Membership Card

by Chuck October 27, 2010

One of the things that I like to play with are retro-computers – old hardware from back in the dark ages of computing, hardware that a 17-year-old could understand, and that a 48-year-old can still wrap his head around.

One of the most famous of the retro computers is the Popular Electronics COSMAC ELF. I, and many others like me, got our start with computers flipping switches and pressing buttons on a home-built ELF. Many, including me, still have their old ELF sitting in a box on the shelf, and have a soft spot in their hearts for the red Q LED and the 8 toggle switches on the input panel.

Back in 2004 SpareTime Gizmos created the ELF 2000, a re-interpretation of the ELF using mostly modern components. The ELF2K is an ELF full-gallon – 32 K RAM, 32 K ROM with monitor and multiple high-level programming languages, support for terminals, Compact Flash – basically everything that you could want in a small computer.

But there is another style of ELF computer out there. These are not ELFs brought into the 21st century, and they are not faithful reproductions of the 1977 COSMAC ELF. Lee Hart’s Membership Card packs the essence of the COSMAC ELF into an Altoid’s tin. Essentially, it’s a microcomputer trainer that you can put in your shirt pocket and take with you everywhere you go.

My Membership Card computer tucked into its candy tin.It’s such a cool idea that I had to have one. So when Lee announced that he was selling kits of the Rev. B version of the Membership Card I jumped on the opportunity and bought one. Lee sent the kit complete with an Altoids tin – with Altoid powder still inside (a nice touch, that).

I hesitated over building it – I’m not 100% confident in my building skills. My ELF2K has an intermittent fault that was probably caused by a soldering error. The last thing that I wanted was another ELF-type computer sitting in my den, not working. But I eventually took the plunge, and over a weekend and a couple of week nights I got the hardware put together and tucked, if not neatly, at least cozily into the candy tin.

Next began an of evenings of frustration for me. Once I had the Membership Card complete I built a power cable for it and plugged it in. I flipped in the simplest “Hello World” program that you can use on an ELF: 7B 30 00. Turn on the Q LED, then loop back and do it again forever. And of course, nothing happened.

Starting to sense a pattern here?

I spent a frustrating evening trying everything that I know to get that tiny little program to run. Nothing. I knew that the program was going in to the RAM, the LEDs were lighting up with every press of the INP switch, and the way the ELF works those LEDs wouldn’t light up if the data wasn’t being written. But I just couldn’t get it to come back out; setting the memory to read-only and pressing INP didn’t cycle through the program that I’d just loaded. Once, and I had no idea why, I put the Membership Card in RUN mode and the Q LED came on. But I couldn’t get it to work again.

I spent a pretty miserable day the next day. At one point I was ready to pack all my 1802-based computers and figuratively put them on the side of the road with a “Free” sign on them. I’ve got four of these things, and not a single one of them works. Not my proudest achievement.

But I went home and tried again. I got out the schematic. I read the documentation. And a light dawned. Switch 9 isn’t the one that you flip to reset the ELF, switch 10 is. So I toggled in the program again. I flipped switch 10 up, then I flipped switch 9 up. And the Q LED came on.

The sun burst through the clouds casting rainbows. Little blue birds flew in carrying banners that said “Joy!” or little hearts in their beaks. There was a fanfare of trumpets and the air was filled with sweet perfume.

Or not. But I was pretty happy.

So I left the Membership Card sitting on my desk, flashing its Q LED like a little happy firework. And I went to bed, happily plotting new and exciting ways to drive myself crazy with this little tin box.



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