nelson_p@apollo.uucp (02/17/88)
I was thinking about a rather off-the-wall project the other day
and trying to work out some of the technical problems involved.
I had in mind an 'electronic time capsule', i.e., a small box
perhaps set in a remote location where it wouldn't be accidentally
disturbed, that would remain in a dormant state for decades or
even centuries at the end of which time it would begin transmitting
a radio signal to call attention to itself (at least during the
day when solar power could provide a current source).
The two main problems I see to overcome would be long-term reli-
ability and how to count the time before 'waking-up'.
I assume reliability could be achieved by careful selection of
components to avoid things like NiCads, electrolytic caps and
other things that may leak or fail after a relativley short time,
especially as a result of the inevitable day-night temperature
cycling it would be subject to. Silicon solar cells and CMOS
circuitry should be pretty reliable if carefully tested ahead
of time to get out of the steep part of the 'bathtub curve'
and then well sealed against the elements. All design would
be extremely conservative.
Timing out decades or centuries is a tougher problem. I had
three ideas but none of them satisfy me:
Some modern batteries have very long shelf-lives (decades,
even). A CMOS gate input to sense the state of the battery
has such high input resistance that it would not appreciably
alter the shelf life. When the battery finally dies the
time-capsule comes to life. Main objection: too short a
time.
Binary day-counter. A CMOS binary counter could be powered
by a few 10's of uF of capacitance using some reliable non-
electrolytic capacitor type. The caps would be kept charged
during the day by the solar cells and would be enough to save
the state of the counters at night. Sensing the output of the
solar cells with a schmitt trigger would result in one 'count'
per day. A 16 bit counter would 'wake' the box up in 179 years.
Objections: If the solar cells were covered for an extended
period of time by a deep snowstorm, leaves, etc, the caps
would discharge, the count would be lost and it would have to
start over.
Built-in failure. Use a component that I *know* will fail
eventually like a Nicad battery or an electrolytic capacitor.
When it no longer holds a charge the box 'wakes up'. Objection:
the wakeup time is *extremely* unpredictable.
I know this is a weird idea but sometimes they are the most fun to
think about. Thank you in advance for any ideas this provokes.
--Peter Nelson (N1CHJ)
phd@SPEECH1.CS.CMU.EDU (Paul Dietz) (02/18/88)
In article <3a56593d.44e6@apollo.uucp> nelson_p@apollo.uucp writes: > I had in mind an 'electronic time capsule', i.e., a small box > perhaps set in a remote location where it wouldn't be accidentally > disturbed, that would remain in a dormant state for decades or > even centuries at the end of which time it would begin transmitting > a radio signal to call attention to itself (at least during the > day when solar power could provide a current source). Probably the hardest part would be finding a place to put it. If you're using solar power, you need to make sure that the cells will remain exposed. There is a simple, if somewhat expensive solution: put it in orbit! You can be pretty sure that the cells will remain exposed, and you can probably rule out external corrosion as a failure mechanism. As for earth-bound techniques, you might want to consider putting the beast under the ocean. For energy, you could harness the currents or even the thermals. Then, when the time had come, it could release itself to the surface, throwing out an array of solar cells to power its transmissions. You have to be pretty careful these days about what IC's you use. Channel lengths are getting awfully short, and gate oxides are getting pretty thin. For long term reliability, you'd probably want to use some low-tech stuff. Any experts out there on long term reliability of sub-micron devices? (So, what do you transmit; old sci.electronics posts? :^O ) Paul H. Dietz ____ ____ Dept. of Electrical and Computer Engineering / oo \ <_<\\\ Carnegie Mellon University /| \/ |\ \\ \\ -------------------------------------------- | | ( ) | | | ||\\ "If God had meant for penguins to fly, -->--<-- / / |\\\ / he would have given them wings." _________^__^_________/ / / \\\\-
neal@weitek.UUCP (Neal Bedard) (02/18/88)
