Restoring an unusual vintage clock display | Hacker News Reader

Restoring an unusual vintage clock display

tinkerings.org

70 pointsmmastrac14 comments

Open articleView on HN

These are known as "projection displays":

http://www.decadecounter.com/vta/tubepage.php?item=10

http://www.decadecounter.com/vta/articleview.php?item=989

One company that makes them is still around:

http://www.ieeinc.com/about-us

A lot of other interesting old display technologies here:

http://www.electricstuff.co.uk/count.html

Thanks for the links. I was curious to know how each digit is projected on the same place. Looks like the masks are on a curved plate.

Oh, those things. I used to use UNIVAC 1108 computers, which had the system clock on the console with those displays.[1] It took about a hundred small printed circuit cards to drive the thing. It actually was the system's time of day clock, read by the computer, not a remote display of a counter elsewhere. If the muffin fans under the console were not regularly cleaned, the clock would make intermittent errors, which caused the operating system to have problems. I once had to write software to detect this.

[1] http://www.silogic.com/Athena/Univac%201108.html

Here's a guy who used a two digit "one-plane display" like this as a "period correct" digital speedometer in his 1973 beetle.

http://thegarage.jalopnik.com/project-make-the-weirdest-peri...

"Which, for a clock showing HH:MM:SS, means 72 light bulbs to replace."

??? There are only ten digits, and you don't even need all of them everywhere. By my reckoning, you would need 3+10+6+10+6+10=45.

If you add the ability to display dd-mm-yy, you till would only need 3+10+6+10+10+10=49. I wonder what they did with the remainder. Spelling out the word "ALARM!"?

Or did they simply ship spare bulbs inside the product?

I would imagine they wanted 6 identical modules just for the manufacturing efficiency.

That still leaves the question of why 12 lights instead of 10. I would bet that the separator colons are actually produced by a separate mask+lamp, rather than having different masks for each digit on those two modules. I.e. to show "8:" you light up both the "8" lamp and the ":" lamp at the same time. That gets us up to 11. No theory on the 12th one though.

Suspect it's just that the devices are a generic component, the application for projecting digits is just one possible application of a projection indicator. The physical constraints of the design require a rectangular projection array. 12 projectors, a 3x4 array, fits in a reasonable aspect ratio area. A 3x3 array would not suffice for this application, a 4x4 array would be overkill, and a 5x2 array, while optimal, would not fit well in the space available.

One for each . In the colon?

Almost certainly this. In one of the links by another commenter here, you can see a voltmeter where the guy changes the decimal. The dots are bizarrely high to be a decimal point, but right where you'd expect it if it's the bottom dot on the colon.

I didn't find that video, but several of these seem to be British made. The decimal point in British use was traditionally centred: 3·141.

(I still write it like that, in handwriting.)

These displays were made with many different mask options, including symbols and letters. I have a set where one mask is red (to give an optional red background to the displayed digit). For metering applications there were + and - masks. Etc.

> there were 12 bulbs, 12 masks, 12 lenses per screen

The detail for what the extra masks were for is unclear, but it does look like there were 12 per digit.

I had figured that it would be about NIXIE tubes but was happy to learn about something I hadn't come across before. Pretty neat.

Here's an interesting channel on youtube I came across and the newest video happens to be about the NIXIE tube. https://www.youtube.com/watch?v=jytF5bvPGcU

When I was a kid, my dad would sometimes bring home scrap electronic equipment from his lab and I'd have fun taking it apart. I remember one of those displays, with the arrays of tiny bulbs.

Reply on news.ycombinator.com