Why vacuum fluorescent displays instead of LCDs? - Page 1
Forum section: electronics / beginners

author: analogo
author_rank: Regular Contributor
timestamp: September 06, 2017, 09:48:48 pm
content: It turns out that there are still sellers of vacuum fluorescent displays, for examplehttp://www.noritake-itron.com/newweb/gvfd/catagory/Em.asp.Why would someone in 2017 use VFD instead of the more readily available (and I suppose also cheaper) LCDs? Are there specific applications that still require or are better served by VFDs?

author: jpanhalt
author_rank: Super Contributor
timestamp: September 06, 2017, 10:02:40 pm
content: The busy time is claimed to be only 2 us. That is a lot faster than any 2x16 or 4x16 etc. LCD display I have used. Never used a VFD, however.

author: Ian.M
author_rank: Super Contributor
timestamp: September 06, 2017, 10:07:17 pm
content: Compared to LCDs, VFDs have a vastly extended temperature range, only really limited by the driver circuitry, and are viewable by users wearing Polaroid sunglasses.

author: Benta
author_rank: Super Contributor
timestamp: September 06, 2017, 10:14:01 pm
content: Vastly superior contrast and readable in sunlight.

author: KuroZ
author_rank: Contributor
timestamp: September 06, 2017, 10:19:22 pm
content: They are cool, too.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 06, 2017, 10:27:01 pm
content: On the downside, they are a bit more expensive, and minimum order at DigiKey is 1000 units for character displays. Need to check other distributors.

author: floobydust
author_rank: Super Contributor
timestamp: September 06, 2017, 10:29:29 pm
content: VFD's rule for outdoor applications that see low temperatures.LCD's don't work at low temperatures or even freeze and crack. Special LCD low temp fluid helps but not much, -20C and they are very slow.VFD's are good in direct sun, good contrast ratio from the coloured display-filter. Transmissive LCD displays no good in sunlight.Main disadvantage to a VFD is power consumption is several watts.OLED is competing but not for large size displays.

author: nanofrog
author_rank: Super Contributor
timestamp: September 06, 2017, 11:44:23 pm
content: Quote from: floobydust on September 06, 2017, 10:29:29 pmFWIW, I only see this as important for portable gear.I'll take the improved contrast on bench equipment any day. Not to say LCD can't look really good with a well developed backlight implementation, I just find VFD's easier to read on my bench (I work in low light when I can as it's less prone to causing eye fatigue; think aircraft flight deck at night).

author: FreddyVictor
author_rank: Regular Contributor
timestamp: September 07, 2017, 11:49:17 am
content: VFDs are also prone toburn-in, I wouldn't say it's a big problem but it is noticeable at times

author: stj
author_rank: Super Contributor
timestamp: September 07, 2017, 01:29:45 pm
content: VFD's look damned good,LCD wont work at low temperatures.notice how some petrol pumps backlight the display with incandescent bulbs - that's to keep the panel warm.LCD is also slowly killed by UV exposure in the sun, and by high temperatures.

author: Kjelt
author_rank: Super Contributor
timestamp: September 07, 2017, 01:37:02 pm
content: This answers them all:http://www.noritake-itron.com/NewWeb/GVFD/Overview/Overview.aspmost important for industry/medical applications:QuoteAnd try to beat this:Quote

author: analogo
author_rank: Regular Contributor
timestamp: September 07, 2017, 04:24:38 pm
content: Quote from: Kjelt on September 07, 2017, 01:37:02 pm114 years ofMeanTime Between Failure? One can only wonder how they tested that.

author: Vtile
author_rank: Super Contributor
timestamp: September 07, 2017, 04:35:08 pm
content: There is also ALD/ELD/TFEL displays:https://beneq.com/displays?gclid=EAIaIQobChMI25DFs8CT1gIVWc-yCh2dYAMfEAAYASAAEgLcG_D_BwE

author: grifftech
author_rank: Frequent Contributor
timestamp: September 07, 2017, 05:36:03 pm
content: they look nice

author: Kjelt
author_rank: Super Contributor
timestamp: September 07, 2017, 08:02:39 pm
content: Quote from: analogo on September 07, 2017, 04:24:38 pmReliability engineering, you can change some parameters and multiply the lifetime by the corresponding factors.I don't know these statistical factors but lets say 100 of your electronic devices are put in a hot chamber of 90 degrees C and a humidity of 80% and the average of those devices last 10 months than with those statistical factors you could for instance multiply that by 50 and get an average expected lifetime of 41 years.

author: Vtile
author_rank: Super Contributor
timestamp: September 07, 2017, 09:21:58 pm
content: Quote from: blueskull on September 07, 2017, 08:28:58 pmHere is interesting comparison table. Interesting that none mentions the TFEL technology, it have been also around for decades by now.https://beneq.com/en/displays/technology

author: AllTheGearNoIdea
author_rank: Unknown
timestamp: September 08, 2017, 05:09:58 am
content: May be a bit off topic but I have recently encountered an electro fluorescent EL display for the first time. I originally thought it was just a LCD display with a EL backlight but is actually quite different. The one I have is faulty with I think a bad driver IC and i will be doing a repair on this in the future. Never one to avoid a bit of shameless self promotion see Part 2 here.This is being used in HP telecoms analyser from what I can tell back in the day they were popular in high end equipment but very expensive. You probably won't want to watch the whole video so start 12 minutes in. Actually if you are interested Part 1 does show more of the display in action as I play with the equipment and as always have no idea what I'm doing.My best regards Chris.https://youtu.be/jKxbjdt8dT8

author: rtsmith54
author_rank: Newbie
timestamp: September 08, 2017, 11:24:59 am
content: VFD's look great and besides they are cool!

