What is old is new again – this is the saga of the PiDP-8.

Back in the 1970s, I was in class and the speaker, I remember his name to this date, told us how he convinced the credit union to offer loans on computers so he could buy a Digital Equipment PDP-8 minicomputer for his personal use. Having used computers extensively in college, I was of course very much intrigued by the concept of a personal use computer…especially since I was developing systems using the Digital Equipment PDP-11 computer. But I couldn’t afford the PDP-8, and it wasn’t until 1975 that I first acquired my first personally owned computer – the Altair 8800.

Fast forward a few decades. I was listening to one of my favorite podcasts – Security Now with Steve Gibson and discovered his “attraction” to the PDP 8. Steve used the simple architecture of the PDP-8 to explain to audiences how computers work. During the same time frame, he mentioned his building a PDP-8 in conjunction with an effort by Bob Armstrong’s Spare Time Gizmos to assemble a kit, with custom panel, using a Harris/Intersil 6120 chip which “emulated” the PDP-8 architecture (see https://www.grc.com/pdp-8/pdp-8.htm). Unfortunately, I missed the opportunity to construct the SBC6120 and the heart of the project, the 6120 chip was in very short supply – so that door was closed.

In early May 2015, by chance I was again listening to a Security Now podcast and Steve just happened to mention a PiDP 8 kit that was being developed. Wow more PDP-8 developments.

The PiDP-8 is a project by Oscar Vermeulen that recreates a replica of the PDP-8/I front panel (all those nice lights and switches) but utilizes a Raspberry Pi and a program called SimH[1] to simulate the PDP-8…all for a few hundred dollars! WoW!

I followed Steve’s links and wound up at Oscar’s site Obsolescence Guaranteed, (http://obsolescence.wix.com/obsolescence#!pidp-8/cbie) and quickly signed up! Oscar replied to the sign-up by sending an update of the project’s progress and I started preparing by acquiring a Raspberry Pi A+ to run the project. I downloaded Oscar’s beta versions of SimH and began reviewing and preparing the kit construction directions. In the course of my delving into this exciting project, I quickly exchanged numerous e-mails with Oscar. One of the nice features of this project is the PDP-8 emulation is a part of SimH (which includes other computing platforms including the PDP-11) and what Oscar has done is to write some code to have the Raspberry Pi (any plus version including the Pi v2 which happens to run Windows 10 IoT) communicate with the switches and lights of his replica PDP-8/I panel. However SimH and the Pi do not need the panel to run the PDP-8 emulator which is seen via keyboard and display. This means that without the panel kit, setup, testing, and running the PDP-8 emulator is possible. I was having fun and learning a lot about the Pi, the Pi operating system, and SimH.

As things with the project progressed, Oscar and I exchanged e-mails several times a week. He was overwhelmed with requests for the PiDP-8/I panel kit and decided to split the “production” into two runs, a July run and a September run based on when one signed on to the project; I was in the second run.

I continued to prepare for the kit by leveraging Oscar’s writings and web pages and assemble a manual for me to use both in setting up the Pi with his beta code as well as the construction steps for building the PiDP-8. For me having a “printed” manual was easier than constructing the kit from web pages (and due to the quirks of web pages, it was not easy to just print the pages). This was also good preparation for me and helped me understand the software setup as well as the assembly of the kit.

As a courtesy to Oscar, I provided him with my suggestions as I walked through the steps. I also found some typographical errors and worked with Oscar to get them corrected. My working with the Pi and his setup instructions provided me with a much greater insight into the Pi and the Raspian Operating System…and this was really exciting.

Then in June, Oscar asked if I wanted to get an early kit and help assess the assembly steps. YES was my instant answer and on 9 July I got the shipment from Switzerland and carefully opened the package (about the size of a “standard” shoebox).

Even more than before, I was amazed at Oscar’s engineering skills in developing this PDP-8/I panel. The circuit board was high quality and the bamboo case, a standard 6” x 12” stackable organizer, a nice “green” touch.   His creating and crafting the kit and the components is on par with Heath Kit – different but on par. The ingenious approach to mounting the 26 switches on the panel is truly amazing and almost an engineering marvel. Brilliant.

As with the PDP-8 (and PDP-11 too) the panel has numerous switches and lights. The PDP-8 being an octal construct, the switches are grouped in threes with alternating colors in each group. In my preparation for painting the switches I had to locate the color Oscar called for…and it was hard…in fact impossible. It appears European and US paint stores operate differently. So I delved more into color and color systems than I ever imagined…and ultimately found a very close color equivalent – but it was quite a rewarding experience.

I’m now in the process of putting the finishing touches on the now working PiDP-8 at the same time as I’m installing the latest Windows 10 Insider Preview on several computers. At each step of the way I updated my manual and provided feedback to Oscar to help make sure the hundreds of kit builders can easily assemble their PiDP-8 kits. I’ll soon be delving into the PDP-8’s OS 8, enjoying the panel lights and switches, and learning more about the 1970’s technology that was the precursor to many computing developments. Thank You Oscar (and thank you Steve Gibson).

Overall I really like the PiDP-8 kit.  My rating for the PiDP-8 — 5 out of 5 stars.

[1] The Computer History Simulation Project, http://simh.trailing-edge.com/