Also... why a RTC ? It seems to be much more complex than it need to be.
Why not a simple counter ? It's all about counting days. (also, i didn't find RTC that will still work after 2099, which is a problem)
Because an RTC is specifically engineered for the job - the counter isn't a huge issue but the oscillator is, and is probably the largest power consumer. Date range is not an issue - just keep any higher-order count seperately - many RTCs have some extra registers for user data, so have a bit for year rollover
The problem is leap year managment :
If the year can be evenly divided by 100, it is NOT a leap year,
unless; The year is also evenly divisible by 400. Then it is a leap year.
This means that 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are NOT leap years.
Also... why a RTC ? It seems to be much more complex than it need to be.
Why not a simple counter ? It's all about counting days. (also, i didn't find RTC that will still work after 2099, which is a problem)
Because an RTC is specifically engineered for the job - the counter isn't a huge issue but the oscillator is, and is probably the largest power consumer. Date range is not an issue - just keep any higher-order count seperately - many RTCs have some extra registers for user data, so have a bit for year rollover
The problem is leap year managment :
If the year can be evenly divided by 100, it is NOT a leap year,
unless; The year is also evenly divisible by 400. Then it is a leap year.
This means that 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are NOT leap years.
This stuff can all be dealt with easily in software whenever the main controller is running - you don't have to use the RTCs logic - all you need is an elaped time count
Just for fun, I went searching for a low-power atomic clocks and found this:
http://www.microsemi.com/products/timing-synchronization-systems/embedded-timing-solutions/components/sa-45s-chip-scale-atomic-clock
Sub-120mW chip-scale atomic clock, sounds interesting. Only rated for 100k hours MTBF though. Sounds like a great fit/upgrade for those Agilent frequency counters with lousy stock oscillator.
Does anyone know how a device like this can be atomic, and yet have such a poor aging characteristic? Atomic clocks are supposed to use very fundamental qualities of matter. How can that age?
It's aging is specified at 3.0E-10/month, doesn't seem too bad to me!
Its not bad if you are used to crystals, but its horrible for an atomic source. My point is, where does it come from? If the source of the timing is an atomic physics measurement, how does that age so much?
The problem is leap year managment :
If the year can be evenly divided by 100, it is NOT a leap year,
unless; The year is also evenly divisible by 400. Then it is a leap year.
This means that 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are NOT leap years.
Why would you worry about leap years if all you do is count days?
100 years contains very low frequencies, so you have very big pink noise.
I don't understand this part
This can include lightnings, nuclear wars, collisions with other space objects... So I would put as much protection devices on board as possible.
I would use an antifuse FPGA for this. The crystal has to be in a super package.
Einstein said, that human stupidity is infinite, so I would power it from that.
I'll write a memo "warranty void if nuclear winter seal is broken"
The problem with stupidity : even if it potentially hold an infinite amount of energy, its power efficiency sux
Well, this comes from an article about pink noise I've read a long time ago. Since our electronics products have a lifetime which measures in years, the 0.00...01 Hz noise is going to be very large. The circuit is switched on, switched off, environment changes, parts are ageing... All of this can be inspected in the frequency region. 0.00001Hz region is something happening every day, and so on. The wider the frequency range on the lower end, the harder to make something work. So making your stuff work is not only a problem in the MHZ region, but also in the microhertz region. And your DC voltage in the specification becomes "1mHz is good enough".
The problem is leap year managment :
If the year can be evenly divided by 100, it is NOT a leap year,
unless; The year is also evenly divisible by 400. Then it is a leap year.
This means that 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are NOT leap years.
Why would you worry about leap years if all you do is count days?
If you use a counter : don't care
If you use a RTC with "days since birth = today date - birth date" then you have a problem with leap year. All rtc seems to handle the 4 years leap, but not the 100 & 400 year leap
The problem is leap year managment :
If the year can be evenly divided by 100, it is NOT a leap year,
unless; The year is also evenly divisible by 400. Then it is a leap year.
This means that 2000 and 2400 are leap years, while 1800, 1900, 2100, 2200, 2300 and 2500 are NOT leap years.
Why would you worry about leap years if all you do is count days?
If you use a counter : don't care
If you use a RTC with "days since birth = today date - birth date" then you have a problem with leap year. All rtc seems to handle the 4 years leap, but not the 100 & 400 year leap
As long as you know how the RTC behaves, you can deal with it. This is an insignificant issue compared to everything else.
Yes, power is the bigest issue. no solution found yet.
I wrote to energizer with a simple description of the project and a simple a question : "is there any battery form factor guaranteed to still exist in 100 years ?"
Perhaps some kind of industrial form factor have a guaranteed minimum EOL.
I'm not expecting a reply but... who knows ?
It's Tadiran you want to write to for this:
http://www.tadiranbat.com. They "only" aim for 40 years lifetime, but given the tiny energy requirements you have for the RTC I suspect they'd manage. They might enjoy the challenge
About battery form factor, coin cell look ideal.
I'm pretty sure we can design a cell holder that can accept a wide range of coin cell form factor.
If you could make it a wearable item you could use body heat for the power source.
Tadiran's french sales manager replied to my mail
I call them monday
Just for fun, I went searching for a low-power atomic clocks and found this:
http://www.microsemi.com/products/timing-synchronization-systems/embedded-timing-solutions/components/sa-45s-chip-scale-atomic-clock
Sub-120mW chip-scale atomic clock, sounds interesting. Only rated for 100k hours MTBF though. Sounds like a great fit/upgrade for those Agilent frequency counters with lousy stock oscillator.
