I think the electronics can be challenging (more so from a reliabilty / redundance point of view), but the power sources are more so.
You probably will need to make some assumptions, without spending a lot of money. I would think of a few back-ups, like solar, geo-thermal, mechanism (wind + water), battery + capacitors, etc.
If all the device does is to keep time + go to sleep, its current consumption cannot be that big (ua range).
Not in the UK - we haven't seen the damn thing for months.
Doesn't matter, solar for 100 years is a no go. Lighting strike, vandals steals the panel or paints it black, etc. Same for wind generation. The whole assembly must be self contained and sealed up securely. He did state " time capsule " now didn't he?
retrolefty:
Doesn't matter, solar for 100 years is a no go. Lighting strike, vandals steals the panel or paints it black, etc. Same for wind generation. The whole assembly must be self contained and sealed up securely. He did state " time capsule " now didn't he?
Lefty
Nuclear it is then.
Seriously now. Where will the device be situated? Can you guarantee that the building/bunker/mountain that will hold it will be there in 100 years?
I'm thinking some sort of thermoelectric device, hooked up to a water flow on one side and something that fluctuates in temperature on other. The batteries would need to be capable of sustaining the device for a few months (which is possible), and would be recharged during summer and winter when there is difference in water/something other temperature.
DirtBiker:
There are batteries based on tritium that are supposed to (theoretically, not promised) last hundreds of years. Just google "Nano tritium battery"
You need deep pockets though. I think I read somewhere they were nearly $2000 each.
The electronics could be very simple - just count equinox using the alignment of the sun (we don't have a specific date in mind), Stonehenge style.
So charging could be very low current, providing charge is greater than leakage.
Mmm, maybe that is what Stonehenge is? It will pop open soon, spouting confetti....
Or non-electronic, pure mechanical, use rise/fall of groundwater changed by tides to run a clock. Electronics could then be turned on during event day, release chemicals into a battery, and play happy birthday etc. One is only concerned with shelf-life. Bearings etc in the "clock" would only receive two 'ticks' per day, so little wear.
Have a little crank on the outside of the time capsule that turns a generator and charges a battery. Put a sign that reads "Please turn crank".
Someone ought to turn it within 100 years.
On a serious note, if you can sleep your processor and it uses 0.35 uA, it would require a 306.6 mAH battery. This assumes a zero internal discharge rate, and some form of battery chemistry that can last 100 years.
BulletMagnet83:
The one thing you won't run out of in the next hundred years is curious people.
Reminds me of when my brother was little, he made a small wooden box with a slot in the top. He wrote "Insert Coin Here". Of course when ever we had guests over, they all had to insert a coin to see what happens XD
The military uses some pretty exotic batteries that I think are supposed to have near-forever shelf-life (well, 20 years, anyway.) In missiles and fuzes and things. They're essentially solid and inert at room temperature and need to be activated by a pyrotechnic charge to melt the relevant parts. After which they produce plenty of power, for long enough for the device to reach the target. Molten-salt battery - Wikipedia
Come to think of it, there's a slightly similar class of water-activated batteries, and a near equivalent in the zinc-air batteries commonly used in hearing aids. I suspect that if you can build a storage container that will hold vacuum for 100 years, a circuit with OTS Zinc-air batteries might still work after 100 years once you let air (and moisture) in.