A Love H8 RelationshipBy Glenn Roberts
My grandfather was what we would today call a "maker." Though never trained as an engineer, he had a knack for pulling inventions together using ordinary household items. When I was 9, he made me a really cool hot rod complete with wheels from an old baby carriage, a seat from a kitchen chair and a wooden vacuum cleaner handle for a steering stick; it had a foot-operated pedal brake too! But my most prized of his creations is the crystal radio set he made. He started with an oak case from something called a Dow Portable Electric Assistant, which was a turn-of-the-century medical device. He reused the case, black wooden panel and switches , and added a holder for the galena crystal. He hand-wound the tuning inductors using old oatmeal boxes for forms. Using that set I became practiced in the art of finding the "sweet spot" for the cat whisker on the crystal to pick up WGLI in my home town of Babylon, New York, or on a good day WOR from New York City.
Fast forward about 50 years. I find myself similarly enamored of playing with thirty year old hand-built electronic technology. This time the object of my affection is the Heathkit H8 digital computer.
The H8 came about during the "Golden Age" of personal computing, a period that lasted only a brief 5 years starting in the late 70s and ending with the 1982 introduction of the IBM PC, which set the standard we still live with today. It's hard to explain the excitement of that time to anyone who didn't live through it. If you were an engineer, or were otherwise technically inclined, the power of actually building, owning and programming your own computer was incredibly seductive. You could easily talk yourself into dropping a month or two's salary and spending many a late night with a soldering iron and a programming manual to get a system up and running.
It was in 1980, my first year of gainful employment, I bought and assembled an H8 system. Based on the infamous Intel 8080 microprocessor, it had a relatively generous 32K of RAM, a 4 port serial I/O card, 100K of disk storage and an H19 video terminal. I still have it and it still works!
Recently something has drawn me back to that world. Turns out I'm not the only one with this affliction. Enter the Society for Eight Bit Heathkit Computerists – SEBHC brought together by a confluence of passion and social networking technology, this ragtag group is gathering, preserving and enhancing these great relics from microcomputing's Golden Age. Though many of us have never met face-to-face, we share a sense of purpose and mission. The group includes people who used to work for Heathkit, as well as the numerous small businesses that built peripherals at the time, and of course many of us for whom this was a hobby. The collective experience and wisdom of the group is substantial, including many who have made their careers in hardware and software design.
Getting one of these old H8 systems back to operational order can be a daunting task, especially if it has been sitting in a garage or attic for 30 years. Heat and humidity are the enemies of any electronics. Fortunately, most of the components are still available (even the original 8080A CPU is still listed at Jameco), and programmable devices like EPROMs and GALs have been cloned by group members. Tantalum capacitors are a notorious problem source, and since they mostly die in a "shorted" mode, there can be a real fireworks show when you lose one!
Last year an SEBHCer sold me a much neglected H8 system and I affectionately nicknamed it Rusty. The rust on the chassis could be fixed with some steel wool and paint, but many of the integrated circuits and other components were corroded beyond repair. I chose to replace all the circuit boards and the backplane with modern equivalents. SEBHCer Les Bird has taken the time to develop new versions of many of the original H8 boards. Working off the original Heathkit schematics (which Heath provided with every kit) Les used the KiCad open source software suite to generate Gerber files that can be used to fabricate modern boards. While he was at it Les took the time to add modern features to the CPU board, like 64K of static RAM and an IDE disk drive interface, plus the ability to power the buss using a modern ATX-style switching power supply.
Using Les' designs I was able to assemble all new versions of the backplane, front panel, Z80 CPU board, serial I/O card and disk drive interface, and house them all – plus an ATX power supply – in the original chassis. With help from the group, I was able to work out the bugs and get the system up and running in short order. What fun it was to see the familiar message "Your H8 is up and running" displayed on the front panel LEDs!
Getting the electronics to work is only half the challenge. It turns out storage is a big issue with these old systems. If you're fortunate enough to have floppy disk drives that still work reliably, your first challenge is to find media to use. Thirty-year-old floppy diskettes can be pretty unreliable, and since Heath chose to use "hard sectored" disks, there are very few sources of new ones.
