A Small Favor

[MICHAEL GARDI]

Hi,

 

I'm thinking of making another version of the Type 30 Display that is somewhat smaller than my current version. I love the way my Type 30 turned out but it feels a little too big and takes up a lot of desk space (and it's already 2:3 scale). The original was a beast! A smaller version would also allow me to use a cheaper display panels and would be more amenable to employing PCB construction down the road. Before I start I would like to get a handle on what scale the PiDP-1 is compared to the original PDP-1 Console. To that end, could I get someone to send me the measurement of the PiDP-1 Console at it's widest point. 

I know that Oscar based the scale on the flat LED size. With this measurement I should be able to get a good approximation of the scale compared to the original.

Don't be afraid to suggest what you think would be a good size, say based on the diameter of the Display's round cutout? For reference the original was 16" in diameter and my reproduction is 10.5" in diameter. 

Thanks

Mike

[Matthias Barthel]

My Display ist printed around a 5" round display. The width ist about 18 to 15cm in height

For me is the size ok. Only for spacewars its a bit to small

Matthias 

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[R Clark]

That width you asked for is ~11 inches across the PDP-1 Console.   My Type 40 round display is same as above -- a waveshare  5" display. My display was built with the PDP-10 rack mount version in mind.

[Bryce Jeannotte]

Just a bit of data that I pulled together.

The Pimoroni PIM-431 10" 4:3 display is 5.8" tall and 768 pixels. 

The  Pimoroni PIM-372 8" 4:3 display is 4.9" tall and 768 pixels.

The Waveshare 5" round display is 5" tall and 1080 pixels.

There might be an advantage to going with the 5" round display. 

Perhaps a Display round cutout of about 8" if you want to closer emulate the Type 30's actual CRT to image proportions, or you could go to 6.25" and be able to print the entire Display Mask part on a 250mm x 210mm print bed. 

Bryce.

[Michael Gardi]

Hey All,

I’m trying to understand how the round display works. Does the PiDP-1 output show up as a smaller square inside the round display? Or asked another way how do the 1080 x 1080 pixels map to the round display?

Mike

On Oct 8, 2025, at 2:39 AM, Bryce Jeannotte <bryc...@gmail.com> wrote:



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[Oscar Vermeulen]

I’m trying to understand how the round display works. Does the PiDP-1 output show up as a smaller square inside the round display? Or asked another way how do the 1080 x 1080 pixels map to the round display?

The round displays pretend to the Pi that they're square and just do not display the corners.

 

Kind regards,

Oscar.

[MICHAEL GARDI]

According to the Computer History Museum the width of the PDP-1 rack was about 27 inches. So I brought this photo into Fusion:

and "calibrated" the image to 27 inches (top blue line). Then I measured the width of the console (bottom blue line) which was 20 inches. So based on the similar PiDP-1 width of 11 inches I calculated that the PiDP-1 is about 55% the size of the original PDP-1. 

Sorry, it's not really all that important but I just tend to get hung up on stuff like this. With respect to wanting to make a smaller Type 30 display it turns out that a 55% scale works out almost perfectly for using the [Pimoroni PIM-372 8" 4:3 display is 4.9" tall and 768 pixels] that Bryce was kind enough to enumerate above. It just feels more right to me that the Type 30 Display is the same "relative size" as the PiDP-1.

Mike

[Oscar Vermeulen]

Hmm! I said scale 2:3 but actually that might have been a mental shortcut.

Here is the most important  measurements I got from Bob Rosembloom @CHM.  (PDF attached).

(Caveat, there might still be some errors in this PDF, there was a long an winding process. But I think this was the final version)

The line you highlight is 19875 mils (504.825mm) on the real PDP-1. It's 283.21mm in the PiDP-1.

...crunching... the exact scale is then 1:0.561.

You're right.

Kind regards,

Oscar.

[Oscar Vermeulen]

CAVEAT: if you ever use that PDF for anything substantial, be aware there are still some minor errors in the placement of parts (lamps, text) in that PDF drawing. The outline I believe is double checked to be correct though. But let me know if anyone needs exact drawings and notes from the whole process.

[MICHAEL GARDI]

Nice to have confirmation. Thanks Oscar.

Mike