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.