A (reasonably) low cost remake of the PDP-11/70

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This is a remake of the 1975 PDP-11/70, the very first computer you could buy a unix for.
It uses the same approach as my PiDP-8, using a modified simh on a Pi, hiding behind a replica front panel. Thanks to simh, it runs pretty much everything: From Unix v6 to Ultrix to 2.11BSD to RSX-11M+... multi-user and all.

This time, CAD design was my learning curve; to reproduce the iconic PDP-11 in spirit, the replica had to have a case with the same slanted, white panel frame. Custom-made switches were also part of the Challenge. Couldn't do without.

Remaining project planning: polishing up the software (May-June), next run of kits in June

In terms of electronics and software, the PiDP-11 is similar to my PiDP-8. The PiDP-11 turned out more costly to make, because of the custom case (injection molding!). I hit the upper limit of the design goal: to stay under $250.

The molds for switches and case will hopefully be useful for other PDP-11 projects as well. The idea is to have these parts available as 'open-source molds'. If such a concept exists. :)

(update - in fact, a plug-in FPGA board for the PiDP-11 is being worked on as part of the PDP2011 project, in case simh on a Pi does not meet your needs)

  • 1 × Raspberry Pi +/2/3/3+/Zero/Zero W
  • 64 × 5mm LEDs, red
  • 37 × Diodes 4148
  • 1 × UDN2981A or equivalent Interface and IO ICs / Peripheral Drivers and Actuators
  • 30 × Custom made switches

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  • Done! The PiDP-11 kit is live

    Oscarv05/13/2018 at 13:58 3 comments

    Ouch - the last update here was almost a year ago to the day.

    As it turns out, injection molding is not for noobs. Many thanks for all the help I got from here, including the massively helpful final check before the mold was made. It only took me 350 revisions of the CAD model, and 30 more from others... And it took custom-made brass inserts to hold the bolts in the case. So Iearned a lot, but it can be summarised: if you consider injection molding for a hobby, don't.

    But! The first 20 PiDP-11 kits went out to beta testers, and other than a slightly too-short hex spacer, no problems during the final shake-out! So here it is, the brand-new PiDP-11/70:

    Over the last few weeks, I've made a web site for the kit, and a Google Group is live as well. Now, the focus shifts to polishing up the (currently pre-alpha) software, and kits will go out from next month. Here are the kit contents:

    Stupidly I forgot to put the back panel of the case in the picture, but it's on my site anyway. That back panel taught me about laser cutting (press-out slots for connectors etc), and after injection molding, that is the way to go for any following project. Easy, low-cost and very precise results.

    I'll post some more updates in the coming weeks. As the PiDP-11 is a simh BlinkenBone device, I just wrapped up a virtual PiDP-11 with Jörg's virtual 11/70 front panel. That'll add to the fun as we go about building a right proper PDP-11 Software Museum into the software. From RT-11 to Unix v5/6/7 via Ultrix to 2.11BSD to RSX-11M Plus with networking, it should all be there of course!

  • Case Progress

    Oscarv04/05/2017 at 13:53 2 comments

    It's been a good few months without an update. Real Life interfered, as it does. But also, I had lots of trouble getting the CAD design ready for injection molding. Stuff you don't think about: selecting brass inserts for screws, and how they should fit in the plastic. Controlling cost by ensuring a hobbyist can mount the inserts himself...

    Hopefully, a professional checkup on the CAD file means it is now good to go. One more 3D printed prototype to check these inserts, and then the case should be done.

    About time, the rest of the project was done 6 months ago. I'm curious if at the end of this I feel injection molding is just a horrible idea for hobbyists, or whether I just was slow climbing the learning curve. We'll see.

  • Case prototype arrives - PiDP-11 in its final shape

    Oscarv10/12/2016 at 18:32 0 comments

    Today was a great day - after 10 months, all the parts were fitted together for the first time. As a 3D printed prototype of the case just arrived.

    Excuse the bad photo quality, late at night again and I still have a low-tech camera that can't deal with dim lighting conditions. But actually, grainy pictures are a Good Thing because there's a lot of finer detail still to be done. The new case is just dropped over my prototype like a hood - not even screwed together yet.

    Still, a fiiiiine day for the project. The PiDP-11 will be pretty, now I know for sure :)

  • Switches! Lots of them...

    Oscarv09/12/2016 at 23:11 0 comments

    Well, it took months but today I got a batch of switches from the factory. Yay!

    That leaves the injection-molded case still to do... Hopefully more progress on that in two weeks' time :)

  • Colour matching - not as simple as you'd think

    Oscarv06/09/2016 at 22:35 3 comments

    The PDP-11 uses a very peculiar colour scheme. Getting the colours right is crucial to get that early '70s feeling across. Unfortunately, getting colour exactly right is much, much harder than you'd think. The problem starts with computer screens, which unless they are professionally calibrated do not show colours faithfully *at all*. Then, the manufacturer of my acrylic panels has the same problem, so I had to make a special acrylic bar with all possible colours to pick the right one.

    And now, I have to make sure the switch manufacturer delivers the exact right colour. Today I went to a local specialist shop, and identified the near-perfect Pantone colours for the switch manufacturer.

