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The RCA COSMAC 1802 “Membership Card”

Computers & Mobile
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You may have seen this little beauty floating through the interwebs. It’s an Altoids Tin-based COSMAC Elf, built around the classic RCA COSMAC 1802 microprocessor. It’s the prototype to a kit that Lee Hart has been developing. P. Todd Decker (Overland Park, KS) sent us a link to this video of his build of the kit prototype. He writes:

I have completed a build of Lee Hart’s “COSMAC Elf Membership Card.” The idea behind Lee’s design was to create an interesting kit to introduce new people to the classic RCA COSMAC 1802 historic microprocessor. This processor has a long, interesting history and is even still used, due to its unique properties when it comes to power and durability. It was the basis for the famous “Elf” home-built computers from the late 1970s. It still has a strong following. Lee’s twist on the old reliable was to rework it into an Arduino-style platform that—best of all for makers—fits into an Altoids can. His design doesn’t require any surface-mount or complicated build techniques. Herb Johnston has done an excellent job of documenting Lee’s efforts to create this kit (see link below).

Lee Hart’s 1802 “Membership Card”

4 thoughts on “The RCA COSMAC 1802 “Membership Card”

  1. says:

    I know of Lee through his electric vehicle interests. Brilliant and friendly guy. Didn’t know he was into these microprocessors too, though I shouldn’t be surprised.

  2. Todd says:

    I’m reposting a good response from Lee Hart on why someone like me (I built the one in the video above) would take the time to do something like this.

    –Start of Repost–

    I’m the idiot that designed this thing. :-) Why? Many of the comments above provide clues!

    To really learn something, you need to begin with the basics. Start at the bottom of the ladder, and work your way up. Master each step, them move up to the next.

    But today’s computers have basically sawed off all the bottom rungs of the ladder. Those that learned “way back when” understand how computers really work, and they can build and improve them further. But those starting off today look at computers as an appliance (or worse, as “magic”). They don’t really have a clue how it works. They depend on someone else to design it, build it, and program it for them.

    This leads to hideously inefficient systems. They think that millions of transistors and megabytes of code are needed to do even simple tasks.

    But the vast majority of microcomputer applications are tiny little gadgets, like a pocket calculator for example. If Windows and a Pentium were required to make one, there would *be* no pocket calculators! There would be no way to “climb the ladder” to invent them, perfect them, and make them affordable.

    The idea of the Membership Card is to show how small and simple a computer can really be. You really *can* build it yourself, from scratch. No surface mount, no custom parts, no proprietary code.

    And, you don’t need any expensive programming hardware or megabyte compilers. Yes, there are 1802 C compilers; but there are also Tiny BASICs and FORTHs that run with 1/1000th of the resources.

    1802 machine language seems odd in light of today’s super-complex CPUs; but it is refreshingly simple. It is Turing-complete; it can do anything that any other computer can do. Basically, it has 16 16-bit registers that can be used for anything; program counters, stack pointers, DMA registers, general purpose storage, etc.

    No stack pointer? Hah! You can have *ten* stack pointers if you like. No CALL instruction? Baloney; you write what amounts to microcode to create one. If you want CALL to push the PC and also save three other registers on the stack, then you can! The 1802 makes you *think* about what you want your instructions to do.

    Hardware wise, the Membership Card has the same sort of bit/byte input and output ports as a BASIC Stamp, Arduino, or any other micro. I’m using mine to make small robots; the stepper motors connect directly to the output port, and the input sensors connect directly to the inputs. I’m using the Q output and EF4 input for a serial port to a PC.

    Another feature of this older technology is low power consumption. The Membership card *runs* on 3v at 1ma. There’s a jumper to disable the LEDs, since one LED takes 10 times more power than the whole computer. Or, you can unplug the front panel once you’ve loaded your program (it’s no longer needed) and use the Membership Card by itself.

    It takes no great genius to bury a problem with brute force. In constast, hacking is all about finding clever ways to do more with less. “Running light without overbyte” as Dr. Dobbs used to sas. The 1802 and Elf computers amply demonstrate this principle!

    Posted at 12:25 pm on Aug 20th, 2010 by Lee Hart

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Gareth Branwyn is a freelance writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor to Boing Boing, Wink Books, and Wink Fun. And he has a new best-of writing collection and “lazy man’s memoir,” called Borg Like Me.

View more articles by Gareth Branwyn
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