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Comment by eschneider | Hacker News Reader

Ah, but 7-segment displays are far easier to drive from a microcontroller, so even if an LCD is cheaper, it might make for a more expensive system.

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> Ah, but 7-segment displays are far easier to drive from a microcontroller, so even if an LCD is cheaper, it might make for a more expensive system.

It's not all about economics either; I can read a 7-seg display from clear across a factory floor from almost any angle in the dark.

Try reading those low-cost LCDs in the same conditions (the dark is worse, because the LCD doesn't have a true black so the contrast is lower).

Which is why standalone digital clocks generally still use them instead of LCDs, and why I'd like to build a 7-segment clock at some point. That condition-agnostic readability is hard to beat.

The reason why most standalone digital clocks use LED seven segment displays is that to this day almost all of them are built around the same weird PMOS Sanyo ASIC from late 1970's.

OLED suggestion is even worse due to lack of longevity, burn-in.

> I can read a 7-seg display from clear across a factory floor from almost any angle in the dark.

Ironically, this is true at lower power/brightness than higher. A few gas stations near me got newer super-bright displays and you can no longer make them out at a distance.

> I can read a 7-seg display from clear across a factory floor from almost any angle in the dark

Is it dark when you are on your factory floor? And what is it that you need to read across the factory floor?

> Is it dark when you are on your factory floor?

Some equipment is placed directly under bright lights.

> And what is it that you need to read across the factory floor?

I don't understand the question. I mean, machines in a factory display something for the operator. If a machine doesn't need to display anything, why have a conversation about 7-seg LED vs LCD?

Also i don’t entirely understand the LCD vs 7-segment comparision. In my mind many (perhaps most?) 7 segment displays use LCD technology.

Are we comparing here pixel-matrix LCD screens with 7-segment screens?

Some 7-segment displays are vacuum-fluorescent rather than LCD. These displays are significantly brighter.

Legacy 7-segment displays use LEDs. Specifically, one LED per segment. The LCD version arose when the power consumption of the LED-based ones was an issue.

You're correct. 7-segment is a display layout, not technology - I think it's implied they mean pixel matrix vs 7 segment.

I'm not convinced that matters much in 2024, especially when this article singles out safety critical systems. Such systems are likely to be fairly expensive to being with, so the marginal cost of adding a display would be minuscule compared to testing and regulatory costs (not to mention the increase in fault tolerance versus a failed segment causing an incorrect reading).

A cracked LCD screen also makes the display unreadable. There are all sorts of ways for anything to fail, so calling out one failure method of one thing while ignoring similar failures for the device being compared comes across as very short sighted

Yes but a cracked LCD is much more obvious than a single LED segment burning out. Also usually physical damage is required to crack an LCD, where as LEDs can burn out (albeit rarely)

The thing I hate about low cost LCD displays is that terrible motion blur when you have changing or scrolling text. It just screams cheap in my mind. 7 segment never had that problem.

I'm not a professional, but I find an LCD or OLED is a lot easier to drive from a microcontroller than a 7 segment or 4. Like a hell of a lot easier.

Depends. I2C only takes two I/O pins.

That’s only part of the equation. Grid displays require a lot more memory and often power to drive. By contrast, a seven segment display requires 7 (or 8) LEDs and 8 bits per digit on the output stage, 4 bit in BCD, which can be fed via a shift register.

Almost any other display that you will reasonably use in a application that makes sense for segmented multiplexed LEDs will integrate internal controller, so instead of having to refresh the thing somehow you have a thing that is simply an peripheral hanging of some or other bus that just does its thing. And well, such things tend to be cheaper than seven segment LEDs (there is a reason why random almost disposable crap has graphical monochrome OLED panels)

Granted, but as a sibling states, the other factor is firmware complexity. I can theoretically drive a high-resolution display on an 8-bit micro (although it may require with some clever bit banging to get I2C to work at all) but its trivial with a 7-segment display.

And as a bonus, you don't have to involve anymore UI/UX design than to answer the question "what number should go here?"

It'll be microcontroller equivalent of running full GNU/Linux to control an Internet of e-waste tea kettle, but CH32V003 + SSD1306 OLED + passives takes less than 10 parts total, no crystals needed, has plenty sample codes online, and costs ~$2 combined. Depending on the price of the final product, it could make financial or product design sense.

In a medical or aerospace application, that added firmware complexity could be a non-starter. Not from a price, or even e-waste standpoint. Its that proving the thing is safe is a lot harder when its complex. That's the real point of keeping it dumb.

Most LCD displays are custom: there are Chinese manufacturers that will design your LCD display and embed a SPI/I2C decoder for very low cost, so the simplest 8-bit PIC can drive one at 1 MHz (or less!)

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