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Don’t use 7-segment displays (2011) [pdf]

109 pointsby pictureabout 4 years ago

18 comments

afandianabout 4 years ago
In Oxford city centre, and probably elsewhere, they replaced the live signage at bus stops. These tell you when the next bus is due, the time and date, etc.<p>They used to be amber LED matrixes. High contrast, high legibility, low resolution.<p>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.<p>And they are <i>completely illegible</i>. The viewing angle is limited, the text is smaller, unnecessary stuff is there because the implementors can.<p>Careful what you ask for.
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exmadscientistabout 4 years ago
Many of the author&#x27;s points are worth consideration (especially regarding use of 7-segment displays for anything other than digits), but come on:<p>&gt; A bespoke display panel was used; itwould have been safer, easier to read, more versatile, andcheaper had a hi-res display been used<p>Obviously the author has never actually tried to design a product both ways. Displays are <i>expensive</i>, and I&#x27;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 &quot;hi-res&quot; display, which has admittedly drifted up in quality since the author wrote this, will push you into application processor (i.MX) territory.<p>That may not sound like much, but typical costs for those levels <i>including supporting circuitry</i> 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&#x27;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 <i>should</i>. But do not pay the cost if your product does not benefit.<p>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 &quot;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.&quot;<p>In operation, the display had a bunch of whiz-bang crap that could have been deleted with no consequence, and two touch buttons for &quot;arm&quot; and &quot;stop&quot;. Of course, you had to use a physical button to actually activate it; IEC 60601 wouldn&#x27;t allow using just a <i>touchscreen</i> to start or stop a medical procedure! So the display really didn&#x27;t do anything functional....<p>So, no, high-res displays are not always the answer. Think carefully about the cost!
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malwarebytessabout 4 years ago
What a quirky paper. I worked at a major winery that had dozens of tanks, up to 100,000 liters each. A single failure in a tank represented many millions of dollars. Our extremely expensive micro-oxygen pump used a standard 7-segment display combined with little red LEDs representing On&#x2F;Off next to a list of tank numbers. The 7-segment display was used to read and to set the units (μg, mg , etc), amount, and rate of oxygen delivery. I never made the mistake of misconfiguring, but one of the senior Winemakers did resulting in some very angry customers, a 7 figure loss, and many contracts.<p>I&#x27;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&#x27;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.<p>So, I think a better conclusion would be don&#x27;t use 7-segment displays in important places.
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tgsovlerkhgselabout 4 years ago
For hobbyist use (where quantity is usually 1 and shipping and work matter more than a $1 part cost), I&#x27;ve found that going overkill is usually worth it.<p>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.<p>I&#x27;m surprised there isn&#x27;t some common &quot;overkill&quot; industrial board similar to a very cheap smartphone, minus battery&#x2F;charging, camera, and GPS, plus connectors for various protocols&#x2F;pins for interfacing with other devices. Cheap smartphones cost less than $30, so such a board shouldn&#x27;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).
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WalterBrightabout 4 years ago
I have severe astigmatism, meaning I see double without glasses. Seven segment displays are hopeless without my glasses on.<p>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.<p>If you want to use 1970&#x27;s technology for that retro look, use nixie tubes.
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detaroabout 4 years ago
And indeed in e.g. avionics one often sees pixel displays, even in older hardware, where it&#x27;s AFAIK often small LED matrices (assuming its new enough to have displays, and not using gauges). Random example via image search: <a href="https:&#x2F;&#x2F;www.comtronic-schoenau.de&#x2F;en&#x2F;solutions&#x2F;afficheurs-led-mesure&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.comtronic-schoenau.de&#x2F;en&#x2F;solutions&#x2F;afficheurs-le...</a><p>Sort-of related maybe, a special font designed for aircraft cockpit screens: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=26373751" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=26373751</a>
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achairapartabout 4 years ago
Years ago I read about a scam where people were tampering 7-segment displays in gas pump stations (e.g. by altering one segment a &quot;9&quot; will be displayed as a &quot;5&quot;, an &quot;8&quot; as a &quot;6&quot; and so on), so you got less gas than what you paid for.<p>This worked at least in two ways:<p>- By showing the wrong price&#x2F;quantity (1.980€&#x2F;l would become 1.560€&#x2F;l)<p>- By showing the wrong quantity dispensed (39.8 liters would become 35.6)<p>I guess the lesson here is to never trust a 7-segment display until you can confirm all segments are working.
LeoPantheraabout 4 years ago
My microwave for some reason uses left-aligned &quot;1&quot; digits and I&#x27;ve always hated it, but after reading this, I choose to believe that it was done intentionally in order to reduce confusion from stuck-on elements.<p>(But I doubt it.)
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causality0about 4 years ago
I find it very strange that this paper ignores the existence of the 16-segment display.
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mjevansabout 4 years ago
Make clearer, monospaced, numeric fonts. Please do NOT use variably placed and sized numbers. IMO, that makes it extremely difficult to read things; and far worse to compare them. I do not need or want numerical calligraphy.<p>Edit: Within a fixed-width space, however, variable _weight_ numbers might work well. A very heavy 9, an extremely light 0.
sneakabout 4 years ago
Yeah, 14-segment displays aren&#x27;t much more expensive but you get alphanumeric. :)<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Fourteen-segment_display" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Fourteen-segment_display</a>
oneeyedpigeonabout 4 years ago
This reminds me of the time I looked over at my friend&#x27;s stereo in his room at uni. &quot;Why&#x27;s it saying &#x27;nod 15c&#x27;?&quot; I enquired, utterly genuinely?
nxpnsvabout 4 years ago
Anecdotal counterpoint - 7 Segs can provide a hard to beat minimalist esthetic to a design, to me it is one of the major appeals o the KORG microKORG synthesizer. (not really arguing with the point of the paper, but design also can matters)
souprockabout 4 years ago
Every digital clock in the store is 7-segment.
mnw21camabout 4 years ago
Darn. And I just used one in my project, too.
ddtaylorabout 4 years ago
Site uses a self-signed cert and HTTPSEverywhere gets mad.
raverbashingabout 4 years ago
A bit of a clickbait title but good list of guidelines<p>7-seg displays are usually used because of cost and constraints, not because they&#x27;re &quot;good&quot;. But for something like a microwave oven they&#x27;re just fine!
IshKebababout 4 years ago
To save you a click the reasons are:<p>* 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&#x27;t tell if a segment is off or broken (e.g. an 8 with a broken middle would be indistinguishable from 0).<p>Honestly not that convincing. I mean they&#x27;re not exactly wrong, but they&#x27;re not really fatal either, and anyway nobody uses 7-segment displays because they think they&#x27;re the best displays possible for the job.<p>However for anyone using a 7-segment display this should be required reading! It has lots of good design advice.