Which display technology has the longest life? - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: August 08, 2019, 04:04:52 pm
content: Something like a Noritake vacuum fluorescent character display, or something like the HCMS-3916 smart LED displays?By longest life, I mean you can pick it up decades later and have a decent hope it will still work as opposed to being left on 24 hours a day everyday for years and years, but may be the answer is the same.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2019, 04:30:09 pm
content: That's a difficult one. Unfortunately I don't think the "answer is the same".HD44780 interface LCD Character displayshavebeen around and interchangeable for decades, and typically long life too. Unfortunately it would be rather optimistic to expect them to survive for decades more now. I wonder how backlit monochrome displays will fare against the competition in the years to come.VFDs seem to be rather more manufacturer specific, and are not physically long lived, as evidenced by the difficulty in finding replacements for displays in older (and even fairly recent) test equipment.Inteligent LEDs don't seem to have fared too well historically. Looking back, there have been many types of chip on board LEDs (HP, TI and others) but these have now reached the status of expensive 'lucky scores' on ebay.OLEDs are still evolving, and fairly short lived [EDIT: whether powered on or not] it's probably too early to predict which interface will prevail longer term.It's a shame you are looking for character displays (?), I'm sure dumb 7 segment LED ones will be available and reliable for decades to come. Unfortunately we seem to be at a juncture where inteligent displays, OLEDS, colour LCDs etc. have become cheap and plentiful but with a wide variety of interfaces.As dumb as possible might be the best starting point?

author: alank2
author_rank: Super Contributor
timestamp: August 08, 2019, 05:13:32 pm
content: Thanks for the reply Gyro!They do make 14 segment LED's as well, but it is hard to not have that 5x7 format where you can display characters cleanly.I've not had that great of luck with 7 segment displays, but it could be that I've bought cheap ones. Even the ones I get from Digikey/Mouser seem to have quality issues from time to time.I've had good luck with the intelligent displays (which you can still buy at Digikey/Mouser, but they are pricy). I've got some of these with date codes that are into the 90's that work perfectly. These are probably my idea of what has the most longevity - maybe they are designed for aerospace applications.I think VFD's are also pretty durable if you get a quality one (Noritake) and they claim 10+ years that can be 20 years real easily.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2019, 06:31:50 pm
content: Yes, 14 segment starburst displays have always been less than aesthetically pleasing, I suspect that their day has passed.Depending on where you bought them you may well have had low quality LED displays, I wouldn't be surprised if a lot of ebay ones weren't parametric rejects even if they do light up. Pretty much any low quality outfit can mount a few LED dies on a PCB, match it up to a plastic moulding and pour some epoxy in. The brand name ones are better at stress relieving the whole thing so that the bond wires don't get pulled off.VFDs are also very variable, premium ones like Noritake are going to last much better. There are loads of variables, vacuum and seal quality, phosphor poisoning - no or absolute minimum Red phosphor area! (the Noritake rep told me that one), Filament coating etc. Getting the drive levels just right is also a major factor (esp. filament voltage).It's just a matter of rolling the dice and picking to most durable intelligent display interface standard.Of course Nixie and Panaplex displays still work after 50+ years storage in cold, damp, ex-military warehouses. They look pretty too.P.S. Is this a one-off application or a product? If it's one-off then you could just buy some spares and be nice to them. If it's a product, then you would probably be better defining an 'intelligent display board interface' instead, and upgrading the display board design over time if you need to.

author: jmelson
author_rank: Super Contributor
timestamp: August 08, 2019, 06:58:45 pm
content: Quote from: Gyro on August 08, 2019, 04:30:09 pmI've got some 20-character LCDs with 44780 controller that have been running in my house 24/7 for almost 30 years.No sign of fade, patterns, etc.LEDs certainly should last a long time if run at reasonable current.VFDs definitely fade after long use, and develop patterns where always-on segments become dimmer.But, for any of these technologies, they should have a very long shelf life. LCDs from the 1970's - 1980's tended to go dark over time, even if not powered on, but I think the stuff made today seems to have much longer shelf life.Jon

author: coromonadalix
author_rank: Super Contributor
timestamp: August 09, 2019, 11:54:20 am
content: For what i've seen : standard lcd's and led displays are the bestWe have +/- 22 years old equipement with lcd's (44780) returning for a checkup and recalibration, still working fine, some 256x64 lcd's too +/- 12 years, even rare old color 256x64 display worked fine, but are obsolete to replace they where cfl backlight and its the backlight who failed, not the lcd itself ?Leds display from 30 years from old test equipment are working fine too.

