Lots of clocks make use of Nixie Tube displays, but a much rarer type of display exists. It's an electromechanical incandescent display based on an array of tiny projectors, all sharing a ground glass rear projection plane.
The displays make use of a small piece of film and 12 lens systems to project whatever of 12 images you want to provide. In this case, the displays show the digits zero through nine and lefthand and righthand decimal points.
Clock power entry.
In the 1960s, these displays would cost more than $100 per digit. Since the cost and size of these displays would have made building a clock with four or six digits prohibitive, I chose to make a single-digit display. In an added twist, I used a mechanical relay to sound out the hours and mark the quarter hours with variable-length clicks for quarter, half, and three-quarters past the hour.
Mechanically, the clock was assembled under a craft store display dome. The esthetic is inspired by steampunk, with as much use of wood, copper, and brass as the budget allowed.
The processor and drive electronics reside on a generic PIC16F88 processor prototyping board with the clock-specific hardware, point to point wired in the bread boarding area. The switches and displays are harnessed to this, and the wiring harness is bound with wire lacing cord the old-fashioned way.
David Christianson's inline clock has an electromechanical incandescent display based on an array of tiny projectors sharing a ground glass rear projection plane.
An AC adapter provides 12V to the circuit. The display and chime relay are powered directly from this bus. The voltage regulator U1 drops this 12V to 5V to power the processor. The processor is configured with a six-pin modular jack to facilitate in-circuit programming and debugging. The processor is clocked at 32.768kHz to make time keeping simple.
Transistor amplifiers provide the power and voltage gain from the digital logic signal from the processor to the levels necessary to power the incandescent bulbs in the inline display. The digits of the inline display are illuminated one at a time by powering the incandescent bulb for that digit.
Setting the clock required a little ingenuity, because the processor had only a single pin available. This was accomplished with a little code that detects whether the switch is connected to VCC or to GND, to advance hours or minutes.
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This is a really cool device and I too love the steam generator look. It triggered a couple thoughts. the time is fast approaching when I will have exhausted my stash of 100 watt incandescent bulbs and I will be forced to fork out the exhorbitant cost of inferior replacements. I am sorry I did not buy more, but I really thought the politicians would come to their senses. How dumb was that?
Then to see C-130 in print made my stomach do flip flops when I remembered the bumpy, jerky ride in those monsters. Guaranteed that at least one guy would heave and there were no barf bags to be had. But not all was bad since one of those things provided a part of my trip home.
I also noticed the hand-crank telephone generator in the background. I had one of those too, and some of the projection readouts. Sometimes, you have to cull, though...
I have a bunch of them, new old stock military surplus. $10 apiece if you just want a few for your own use and won't try to resell them for a profit. Will put them on ebay at some point for more money, but thought I'd give the guys here first crack at them. Films have various cryptic military-related legends on them so you'll need to make your own with numbers. Note that color is a definite option with these if you can make a color transparency or use colored LEDs instead of incandescent bulbs (not included, T1-3/4 size)
I've been dragging these around in my junk bin for 30 years, since I was a student. When I was a student tech in a physics lab, we would scavenge old equipment for parts. These were deamed obsolete at the time, but too cool for the trash bin!
Unfortunately I didn't keep the big ones.
Search Ebay for "one plane readout", they are listed sometimes.
I think the bulb life is a function of the bulb, and how bright (applied voltage) you run it. This clock has been running for a year with no issues so far. Last time I checked they were still availble for this display anyway, its a common indicator bulb. Some of the types have a 300,000 hour MTBF so I think I'm good with it for my clock.
I remember these displays quite well. They were used on a specialized Xerox copier that I helped buld in the 60s called "System 3-2-1". They were made by IEE, Industrial Electronic Engineers of North Hollywood, CA. The company is still in business. See: http://www.ieeinc.com/about-us Also, there is a very nice descriptive page about the displays including a disassembled view at: http://www.decadecounter.com/vta/articleview.php?item=511
They were great. Much easier to deal with than Nixie Tubes. No special power supply needed.
I don't think an segmented display will look like a projector display because they are completely different schemes. The projector device is actually an array of miniature slide projectors, each with its own lamp, "film", and lens, but all projecting onto the back side of one screen. The "film" can be any image at all, which means that in the case of numbers, they can be formed complete in any font that one wants, rather than being approximated by means of segments. Of course one could use the appropriate images in a projector display to simulated a segmented display, but where's the fun in that?
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