Well, I think the solar cell and large electrolytic capacitor idea is a good one ... however, if you really want a reliable system, use a radioactive-decay thermal unit like those used on deep-space probes (e.g., Voyager, Galileo.) The biggest drawback to these units is their expense - in the tens of thousands of dollars. However, they are rugged, and have lives in thousands of years. Also, they put out current in 500 mA-2 A range, enough to run a *hefty* transmitter. If you pick a spot that has relatively constant (or at least predictably cyclic) winds, a small windmill + a solar panel to charge the energy-storage system would do the trick. Or, you could play games with thermocouples if you have a constant temperature gradient available to you. As to energy storage, I seem to recall a "high-farad" capacitor that one of the oil comapanies put out (Sohio?) - it acts almost like a battery, but it isn't: it provides current all the way down to zero volts, unlike a battery. They are available in 1-10 *Farad* denominations; however they might suffer from the same lifetime problems as 'lytics, though. Now, as to the *system* itself, my suggestion is to use a very-low power 8-bit microcontroller and EEPROM: you measure off one "day" by using a timer interrupt and a soft counter, then you update the 16-bit "day" in EEPROM. (Come to think of it, there may be uC's out there with EEPROM *on-chip*.) To save power and EEPROM erasure cycles (most rate their parts at about 1000 to 10,000 cycles), one could program the uC to zap the EEPROM with the timer-state only when the power sensor says that the supply is almost exhausted. When the day counter finally rolls over, the uC would instead run the attention transmitter until the power is discharged each time the power sensor wakes it up. From there on out, it transmits if there's power, rather than counting. Interesting problem. -Neal
todd@uop.edu (Dr. Nethack) (02/19/88)
If you are going to use nuclear power, why not use some cesium in the unit somewhere, and have an atomic clock?
jbn@glacier.STANFORD.EDU (John B. Nagle) (02/19/88)
Timing is the easy part. It's not at all clear that we have the
technology to make electronics with a shelf life of a century, let alone
an operating life that long.
Capacitive-type EPROMS will probably discharge within a decade or
two. Lifetimes of other components are more problematical. Ceramic-packaged
militarized ICs might make it. Electrolytic capacitors probably wouldn't.
A good first step would be to build something that would survive
a year of 2-hour freeze/bake cycling.
Whatever it is, it should have redundancy. It would be useful to
have two units checking each other, and as soon as one failed, the
other would go on the air, so it would make itself known rather than
being forgotten.
John Naglenelson_p@apollo.uucp (02/20/88)
In reference to my idea of an electronic time capsule (a solar- powered device which remains mostly dormant for decades or centuries, ultimately 'waking up' and calling attention to itself via a radio signal) I got the following suggestion on how to time out all those years before awakening: > try radioactive decay for timing. Inherently stable, easy to count, > small, low power. This is potentially a very good idea, having many advantages over my other proposals. Questions: How can I sense the radioactivity? G-M tubes are not particularly long-lived devices; depending on how they're quenched and how much radiation they're exposed to, they may be good for a few decades at best. Are there reliable solid-state detectors? Also what materials would have a sufficiently short half-life to be suitable? --Peter Nelson
todd@uop.edu (Dr. Nethack) (02/21/88)
With all the talk over the time capsule, what a great way to start a science fiction story.. Can you imagine if something 1000 years old like that started beeping today??!!
jimc@iscuva.ISCS.COM (Jim Cathey) (02/23/88)
In article <3a623999.44e6@apollo.uucp> nelson_p@apollo.uucp writes: > This is potentially a very good idea, having many advantages > over my other proposals. Questions: How can I sense the > radioactivity? G-M tubes are not particularly long-lived devices; > depending on how they're quenched and how much radiation they're > exposed to, they may be good for a few decades at best. Are there > reliable solid-state detectors? Also what materials would have a > sufficiently short half-life to be suitable? I have an old gamma counter at home (medical surplus). I think it uses a sodium iodide crystal as a scintillation detector followed by a photomultiplier tube as the active ingredients. I don't know if there are any more modern optical sensors than the PM tube that are solid state. (I think the PM tube was heaterless, so it might be ok so far as life went, but it does require HV to operate.) The only radioactive thing I had that tickled the thing was Coleman lantern mantles. I think they're dipped in thorium oxide. Anybody know the half-life of this stuff? I don't have my CRC handbook nearby. +----------------+ ! II CCCCCC ! Jim Cathey ! II SSSSCC ! ISC Systems Corp. ! II CC ! TAF-C8; Spokane, WA 99220 ! IISSSS CC ! UUCP: uunet!iscuva!jimc ! II CCCCCC ! (509) 927-5757 +----------------+ "With excitement like this, who is needing enemas?"