author: ArthurDent
author_rank: Super Contributor
timestamp: August 09, 2019, 05:12:26 pm
content: Here’s what I’ve found from the equipment I’ve owned.The VFD displays look great when new but if you check for videos on repairs you will find that they all seem to dim over age. Attempts to raise the voltage or shock the filaments generally end in abrupt failure. I have an HP 53132A that is a little dim but is still quite usable. Not worth replacing it yet for about $90.The equipment I have with LCD displays that use electroluminescent backlights all seem to die or totally darken with age but I’ve managed to repair them by replacing the backlight strip with cheap ones I’ve bought on eBay. This also allows me to change the display color if I want to.I just repaired a LCD display I have in a GPSDO that runs 24/7. It was getting both dim and yellowish. There were 2 LEDs that illuminated the plastic backlight strip from one end and one of the LEDs was very dim and definitely yellow. I’ve had a couple of LEDs in displays that died that same way.The HP or similar 7-segment LED displays I have seem to age and dim somewhat randomly so I have time displays that have bright and dim digits and sometimes even a dim segment in a bright display.I have had 2 LCD displays that weren’t backlit that had seal failures along the edge and black started creeping into the segment area. I suspect that these had been subjected to well below freezing temperatures and that was the cause but I’m not 100% positive. Definitely a leaking seal though.While this isn’t a large enough sample to say all displays will behave this way, this is what can happen. Keep in mind that some of the equipment I’ve mentioned could be 40+ years old and it worked just fine for a very long time. If you’re buying new then the display probably isn’t at the top of the list of features you worry about. If you’re buying some used equipment the display brightness might be something you want to check.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 09, 2019, 05:57:45 pm
content: LEDs are the most stable/long lasting technology vs. VFDs (losing vacuum), LCDs (temperature damage), etc., you just want to under-drive the specification to get maximum lifetime. Beyond that? Not sure there's that much you can control for without extensive testing.My method would be pick your type (7 segment, alphanumeric, dot matrix), pick a decent vendor, pick a part with a good lifetime specification, then drive it at no more than half rated current (less if it's a hot environment). Even mediocre quality LEDs could probably get well over 100,000 hours or more of lifetime under those circumstances, and since they're light, small, and solid state, they're not going to run into many of the physical issues that can come up with long term storage.LCDs probably last fine but the size of the screen and relatively less support in the center can be more prone to damage, and unless you get screens rated for a wide temperature range, even freezing temperatures can do permanent damage, so they're probably not ideal for anything you expect to last through uncontrolled climate storage, though the technology itself is very long lasting.

author: alank2
author_rank: Super Contributor
timestamp: August 09, 2019, 06:03:48 pm
content: I didn't think about LCD damage at lower temperatures for some reason, good points guys!

author: David Hess
author_rank: Super Contributor
timestamp: August 09, 2019, 06:40:02 pm
content: I would have to go with dumb LED displays followed by LCD displays.LED displays come in 7, 9, 14, and 16 segment models but dot matrix parts are also available. Failures tend to be single segments or dots leaving them still usable. The external drivers tend to be either very reliable or easily replaceable at least in the past with through hole parts.LCD displays are more like to have catastrophic failure like turning black or having the polarizer eaten by a fungus but they never seem to wear out unlike the alternatives except for their backlight if present.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 09, 2019, 07:02:16 pm
content: We need to know whether we're talking about operating life or storage life.I guess a big factor would be storage conditions.LCD displays will tend to age pretty badly if they are stored in hot environments, subjected to high levels of moisture, exposed to sunlight, even indirectly...Another key factor for those connected with rubber (elastomeric connectors): those connectors will also age and eventually develop bad contacts. That's almost inevitable.LEDs will be a little more forgiving. But OTOH, they have a limited operating life (usually in the order of a few thousand hours), beyond which they'll be dimmer and dimmer.

