The 2N2/256 bit-serial computer project
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Posted by Bobby Nansel on December 19, 2007, 10:40 pm
Please log in for more thread options lines of an LGP-30, a Bendix G-15, or a Packard Bell PB-250. To keep costs down and keep it interesting, I want to use only components available to mortals in the mid sixties (no ICs). I'm limiting my madness to discrete transistors, specifically the 2N2222. I'm further limiting the number of transistors semi-arbitrarily to 256. (The 2N2/256 name is a nod to ham homebrewer Jim Kortge (K8IQY) who designed a QRP rig called the 2N2/40 for a design contest about ten years ago. The contest objective was to design and build a functional amateur radio transceiver, using a maximum of 22, 2N2222 type transistors. My challenge is to build a complete functional computer, including memory, using no more than 256 2N2222-ish transistors.) Of course there will be a pile of si diodes, resistors and capacitors involved, but the idea is to keep the number of active components down -- if only so this beast will fit in the boot of my car! Toward that end, I am building everything to fit in a few 35mm cube modules. I've scavenged the web for information on bit-serial magnetic drum machines of the Elder Years, and I think I have a pretty good notion of how they worked (mostly very slowly). What I haven't been able to get a handle on is how to make a serviceable magnetic drum. I reckon I can do some simple prototyping with some CMOS 64-bit shift registers to emulate the drum so I don't have to debug both the logic and the magnetic read/write electronics at the same time. After asking lots of questions on the classiccmp.org talk list I've determined that using a 14" disk & spindle from an old "washing machine" disk drive might be the best route (much less precision machine work needed). The separate read and write heads are fixed (not flying), one pair per track, so zero seek time, only disk rotational latency. Magnetostrictive ultrasonic delay lines are also an option. Any thoughts? | ||||||||||
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