18 ms·

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

109 points by parsecs 6y ago

malwarebytess 6y 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/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. 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.
- viraptor 6y ago
  Alternatively, if the failure would cost you millions, stick in 2 of those displays which will cost you $1 each, so if they fail you're likely to notice.
  - sneak 6y ago
    For a seven figure potential loss, this probably justifies a raspberry pi or two, on different UPSes, hooked up to backup sensors that can email a few different supervisors when the parameters exit the acceptable envelope.
- skavi 6y ago
  > 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. How does your conclusion differ from their initial recommendation?
- gerardnll 6y ago
  You didn't even read the introduction. > 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.
LeoPanthera 6y ago
My microwave for some reason uses left-aligned "1" digits and I'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. (But I doubt it.)
- ThePowerOfFuet 6y ago
  Panasonic?
  - LeoPanthera 6y ago
    It's a Thermador.
detaro 6y ago
And indeed in e.g. avionics one often sees pixel displays, even in older hardware, where it's AFAIK often small LED matrices (assuming its new enough to have displays, and not using gauges). Random example via image search: https://www.comtronic-schoenau.de/en/solutions/afficheurs-led-mesure/ https://www.comtronic-schoenau.de/en/solutions/afficheurs-le... Sort-of related maybe, a special font designed for aircraft cockpit screens: https://news.ycombinator.com/item?id=26373751 https://news.ycombinator.com/item?id=26373751
- tal8d 6y ago
  Yeah, the HDSP-2132 is a common display component in military hardware. I'm sure that readability figures into it (especially for NVGs), but so does hardiness. My hopes of an 80x24 dumb terminal were dashed when I finally learned the unit replacement price... I don't need a rad hardened serial display that bad.
  - parsecs 6y ago
    I've been looking into those Avago/Broadcom dot matrix displays recently. I don't think it'd be too hard to recreate something similar with tiny SMD LEDs on a PCB and a slightly intelligent driver board, for much cheaper. Would there be a market for something like that?
    - exmadscientist 6y ago
      Only if you can get them listed at Digi-Key/Mouser/etc. Even if it's under a "maker" brand like Adafruit, Sparkfun, etc. Anyone who can replacement TIL311 and friends displays in there, and advertise them, will sell quite a few. 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!
    - tal8d 6y ago
      It has been done a few times, but I doubt there would be any kind of market for it. https://hackaday.io/project/85515-redotmatrix https://hackaday.io/project/85515-redotmatrix Electroluminescent glass panels on the other hand... https://www.youtube.com/watch?v=Z2o_Sp2-aBo https://www.youtube.com/watch?v=Z2o_Sp2-aBo
farrarstan 6y ago
Never in one million years would i read that insanely formatted article, or care about whatever dumb micro problem they think they have
causality0 6y ago
I find it very strange that this paper ignores the existence of the 16-segment display.
- parsecs 6y ago
  Or any of the other non 7 or 8 segment displays.
- ComputerGuru 6y ago
  I had a hell of a hard time sourcing them a few years back at anything remotely resembling decent prices. 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.
WalterBright 6y ago
I have severe astigmatism, meaning I see double without glasses. Seven segment displays are hopeless without my glasses on. 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.
- gifnamething 6y ago
  Do you dislike digital speedometers?
  - Causality1 6y ago
    Digital speedometers are horrible. A constantly-changing digit is so much less pleasant to look at than a smoothly-moving needle.
    - WalterBright 6y ago
      A changing digit display also gives no feel for how fast it is changing, which can be just as important as the value. (The same goes for my volt-ohm meter.)
  - WalterBright 6y ago
    Yes. Although I always wear glasses when driving, with an analog speedo I can see it and know the speed without needing to directly look and focus on it. 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.
- ferongr 6y ago
  You should wear glasses constantly both to be safer towards yourself and towards others and to also reduce the cognitive load you experience.
souprock 6y ago
Every digital clock in the store is 7-segment.
ddtaylor 6y ago
Site uses a self-signed cert and HTTPSEverywhere gets mad.
mjevans 6y 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. Edit: Within a fixed-width space, however, variable _weight_ numbers might work well. A very heavy 9, an extremely light 0.
raverbashing 6y ago
A bit of a clickbait title but good list of guidelines 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!
exmadscientist 6y ago
Many of the author's points are worth consideration (especially regarding use of 7-segment displays for anything other than digits), but come on: > 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!
- detaro 6y ago
  I think in the sense they are using it, even b/w 128x64 would be "high-res": enough to draw nicely readable digits. (design trade-offs of course also apply to that, but not as starkly)
nxpnsv 6y 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)
mnw21cam 6y ago
Darn. And I just used one in my project, too.
tgsovlerkhgsel 6y ago
For hobbyist use (where quantity is usually 1 and shipping and work matter more than a $1 part cost), I've found that going overkill is usually worth it. 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).
- omneity 6y ago
  You might be interested in this: https://m5stack.com/ https://m5stack.com/ (not affiliated)
  - colejohnson66 6y ago
    That’s actually a really slick design!
afandian 6y 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. 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.
- avianlyric 6y ago
  Colour LCD panels probably work out cheaper that LED matrixes. 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.
  - rzzzt 6y ago
    I'm not sure if/why they would be hand-assembled, as SMD pick & place machines exist for the lighting industry: https://youtu.be/Y45COU2LdXg https://youtu.be/Y45COU2LdXg (Granted, these are not individually addressable, but that depends on the PCB.)
  - bsdubernerd 6y ago
    The biggest issue for LED matrix displays is not construction, but 1) density of the display and 2) size/power draw requirements. 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.
oneeyedpigeon 6y ago
This reminds me of the time I looked over at my friend's stereo in his room at uni. "Why's it saying 'nod 15c'?" I enquired, utterly genuinely?
achairapart 6y 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 "9" will be displayed as a "5", an "8" as a "6" and so on), so you got less gas than what you paid for. 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.
sneak 6y ago
Yeah, 14-segment displays aren't much more expensive but you get alphanumeric. :) https://en.wikipedia.org/wiki/Fourteen-segment_display https://en.wikipedia.org/wiki/Fourteen-segment_display
IshKebab 6y ago
To save you a click the reasons are: * 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.