author: alank2
author_rank: Super Contributor
timestamp: August 09, 2019, 07:06:28 pm
content: Both really, but I'd say prioritize storage life over operating life. I'm fascinated with the idea of making something and have it still work 30-50 years later. I'm sure the idea goes way past displays into a lot of other topics like no electrolytic caps, etc.

author: Gyro
author_rank: Super Contributor
timestamp: August 09, 2019, 07:11:12 pm
content: I mentioned the question of whether it was a one-off or production situation?It sounds like a one-off. In that case, make yourself a well packed spares kit of everything (including most of the silicon) which will have gone obsolete in 30-50 years. Actually , that's probably pretty much everything.I said that the HD44780 had already survived for decades - your problem now is stuff that has already served its term, probably most things through hole in that sort of timespan.P.S. That said, I've got test gear that's 50 years old that is still running on orignal Panaplex displays and original (healthy) electrolyics. It just goes to show.

author: texaspyro
author_rank: Super Contributor
timestamp: August 10, 2019, 02:51:28 am
content: Quote from: alank2 on August 09, 2019, 07:06:28 pmAround 1972 I built an LED alarm clock using PCBs and a National Semiconductor clock chip sold by Radio Shack. The clock chips were rejects from NS that had some bug in them. I used what was then unheard of green 7-segment displays. The clock has been running 24/7/365.25 for close to 50 years. Around 5 years ago it stopped working... I thought it was the clock chip (I had a replacement), but it turned out to be a bad transistor on the display board.The LEDs are around half their original brightness... I've been thinking about replacing them, but my current alarm clock is a Raspberry Pi, 800x480 touchscreen, SIRF GPS module, running Lady Heather... I hate waking up more than a millisecond early.

author: David Hess
author_rank: Super Contributor
timestamp: August 10, 2019, 04:06:56 pm
content: Quote from: texaspyro on August 10, 2019, 02:51:28 amI have several test instruments from the early 1970s with LED displays and the failures have all been in logic ICs but *not* the LED drivers themselves.

author: texaspyro
author_rank: Super Contributor
timestamp: August 10, 2019, 04:18:42 pm
content: The main failure in 7-sgement LEDs seems to be missing segments. A lot of the failures seem to be caused by bond wire failure between the die and the lead frame. Apparently the material of the LED die behaves differently than silicon.

author: cvanc
author_rank: Frequent Contributor
timestamp: August 10, 2019, 04:20:17 pm
content: Quote from: texaspyro on August 10, 2019, 02:51:28 am"EEVBlog Phrase Of The Day"

author: David Hess
author_rank: Super Contributor
timestamp: August 10, 2019, 04:24:04 pm
content: Quote from: texaspyro on August 10, 2019, 04:18:42 pmThat certainly happens but I do not remember encountering it myself. I know others who have.

author: texaspyro
author_rank: Super Contributor
timestamp: August 10, 2019, 04:32:35 pm
content: Quote from: David Hess on August 10, 2019, 04:24:04 pmI once came across a failure analysis report that had the gory details...A friend of mine worked in the semiconductor business and had access to all sorts of chip prototyping equipment. He had one of the first LED watches with green displays. One of the segments died. He really liked the watch and spent a weekend digging into the display package and re-bonding a connection.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 10, 2019, 04:33:07 pm
content: Quote from: David Hess on August 10, 2019, 04:24:04 pmNever seen that either. Missing segments in LCD displays OTOH, quite often.

author: Gyro
author_rank: Super Contributor
timestamp: August 10, 2019, 07:05:20 pm
content: That's usually down to the zebra strip or, less likely, the driver rather than the LCD itself. Normally fixable without display replacement.