    That is, if anyone is ever interested, Pantone numbers 222 and 187. For fun or otherwise, below are colour sets I got off high-quality photos of the PDP-11. Even good cameras are off no matter what you do. Seriously, that is how far off you get without 'professional' colour calibration. It illustrates the misery of colour matching:

    I just hope the switch guys are precise with their colour matching. Otherwise, the test sample (minimum size 4000 switches!) will be a very expensive write-off :(

  • Test Samples of Replica Switches

    Oscarv05/23/2016 at 07:13 1 comment

    After 4 months of waiting, the pre-production samples of the switches came from the factory! Yay! They look exactly as I had intended, so that is a relief. Having to change the mold is an expensive thing to do. Now, all that's left is to ensure they are produced in the right colours - as is obvious from the picture, these samples are in black.

    Now, back to making a CAD design that works for the case...

  • Pondering Case Design...

    Oscarv05/06/2016 at 01:07 0 comments

    It will be horribly expensive to make, but this is the case for which I'll ask quotes from a few manufacturers, using different techniques. Just to see what's feasible:

  • Case Design

    Oscarv05/05/2016 at 00:11 0 comments

    It's been a month or so since my last post, but progress has been made. Samples of the replica switches will arrive on Friday. And thanks to Henk of, I started in earnest on case design. He let me borrow one of his original bezels/frames - thank you, I'll be careful with it!

    It would have been impossible, with hindsight, to exactly replicate the bezel without having the real one at my desk.

    I started the CAD work yesterday, and followed the path of least resistance by doing it in Sketchup. Which, maybe, will not be the best idea in the end but I will see. At least I've got all the measurements done for a mostly-finished v0.1 version:

    Next version should be good enough to go to a plastics manufacturer for evaluation and testing. Hopefully in the next two weeks, as I visited two of them recently to learn more about the whole process.

  • Progress: Got To Blinky!

    Oscarv03/24/2016 at 00:02 1 comment

    A blinkenlight movie means progress. Not there yet, but here's the PiDP-11 doing the '11's signature pattern:

    To be continued. As in, tomorrow night.

  • Prototype #1...

    Oscarv03/19/2016 at 20:24 0 comments

    Not in the right case, not with the right switches, with an imperfect acrylic panel and most certainly not in the right colours. But it seems to work with initial tests...

    Magically, the encoder switches turned up this morning just when I needed them. So they are in! Tomorrow I'll start adapting the BlinkenBone server. Five days left before I leave for VCF SE.

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Modzer0 wrote 05/13/2018 at 17:17 point

Oscar! I was actually wondering about the PiDP-11 a few days ago. I have a pair of J-11 processors and a few Russian clones from planning on participating in the PDPII project. What's the usable dimensions inside the case if a board was mounted on the back with about 1cm standoff? I can barely find time for personal projects, but I want to do a PDP-11 build with expansion so will add a port to the back, or have a new casing made that will fit the front panel and board.

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Oscarv wrote 05/13/2018 at 17:28 point

The back panel (which fits exactly in the case) is 313.5mm by 171.5mm. I can mail you the drawings if you want. You could mount a PCB behind it easily, flush to the panel. The guy behind the PDP2011 (FPGA version) is doing that; there is enough space for a PCB plus parts on the front; and the connectors mounted on the back of the PCB so they come out of the back panel. It would be amazing to fit a real J-11 board...

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Kevin Szabo wrote 01/25/2018 at 18:44 point

Will the final PiDP-11 console be the exact dimensions of the real PDP-11/70, or slightly smaller?  One reason i ask is that I have a physical PDP-11/70 front panel but it is lacking the white bezel that you are getting injection-molded.  If this bezel is close to the original dimensions then I can hopefully purchase one from you and upgrade my 11/70 panel :-)  And I would probably buy a full PiDP-11/70 kit anyway because it is so cool.

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Carl wrote 07/16/2017 at 13:18 point

Saw the PDP--8 project and, while reading, thought, "Man, I really would love to have a PDP-11 sitting on the bookshelf!" and then...  Thank you for all of the work you put into the details. Signed up with hackaday to follow and looking forward to the release!

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hackerday wrote 05/19/2016 at 20:12 point

Saw this at VFCe in Munich. Love it! Tell me when it's available, please.

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andy wrote 04/04/2016 at 01:46 point

Oscar- I would love to sign up for your PiDP-11 Early Adopter Program :-)...very excited about this project ... oh and thanks for the 2x PiDP8s by the way, one is assembled and working, the other will be a gift that I will surely assemble more quickly than the first one!  best wishes, Andy

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S.Edwards wrote 03/05/2016 at 01:11 point

Let me know as soon as you have a kit or an assembled product for sale.  I will buy at least one of them.  It was with a pdp11/70 that I learned Unix back in the 1970s.

pdp11/70 trivia: the unlabeled toggle switch (to the right of bit zero) is the secret "lamp test".  It is unlabeled because it was thought that LEDs, unlike the incandescent bulbs in earlier pdp models, would never fail.  When activated, all of the LEDs are lit.

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Andrew Wasson wrote 12/06/2015 at 01:40 point

Looking forward to this one. My PiPDP-8 went together extremely well and is happily blinking away. The PDP-11/70 front panel and switches sure is a thing of beauty. 

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Oscarv wrote 10/14/2015 at 19:53 point

Thanks! This one will hopefully teach me much more about manufacturing, CAD, and whatnot. Whole new world... Electronically, it's the same trick as the PiDP-8. 

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Benchoff wrote 10/14/2015 at 19:47 point

It begins! Can't wait to see it finished

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