine Analyzer Alarm solid state switch, which is 1.5 to 1.6 volts according to your voltage measurements.  An easy way to drop that voltage is to add a red LED in series to the other annunciator circuits.  Then each LED circuit will have the same voltage drop.

_________________
Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1940
Location: Riley TWP Michigan

Posted: Sat Jun 21, 2014 6:08 am Post subject: Re: LED Ghosting

The output of the Engine Analyzer Alarm should not be connected directly to positive voltage because it will be a short circuit.  Connect a 10K resistor between the gate and source instead.

  The dimmer output should be connected directly to the MOSFET source.  The load (LEDs and resistor) should be connected between the drain and ground.

A zener diode (15 to 20 volts) could be connected between the gate and source to protect the MOSFET against voltage spikes.

  Someone please correct me if I am wrong.  I do not want to give bad advice.

_________________
Joe Gores

sprocket(at)vx-aviation.c
Guest

Posted: Sat Jun 21, 2014 6:24 am Post subject: LED Ghosting

The inherent inversion of this circuit will turn the lamp on when the EMS 

turns it off... not so good.

Vern



--

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Sat Jun 21, 2014 6:51 am Post subject: Re: LED Ghosting

 	  user9253 wrote: 	
		  The output of the Engine Analyzer Alarm should not be connected directly to positive voltage because it will be a short circuit.  Connect a 10K resistor between the gate and source instead.

  The dimmer output should be connected directly to the MOSFET source.  The load (LEDs and resistor) should be connected between the drain and ground.

A zener diode (15 to 20 volts) could be connected between the gate and source to protect the MOSFET against voltage spikes.

  Someone please correct me if I am wrong.  I do not want to give bad advice. 	




I probably mis-interpreted the original suggestion. Thanks for the correction.



 	  user9253 wrote: 	
		  If it doesn't work out and it is desired not to use a relay, then another option is to make the other LED circuits drop the same same voltage as the Engine Analyzer Alarm solid state switch, which is 1.5 to 1.6 volts according to your voltage measurements. An easy way to drop that voltage is to add a red LED in series to the other annunciator circuits. Then each LED circuit will have the same voltage drop. 	


That was my original backup plan. I thought that there would be a better solution. 

And this is on a PCB. I have a little flexibility (adding a resistor or two), but adding another LED wouldn't work.

user9253

Joined: 28 Mar 2008
Posts: 1940
Location: Riley TWP Michigan

Posted: Sat Jun 21, 2014 7:11 am Post subject: Re: LED Ghosting

 	  Quote: 	
		  this is on a PCB. I have a little flexibility (adding a resistor or two), but adding another LED wouldn't work. 	


I did not mean to locate a red LED next to the other LEDs.  I meant to add a red LED on the circuit board, out of sight.  It can mounted as easily as a resistor.  Red LEDs have about the same voltage drop as the Engine Analyzer Alarm, which is about 1.5 volts.  With each LED circuit dropping the same voltage, they should have the same brightness, in theory anyway.  I have never built this circuit.

_________________
Joe Gores

edpav8r(at)yahoo.com
Guest

Posted: Sat Jun 21, 2014 7:31 am Post subject: LED Ghosting

Don & Joe,



I think this is a case of there being more than one way to skin a cat.  Joe is just changing the MOSFET from a low-side to a high-side switch, which will work fine as well.



The gate zener isn't a bad idea (it will protect the gate against wild voltage excursions on the bus), but is probably unnecessary; this MOSFET will tolerate a 30V difference between gate and source.  For the same reason, it's safe to use 12V as gate pull-up (through a resistor!) instead of the variable dimmer output.  Again, pay your money and take your choice.



Definitely heed Joe's advice re *not* tying the gate directly to 12V.  This would probably not end well for your engine analyzer's alarm circuit!



I've attached a diagram of my suggestion.  Let me  know if it doesn't come through.



Eric

On Jun 21, 2014, at 7:08 AM, "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

 	  Quote: 	
		   The output of the Engine Analyzer Alarm should not be connected directly to positive voltage because it will be a short circuit.  Connect a 10K resistor between the gate and source instead.

 The dimmer output should be connected directly to the MOSFET source.  The load (LEDs and resistor) should be connected between the drain and ground.

