NASA Apollo / Saturn V Clock / Countdown Display

Vintage 7 Segment displays salvaged from Kennedy Space Center control room, dating from the time of the Apollo missions

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As a collector of vintage technology (in particular LEDs and displays) I was very excited to find these rare 7 segment displays from a seller on ebay around a year ago. They have the wonderful history of being from one of the count down clock / timers from the launch control center / rocket firing control room at Kennedy Space Center and were probably used during Apollo / Saturn V lunar mission launches! Since this weekend is the 50th anniversary of the first humans landing on the Moon, I decided to share the project so far…

I bought 2 different readout displays with the aim of figuring how to light them up using modern LED technology and microcontrollers, and eventually build some clocks / timers resembling the original units in the firing room. At over $200 per digit it would be prohibitive to build a clock using these rare artifacts, in any case, I doubt there will be many more available for sale or that still exist. Hopefully through the convenience of 3-D printing and some hacking I can build enough replicas to build a 6 digit clock and make them available for other people to incorporate into other projects.

These displays are estimated to be well over 50 years old, and according to the seller originated from collection of Charles H Bell, who was apparently in charge of decommissioning / updating the control room for the KSC visitor center / museum. Initial inspection leads me to believe that they use 7 incandescent lamps to light up the individual segments, although I have yet to determine what type – there were very few early LEDs available at the time ~1969.

2 different types of NASA 7 segment displays
"Type A" (left); "Type B" (right).

 The displays are machined from solid chunks of aluminium and have heat sink/cooling fins – presumably if they did use incandescent lamps, these would get hot and needed to dissipate the heat.

Type A display
Showing the chunky heat sink fins and thin front mask

The smaller type of the displays (I will refer to as TYPE A) uses a metal plate with cut-out mask and some kind of diffuser - it is very thin and looks like fibre glass or a very PCB. I am not sure how the mask was created but it looks like it may have been etched from the metal material which looks like brass or copper. The mask is riveted to the main body.

Initial ideas for producing a replica assembly consisting of 3 main parts.

(1) Front face mask:

  • (a)Multi layer mask with laser cut vinyl stuck on thin diffuser material.
  • (b)Black PCB with pre-cut cut apertures for segments
  • (c)Laser cut acrylic filled with opaque epoxy filled segments

(2) Central body/housing:

3D printed plastic body with holes for lamps; CNC aluminium would be awesome.

(3) Back plate PCB

To house the LED lamps, resistors and wiring. The PCB would connect through a bundle of 8 wires. Further improvements would be to put a dedicated microcontroller on each digit, like the Texas Instruments TIL-311 or Hewlett Packard latched BCD displays to reduce the wiring burden.

Lighting up the original "Type A" display.

After various experiments shining LEDs through the holes, I decided to use a diffused 5mm white LED, and got to work marking on a prototype PCB the hole positions.  The next task was to layout LEDS as close to the hole positions and connect in a common cathode configuration. I soldered 7 current limiting resistors (200 Ohm) directly to the back, and made a connection loom via single core hook up wires. 

Rear view of Type A housing and the prototype LED module
Type A display and LED assembly
Type A display
All segments lit up

Conveniently I had already built a tester based on an Arduino pro mini for 7 segment numitron / pinlites (project write up coming soon) so have used this for initial testing.

Arduino Pro Mini tester
7 segment display tester wired up
Type A display
LEDs lit up to display number 5

Further development is underway, I have various photos of the segments lit up from 0-9 and some alphanumeric characters in testing – perhaps someone could make a virtual clock using these images.  I would very much welcome comments and suggestions… are there any NASA engineers out there?!

The larger displays (referred to as TYPE B) use internal reflected light scattering to illuminate the segments and the cavities inside are painted with white paint..

Type B display

Presumably a side emitting lamp would work best for this design. For future development I might consider using a diffused epoxy resin to fill the segments, a sheet of paper or perhaps some opaque laser cut acrylic lenses .

Type B display (rear view)
Type B display
Type B display together with spacer and end support (front view)

Type B Display

Rear view of Type B display together with separator...
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  • A look inside the original countdown clock!

    Patrick Hickey07/30/2019 at 22:15 1 comment

    The seller from whom I bought the displays  (spacemissionmarket / eBay seller: rocket-broker  eBay Store) kindly sent me some photos of a partially disassembled “Type A” clock, showing the wiring and PCBs with 8 digits and +/- symbol. Thanks to Diana and the owner of the clock, these images are a tremendous help to the project. I had not seen these images when I built the LED test PCBs; they look remarkably similar, but of superior build quality, which you would expect from NASA! 

