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6 segments suffice

A rethink of the number of segments required to display a digit

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A half-century old project finished

History

Did I invent this? No and yes.

No because I was inspired by a Sharp calculator display I saw some 50-60 years ago, with a display shown on these pages:

http://www.vintagecalculators.com/html/sharp_qt-8d.html
http://www.mrmartinweb.com/calculator.html#sharp
http://www.vintagecalculators.com/html/sharp_el-811_-_derivatives.html

This is possible only because of VFDs used at the time. The first article didn't latch onto the distinctive font other than commenting on the half-height zero. The second article mentions "strange shaped" numerals but didn't analyse them. The last article has a good close-up of the VFD tubes showing the arrangement of the segments.

You can see that the Sharp display actually uses 8 segments. However it is possible to do away with the two vertical segments for a decrease of readability of the 1, 4, 7 and 9. The half-height 0 is irremediable.

Yes because in reducing to 6 segments I have altered the original font. This was inadvertent, my memory played a trick on me and I had forgotten about the vertical segments.

How readable is the font? Let's see:

2, 3, 5: curvy like they should be
6, 8, 9: tolerable
1, 4, 7: the diagonal stroke compromises them
0: half-height, there's no getting around that

The half-height 0 was claimed by one of the references above as a perverse advantage before leading zero blanking was available. 😹

Looking at the board, I realise that pairs of digits are too close. The space between the 2nd and 3rd digit is alright. There are tracks for a colon there, but it doesn't work there.

I don't think this will displace the 7 segment font in use; that ship has already sailed. If anything I think the 14 or 16 segment displays are best and can also display the alphabet, but economics is against them

Another question is since I'm already using 6x4 = 24 LEDs, why not just go to 35 in a 5x7 matrix and then I can have a decent font? Good question. Well 50% more LEDs for one thing, and more drivers for another thing. But controllers are cheap enough to deploy one per array using multiplexing and accept serial input (SPI, I2C, etc), which could be 8 bit characters. Then cascade for more characters. Or just use those off-the-shelf 8x8 LED matrices.

So more than half a century later a very old project completed. 😹 I'll make displays with this font for novelty gifts, because it only takes a moment to grasp, then comes curiosity.

The board design files have been published at https://hackaday.io/project/175397-6-segment-2-digit-led-display-board

I might have a go at the 8 segment font some day.

  • 6 segments reloaded

    Ken Yap02/05/2022 at 12:34 0 comments

    A final go at a 6 segment font

    Some time after I published my experiment in a 6 segment font I decided to see if I could apply the lessons learnt and improve the font a little before closing off this line of experimentation for good.

    I decided that:

    • Curved segments with only a few dots were er, pointless. I decided to make all the segments straight lines. Somehow viewers are more forgiving if the lines are constrained to be straight.
    • Keep the digit upright, a slant doesn't look good.
    • Use symmetry.
    • Close the gap in the middle, most visible in the 5 in the initial attempt.
    • Implement a high-zero, which would partly compensate for the half-height zero. This was the one change that spurred me to make another attempt.

    I first laid out the LED positions in KiCad and made a print of the silk screen layer of the PCB. Then I filled in the dots with a marker pen to give me a preview of how the font would look. It was promising so I went ahead and ordered 5 boards from ALLPCB.

    In addition, the positions of the LEDs on the board made it possible to have a reasonable colon again, although this is not demonstrated here.

    The link to the design files for the board on GitHub are in the links section.

    I do think it's an improvement over my initial effort. It's too late to displace the 7-segment font, and high-resolution displays are so much more attractive wherever they can be deployed, so this is just me tinkering. I think the best I can hope for is for a futurepunk film or video to make use of this strange looking font. 🤗

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Eduardo wrote 09/28/2021 at 16:57 point

Sorry for come to ruin the party but... "the Sharp display actually uses 8 segments" Its actually 9 segments (without " . " and " ' ").

Your'e forgetting the segment that is only used for the number 4. However are a version of this display with just 8 segments, that forgets that segment for the number four, but was made for just one calculator, a "mini" model, so the display losses readability thats why they quit that segment.

Yhea, the numbers 1 and 4 in you're display are a crime... my brain its reading: /23yS6789໐ (the number seven have good readability).

You really can find a way more easy solution for the zero dilemma on your dot layout, just forget the multiplexing. 

And for do big low resolution matrix better use a LCD that are extremely cheap this days, just follow your heart and use as many LEDs you want to fullfill your dreams without following any grid.

  Are you sure? yes | no

Ken Yap wrote 09/28/2021 at 22:26 point

That extra segment for 4 was also proposed for the 7 segment font, an early calculator chip had an extra pin for it but that feature never gained traction. Going from 8 to 9 segments also crosses an important cost border, the 8 bit byte, and economics wins. Also curved segments really only work well with VFDs (and LCDs, but that was too late to rescue the font) and don't work as well with LEDs with light diffusers. Attempting to improve the strokes with more point light sources simply is a step towards high resolution matrix displays. Having scratched a decades old itch, I decided to leave it there.

  Are you sure? yes | no

Mark Jeronimus wrote 10/19/2020 at 14:37 point

Since you already use discrete LEDs instead of solid segments, you could diode-OR signals together such that LEDs at crossings (like the "5") light up when either of the adjacent segments is ON.

When you've mastered that, you could extend the horizontal bar of the "4" one more LED to make it more obvious

  Are you sure? yes | no

Ken Yap wrote 10/19/2020 at 15:01 point

That adds complexity to the circuit as I have to take into account the differing voltages of the segments for the current limiting resistor, unless using a constant current IC. Remember too that the digits are multiplexed so at first glance I'm not sure where the common LED can be inserted. And there wouldn't be much gain for it; it would still be a novelty font. There are however a few shape tweaks I have considered which I have noted in the details of #6 segment 2 digit LED display board 

  Are you sure? yes | no

Ken Yap wrote 10/18/2020 at 21:01 point

Oh wow! Better enjoy my 15 minutes... 😉

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crun wrote 10/16/2020 at 03:33 point

Clive Sinclair is pissed that he missed  a cost down.....

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Ken Yap wrote 10/16/2020 at 03:35 point

Haha, I saw that discussion on EEVblog too.

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Dan Julio wrote 10/16/2020 at 02:17 point

Well done!  My boyhood best friend's father - an accountant - had that calculator.  I remember sneaking off to play with it when I would stay over.  And I never forgot that strange display.

  Are you sure? yes | no

Ken Yap wrote 10/16/2020 at 02:39 point

Great thanks, someone else who also remembers. Gotta hold on to memories!

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Dan Maloney wrote 10/15/2020 at 20:01 point

Gotta sort of cross your eyes a little and use your imagination, but I can see what your doing here. Nice work!

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Ken Yap wrote 10/15/2020 at 20:21 point

Thanks! It was a lovely feeling of closure to make an old idea concrete.

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