RE: [time-nuts] Low cost synchronization
From Chuck Shepherd's News of the weird comes this item: In July, film director David Lynch announced that he had formed a foundation to raise $7 billion to fund 8000 Transcendental Meditation practitioners to bring world peace by creating a unified field of stress-free brain waves over the Earth, which TMers accomplish, as they describe it, by detaching their minds from the 'thinking process.' He goes on to say that the cost of training has gone up since John Hagelin needed only $4.2 million in 1993 to take 4000 TMers to Washington, D.C., to reduce crime for eight weeks. Is there any tie-in? We don't know. You are free to speculate. Personally, I think the only way to world peace is to eliminate the human predators, leaving only the sheep. Good leadership might be hard to find, though. Regards, Bill Hawkins ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Low cost synchronization
What about this: Use an NTP client running on a Smartphone. Such NTP clients are available for Pocket PCs, Symbian OS, etc. Dominik Schneuwly -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak Sent: samedi, 20. août 2005 21:00 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Low cost synchronization Hi Mike, Sorry for the late reply. You raise an interesting question and here are some thoughts. 1. Crystal Modeling Standard 32 kHz crystals won't work. TCXO aren't good enough either. OCXO are too power hungry. A couple of quartz wrist watches are good to 5 or 10 seconds per year. This may be close enough for your needs. The Pulsar PRS10 is one example. I think they use dual mode crystals to achieve their exceptional accuracy and relative temperature insensitivity. With the quantities you are talking about a dual mode crystal may fit the requirement. Dual-mode crystals are a niche market, however, so making arrangements with a manufacturer will not be simple. 2. WWVB Receiver These are exceedingly cheap now and should fit all your requirements. Contact Rod Mack who has probably done more WWVB RD than anyone on the list (he did the Ultralink receivers using Temic chips). Email me offline for his contact info. WWVB reception quality is not an issue since it's only used to intermittently re-synchronize the internal XO. One decent reception every couple of days or even weeks will take care of your requirements. Note also that many WWVB chipsets are now global, meaning they will also receive signals from LF time services in Europe and Japan 3. GPS Receiver 4. GPS Time Receiver As many cell phones now include GPS receivers sizes and prices are dropping. But I'm guessing you are not going to meet your fob-size nor power specs with GPS (or other satellite nav systems). 5. Cellular What percent of your thousands to millions of users world-wide already have a cell phone? To me this is the obvious solution. I would guess all cell phones know the time to a millisecond internally and this means a billion people on the planet are already carrying just what you need. Battery life is not a problem because all users already know how to recharge theirs. Now if each brand of cell phone would just have a standardized 1PPS output connector you'd be all set. 6. TV Stations Two methods come to mind. The XDS timecode (used by PBS stations) is good in principle but perhaps not in practice. The other approach is to discipline a 32 kHz XO against the 3.58 MHz colorburst frequency. This seems dated, though. 7. Atomic Reference In 10 years maybe. 8. Other? 1) Look into an interface with Sirius/XM satellite radio. 2) Or piggy-back on the existing paging networks. 3) Lock onto the carrier of a high-power local AM or FM station. If these stations use Rb or GPSDO referenced carriers you'll get a long-term stable frequency for free. 3b) For extra credit use DSP. Since AM/FM radio and TV frequencies have assigned slots world-wide you can simultaneously receive many local stations and combine their frequency stabilities to a common mean time/frequency. This would make a wonderful project for someone; commercial or university. For any solutions that give you stable frequency only (XO, RF carriers, 60 Hz) you will need a way to set the initial time and to reset the time when the batteries fail. For any solutions that give you time only you will presumably need to convert from UTC to local time. Also, are you concerned with DST? At least with your requirements, you don't have to worry about leap seconds! /tvb http://www.LeapSecond.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Magnus Danielson wrote: For any solutions that give you stable frequency only (XO, RF carriers, 60 Hz) you will need a way to set the initial time and to reset the time when the batteries fail. For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h basis, so it may be a bad idea to depend on it. I keep hearing, on this group, that the powerline is no longer sync'd to utc, and evidence for that fact being a lack of motorized wall clocks. Well, clocks that sync to the powerline are in universal abundance in the US. Virtually every clock on kitchen appliances is sync'd this way. The clocks on VCR's may be reset from time to time by a tv station, but the timing signal is still the powerline. Basically, any appliance, or device that plugs into the powerline is likely to use the powerline for its timing function. -chuck ___ time-nuts mailing list [EMAIL PROTECTED] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization, kitchen appliances