    Complete clock assembly
    Clock complete with front panel. Image courtesy of Space Mission Museum & Market
    Internal wiring of clock assembly
    PCBs, wiring and digit separators. Image courtesy of Space Mission Museum & Market

    I cannot clearly make out bands on the carbon composition resistors, but it looks like brown/yellow/red which would make them 1400 ohms. A lot of aircraft control panels use ~ 28 Volts supply so perhaps these are current limiting resistors to operate 5 - 6 Volt lamps around 20-40mA?

    Close up
    Detailed view of PCBs. Image courtesy of Space Mission Museum & Market

    There is seriously big loom of wires; they are colour coded Brown, Red, Orange, Yellow, Green, Blue, Violet and it appears that Violet connects to segment “a”; Blue segment “b” etc… Looking at the cross section of the cut cable bundle, I’m assuming there’s a total of 56 wires for the 8 x 7 segments and 2 for the +/- indicator.  

    Details of clock housing and internal mounting.
    Rear enclosure cover and mounting using spacers. Image courtesy of Space Mission Museum & Market

    It appears that the common connection (cathode / anode?) is connected in parallel to all digits, as there are 2 black wires linked on each PCB. From this I would deduce that the displays are not driven by multiplexing, indeed if they are incandescent bulbs these would be too slow for strobe control.

    Rear of clock showing PCB assembly.
    The +/- indicator is on the right side. Image courtesy of Space Mission Museum & Market

    I am hoping to find out more about the types of lamps used, and I am also curious about the colon separators, are these illuminated at all? 

    Finally, I have discovered a you tube video from Fran Blanche who has 3D printed a segment display which looks almost identical to the "Type B" units, however there is no reference to their use in the NASA control room equipment. It would be interesting to check the dimensions on the drawing files and compare to the original artifacts. Instead of 3D printing a plastic backing I would probably use a white PCB to help reflect the light through the segments. 

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Alysson Rowan wrote 01/08/2020 at 18:38 point

I love these old displays (even though they are electrically thirsty and get awfully hot). Re-creation of the designs is one of my great vicarious joys - and one day I may even reproduce some Dekatron counter tubes using LEDs.

Having had some experience with this style of display (but not these actual units), the lamps are probably: 90V wire-ended neon tubes with thoriated electrodes were often used. The 1400 Ohm 250mW resistors on the original would suggest this to be the case.

Under-driven 36V or fully driven 28V wire-ended peanut bulbs might be used, but these wouldn't require resistors, and would almost certainly overheat the display regardless of the cooling fins.

The diffuser/masks on your Type A will be ~0.25mm glass fibre PCB with chemically blackened etched copper masks. Multi-message status arrays using this style of mask used to be popular - 1 lamp per message.

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colton.baldridge wrote 08/20/2019 at 01:54 point

Any chance of a 3D model of either type? Would love to replicate this myself

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Pataki 'Ash' Ábris wrote 09/19/2021 at 19:45 point

A bit late for the show, I am, but I was messing around with the smaller one. Not printed it yet, but got an about 90%isly accurate 3D model of it, I can definitely drop it to you, if you are still interested. Probably gonna get around to do the bigger one, with the spacers too eventually, but I might get distracted, so it could take weeks.

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colton.baldridge wrote 09/21/2021 at 05:15 point

Heck yeah! Funny to see someone still looking at this 2 years later. If you can model the metal part, I might get around to designing a PCB to get a working one as a clock for another project.

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sjm4306 wrote 07/31/2019 at 12:20 point

It'd be easy to recreate the front pcb by setting the soldermask and copper pour restrict layers to let light through just the segments. I did something very similar in my word clock and it is cheap and very effective to give a similar effect as the original.

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Tom Nardi wrote 07/21/2019 at 05:12 point

Creating the 3D model of the Type A should be easy enough; you could put that right on a flatbed scanner, convert the image to a DXF, and then import that into your CAD software of choice to scale it to the proper X/Y dimensions and give it a Z dimension. Unless there's some internal baffling to keep the light from bleeding through to the adjacent segments?

Incidentally, I'm fairly sure I've bought stuff from this same eBay seller, and have seen them list very similar (the same?) digits as these. As Ken said, glad to see you trying to document/replicate them for others.

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Ken Yap wrote 07/21/2019 at 01:09 point

Fascinating. Thanks for rescuing these displays and posting their history and workings. Looking forward to updates.

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