They used to be amber LED matrixes. High contrast, high legibility, low resolution.
Now they are colour LCD panels. High resolution, high tech, probably high cost. Now they can show the logos of the bus operators, smooth scrolling text and any arbitrary images. None of which anyone really needs except perhaps the egos of the bus companies.
And they are completely illegible. The viewing angle is limited, the text is smaller, unnecessary stuff is there because the implementors can.
Careful what you ask for.
Still, this article is about 7 segment displays. It's a quirky article, but I get the point: many people abuse 7-segment displays as an aesthetic choice where there wouldn't be no point in it.
7 and 16-segment displays can still be a superb choice in many scenarios. The contrast is still unmatched to other display techs. For bench instruments, 7-segment displays (especially the VFD ones) are much more readable than the alternatives IMHO. The second best choice IMHO is OLED, however glare in bright environments is still worse, and getting a large OLED gets expensive very quickly.
For big machinery, a large 7-segment display can be read across the room in any condition. A large readable display on a lathe is much better in terms of safety than an smaller OLED display, even considering the chance of a stuck segment.
And now they periodically show full screen ads instead of arrival / departure information.
It makes me miss the big red letter panel from the early 2000s.
Oxford's travel signage has always been a bit crap, though (and not alone, of course, in this - lots of places in the UK and Europe (and I'm sure US) have crap signage following similar patterns).
The amber matrices were at least clearly readable, but the presentation of information left a lot to be desired. Even on legible displays, constant scrolling displays that alternate between scrolling directions for different text displays for no good reason, and other such madness make it so hard to actually get information about stops that I ended up writing my own wrappers around APIs/website scraping to make a legible display on my phone.
This sort of thing should really be considered in terms of accessibility - for able-bodied people with good eyesight and a quick mind these displays may be legible, but a good % of your users are disabled, elderly, etc - none of the moving display, low-viewing-angle, small-text displays will be usable, but partially sighted/elderly people will generally make do with big friendly text that doesn't change except when it needs to.
The burn-down is a real issue with OLEDs, though :(
An LED matrix has a great number of individual components, and is probably hand assembled due to low demand (compared to an LCD panel). Whereas an LCD panel are mass produced in every size and shape, with standard controllers you can pick up for pennies.
(Granted, these are not individually addressable, but that depends on the PCB.)
You need to consider there's half a million of LEDs in a typical signage device. These consume and heat-up significantly compared to an OLED/LCD panel.
For a panel of the same size, OLED/LCD has higher density, which allows to pack more information (or have better quality signage in general).
It all depends on the usage scenario. In an indoor setting with fixed lighting, a larger LCD screen can be just as readable as OLED, can be very large nowdays (or tiled to achieve the same), and cost a fraction of a LED matrix.
OLED could definitely replace LCDs entirely, but it's still very expensive when it comes to larger panels, which is why it's just slowly replacing smaller displays at the moment.
There's also a cheap kind of panel family where they don't put every color on every pixel. That is, rather than RGB RGB RGB, they are RG GB RG GB RG GB. For most video is hard to tell the difference, but it trashes text. Someone put a TV that was both TN and this reduced color in a conference room.... took me a few months to get it swapped out, but enough people finally saw it and realized it was the TV and not the computer or their eyes that I was able to get it done.
A big problem stems from the fact that to most people "flat panels" are all the same (LCD-whatever, OLED, even plasma)..
Are there new devices which make use of this display tech?
Also Garmin makes navigators with such screens, e.g. Garmin Montana.
The new voip phones had hard to read LCD displays and previous hard key features buried in menus - they made the office look more modern but sucked otherwise.
> A bespoke display panel was used; itwould have been safer, easier to read, more versatile, andcheaper had a hi-res display been used
Obviously the author has never actually tried to design a product both ways. Displays are expensive, and I'm not just talking about the panel itself. Usually you must go up a level or two on your processor hierarchy: a 7-segment display or matrix can be driven by a 4-bit microcontroller. A VGA-resolution display will require a high-end microcontroller, usually a 32-bit Cortex-M3 or M4 these days. A true "hi-res" display, which has admittedly drifted up in quality since the author wrote this, will push you into application processor (i.MX) territory.