For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h basis, so it may be a bad idea to depend on it. I keep hearing, on this group, that the powerline is no longer sync'd to utc, and evidence for that fact being a lack of motorized wall clocks. Well, clocks that sync to the powerline are in universal abundance in the US. Virtually every clock on kitchen appliances is sync'd this way. The clocks on VCR's may be reset from time to time by a tv station, but the timing signal is still the powerline. Basically, any appliance, or device that plugs into the powerline is likely to use the powerline for its timing function. -chuck Correct, my measurements clearly show that mains power is steered to UTC. See: http://www.leapsecond.com/pages/mains/ If there's anyone from the power industry on the list I'd be interested to hear first-person technical details of how phase is synchronized, both short- and long-term. But I'm not sure I agree with your claim about kitchen appliances. It seems to me almost every kitchen, electronic, wall-clock, and entertainment appliance being sold these days uses quartz-based clocks, regardless if they are mains, wall-wart, or battery powered. I'm not sure how to confirm the accuracy of this hunch, though. I suspect there are several factors in the trend away from mains-clocks to quartz-clocks: 1) Digital or analog quartz movements are dirt cheap (so it's a cost saving measure). 2) If the product is intended for sale in Japan (where both 50 Hz and 60 Hz mains co-exist). 3) If the product is intended for sale world-wide (there is a healthy mix of 50 vs. 60 Hz and 120 vs. 240 V across the planet). 4) The explosion in the use of switching power supplies in home electronics (which are immune to local voltage / frequency conventions). 5) The explosion in the use of microprocessor based control of appliances (where the CPU(s) are driven by an n MHz XO and date/time/display functions are managed in firmware). /tvb ___ time-nuts mailing list [EMAIL PROTECTED] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization, kitchen appliances
Tom Van Baak wrote: still the powerline. Basically, any appliance, or device that plugs into the powerline is likely to use the powerline for its timing function. -chuck Correct, my measurements clearly show that mains power is steered to UTC. See: http://www.leapsecond.com/pages/mains/ If there's anyone from the power industry on the list I'd be interested to hear first-person technical details of how phase is synchronized, both short- and long-term. But I'm not sure I agree with your claim about kitchen appliances. It seems to me almost every kitchen, electronic, wall-clock, and entertainment appliance being sold these days uses quartz-based clocks, regardless if they are mains, wall-wart, or battery powered. I'm not sure how to confirm the accuracy of this hunch, though. I am just relating my experience with having mucked about in the insides of these appliances. Some are quartz, but those are generally the sort that have an alarm clock feature (coffee makers) Any that blink up at 12:00, or, lose time while the power is off are most certainly AC derived. My most recent exposure to an appliance clock is in a high end electric double oven made by DCS. It uses a powerline derived clock on its controller board. The DCS uses the same controller board as do the GE, Dacor, Kenmore, and numerous other ovens. The ovens are of current manufacture. You can be almost 100% certain that all domestic ovens will use line derived clocks. It would take one heck of a crystal to remain accurate when exposed to the temperature variations that exist around such a device's controller board. -Chuck ___ time-nuts mailing list [EMAIL PROTECTED] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
