5 ms·

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

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)
ivoras 6y ago
To be fair, it's not always either-or: an OLED display of 128x32 or 128x64 resolution costs peanuts and requires 4 lines for routing (I2C), and I've used them on 8bit uCs. Like https://s.click.aliexpress.com/e/_9flw1u https://s.click.aliexpress.com/e/_9flw1u And there are higher resolution and higher color fidelity displays which are also cheap and driven by I2C.
- bsder 6y ago
  $1.30 isn't peanuts. 1 penny is peanuts: https://www.alibaba.com/product-detail/6-digit-8-characters-pen-Segment_60347971499.html?spm=a2700.galleryofferlist.normal_offer.d_title.757211f6FVMZKy https://www.alibaba.com/product-detail/6-digit-8-characters-... https://www.alibaba.com/product-detail/TN-segment-custom-LCD-display-pen_60347119657.html?spm=a2700.details.0.0.5dd53f53hbCjRp https://www.alibaba.com/product-detail/TN-segment-custom-LCD... People use seven segment LCDs because they're cheap. No more, no less.
  - yholio 6y ago
    I think the author's argument stands: except for novelty products, there are very few applications where the misinterpretation risk is worth less than $1. Certainly nothing that has to do with safety, medical equipment, professional and industrial tooling, food processing, automotive (pressures, temperatures etc.). An one segment error leading to a 30 PSI reading when the pump is set at 90 could mean instant death when the tire blows up.
    - bsder 6y ago
      > there are very few applications where the misinterpretation risk is worth less than $1 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.
thebruce87m 6y ago
The STM32G0 line might surprise you. It’s a Cortex M0+ and allows using SPI flash for graphics assets: http://blog.st.com/x-nucleo-gfx01m1/ http://blog.st.com/x-nucleo-gfx01m1/

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)

ivoras 6y ago

To be fair, it's not always either-or: an OLED display of 128x32 or 128x64 resolution costs peanuts and requires 4 lines for routing (I2C), and I've used them on 8bit uCs. Like https://s.click.aliexpress.com/e/_9flw1u https://s.click.aliexpress.com/e/_9flw1u And there are higher resolution and higher color fidelity displays which are also cheap and driven by I2C.

bsder 6y ago
$1.30 isn't peanuts. 1 penny is peanuts: https://www.alibaba.com/product-detail/6-digit-8-characters-pen-Segment_60347971499.html?spm=a2700.galleryofferlist.normal_offer.d_title.757211f6FVMZKy https://www.alibaba.com/product-detail/6-digit-8-characters-... https://www.alibaba.com/product-detail/TN-segment-custom-LCD-display-pen_60347119657.html?spm=a2700.details.0.0.5dd53f53hbCjRp https://www.alibaba.com/product-detail/TN-segment-custom-LCD... People use seven segment LCDs because they're cheap. No more, no less.
- yholio 6y ago
  I think the author's argument stands: except for novelty products, there are very few applications where the misinterpretation risk is worth less than $1. Certainly nothing that has to do with safety, medical equipment, professional and industrial tooling, food processing, automotive (pressures, temperatures etc.). An one segment error leading to a 30 PSI reading when the pump is set at 90 could mean instant death when the tire blows up.
  - bsder 6y ago
    > there are very few applications where the misinterpretation risk is worth less than $1 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.

thebruce87m 6y ago

The STM32G0 line might surprise you. It’s a Cortex M0+ and allows using SPI flash for graphics assets: http://blog.st.com/x-nucleo-gfx01m1/ http://blog.st.com/x-nucleo-gfx01m1/