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+++ title = "Towards Manufacturing Logic Devices at Home" description = "" +++
open source rules the software ecosystem. we have Linux, GNU, and all the applications on top. your device is near-infinitely hackable... at the software layer.
with Risc-V, Framework, and earlier projects like Novena, we're beginning to achieve some of this same hackability at the hardware layer.
but the base layer -- the actual manufacturing of integrated circuits -- remains this impenetrable wall. players like Sam Zeloof do some (small-scale, proof-of-concept) IC manufacturing at home. and there's some defunct projects like HomeCMOS. but otherwise, the space is close to a vacuum. how do we make inroads?
We Don't Need Perfection
we don't need 5 GHz clock speeds and mobile-level power-consumption out of the gate. even a 10 kHz, 1000 logic-element device has some value (say, as a keyboard driver). once we have a foot in the door, incremental improvements can make the technology more widely applicable. our problem of open-source computation is one of bootstrapping.
Silicon devices aren't friendly to manufacture. the equipment is expensive, the chemicals are dangerous, the tolerances are small, and the physics/chemistry is college-level to Phd-level.
when i was in middle school, i learned about electromagnets. my dad took me to the hardware store and we bought several iron bolts, annealed copper wire, paperclips, thumbtacks, and a lantern battery. within a day, i had a two-bit electro-mechanical adder. each bit was represented by three tacks and a paperclip. the paperclip was fixed to one tack (A) and freely rotatable such that at one rotation it would bridge an electrical connection to tack B and at a different rotation it would instead bridge a connection to tack C (logic '0' and logic '1', respectively). by introducing an electromagnet, i could conditionally pull the paperclip to one orientation or another. it was in effect a relay, and since the tacks and paperclips could conduct electricity, the relays could feed into each other.
relay computers were a thing. and they're simple enough that a motivated 12-year-old can build one. they have a few notable downsides, but the largest for us in this context is that they're very labor intensive to manufacture/assemble.
Non-Silicon Forms of Computation
Wikipedia has an entire page on Unconventional Computing, and it's not even complete. there's also Fluidics, Optical Computing, Chemical Computing Electrochemical Transistors, and of course, vacuum tubes!
these things aren't just the realm of theory. they all had use before the reign of the transistor:
- vacuum tubes were the go-to before transistors. TODO: link.
- the MONIAC used fluids to model economic activity.
- OECTs are used in bio-sensing applications because they're safer than silicon in such settings. TODO: link
the point of listing these is break the misconception that computation must take place on silicon, or even semiconductors in general. the most alluring technology for my purpose looks to be ferromagnetics.
magnetic core memory was widespread before we had integrated circuits. the Apollo Guidance Computer used core memory for its program data. lesser known, the Elliott 803 repurposed core memory into logic gates.
magnetic cores are really simple: you have some ferromagnetic material which has some interesting, often nonlinear relationship between its electric and magnetic field, and you have some conductor (copper) to carry these fields from one place to another. that's two, easily procurable materials, plus an insulator (air). and it's all solid state and (at a high level) operates on classical mechanics -- making it scale independent: a 1cm core behaves roughly the same as a 100um core, only with power scaled accordingly. you don't need precise fabrication, so with some effort it should be possible to manufacture an integrated circuit out of these materials using something like selective laser sintering (which could pair nicely with non-electronic home-manufacturing).
Ferromagnetic Computing
it's widely known that any combinatorial circuit can be reduced to a representation which uses only NAND gates
(this includes flipflops, allowing not just combinatorial logic but also volatile storage, and hence general-purpose computation).
one could alternatively use NOR gates, XOR gates, or inhibit gates (Y = A and not B).
the Elliott 803 demonstrates a sort of inhibit gate, at an analog level: Y = A - B (based on the gate wiring, it could perform Y = +/-A +/- B +/- C with the sign configurable).
the reason it required transistors is because these analog operations were lossy, and needed amplification to achieve the desired digital operation.
that is, the "inhibit gate" might actually look something like Y = 0.5*A - 0.5*B and in order to feed this into the next gate you would need to amplify Y by 2,
which a transistor does nicely.
but that's not to say one couldn't perform this amplification using ferromagnetics. in fact, magnetic amplifiers are all around us: transformers.
can we assemble these components into one of the primitive digital logic gates?
TODO: review magnetic core theory
NOTES: Pneumatic Logic: https://www.instructables.com/Pneumatic-Logic-Gates-Made-With-Simple-Tools/
TODO: read 2020-09-25-technology.txt
TODO: read http://www.hpfriedrichs.com/radioroom/cu-diode/rr-cu-diode.htm
TODO: read 2020-10-04-other-magnetic-logic.txt
TODO: magnetic amplifiers https://en.wikipedia.org/wiki/Elliott_803#Hardware_description (it uses cores for computation, and transistors to amplify the output)
TODO: read 2019-08-18-resources.txt
TODO: 2020-04-05-unconventional-computing.txt Material Matters Basics Vol. 8: covers PDOT/PSS; conductive polymers TODO: Acquire: Material Matters Basics Vol. 6: The Fundamentals of Organic Transistors
ion-beam lithography