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)
Raspberry Pi +/2/3/3+/Zero/Zero W
5mm LEDs, red
UDN2981A or equivalent
Interface and IO ICs / Peripheral Drivers and Actuators
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 simhBlinkenBone 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!
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.
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 :)
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 :(
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...
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 pdp-11.nl, 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.