My Quest for Blinkenlights

Submitted by gerry on Tue, 07/21/2015 - 13:51

I have always been a fan of DEC minicomputers... 
I grew up in Galway, Ireland... often seen on the front panel of PDPs instead of the more common Maynard, Massechusetts, since DEC had a manufacturing plant there until the late 80s. 
When in school, DEC provided a VAX 11/750 to the 6 or 7 secondary schools in Galway city, and provided terminals to each school. When most kids my age were getting their first computer experiences with Sinclair SpectrumsCommodore 64s and BBC Micros, we logged into a real multi-user OS, VMS, via VT100 and VT52 terminals. We had the small micros too, but there was something about a multi-user system with usernames&passwords, email and chat (DEC talk) that really fired the imagination.

I have, over the last few years, acquired a couple of MicroVAXen, which I have played with a bit, and configured as a cluster... I mean who has a VAX cluster in their office? They didn't fully satisfy my retro-desire though... years of TV shows like The 6 Million Dollar Man, The Man from UNCLE and many others depicted computers as walls of blinkenlights and tape drives, and this depiction still has magic for me.

Thing is, PDPs and IBM 370s and the many other blinkenlight computers are rare, often collector's items, and command collector prices. One day a few years back, I heard of a project to reproduce the PDP8/e using a Harris Semiconductors 6120 PDP8-on-a-chip as the compute core, and with a custom, silk-screened front panel... this got my attention. However, when the time came for pre-orders, the price was still a bit on the high side... $600 is a lot to pay for basically a display piece. Eventually, this very limited quantity project sold out without me making a purchase, and I had to continue to defer my blinkenlights gratification.

About a year ago, while browsing yet another retro-computing site, I came across a project by Oscar Vermeulen to reproduce the KIM-1, the first microcomputer based on the MOS 6502I have a sentimentality for the 6502, since I learned to code primarily on a C64, and the first machine code I learned was 6502I built the KIM-1 kit and really enjoyed it, but the crucial point is that it put me in touch with Oscar, who has probably a greater fascination with retro-computing then me. We had discussed the possibility of a PDP emulator or reproduction, but there weren't any concrete plans, so I kept looking...

Eventually I came across a page by Ricardo Guerriero, where he documented porting Doug Jones' PDP8 emulator to the Arduino Mega. I had a few Megas lying around, so jumped on this project. The result is a bit of a hack, but many of the most fun things are... it uses a 16K CMOS to provide the 8K-word main memory, and a couple of LS256 EEPROMS read and written to over i2c to simulate paper-tape storage. I have yet to build a blinkenlights panel for it, though, but it boots and runs fine. My github repo here.

One day while yet again browsing retro-computing sites, I visited Oscar'sObsolescence Guaranteed and noticed a new post... the topic was creating a PDP8 emulator! The project was already at the prototype stage, and a front-panel had been built. I immediately got in touch and told Oscar of my interest if ever he decided to make the parts available. He eventually decided to do a kit, once he had the bugs worked out. Many months passed with many updates from Oscar in the development process, when finally I got an email to confirm interest, followed by a Paypal invoice, and within about 2 weeks, received the kit... I will post a build log when I commence, but for now, here it is.

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