tedk@ihuxv.ATT.COM (Kekatos) (02/23/88)
Regarding the construction of a "Electronic TIME Capsule, This sound alot like the monoliths of "2001, a space odyssey".
nelson_p@apollo.uucp (02/25/88)
In response to my proposal for an electronic time capsule, John Nagle observes: > Timing is the easy part. It's not at all clear that we have the >technology to make electronics with a shelf life of a century, let alone >an operating life that long. > > Capacitive-type EPROMS will probably discharge within a decade or >two. Lifetimes of other components are more problematical. Ceramic-packaged >militarized ICs might make it. Electrolytic capacitors probably wouldn't. > > A good first step would be to build something that would survive >a year of 2-hour freeze/bake cycling. > > Whatever it is, it should have redundancy. It would be useful to >have two units checking each other, and as soon as one failed, the >other would go on the air, so it would make itself known rather than >being forgotten. Of course, everything would be MIL-SPEC and I've tried to keep the design simple to promote reliability. I've been quite amused by some of the proposals for wind generators, atomic power, microcomputers with EAROM, etc. These people have never heard the KISS rule and I doubt that such designs would last a decade. Another advantage of keeping it simple is low cost. If it's cheap then I can make a dozen or more and that way increase the odds that at least a few might last a century or two. My prototype has 6 CMOS IC's, all SSI and MSI and one transistor (for the transmitter). It transmits a short message in CW with a power of a couple hundred milliwatts. Of course, in centuries to come nobody will probably use CW so I should change that (to what?). I assume that because of the larger chip geometry features relative to LSI or VLSI devices, SSI and MSI devices should be more reliable. But I admit that I don't know what the long-term failure modes for CMOS logic are. If it's contamination from the air then perhaps I can seal the board or individual devices. If it's the result of micro- fracturing due to constant temperature cycling then maybe using an enclosure with a large thermal mass will reduce the *rate* of temperature change to reduce thermal shock. I don't know. What did you mean, 'timing is the easy part'? To me that is still the biggest unsolved part of the problem. --Peter Nelson
mikkel@cg-atla.UUCP (Carl Mikkelsen) (02/25/88)
In article <3a623999.44e6@apollo.uucp> nelson_p@apollo.uucp writes: > I got the following suggestion on how to > time out all those years before awakening: > >> try radioactive decay for timing. Inherently stable, easy to count, >> small, low power. > > What materials would have a sufficiently short half-life to be suitable? Try tritium, like was used in the old TI backlit LCD watches. > How can I sense the radioactivity? If you used a TI-like back-lighting module, you could sense the radiation with one of several photon (not alpha, beta, or gamma) detectors. > Are there reliable solid-state detectors? I would think that a good phototransistor should be as reliable as any other semiconductor device. > --Peter Nelson - Carl +--------------------------+--------------------------------+ | Carl Mikkelsen | ..!ism780c\ | | | ..!cbosgd!ima>!cg-atla!mikkel | | Compugraphic Corporation | ..!ulowell/ | | 200 Ballardvale St. | ..!decvax/ | | Wilmington, Ma. 01887 | (617) 658-5600 x 5220 (voice) | | | (617) 658-0200 x 5220 (TT-auto)| +--------------------------+--------------------------------+
torkil@psivax.UUCP (Torkil Hammer) (02/26/88)
If you want centuries, go mechanical. Use an odometer as timekeeper, at a rate of one click per day. Odometers donot reset to a strange number after a hiccup. You drive it from bimetal springs, like the ones in a wall thermostat. You need one that tracks the average daily temperature and adjusts to the annual variation, i.e. a time constant of a few days. A block of soapstone will do nicely. You need another with a time constant of about 4 hours, that tracks the daily temp curve. The odometer body is mounted on the first spring, the second carries a pawl arm that provides hysteresis and usually gets you one click per day. It is comparable with the 10 ppm accuracy you can get from a quartz clock and has better long term stability. You need a reliable power source at wakeup time, such as a two component chemical setup that is mixed when the flag falls. A glass vial with sulphuric acid is stable over centuries. The odometer rolls around and breaks the vial. For an simple "hello, world", just make a precharged lead-sulfate battery. The battery plates are made from lead and leadperoxide and are stable as long as the unit is sealed, so build the whole contraption into a glass cage. You get several months of service life once it starts, and you have lots of power. If you are celebrating something big, let the sulphuric acid etch away a rod of magnesium that prevents 20 pounds of plutonium from joining another 100 pounds. Please start your 6 digit odometer at zero, though. For an expert treatise on the subject, read Arthur C. Clarke's story about the fire alarm and enjoy how he makes the timer and gets the nuclear device to its place and to go off when the timer expires. Arthur needs no chemicals or odometers or built in bombs to get things going. ;----------------------------------------------------------------------- Standard disclaimer: Opinions void where prohibited by law. We have additional ways to get you which depends on your state of residence and your state of mind; the phase of the moon and the faze of never mind. ;----------------------------------------------------------------------- torkil
spikes@hpscdd.HP.COM (Bill Spikes) (02/27/88)
Hi,
Your time capsule problem is a good puzzle. It sounds like you have
the electronics worked out. How is the oscillator going to fire up? Is
it going to have a capacitor or a crystal? What are the shelf lives of these?
My input to the problem of the 200 year timer and protection of the
device is thus: Why not put it a few feet above the floor of the ocean in
a fairly deep spot? Probably nobody will find it, there is practically no
radiation, either man made or natural that will "age" the electronics, and
that is the last area man will be able to pollute.
Now for the turn-on timer. The capsule is a fully sealed unit, antenna
included, weighted at the non-antenna end, filled with a non-corrosive
inert gas. It has photocells embedded in it on it's top surfaces for power
and in the bottom, a wave action generator (pendulum action, moving magnet
within coils) giving it two types of power. The capsule lives upside down
inside another container whose lower end is anchored to a weight via a cable
all made of the same indestructible materials as the capsule. The material
would probably be some kind of plastic, maybe the same type used to keep
Dick Clark from aging. The bottom end cap of the outer capsule has a seal
made of a substance that has a known corrosion resistance to salt water
and pollution products. I would think that boat, marina, and oil companies
would have much information on what the lifetimes of various materials
are in a ocean environment. You just pick one that will be mostly gone
in 200 or so years. There is no way to be super accurate about this as
man and Mom nature continue to change the environment, but I would bet that
our atmosphere will be in worse shape in 200 years than will the oceans.
When the seal lets go, the top comes off of the outer container. The
weights in the bottom of both containers (until now on the "top" or surface
end) plus the "air" in the top of the capsule now turn the whole thing
right side up. The inner capsule then slides out and heads for the surface.
The outer capsule has served its purpose. It kept the inner capsule dry,
and shielded it from what divers call "critters".
You now have on the surface a clean, unweathered, and yet to be powered
up electronics package. If we haven't yet blown the earth out of orbit, the
sunlight hits the cells and hopefully the thing starts beeping. If there
is no sunlight, the wave action generator in the bottom of the capsule
provides power. This assumes, of course, that it's pivot has not fused itself
together.
The best feature of the Ocean Release System (tm) is that the capsule is
now free to move around. This means that it has a better chance of finding
what is left of humanity. Also, even if the electronics don't function, it
still may wander past some type of intelligent life, that won't eat it, and
be opened. Although the scenario I have expressed here is somewhat fatalistic,
it is not unrealistic. Plan for the worst and hope for the best.
If you are not sure of the oscillator starting after all this time, how
about letting wave action do the keying of the transmitter with the help
of something like a hall effect switch? It won't send perfect code but then
again, maybe it would stand out more in a cluttered frequency spectrum,
especially if was annoying. :-)
I would like to see some of the responses you have received and what
the final design turns out to be like.
