Friday, September 18, 2015

PDP-8 Minicomputer Interfacing - How to connect your PDP-8 to the outside world 1972

Heath Schlumberger
Heath Schlumberger logo
BugbookHeath / Schlumberger computer interface brings the inside of your PDP-8 computer outside to the real world - 1972.        This was the advertising byline for the interface unit.
Click photo to enlarge -
Heath Schlumberger EU-801E PDP-8 Interface
Heath Schlumberger EU-801E PDP-8 Interface

 The Heath/Schlumberger interface unit brings all the address/data bus and control signals to the outside world in the instrument you see to the left of the PDP-8 computer in the photo. I have found very little information on the web about this unit.

Here is the interface connected to a PDP-8L minicomputer with a graduate student testing the operation.

 I was a consultant for the Heath/Schlumberger company on this project - Here is the short story of this adventure.

 Dr. Howard Malmstadt at the University of Illinois was a pioneer in the teaching electronic instrumentation to who people who were not engineers but were scientist and technicians needing to know about electronics and electronic measurements. Howard  did this work in the early 1960's with the help of Dr. Chris Enke at Princeton University.  Dr. Malmstadt named this teaching technique and equipment "Electronics for Scientist".  The course work consisted of a text books and a equipment in a teaching station.

I was fortunate in 1967 to attend 4 week workshop"Electronics for Scientist" at the University of Illinois taught by Dr. Howard Malmstadt.  Professor Malmstadt invited me back to be an assistant for his workshops for the next 4 Summers. Working with Dr. Malmstadt during this time developed into an invitation to consult with the Heath Schlumberger company in Benton Harbor, Michigan. Professor Malmstadt and Professor Chris Enke were working with the Heath Schlumberger company on the  interface package for the PDP-8 minicomputer.This device was the EU-801E. It simplified the teaching of computer interfacing/automated instrumentation and designing projects using PDP-8 minicomputers.

While writing this blog I was able to make contact with Chas Gilmore the Engineering Manager for this product at Heath Schlumberger.  Chas had some interesting information about the development of the EU-801E.

 Chas Gilmore - Here is a synopsis of what I remember of the EU-800 saga--Dave may well be able to add more. Way back when, I worked with Dave Larsen when he was consulting on the EU-800 Series. He was at Blacksburg--Virginia Tech at the time if I remember correctly. I was the design engineer on the EU-805,
When I got to Heath in 1966 that system was in its very beginnings and the design was mostly discrete components (jam packed cards) and was pretty impractical. They then decided to use RTL but still struggled with cards, especially for the instrument which were really too complex. I found digital integrated circuits intriguing as can be and started doing investigation in that area on my own. That was when I found this new technology called TTL. So, just for grins I took some of the functional blocks, they had designed (one card was a decade counter and it drove a second card that had latches and Nixie tube decoder/drivers--again all discrete) and redesigned it in TTL. That reduced the design to a single card and not a lot of parts. I took it to the project engineer who scoffed at the design. That got my back up so I took it to the department Chief Engineer--our common boss. He was intrigued and arranged a meeting with Malmstadt and Enke. They were also very intrigued--and liked using the latest technology. The net result was the other guy was relieved of project responsibility and I became the project engineer--and the whole project went to TTL. We also boosted the speed of the counter from 2 - 3 MHz to 12.5 MHz (a truly blinding speed!!).

I still have manuals for these products but no longer have either an EU-805 nor an EU-801.

The EU-801-E came along later as a companion to the recently introduced PDP-8L--a PDP-8 computer available for just under $10,000. What a breakthrough. By then I was the Engineering Manager for the department. This extension of the EU-800 series came along after the EU-805 and EU-801 had been on the market for a couple of years. Unfortunately, none of it sold terribly well and it didn't take long for Jimmy Lee (who had been brought in to head up the Scientific Instruments Department and was my boss) started to push for non-EU products (all of the EU-series were related to the Malmstadt/Enke Electronics for Scientists systems which were created as laboratory hardware which supported experiments for the Malmstadt/Enke textbooks.) I don't remember exactly when Dave became associated with the project but it may well have been in conjunction with the EU-801-E.

PDP-8 minicomputer Interface
Advertisement Heath Schlumberger EU-801E

Here is an advertisement for the PDP-8 Heath/Schlumberger interface equipment in the June 1972 issue of the Analytical Chemistry  journal.

This is about the only item I can find online about this Heath/Schlumberger product.

I have one of the interface units in my museum warehouse and this is the buffer amplifier used to connect the PDP-8 interface signal to the the interface  trainer.

Card to access all the PDP-8 I/O signals
Card to access all the PDP-8 I/O signals

The computer signals from the buffer box come out to this interface card giving you access to the computer address and data bus plus control signals. 

Bugbook computer museum
Heath Schlumberger Digital Trainer
The interface card above plugs into this unit for power and wiring your custom interface.

Heath Schlumberger EU-801E PDP-8 Interface
Heath Schlumberger EU-801E PDP-8 Interface

Here is a view of the interface unit wired to a PDP-8L with a custom interface being tested.

I found more photos of the PDP-8 interface system see album

bugbook computer museum
David Larsen
These units never became widely used - I would estimate that only a few hundred were sold. It was just to complicated for most people to consider making their own custom interface to a minicomputer. 

This is me using one of the interface units teaching about minicomputer interfacing.

Professor Dessy and I taught a number of workshop using this equipment until the microcomputers made the PDP-8 minicomputer obsolete.  Teaching these workshops away from home was a real challenge - we packed the PDP-8 in a crate with the other equipment and sent it ahead for the workshop. This must have been a least 400 lbs of equipment.  We went as far as San Francisco for one program and in the early 70's. This was the start of my 22 years of teaching various Computer Interfacing and Instrumentation workshops in many parts of the world including the old Soviet Union.

Heath Malstadt teaching station

My experience with Dr. Malmstadt helped develop my teaching technique used for  31 years as a faculty member at Virginia Tech. I used his books and equipment as part of my courses in "Electronic Instrumentation".

 Here is advertisement of Professor Malmstadt's teaching station sold by Heath Schlumberger 1963.

I owe Dr. Malmstadt a lot of gratitude for all the help he gave me in my early years of teaching. Howard was one of the most kind and humble professors I have known. He was just a great and wonderful person.

Take a look here  about Dr. Howard Malmstadt's work at the University of Illinois. Dr. Malmstadt passed away July 7, 2003.

David G Larsen
David G Larsen

John Simkiss visited the museum on Friday September 4th and picked up
his Altair 8800 computer. The computer has been restored to full working condition and is low serial # 414. We had a great day talking about the history of microcomputers and visiting the museum & warehouse.

"by David Larsen" KK4WW Computer Collector / Historian         
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