- Original Message - From: Magnus Danielson [EMAIL PROTECTED] snip BTW, measuring the 53rd overtone frequency may not give a clear picture of the frequency deviations at the base frequency. Overtone spectras experience quite a different phase shift from the way it is produced by a number of devices which vector-add to become the seen frequency and phase. Turn on or off a strong producer of that frequency may shift that phase quite a bit while the fundamental is barly shifted. Quite true, the majority of loads that produce high order harmonics back into the grid are almost always varying considerably in the short term-thus they produce short term variations in the resultant harmonic spectra that renders the lines somewhat broader than you might think. Ski lift motor drives are a good example of this. Such loads, without adequate filterimg at the point of supply for the load, produce high harmonic levels in the associated supply network, to the detriment of any telecom cable network that happens to run parallel for significant distances-as they always do in rural areas! The old manual method that used to be used for power grid frequency checking involved a comparison of two clocks, one driven from a reference and the other from the grid itself-more usually the output of a local generator in the days prior to strong grid linkages. The comparison was typically done once or twice a day and appropriate adjustments to the generation plant made to correct the grid driven clock and keep its reading 'syncronised' to the reference clock. I have here the remains of an attempt in the early seventies to bring this type of system up to date - it comprised an HP 105 series quartz reference, a K20- HP 5280A up down counter and an HP 5321B clock. The up down counter was driven from 100 Hz signals derived from both the 105B and the power grid. An HP 6933A D/A converter on the BCD output from the counter had its plus/minus 10 volt output interfaced to the generation plant. The 5321B clock reading was initialised from the local time service(radio time pips) and then used to fine tune the control system (D/A conveter to generator coupling) so the up down counter stayed at or near zero reading and grid time ran in sync with national standard time. I dont know how successful this system was but I think it was in service for several years. I have the up down counter and the D/A converter almost fully operational again- but only have parts ratted circuit boards from the 5321B clock and I never got the 105B. DaveB, NZ -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.10.13/78 - Release Date: 19/08/2005 ___ time-nuts mailing list [EMAIL PROTECTED] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Poul-Henning Kamp wrote: In message [EMAIL PROTECTED], Magnus Danielson writes: The interesting thing is that they have been seriously thinking about transmitting UTC and tarriff information on the grid, but it looks it is cheaper to just use GPRS mobile phones. Indeed. In Sweden that has become a big thing, with the deregulated market we have. We haven't chosen that path here at home yeat, but I guess it is a question of time like everything else. In Denmark they charge you $1000 extra to get a three-tariff meter :-( Here in the UK we have Economy 7 (it should be renamed Rip-off 7) where electricity is sold cheaper overnight. As far as I know, there is no installation fee for that, but if you have Economy 7 you pay more for electricity during the day. So unless you make heavy usage overnight (as one does with electrical storage heaters), it is not a good idea. My meter, uses a clock that used to keep accurate, but which is now usually wrong. Whether the meter uses the 50Hz for timing I do not know, but there is battery in there too. It may be wrong since the battery has failed and so the clock stops when there is a power failure, or it might be low in voltage which means the clock runs slow. But here at least, there is nothing very clever about how the time on those clocks is kept. Which suits me, as sometimes I get electricity cheap during the day now! -- David Kirkby, G8WRB Please check out http://www.g8wrb.org/ of if you live in Essex http://www.southminster-branch-line.org.uk/ ___ time-nuts mailing list [EMAIL PROTECTED] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Hi Mike, Sorry for the late reply. You raise an interesting question and here are some thoughts. 1. Crystal Modeling Standard 32 kHz crystals won't work. TCXO aren't good enough either. OCXO are too power hungry. A couple of quartz wrist watches are good to 5 or 10 seconds per year. This may be close enough for your needs. The Pulsar PRS10 is one example. I think they use dual mode crystals to achieve their exceptional accuracy and relative temperature insensitivity. With the quantities you are talking about a dual mode crystal may fit the requirement. Dual-mode crystals are a niche market, however, so making arrangements with a manufacturer will not be simple. 2. WWVB Receiver These are exceedingly cheap now and should fit all your requirements. Contact Rod Mack who has probably done more WWVB RD than anyone on the list (he did the Ultralink receivers using Temic chips). Email me offline for his contact info. WWVB reception quality is not an issue since it's only used to intermittently re-synchronize the internal XO. One decent reception every couple of days or even weeks will take care of your requirements. Note also that many WWVB chipsets are now global, meaning they will also receive signals from LF time services in Europe and Japan 3. GPS Receiver 4. GPS Time Receiver As many cell phones now include GPS receivers sizes and prices are dropping. But I'm guessing you are not going to meet your fob-size nor power specs with GPS (or other satellite nav systems). 