That may not sound like much, but typical costs for those levels including supporting circuitry are in the neighborhood of $1, $10, and $100. This is because the tiny microcontroller needs nothing; the fancy apps processor needs DDR SDRAM, NAND flash, a PMIC, and is probably a BGA you have to route on an 8-layer board, with GHz MIPI signalling flying around, and don't even get me started on the software complexity.... You can do all of these things, and if it genuinely makes your product better, you should. But do not pay the cost if your product does not benefit.
A coworker of mine likes to tell a story about cutting the sales price of a medical device from $5,000 to $500. The main source of that savings would have been removing the display. (Yes, really. Medical displays are expensive.) This was rejected by product management, on the reason that "The people who buy this stuff are not the people who use it. The people who buy it like shiny-looking things. It is much easier to sell a product that looks complicated and expensive to a procurement officer than one that looks simple and possibly less advanced, even if they are the same inside. That display does do something -- it sells units."
In operation, the display had a bunch of whiz-bang crap that could have been deleted with no consequence, and two touch buttons for "arm" and "stop". Of course, you had to use a physical button to actually activate it; IEC 60601 wouldn't allow using just a touchscreen to start or stop a medical procedure! So the display really didn't do anything functional....
So, no, high-res displays are not always the answer. Think carefully about the cost!
And there are higher resolution and higher color fidelity displays which are also cheap and driven by I2C.
1 penny is peanuts:
People use seven segment LCDs because they're cheap. No more, no less.
I'm kidding about the knives. But cost reduction meetings can be pretty brutal, especially when the HW team is looking at the SW and firmware folks across the table and saying, "Sure, this is painful, but you can program around it. It saves us ten cents." Ten cents is a fortune.
In pre-ARM days I once saw a HW team seriously propose half populating memory. No, not that way. The other direction, where they'd just take away the upper half of each byte of RAM and thus save a chip. "Only use the low four bits of each byte, you can just program around that, right?" The only reason that cost reduction didn't fly was there was no way to make the stack work properly for interrupts.
First rule of consumer electronics: "No one cares how much you suffered getting it out the door."
Any product required to run on a battery 5+ years can only be met by seven segment LCDs. That's includes safety equipment. Now what?
In addition, that seven segment display has well characterized failure modes and you can make very solid statistical predictions. When was the last time you actually remember a burnt out LCD segment (I can't remember one) vs. the last time you had nasty lines running through a dot matrix LCD (happens to flat panels all the time)? On a matrix, display RAM failure is a display failure. Seven segment LCDs don't need RAM backing.
Are you willing to have your medical device offline because you lost an LCD matrix row and now you are required by process to wait for a replacement? How much time and money did that cost you?
These are the exceptions. LCDs are normally about cheap. And if the device isn't cheap enough, you won't have that safety/medical device at all because nobody will buy it.
Engineering is tradeoffs, not absolutes.
While I agree with your engineering tradeoffs perspective, failing safe is also a major recurring theme in engineering. When errors or loss of functionality happen they should be obvious and stop the system (machine + human operators) from spiraling out of control. A compiler won't silently write integers to a byte* pointer, because that might kill your patient where the parameter goes over 255. A failed display is preferable to a working display that outputs wrong data.
By the way, 14 and 16 segment displays are widely available in passive LCD formats and draw the same power, while the upgrade to dot matrix LCD is not that prohibitive, I had it on my MP3 player 15 years ago.
14/16 segment displays require more microcontroller pins (twice as many, in fact). That goes back to cost.
Your MP3 has a very expensive, high-capacity rechargeable battery which will not hold a charge 5 years even if you connect it to nothing.
Of course, when absolute $ savings are more important than resolution / legibility, tens of cents are worth looking into.
Power requirements are another topic, and monochrome LCDs are unmatched there.
That said, I mostly agree that a small OLED or similar is usually a lot better to read.
I'm left with two opinions: 7-segment displays are not usually fail-safe, and have the potential to be fail-deadly (figure 1). In my entire life I've never had occasion to use a tool with a 7-segment readout, handheld or otherwise, that actually failed or that I misread due to ambiguity.
