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Comment by argvargc | Hacker News Reader

Genuine question: what are some practical advantages of a split-flap display over, well... any other kind of dynamic character display?

The only two I could think of are:

- they don't emit light, so maybe there could be some kind of light-sensitive situation where this would be required (though in that case e-ink would surely surpass it).

- the sound passively-alerting those present to updates. It's not obtrusive or attention-getting like a bell or spoken announcement, so only those wishing to notice the updates can listen for the sound, while others can go about their business unperturbed.

Anyone know of, or could imagine any others?

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- Visibility angle is much better than any other alternative. This is crucial when one big display is used in a very large room instead of many small displays.

- Image sharpness and contrast is excellent. You can read text on an old flip display far away that you would struggle to read on a modern LCD if you have mild astigmatism.

- Perfectly readable on a sunny day.

- They can show colored logos and symbols (e.g. train type, airline, highlight warnings)

- Better failure mode than LCD: single digits fail independently from each other and can be replaced. But it's less likely that the entire display fails.

- They are either working or stuck - no fading out like CRTs.

- oddly pleasant sound indicates change in data

Nostalgia, really -- I have fond associations of these with childhood train journeys.

I could just about imagine a genuine use case in some kind of hostile environment. You could probably make one of these very resistant to water/temperature/radiation, with the controller kept safely out of the way.

That sparked an interesting idea: would these work in a zero-gravity situation (mechanically I mean), and if not, how to adapt them so they would?

(And agree with the nostalgia - I'm sure for many the sound is associated with a quiet anticipation or excitement of embarking on a journey.)

They probably won't.

After a flap has passed the upper lip, which is kind of holding it back to have a precise "flipping point", gravity will take care of moving it down.

No gravity, no flap. ;-)

You could use suction or flow of air to overcome this. Or perhaps even a spring.

Or just some kind of display that does not rely on gravity, yes.

> how to adapt them so they would?

Add rotary springs (is this a valid term?) to the flap hinges so they're forced down once released from the top edge of the frame.

I think they'll work... Somewhat? As the card is pushed through the face, there's a small amount of spring energy that it stores by bending, which gets released when it makes it through the opening and propels it forward + downwards. Normal gravity just adds to that motion and keeps the flap moving down. Zero g doesn't help as much but the card should already have momentum out of the gate. In zero g the problem may be more dealing with the rebound as the flap hits the bottom of the frame - it may bounce back up and float. May need some dampening or magnetic trick to keep it down...

In any case they probably won't work upside down.

I used to have one of these, but left it above the radiator. All flaps warped beyond repair :( So if you're going for resistance to harsh environments you'd have to source a better material for the flaps, at least.

Hm, after watching and listening to videos of these displays at airports and train stations (don't think I've ever seen one in person), I thought the flaps in the commercial ones were made of thin sheet metal because the flipping sound was somewhat sharper than the OP version.

The traditional uses of split-flap displays were sports arena scoreboards, airports and train stations.

i.e. places where you want a very large display that's readable in direct sunlight.

If you were equipping a train station or airport in the 1980s, your options were split-flap displays, CRTs with sunshades over them (maximum size ~20 inches), a multi-CRT video wall ($$$$$$$$), a vane display (numbers only) or a flip-dot display. And a lot of places that were equipped with them in the 1980s still had them in the late 1990s.

These days you'd use an LED display, or a sunlight-readable TFT.

When I was a kid our hifi-system had a split-flap clock built in (around 1980 or so)

Worth noting not all LED displays are sunlight readable. Typically, outdoor requires old fashioned through-hole, separate LEDS, and at least 1/4 duty pwm refresh.

> And a lot of places that were equipped with them in the 1980s still had them in the late 1990s

Many UK rail stations had them into the early to mid 00s. If I'm not misremembering, the boards at London Kings Cross were not moved to different tech until at least 2005. Manchester Piccadilly had them replaced around 2001 (at the time I was passing through there a fair bit, travelling between York & North Wales).

I had never realized that the original Sony Jumbotrons were CRT (one CRT per pixel) https://youtu.be/AclwH64eAkU

As someone who used to travel a lot by rail in the not so distant past, every station that replaced one of these boards was a downgrade. Most stations had maybe 1 or 2 of these signs with the rest of the smaller ones already LCDs, so it’s not like there weren’t already places to get the info you couldn’t show on a sign like this.

Part of the problem with the LCD signs is they show too much information. It’s not really an advantage to show the next 30 trains incoming on the big board when only the closest 2 or 3 have gates assigned. They also tend to be themed in colors that are harder to read (Amtrak does blue on white, which is harder to read than white on black). Some stations tried replacing the split flaps with single-character LCD displays to mimic, but they always ended up breaking faster (and never getting fixed) for some reason.

From what I recall in an article about these signs, industrial versions were ungodly expensive to begin with, but the real reason they’re being replaced is that the companies that originally made them are all out of business and you simply can’t get parts for them. It’s cheaper to replace an entire LCD panel than it is to fix one of the mechanical signs once and you don’t have to wait 6 weeks with a broken sign for parts to be manufactured.

similarly to an e-ink display, it doesn't take energy to show the current/last status, it's required only for transitions. If there's a blackout, the display is still visible.

> If there's a blackout, the display is still visible

And dangerously out of date in airports and train stations.

When they break down they had to be covered to prevent misleading passengers.

- they don't require energy to maintain their state - a property which they share with eInk displays, but a split-flap display is unrestricted in size.

- assuming a fixed output selection, a split-flap display can also achieve far greater visual quality than other competitors like flip-dot displays

- defective units can be automatically detected (by comparing the position of the indicator magnet), whereas stuck pixels in flip-dot, matrix or LC displays require a human to spot them

Zero power needed to retain image, not encumbered by e-ink patent and manufacturing monopoly, simple and repairable, and you can build it yourself at home

Readability and ultra low energy consumption (plus: they are awesome and produce a soft sound like a distant waterfall).

Also, contrary on what I have seen on LED matrices or other RGB/pixel based displays: they won’t display advertisement which otherwise manages to sneak in – too close to information.

I wonder how their energy consumption actually compares. Electric motors moving relatively heavy physical cards is far from free. I wouldn't be surprised at all to find that an eink display beats the pants of of a split flap display in terms of energy consumption, but I don't have the necessary equipment to test it.

They offer high resolution full color semi-dynamic display without needing any semiconductor circuitries.

You can simply fabricate the flap by cutting the flap to dimensions and affixing letterings onto them. That’s not possible with LCDs or LED arrays.

There is the advantage of extremely high resolution and crisp contrast. The digits can be printed in any colour and on (kind of) any texture you like. It scales also very well to very large displays.

The contrast is very high, so easy to read in bright sunlight

To me it's as simple as they look really cool and satisfying.

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