109 points by parsecs 6y 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/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. 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.

viraptor 6y ago
Alternatively, if the failure would cost you millions, stick in 2 of those displays which will cost you $1 each, so if they fail you're likely to notice.
- sneak 6y ago
  For a seven figure potential loss, this probably justifies a raspberry pi or two, on different UPSes, hooked up to backup sensors that can email a few different supervisors when the parameters exit the acceptable envelope.
skavi 6y ago
> 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. How does your conclusion differ from their initial recommendation?
gerardnll 6y ago
You didn't even read the introduction. > 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.

LeoPanthera 6y ago

My microwave for some reason uses left-aligned "1" digits and I'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. (But I doubt it.)

ThePowerOfFuet 6y ago
Panasonic?
- LeoPanthera 6y ago
  It's a Thermador.

detaro 6y ago

And indeed in e.g. avionics one often sees pixel displays, even in older hardware, where it's AFAIK often small LED matrices (assuming its new enough to have displays, and not using gauges). Random example via image search: https://www.comtronic-schoenau.de/en/solutions/afficheurs-led-mesure/ https://www.comtronic-schoenau.de/en/solutions/afficheurs-le... Sort-of related maybe, a special font designed for aircraft cockpit screens: https://news.ycombinator.com/item?id=26373751 https://news.ycombinator.com/item?id=26373751

tal8d 6y ago
Yeah, the HDSP-2132 is a common display component in military hardware. I'm sure that readability figures into it (especially for NVGs), but so does hardiness. My hopes of an 80x24 dumb terminal were dashed when I finally learned the unit replacement price... I don't need a rad hardened serial display that bad.
- parsecs 6y ago
  I've been looking into those Avago/Broadcom dot matrix displays recently. I don't think it'd be too hard to recreate something similar with tiny SMD LEDs on a PCB and a slightly intelligent driver board, for much cheaper. Would there be a market for something like that?
  - exmadscientist 6y ago
    Only if you can get them listed at Digi-Key/Mouser/etc. Even if it's under a "maker" brand like Adafruit, Sparkfun, etc. Anyone who can replacement TIL311 and friends displays in there, and advertise them, will sell quite a few. 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!
  - tal8d 6y ago
    It has been done a few times, but I doubt there would be any kind of market for it. https://hackaday.io/project/85515-redotmatrix https://hackaday.io/project/85515-redotmatrix Electroluminescent glass panels on the other hand... https://www.youtube.com/watch?v=Z2o_Sp2-aBo https://www.youtube.com/watch?v=Z2o_Sp2-aBo

