More From John Hughes

A project log for DEC H-500 Computer Lab Reproduction

Reproduce the Digital Computer Lab H-500, a training tool from the late 60's aimed at teaching people the basics of logic circuits.

Michael GardiMichael Gardi 10/31/2020 at 00:542 Comments

John Hughes, the designer of the H-500 Computer Lab and author of the accompanying Workbook was kind enough to answer a few of my questions.

I asked John how the patch panel was constructed:

 The patch panel surface of the Computer Lab is actually two layers.  The top layer is a white plastic sheet with the component symbols silk screened on.  The bottom layer was a PCB that was affixed to the top layer by soldering the patch panel rivets to the PCB panel.  The layout of the patch panel PCB was single-sided and pretty simple.

I commented that the surface mounting of the components was way ahead of its time:

 Yup surface mounting PCB components was bleeding edge mechanical technology in 1968-9.  Computer Labs were totally hand assembled on a small DEC production line in Kanata, Ontario (just outside Ottawa).  Surface mounting components did require special soldering tools and operator training.  By the way while I said I designed the Computer Lab, my focus was on the EE part of the work.  DEC had a mechanical design team in Maynard MA that did a great job on that part of the design effort.  One additional point, there are two PCB’s, one for the IC part of the patch panel, the other for switches, lights, clock and power supply.  The two boards are joined with soldered jumpers.

Here is a very good picture of the inside of his personal H-500:

 Attached is an inside picture of my Computer Lab.  In it you can see the color difference line between the two PCBs as well at the jumpers between the two boards.  

I asked John if he had a copy of the schematic for the switches, lights, clock and power supply and sent him a fuzzy picture of one that was attached to the back panel of a unit. He was kind enough to check for me:

 I opened my Computer Lab to see if there was an attached schematic inside the back cover as in your picture – unfortunately no luck.

I learned a lot from John today, and I certainly appreciate his reaching out and taking the time to share and even answer a few questions.


Michael Gardi wrote 11/06/2020 at 15:21 point

Hearing from John was an incredible experience for me. I'm so appreciative that he reached out.

I'm of an age where I could have intersected with the H-500 but unfortunately did not. Being a CS and not an EE guy probably contributed to the miss. 

Thanks for sharing Andrew.

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Andrew Wasson wrote 11/05/2020 at 01:38 point

Thanks for posting the correspondence with John Hughes. That's an extra bit of goodness I hadn’t expected to see.

The first photos I saw of the Compu Lab were in my dad’s electronics magazine collection. It spanned about 1940 - 1970 or so.  Then when I was in high school (1977 - 1982), I saw the real deal but by the time I was of age, they had been archived and we learned digital electronics with the aid of an expanded Netronics ELF II. I always thought the DEC Compu Lab was an awesome piece of electronics/art. 



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