 A zener diode (15 to 20 volts) could be connected between the gate and source to protect the MOSFET against voltage spikes.

 Someone please correct me if I am wrong.  I do not want to give bad advice.

 

 --------

 Joe Gores

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user9253

Joined: 28 Mar 2008
Posts: 1940
Location: Riley TWP Michigan

Posted: Sat Jun 21, 2014 10:08 am Post subject: Re: LED Ghosting

To turn on a P-channel MOSFET, a negative voltage must be applied to the gate with respect to the source.  If the load is connected between the source and positive supply, then the source is positive when the MOSFET is off.  But as soon as the MOSFET starts to conduct, the source will then become negative and the gate is no longer negative in respect to the source.  The MOSFET will then shut off, (if it ever actually turned on)

Here is a website that shows how N-Channel and P-Channel MOSFETs are wired.  http://electronics.stackexchange.com/questions/3599/basic-p-type-mosfet-question

_________________
Joe Gores

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Sat Jun 21, 2014 10:31 am Post subject: Re: LED Ghosting

Unfortunately, I am way outside my element. Not quite sure how to wire this sucker now.

kleh(at)dialupatcost.ca
Guest

Posted: Sat Jun 21, 2014 11:17 am Post subject: LED Ghosting

If Radio Shack still sells the paperback comic style books by Forrest 

Mimms III, there is a great go to book for simple circuits "Getting 

Started in Electronics" cat.No. 276-5003. My copy was $3.59 years ago 

and as an occasional hobbyist I often refer to it when starting a new 

project. Highly recommended for understanding and wiring this circuit.

Ken



On 21/06/2014 2:31 PM, donjohnston wrote:

 	  Quote: 	
		   



 Unfortunately, I am way outside my element.  Not quite sure how to wire this sucker now.

raymondj(at)frontiernet.n
Guest

Posted: Sat Jun 21, 2014 12:14 pm Post subject: LED Ghosting

Just finished reading it,  I second the recommendation.

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 06/21/2014 02:13 PM, Ken wrote:

 	  Quote: 	

 If Radio Shack still sells the paperback comic style books by Forrest

 Mimms III, there is a great go to book for simple circuits "Getting

 Started in Electronics" cat.No. 276-5003. My copy was $3.59 years ago

 and as an occasional hobbyist I often refer to it when starting a new

 project. Highly recommended for understanding and wiring this circuit.

 Ken

 On 21/06/2014 2:31 PM, donjohnston wrote:

> 

> <don(at)velocity-xl.com>

>

> Unfortunately, I am way outside my element.  Not quite sure how to

> wire this sucker now.

edpav8r(at)yahoo.com
Guest

Posted: Sat Jun 21, 2014 12:40 pm Post subject: LED Ghosting

Gents,



Sorry, I was apparently groggy this morning and had N and P-channel devices mixed up in my head.  Joe is absolutely correct; please ignore my earlier diagram.  I'm not at my computer and won't be for several days, so I can't make a new one.  I'll try to explain it in words...



1. Connect dimmer output directly to MOSFET source.

2. At MOSFET drain, install current limiting resistor and LEDs in series, with the last LED connected to ground.

3. Install a pull-up resistor of 10-100k between MOSFET gate and source.

4. Connect engine analyzer alarm output to MOSFET gate.



So, two connections at source: dimmer output and pull-up resistor.  One connection at drain: resistor and LED string.  Two connections at gate: pull-up resistor and alarm output.



Hope that's understandable.  Best I can do standing in an airport terminal waiting to board...



Cheers, and sincere apologies for causing so much confusion!  Thank you, Joe.  Good to have smart guys QC-ing everything on here.



Eric

On Jun 21, 2014, at 11:09 AM, "user9253" <fransew(at)gmail.com> wrote:

 	  Quote: 	
		   To turn on a P-channel MOSFET, a negative voltage must be applied to the gate with respect to the source.  If the load is connected between the source and positive supply, then the source is positive when the MOSFET is off.  But as soon as the MOSFET starts to conduct, the source will then become negative and the gate is no longer negative in respect to the source.  The MOSFET will then shut off, (if it ever actually turned on)

 Here is a website that shows how N-Channel and P-Channel MOSFETs are wired.  http://electronics.stackexchange.com/questions/3599/basic-p-type-mosfet-question

 

 --------

 Joe Gores

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