author: macboy
author_rank: Super Contributor
timestamp: September 08, 2017, 02:51:37 pm
content: It's like asking "Why a Range Rover SUV instead of a Toyota?"Well, the Toyota is cheaper and more readily available, and it performs a similar basic function. But you can't depend on the Toyota to cross the same terrain, or to look as good while doing it, as the Range Rover. And that essentially echos all the sentiments expressed above.

author: stj
author_rank: Super Contributor
timestamp: September 08, 2017, 04:29:30 pm
content: Quote from: macboy on September 08, 2017, 02:51:37 pmi doubt you'v been in a modern range-rover.just an expensive brick with plastic guards that tear off if you go offroad as much as mounting a high kerb!!

author: jmelson
author_rank: Super Contributor
timestamp: September 08, 2017, 04:58:53 pm
content: Quote from: Kjelt on September 07, 2017, 08:02:39 pmAnd, since a VFD is a vacuum tube, they laugh at 90C! So, the life at 90C is the same as 20C. Apply the Boltzman curve, and you extrapolate a crazy MTBF. Yes, it is all a house of mirrors.My favorite was the tantalum capacitor debacle. A well-known failure mechanism of tantalum capacitors is you run a device for a while, put it on a shelf for 2-5 years, turn it back on and several tantalum caps fail shorted when the DC power abruptly turns on. So, the US military specified tantalum caps for a wide range of gear, severe accelerated life testing showed great results, and then they built thousands of radios, radars, computers and such, and after a good test run at the factory, it all went on the shelf at the supply depot! Perfect recipe for this problem.But, if you know the system for doing this MTBF estimation, it is so TOTALLY bogus. You count the number of each type of component, look up the MTBF for each type, and then combine it all with a formula, and there's your MTBF number! This is all done with a spreadsheet, not with any sort of testing of the complete device. It totally ignores such factors as the load a component carries, the duty cycle of the load, thermal cycling, ESD at external connections, physical handling, and many other issues. But, this bogus system produces totally WHACKY numbers like a whole military field radio with 100+ years MTBF. Oh, RIGHT!(Now, military and aerospace gear IS tested rigorously, with heat, cold, thermal cycling, vibration, salt spray, humidity, and on and on, and that weeds out marginal parts and designs. I'm not badmouthing that. Just the MTBF calculation craze that DOD and others went through some years ago. They still insist on it, but I think they have come to realize it isn't as predictive as they had hoped.)Jon

author: macboy
author_rank: Super Contributor
timestamp: September 08, 2017, 05:39:11 pm
content: Quote from: jmelson on September 08, 2017, 04:58:53 pmI don't think you quite grasp MTBF. It is not the average time for a single example of the device to fail. It tells you the average aggregated failure rate. So for your military radio with 100 year MTBF ... if they have for example 5000 of those radios in service, they will expect 5000units/100yr = 50 units/year fail, or about one failure per week failure rate out of the 5000 unit fleet. Generally, the rate is higher initially (infant mortality), tapers off to a lower steady rate, then climbs again near end of design lifetime, at which point you retire the lot, working or not (unless you want to expose your organization to the climbing failure rate). MTBF tells you the average rate of failures in a fleet of units between deployment and retirement, not the individual unit lifetime.

author: SeanB
author_rank: Super Contributor
timestamp: September 08, 2017, 05:49:18 pm
content: Saw the first generation Freelanders a lot in the workshop, all with the same faults of blown drivetrains ( they tended to grenade the entire gearbox and differentials all at once, generally just from regular driving, as they have near no offroad ability other than pavements and parking lots) that were solved by the installation of an upgraded ( refurbished and hopefully not going to detonate) drivetrain and controller, probably designed to limit power in there at all costs. There was typically a 2 month delay on sending the big box of spares removed to Solihull and getting another back, so there were quite a few queens in waiting in that workshop. Lots of loaner vehicles there as well in the interim.I used to park the 'weekend car" in it's own bay next to them. Security there thought I was an employee, as I was there so often.As to VFD displays, they can be incredibly reliable, and direct sunlight viewable just by having a dark front panel and winding up the display intensity behind to compensate, and then dim for night use ( or else you have a lovely room light as well) so they are used in point of sale displays a lot for this, and for any application where you want a really bright easy to read display, with a pretty good variety of colours and mix and match in the same segment as well. They also are very easy to have custom characters in there with almost no complexity limit on them, as all the segments can have a separate rear connection, and multiple grids for segmentation to reduce pin count, and you can also have multiple bare dies in the package as well for driving them. gold bonded to a silkscreened silver pad and with bond wires to attach to the traces, so that all you need is serial data in and power. They also survive operation in high temperatures a lot better than LCD, and will handle sub zero operation a lot better than any LCD panel, and have, with the right filament designs, pretty good vibration performance.

author: Old Don
author_rank: Regular Contributor
timestamp: September 08, 2017, 05:54:16 pm
content: As other's have stated LCD's suck in bright sunlight. Several of our cars have had fluorescent displays built into the rear view mirror for use as a compass readout. I'd guess an LCD wouldn't do as well for this purpose.

author: Cliff Matthews
author_rank: Unknown
timestamp: September 08, 2017, 07:47:57 pm
content: Quote from: AllTheGearNoIdea onTodayat 01:09:58 AMhttps://youtu.be/jKxbjdt8dT8Chris, I won't to detract too much from the OP's thread, but on the off-chance any here have worked with these 160x128 shift register-based display boards, I post here the front/back view's of the problem you're having. Perhaps someone could post a helpful comment visiting your fine YouTube channel. Good luck!