Bill Spikes
Hewlett Packard
Santa Clara Division
nelson_p@apollo.uucp (02/27/88)
RE: My 'electronic time capsule'... >If you put it under water, like I suggested, you will have an excellent >time base available: the tides! These are fairly trivial to detect, and >are predictable over many centuries! I am quite pleased with the creativity and originality shown by some respondents to my question: 'How can I count off the time before my time capsule 'wakes up' a century or two down the road?' I'm not sure about tides. First of all, there's the question of how to power it under water. I had been planning to use solar cells for a source of power; when the system finally wakes up it would transmit during the day. Then there's the question of how to detect the tides. Remember that systems involving moving parts would probably fail after a few decades in the best of conditions, and the ocean is NOT the best of conditions. Which brings us to reliability. Underwater it would be subject to barnicle growth and marine plants. Ships sunk during WW II are totally encrusted now, a scant 45 years later. And I don't know what I would use for an antenna. Somebody else suggested tritium. Watches used to be made with a substance which would light up in the presence of the alpha particles emitted by the tritium. This bears some investigation: I will have to look up the half-life of tritium and also find out about the material used. It would have to work over a century or more and not be subject to leakage or breakdown as a result of temperature cycling. I mention the latter because I seem to recall that it was in a liquid medium. Good ideas though, keep 'em coming and thank you. --Peter Nelson
phd@SPEECH1.CS.CMU.EDU (Paul Dietz) (02/28/88)
Just a short summary: Power sources: Batteries Get serious... Solar How do you make sure that the cells remain exposed? Nuclear Not feasible for the the basement project... mechanical (i.e. tides, wind, etc.) subject to failure. thermal Very good reliability, low power output. Timing sources: crystal mechanical reliability problems. rc reliable, accuracy ~1% fairly easy to achieve mechanical won't last if built in a basement... chemical (clock reactions, or how about an Hg filled speaker cable, with a copper plug that gets dissolved away, and allows the mercury to close a circuit?) Reliable, but timing accuracy is poor. daylight Same problems as solar power... thermals Could be a possibility since unit would not have to be exposed, and earth/water (depending where you put it) give a nice slow time constant. (these effects are both daily, and yearly...) As for putting it underwater, I'm sure it is possible to find materials which would be extremely resistant to things like barnical growth. (How about teflon, aluminum, or maybe lead?) Paul H. Dietz ____ ____ Dept. of Electrical and Computer Engineering / oo \ <_<\\\ Carnegie Mellon University /| \/ |\ \\ \\ -------------------------------------------- | | ( ) | | | ||\\ "If God had meant for penguins to fly, -->--<-- / / |\\\ / he would have given them wings." _________^__^_________/ / / \\\\-
cgs@umd5.umd.edu (Chris Sylvain) (03/01/88)
In article <3a7af473.44e6@apollo.uucp> nelson_p@apollo.uucp writes:
<
< ... It transmits a short message in CW with a power of a couple hundred
< milliwatts. Of course, in centuries to come nobody will probably use CW
< so I should change that (to what?). ...
Maybe in centuries *Morse Code* won't be used any longer, but *CW* is just
too useful for narrow bandwidth, slow signalling, human demodulated signals.
I know phase modulation can just about pull information (signals) "out of a
hat" ( S/N ratio darn near unity [or less (?)] ), but CW is simpler.
Maybe you will want to use a simpler binary code?
--
--==---==---==--
.. he went galumphing back. ..
ARPA: cgs@umd5.UMD.EDU BITNET: cgs%umd5@umd2
UUCP: ..!uunet!umd5.umd.edu!cgsmb@camcon.uucp (Mike Bell) (03/01/88)
A few thoughts:
using solar power may be a problem. Within a hundred years grass grows,
soil is eroded or deposited. Ensuring that a solar collector can still
pick up enough light (and is not totally eroded) may be difficult. I
guess some remoter sites may be OK assuming no global changes in the
weather.
Other sources of power:
thermal (cooling/heating due to day/night)? differential cooling/heating
rate provides temperature difference = work
nuclear (not very practical for DIY).
geo-thermal (dig a deep hole?)
Timing:
thermal changes with day/night? with season? used to drive counter?
changes in direction of the earth's magnetic field as a trigger?
cessation of a radio signal (eg. standard time signal) enables transmitter?
changes in gravity? (eg. lunar/planetary effects)
Any thoughts as to what frequency/message to transmit?
--
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