The "soft sectored" diskettes that were used in the IBM PC and many other systems are much more widely available. Soft sectored disks have a single index hole which is used in conjunction with an LED sensor to accurately lay out the sectors on the disk. Earlier "hard sectored" designs, such as Heath's, required a hole at each sector boundary, plus a general index hole – 11 index holes all together. The challenge to the group was to find a way to accurately punch the additional 10 holes in a disk. If we could do this then we could easily convert the IBM-style disks for use with the Heathkits. Sure enough, member Chris Elmquist was able to find a machinist who designed a simple and elegant hole punching device to do the job!
It would be cool to be able to use the more modern 3-1/2 inch diskettes since the media and drives are still available, but punching index holes in these was out of the question. Chris and other group members devised an ingenious solution – the Hard Sectored Floppy Emulator (HSFE). This clever device synthesizes the missing index pulses to make the computer think that it is talking to a hard sectored drive!
Why not go one better and eliminate mechanical disk drives altogether? Heath originally sold the H67 disk expansion system.
It had an 11 megabyte capacity and cost $5,800, so very few hobbyists could afford one back then, but SEBHCer Norberto Collado developed a microcontroller-based card that speaks the required SASI protocol and converts I/O requests to the IDE protocol. Add an IDE-to-Compact Flash adapter from eBay and a CF card, and suddenly you've got two or more gigabytes of storage on your H8 and five second boot time!
Norberto has been an innovation engine for the group, creating a CPU speed up board, a real time clock, soft sectored disk controller, a USB card and even an Ethernet interface!
You may ask, "Where does one find an old computer like this?" They're occasionally available on eBay, usually as partial systems and often in questionable states of repair. H8 computers can go for $300 to $500 or more, depending on condition and the numbers and types of installed interface cards – complete systems with a terminal, printer and disk drives (though rare) go for much more. The best source is word of mouth through the group, many of whom scour Craigslist, ham fests and estate sales. Deals can be found. I recently bought an H17 disk drive for $25 on eBay and was able to restore it to full operational condition.
If you're still reading this, you no doubt are wondering what drives the passion of the members of this unusual club. We each have our own answer to that question. There's certainly a nostalgic element, but part of it is that it's just a lot of fun to work on a system where you can get so close to the hardware and software. Part of it is the engineering challenge with modern breakout boards and microcontrollers, we can make these systems do things that we only dreamed of 30 years ago! Also, for some in the group this is just an enjoyable retirement pastime.
For me personally a big part of it is a sense of preserving something great. Heathkit was a fascinating company and any engineer who came of age in the 20th century was familiar with their wonderfully designed and documented kits. Their instruction manuals were legendary. Heathkit ham radios were world class pieces of equipment. The H8 and its companion the H89 "all-in-one" computer were, in many ways, Heathkit's last great hurrah. Ironically Heath's success in digital computers attracted the attention of Zenith Corporation which was anxious to get in on the PC boom, so they acquired Heathkit in the early 80s, and Heath/Zenith Data Systems was born. After that Heathkit never returned to its former glory and the last remnants of their operation were only recently auctioned off.
The computer revolution has proceeded at such a fast pace that I can't help but wonder if some day when we stop to look back we will realize that something wonderful has been lost. Oh there are computer museums where you can look at inanimate boxes sitting in glass cases, but the soul of these machines is in the software and the experience of using them and interacting with the hardware. It's about writing software that will fit in 8K instead of 8MB! These were among the first truly personal computers and I feel privileged to be playing a part in restoring and preserving them, hopefully for future generations of technologists to enjoy and learn from.
For more information visit:
Glenn Roberts has a Ph.D. in Computer and Systems Engineering and by day is a director overseeing research to modernize the U.S. air traffic control system. He grew up on New York's Long Island but now calls suburban Washington D.C. home. When he's not tinkering with old computers, you might find him biking the Washington and Old Dominion trails, or spending time with his family at the Delaware shore.
If you have an electronics story or project you'd like to share, please email [email protected].