Does anyone know how a device like this can be atomic, and yet have such a poor aging characteristic? Atomic clocks are supposed to use very fundamental qualities of matter. How can that age?
It's aging is specified at 3.0E-10/month, doesn't seem too bad to me!
Its not bad if you are used to crystals, but its horrible for an atomic source. My point is, where does it come from? If the source of the timing is an atomic physics measurement, how does that age so much?
Rubidium references work by using a PLL to discipline a normal ovenized crystal to a ~7GHz microwave source that causes a 0.1% droop in the output of a rubidium lamp when it locks. There are a lot of potential sources of drift, from the electronics to the resonant cell. Even high performance devices are usually only 4e-11/month, not even an order of magnitude better. When it comes right down to it, rubidium gas cells simply aren't very good atomic clocks.
Anyways, they also have their yearly aging rate given as 1e-9/yr, which means only a couple minutes error accumulated over 100 years. Not too bad. Unfortunately they usually only have a design life of something like ~20 years so wouldn't be usable in this application.
Just for fun, I went searching for a low-power atomic clocks and found this:
http://www.microsemi.com/products/timing-synchronization-systems/embedded-timing-solutions/components/sa-45s-chip-scale-atomic-clock
Sub-120mW chip-scale atomic clock, sounds interesting. Only rated for 100k hours MTBF though. Sounds like a great fit/upgrade for those Agilent frequency counters with lousy stock oscillator.
Does anyone know how a device like this can be atomic, and yet have such a poor aging characteristic? Atomic clocks are supposed to use very fundamental qualities of matter. How can that age?
The same way rubidium and cesium clocks age: the material used in the oscillator evaporates, embeds itself in the resonating cavity's walls, is no longer part of the resonant cavity and the loss of vapor pressure is enough to cause minor drift. You also have the atoms' decay rate, possible impurities, the VCSEL and sensor's aging, etc. National standard atomic clocks require periodic maintenance to maintain their stability so expecting perfect long-term stability out of a sealed, maintenance-free autonomous module is not very realistic.
Dave did a video about a museum HP/Agilent cesium clock source and the HP guy said those cesium sources have a useful life of about 20 years due to material evaporation... but that is for a lab-grade time reference; not a national-grade one.
Even those million-dollars national time standards cannot agree perfectly with each other and require cross-checking with other national-grade references to correct their drift.
Someone who is less lazy than me still should work out the math... what would the TOTAL power consumption of the device be over 100 years?
Because I don't think you can get around the power issue unless you use nuclear materials (might be hard to source now that Ghaddafi is gone) or go with the mechanically stored power.
Anything else - heat, light, batteries or whatever else will always require human interaction, and I think the fact that it will run for 100 years untouched is the appeal of the device.
If the total amount of power needed was known, the mass and height of a weight could be calculated needed to power the device. Plus, it would be pretty cool that, year-after-year, the weight drops fractionally... like a few millimeters or less. Almost like... "when the weight reaches the bottom... you're dead"
The Atmos clock solved the problem a while back, and the earliest ones seem to have made significant progress toward the 100 year lifetime.
http://en.wikipedia.org/wiki/Atmos_clockThey get their energy based on small variations in temperature and pressure. As long as the weather doesn't stop, they'll have energy to keep running.
If the total amount of power needed was known, the mass and height of a weight could be calculated needed to power the device. Plus, it would be pretty cool that, year-after-year, the weight drops fractionally... like a few millimeters or less. Almost like... "when the weight reaches the bottom... you're dead"
If my Wolfram Alpha Fu is correct, a device using 3 volts at 1 uA for ONE year would use the potential energy of a 9.6 kg weight lifted by one meter.
(3V * 1 uA * 1 year) / (1 m * 9.81 m/s^2)
Someone who is less lazy than me still should work out the math... what would the TOTAL power consumption of the device be over 100 years?
Because I don't think you can get around the power issue unless you use nuclear materials (might be hard to source now that Ghaddafi is gone) or go with the mechanically stored power.
Anything else - heat, light, batteries or whatever else will always require human interaction, and I think the fact that it will run for 100 years untouched is the appeal of the device.
If the total amount of power needed was known, the mass and height of a weight could be calculated needed to power the device. Plus, it would be pretty cool that, year-after-year, the weight drops fractionally... like a few millimeters or less. Almost like... "when the weight reaches the bottom... you're dead"
Nuclear will probably require servicing too.
I can't think of any solution that doesn't require some kind of battery change or regular servicing (even if "regular" = 40 years)
A device that require a new battery every 40 years could be an acceptable solution... perhaps... i don't tknow
And perhaps in 40y we'll have battery that last 100years ?
But there is the form factor problem. What kind of battery form factor will be available at this time ?
Someone who is less lazy than me still should work out the math... what would the TOTAL power consumption of the device be over 100 years?
1uA over 100 years is 876mAh so in principle an AA cell or 2477 lithium, but shelf-life is going to be the dominant factor by far with any chemical battery.
I'd say for a solution based on readily available tech, solar plus large value low-leakage capacitor probably has the best chance, as long as it's kept somewhere that receives some light each day.
Dave found some lithium powered sram seemlingy working after 27 years. (ep 615)