PDP-11

Building a PDP-11 Kit (PiDP-11)

A few years ago I put together a kit from Oscar from http://obsolescence.wixsite.com/obsolescence. It started with soldering, went through setting up a Raspberry Pi image to emulate a PDP-8, and ended with a functioning simulated PDP-8 with working front panel! I was having some issues with one of the integrated circuits; but Oscar, being a great guy, sent me another one and I was able to prove to myself I wasn’t crazy and everything worked. Enjoying the project a lot, I was excited to see he has started production of a PDP-11 kit, this time with a nice plastic injection molded case, and compared to my rev 1 PiDP-8, nicer switches. So I had to order one.

I was able to get the kit working within a few hours of starting, I think part of this is Oscar has gotten better at making these kits; with having the board illustrate where parts go, and having a clean layout, it was fairly easy to put together and solder up. Also my poor soldering skills may have gotten a bit sharper.

While I was at it, I thought I would get my brother a kit so he could get into soldering, which he hasn’t done much of. In going through the instructions I found them a bit light for a novice. To remedy this, I took a bunch of photos during the process and will post them below. The official instructions have more details so I intend just to be additive to those with additional hints, details, and photos.

To start, 30 diodes must be soldered to the board, followed by a few resistors. The tan ones are the 1K ones and go in between some diodes on the bottom row, these spots are labeled “1K”. The 390 ohm resistors go in their labeled spot in the middle of the board. These are put through the board, soldered in, then their legs are cut. Polarity doesn’t matter for these.

Now the GPIO connector for the Raspberry Pi can be soldered in THE BACK of the board, making sure its flat. Followed by the chip socket that goes on the front, in the middle-ish near the rotary encoders. Don’t solder this in with the integrated circuit in it. Note my board is a newer one with some expansion options that Oscars site doesn’t show, make sure to use the correct chip socket location.

Later photo with chip socket and chip installed

This step is the longest and a bit tedious, you need to get 64 LEDs, each with a little riser, and stick it into the board with the correct polarity. That is long leg matching the icon to on the board, for me it was to the left.

Soldered LEDs with board indicator

Now there is a piece of board that comes with the kit, that can sit over all the LEDs to line them up, and once they are all in straight and aligned, they can be soldered in. I would recommend not snipping the legs off until you have tested and are sure they all work. The last soldering steps are to solder the rotary encoders in. After that put the integrated circuit in the socket, and test it out!

Oscar has a bunch on how to test the board so I will leave that to him. One note I will add, my Raspberry Pi had to be a good amount in the socket before it would work well, but this led to the RJ45 port hitting some of the LED contacts and shorting a row. I found getting the anti-static bag the Pi came in, and placing it between the top side of the Pi and the board solved all these problems.

Jumping ahead, I want to mention putting the switches in since this is the one other part of the kit that is a bit confusing and may give people issues. Using the switch lining up tool, that is included with the kit, I found the easiest way to hold everything in place and solder was suggested by Neil over at the PiDP-11 Google group, https://groups.google.com/forum/#!topic/pidp-11/E-RMRVQ15NQ%5B1-25%5D

Neil’s way to hold switches in place

Using this technique, I was able to solder the switches in easily and without difficulty. Follow what the tool says and you should be good. Make sure you are in a well lit room, since in the dark the red and purple can be a bit hard to distinguish.

Using this technique, I was able to solder the switches in easily and without difficulty. Follow what the tool says and you should be good. Make sure you are in a well lit room, since in the dark the red and purple can be a bit hard to distinguish.

Finishing up, consists of more testing with the Pi installed; then going and screwing it all into the case. Be careful, these don’t need to be screwed in very tightly and you can fairly easily crack the acrylic (this I have learned from other projects in the past).

This was a fun kit, and I hope Oscar keeps making more of them. If you have any issues head on over to the PiDP-11 Google Group, and if my guide helped out out, please let me know in a comment below. 🙂