---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 06/20/14: 10 ---------------------------------------------------------- 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 _____________________________________ Time: 05:51:11 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 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 _____________________________________ Time: 05:51:12 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: Re: LED Ghosting At 03:15 PM 6/19/2014, you 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. 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 _____________________________________ Time: 06:57:10 AM PST US From: "Robert L. Nuckolls, III" Subject: RE: AeroElectric-List: 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 _____________________________________ Time: 10:51:22 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: P-leads 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 _____________________________________ Time: 11:42:02 AM PST US From: rayj Subject: Re: AeroElectric-List: Re: P-leads 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: > > > 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. ========================== SNIP ==================================== ________________________________ Message 6 _____________________________________ Time: 04:35:33 PM PST US Subject: AeroElectric-List: Re: LED Ghosting From: "donjohnston" 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 _____________________________________ Time: 06:04:59 PM PST US Subject: Re: AeroElectric-List: Re: LED Ghosting From: Charlie England 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 _____________________________________ Time: 06:07:09 PM PST US Subject: AeroElectric-List: Re: LED Ghosting From: "donjohnston" 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 _____________________________________ Time: 06:44:42 PM PST US Subject: AeroElectric-List: Re: LED Ghosting From: "donjohnston" 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 ____________________________________ Time: 07:23:27 PM PST US From: Henador Titzoff Subject: Re: AeroElectric-List: 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 =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" =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> ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.