thanks! your ideas are mostly pretty good

i agree that the machine should be fully self-describing, like darius bacon's 'book in itself'. of course, that won't help you if it won't turn on...

rather than just conformal coating and seals, i'm thinking i'll not just conformally coat the boards, but also pot the whole assembly in something like silicone or toilet-ring wax, so that the potting material can be removed, but otherwise it's trivially ip68. except for the keyswitches, but the keyswitches can be a magnetic type that doesn't have any exposed electrical contacts or any springs

solar-powered devices generally don't have to worry too much about cooling, though. or if they do it's from the heat they passively absorb from the sun, not from anything they dissipate internally. if your solar panels are 10% efficient (the best you can get out of amorphous silicon, which is the only kind that works under indoor lighting) and cover 30% of your device, they only harness 3% of the illuminance, which is later converted to heat in the circuitry. the other 97% is either reflected or converted into heat immediately. so the heat produced internally is only about 5% of the heat it has to deal with. now think about how much heat you feel on your skin from indoor illumination; we're talking about 5% of that

socket-mounted chips tend to induce a lot of unreliability, so i don't favor them. desoldering surface-mount chips is a bit of a pain but still done routinely in cellphone repair shops around the world. but i want it to make it to its design lifetime without replacing components, and one reason for that is that i don't want to depend on the economy. (consider what components were commonplace in 01971 and how many of them are hard to obtain nowadays — and that was 53 years of relative peacetime. imagine trying to get parts today in moscow.)

unlike batteries, chips do have a long shelf life, so you could conceivably stockpile chips today for future repairs. but if you're going to do that, probably the best place to stockpile them is on circuit boards inside the device, so you don't have to solder anything to fail over to them. that's not applicable for every device, but fortunately things like voltage regulators have very low failure rates, and you can still probably build in redundancy at a higher level. that's what we did when i worked on satellite systems: of n identical systems onboard, we only needed one to survive to run the satellite. there were even multiple power buses, so that even a failure that shorted a voltage rail to ground would only disable part of the satellite

as i understand it (not having taken the measurements yet myself) over-rating is especially important for bypass capacitors in this context — not because they're prone to failure (unless you're using tantalums) but because capacitors have enormously higher leakage near their rated voltage

if you want to build such a thing and have a mechanical charging option, i think a pullstring like 20th-century children's windup toys is the best option. it's compact, the spring constrains how much force you can apply to the generator and runs it at a predictable speed, and the pullstring grommet constrains the direction of force applied to the mechanism so that kofi annan can't break it by applying side-loading to your crank handle like he did with olpc. but i don't think electromechanical generators are likely to fit into the reliability budget

for screws, i think protruding screws would catch on my pockets. but there are lots of ways to fasten things together in reopenable ways, especially if you don't need seals. if you did want to use conventional milled-head screws, well, i filed a flathead screwdriver out of a bolt a few months ago. i used a file, a vise, and a steel bolt. but exposed screws would tend to rust unless you made them out of titanium or something, which isn't an option for me

a metal case has advantages and disadvantages. being able to take input power inductively (qi style) or communicate over rf could be useful, which you can't do with an all-metal case. metals are not very chemically stable, except for gold, silver, platinum, iridium, palladium, lead, nickel, aluminum, titanium, tin, and chromium. most of these have major disadvantages of their own, though titanium would be a pretty good option. many plastics are very chemically stable, including polypropylene, polyester terephthalate, silicones, and epoxy resins, and the epoxies in particular can be glass-fiber reinforced up to steel-like strengths and stiffnesses. so that was my plan

why 53? i just like 53