So, first post here, never designed a project from idea to pcb to mini-production. (never design anything actually, i buy "starter kit".
i got a gift idea for a birth : let's offer a clock that will count day from birth to infinity and beyond.
That's around a 100 year lifetime, and it need to need a stability of 1 day per century.
it need to be rock solid, it need power, it need some kind of super simple display, it need to be switched on.
after a few minute of thinking about it ... doh! is it even possible ?
I'm stuck at the very first problem : power !
does a battery that last 100y exist ?
solar panel ? can a solar panel live for 100y ? and it still need some kind of battery anyway
replaceable battery ? who know what kind of battery will be available in 100y ? Perhaps lead-acid battery will be forbidden in 50y, who know ?
i tought about sealing the project in a glass cube. Well not glass because the melting temperature is too hot for the electronic to survive, but some kind of transparent plastic ?
Transparent so the solar panel can be sealed, and the display is still readable but not exposed to the elements.
But if it's sealed, how to switch it on ? i switch it on before sealing it ? (there is no need to switch it off)
human interface :
What kind of display ?
It can't be always on, to save power.
But if it's sealed : no push button. perhaps an IR receiver ?
Power again :
i know it's hated but : "energy harvesting" ?
i mean... this think will probably need a few picoAmps (random prefix, i like pico... will it be nano ? femto ? micro ? dunno...), isn't it ?
Any random tought ? some "very important" stuff i didn't mention and forgot about it because i'm a noob ?
Perhaps it shouldn't be on a PCB, i don't know...
EDIT (where are we now) :
- pure mechanical solution (eg : good old clock) is out of topic
- Mechanical part may be introduced if it improve the lifespan and do not require regular servicing (eg : lubrication). But it may greatly increase the manufacturing complexity & cost
- no solution found yet
- battery self discharge is a major problem
- super/ultra capacitor are given for < 20 years
- LED (green one apparently have a better lifespan than red one)
- Electromechanical counter may be a viable option ( [url]https://www.google.com/search?q=electromechanical+counter[/url] )
- Apparently, aging is not a problem.
- stability may be a problem
- frequency ?
- 100 year doesn't seems to be a problem
- but we need redondancy/error detection
- it can be done.
- need protection from rust/oxidation/moist
- http://en.wikipedia.org/wiki/Poly(methyl_methacrylate)#Acrylate_resin_casting ?
- A lot :)
- Grab/post/archive datasheet for future reference
- Power is the main topic.