farrarstan 6y ago

Never in one million years would i read that insanely formatted article, or care about whatever dumb micro problem they think they have

causality0 6y ago

I find it very strange that this paper ignores the existence of the 16-segment display.

parsecs 6y ago
Or any of the other non 7 or 8 segment displays.
ComputerGuru 6y ago
I had a hell of a hard time sourcing them a few years back at anything remotely resembling decent prices. 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.

WalterBright 6y ago

I have severe astigmatism, meaning I see double without glasses. Seven segment displays are hopeless without my glasses on. 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.

gifnamething 6y ago
Do you dislike digital speedometers?
- Causality1 6y ago
  Digital speedometers are horrible. A constantly-changing digit is so much less pleasant to look at than a smoothly-moving needle.
  - WalterBright 6y ago
    A changing digit display also gives no feel for how fast it is changing, which can be just as important as the value. (The same goes for my volt-ohm meter.)
- WalterBright 6y ago
  Yes. Although I always wear glasses when driving, with an analog speedo I can see it and know the speed without needing to directly look and focus on it. 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.
ferongr 6y ago
You should wear glasses constantly both to be safer towards yourself and towards others and to also reduce the cognitive load you experience.

souprock 6y ago

Every digital clock in the store is 7-segment.

ddtaylor 6y ago

Site uses a self-signed cert and HTTPSEverywhere gets mad.

mjevans 6y 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. Edit: Within a fixed-width space, however, variable _weight_ numbers might work well. A very heavy 9, an extremely light 0.

raverbashing 6y ago

A bit of a clickbait title but good list of guidelines 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!

exmadscientist 6y ago

Many of the author's points are worth consideration (especially regarding use of 7-segment displays for anything other than digits), but come on: > 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!

detaro 6y ago
I think in the sense they are using it, even b/w 128x64 would be "high-res": enough to draw nicely readable digits. (design trade-offs of course also apply to that, but not as starkly)

nxpnsv 6y 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)

mnw21cam 6y ago

Darn. And I just used one in my project, too.

tgsovlerkhgsel 6y ago

For hobbyist use (where quantity is usually 1 and shipping and work matter more than a $1 part cost), I've found that going overkill is usually worth it. 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).

omneity 6y ago
You might be interested in this: https://m5stack.com/ https://m5stack.com/ (not affiliated)
- colejohnson66 6y ago
  That’s actually a really slick design!

afandian 6y 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. 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.

avianlyric 6y ago
Colour LCD panels probably work out cheaper that LED matrixes. 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.
- rzzzt 6y ago
  I'm not sure if/why they would be hand-assembled, as SMD pick & place machines exist for the lighting industry: https://youtu.be/Y45COU2LdXg https://youtu.be/Y45COU2LdXg (Granted, these are not individually addressable, but that depends on the PCB.)
- bsdubernerd 6y ago
  The biggest issue for LED matrix displays is not construction, but 1) density of the display and 2) size/power draw requirements. 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.

oneeyedpigeon 6y ago

This reminds me of the time I looked over at my friend's stereo in his room at uni. "Why's it saying 'nod 15c'?" I enquired, utterly genuinely?

achairapart 6y 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 "9" will be displayed as a "5", an "8" as a "6" and so on), so you got less gas than what you paid for. 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.

sneak 6y ago

Yeah, 14-segment displays aren't much more expensive but you get alphanumeric. :) https://en.wikipedia.org/wiki/Fourteen-segment_display https://en.wikipedia.org/wiki/Fourteen-segment_display

IshKebab 6y ago

To save you a click the reasons are: * 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.