So, I think a better conclusion would be don't use 7-segment displays in important places.
> In this paper, we raise design issues and present
recommendations; for clarity we say “never” for
design choices that are inappropriate for dependable
or safety-critical applications. For novelty and other
non-dependable applications, obviously examination
of cost and design trade-offs may lead to other
decisions, and such decisions should be backed by
competent empirical evaluation.
How does your conclusion differ from their initial recommendation?
A ESP32 board with a built in display costs around $10, and is pretty universal and easy to use, and scale makes them cheap. Need more? Stick a phone to it.
I'm surprised there isn't some common "overkill" industrial board similar to a very cheap smartphone, minus battery/charging, camera, and GPS, plus connectors for various protocols/pins for interfacing with other devices. Cheap smartphones cost less than $30, so such a board shouldn't the very expensive, and it could save a lot of development time and costs for bespoke hardware design when building devices that need a touchscreen and WiFi (think a fancy washing machine or fridge).
This is why I prefer analog clock faces, and an analog watch. I can read those just fine without my glasses on. I never liked digital volt-ohm meters, either, preferring an old fashioned analog one.
If you want to use 1970's technology for that retro look, use nixie tubes.
Boeing recognized this on their flight deck gauges. A gauge would use both a needle (digitally rendered) and a numeric value, reaping the benefits of both. They went even further - the gauge display would be green, amber, or red depending on good, caution, bad. This makes it real easy to check the instruments quickly - all green => everything is good.
Sort-of related maybe, a special font designed for aircraft cockpit screens: https://news.ycombinator.com/item?id=26373751
They're not hard to make, but they're the sort of thing that no one really wants to make in-house, since they're a means to an end rather than an end in themselves. Great thing to sell, though!
Electroluminescent glass panels on the other hand... https://www.youtube.com/watch?v=Z2o_Sp2-aBo
At today's price of $50 it might be cost effective to do as you say, but I imagine there's not a huge market.
Not rad hardened, and not quite 0.75mm, but you can buy a 1.25mm pitch LED matrix panel for a relatively low cost. It's an RGB panel instead of monochrome for the HDSP-2132.
The HDSP-2132 is made of 8 character elements, each element has a resolution of 5x7. So a 80x24 terminal would have a resolution of 400x168... 67,200 LEDs.
So about a magnitude off, even before ignoring the built in character spacing :)
I believe each module would be 160 x 120 dots (19,200 dots total) though, based on module size and LED pitch. I'm unclear on where you got 104x78.
Module Res Size
P1.923 104*78 200*150
Here's a better link: https://www.aliexpress.com/item/32965783207.html
It's 160x120, as I mentioned for a 200x150mm P1.25 led module. You just divide the width/height by the pitch to see the number of dots.
As far as I can tell, 1.25mm is the smallest pitch available for these modules.
1.25mm x 160 = 200mm
1.25mm x 120 = 150mm
This worked at least in two ways:
- By showing the wrong price/quantity (1.980€/l would become 1.560€/l)
- By showing the wrong quantity dispensed (39.8 liters would become 35.6)
I guess the lesson here is to never trust a 7-segment display until you can confirm all segments are working.
(But I doubt it.)
Their cost exceeded that of using wristwatch lcd displays (the kind with fixed patterns) and the results there were far superior. The complexity of a 16-segment display is probably slightly lower, but the runtime power savings made the LCD option more lucrative.
Edit: Within a fixed-width space, however, variable _weight_ numbers might work well. A very heavy 9, an extremely light 0.
7-seg displays are usually used because of cost and constraints, not because they're "good". But for something like a microwave oven they're just fine!
* Some digits can be easily mistaken (e.g. 8 and 0).
* Sometimes the contrast between lit and unlit segments is too low.
* If you turn the display upside down it might still look valid (pretty sure this was a Jonathon Creek plot).
* You can't tell if a segment is off or broken (e.g. an 8 with a broken middle would be indistinguishable from 0).
Honestly not that convincing. I mean they're not exactly wrong, but they're not really fatal either, and anyway nobody uses 7-segment displays because they think they're the best displays possible for the job.
However for anyone using a 7-segment display this should be required reading! It has lots of good design advice.