5. Cellular What percent of your thousands to millions of users world-wide already have a cell phone? To me this is the obvious solution. I would guess all cell phones know the time to a millisecond internally and this means a billion people on the planet are already carrying just what you need. Battery life is not a problem because all users already know how to recharge theirs. Now if each brand of cell phone would just have a standardized 1PPS output connector you'd be all set. 6. TV Stations Two methods come to mind. The XDS timecode (used by PBS stations) is good in principle but perhaps not in practice. The other approach is to discipline a 32 kHz XO against the 3.58 MHz colorburst frequency. This seems dated, though. 7. Atomic Reference In 10 years maybe. 8. Other? 1) Look into an interface with Sirius/XM satellite radio. 2) Or piggy-back on the existing paging networks. 3) Lock onto the carrier of a high-power local AM or FM station. If these stations use Rb or GPSDO referenced carriers you'll get a long-term stable frequency for free. 3b) For extra credit use DSP. Since AM/FM radio and TV frequencies have assigned slots world-wide you can simultaneously receive many local stations and combine their frequency stabilities to a common mean time/frequency. This would make a wonderful project for someone; commercial or university. For any solutions that give you stable frequency only (XO, RF carriers, 60 Hz) you will need a way to set the initial time and to reset the time when the batteries fail. For any solutions that give you time only you will presumably need to convert from UTC to local time. Also, are you concerned with DST? At least with your requirements, you don't have to worry about leap seconds! /tvb http://www.LeapSecond.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Just as with WWVB receivers, he does not have to have the GPS powered up very long for and then only once a week or so to keep the oscillator tuned up. Once a GPS solution has been found, the local time and the GPS solution time give a time-difference and by remembering the GPS solution time from the last time you have the /|t you need to calculate the frequency error. So, a GPS solution could be possible. I'm curious what the power requirements are. My Casio WWVB wrist watch works on one battery for two years while my Casio GPS wristwatch is lucky to run for more than a two days, even when in intermittent mode. Depending on which standard you have, the phones only may have a sense of real time. In GSM for instance, the phones traces network time only in a relative aspect, but there is no real way to get an accurate UTC. The phones is being synchronised to the base This sounds odd to me given that cell phones I've seen can display the date time and they appear to be accurate to a second. All we need are some counter-examples. Does anyone on this list have a cell phone that displays the time of day with an error greater than a few seconds? (if yours has a HH:MM-only display compare the instant when MM changes). If so, then Mike can scratch cell phones from his list of accurate time sources. By the way, Mike, have you considered if your battery-operated, fob-sized, world-wide, low-cost, synchronization device will be allowed through US airports? /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
On Sat, 20 Aug 2005, Tom Van Baak wrote: 1. Crystal Modeling Standard 32 kHz crystals won't work. TCXO aren't good enough either. OCXO are too power hungry. Yup. A couple of quartz wrist watches are good to 5 or 10 seconds per year. This may be close enough for your needs. Yes, that would be very tempting, especially the 5 seconds number. If we could do that, we'd probably go for it and live with the error. The Pulsar PRS10 is one example. I found web reports of them being off 15-20 seconds per year, so the claims might not be valid for this watch. I fear the same issue with us, great research effort to develop a stable timing reference in the lab, but it fails to deliver in the field. There are just so many variables. I think they use dual mode crystals to achieve their exceptional accuracy and relative temperature insensitivity. With the quantities you are talking about a dual mode crystal may fit the requirement. Dual-mode crystals are a niche market, however, so making arrangements with a manufacturer will not be simple. Time to expose my ignorance, what is a dual mode crystal? Can you give me pointers to the manufacturers? If they would work, we can invest the time to make the arrangements. 2. WWVB Receiver WWVB reception quality is not an issue since it's only used to intermittently re-synchronize the internal XO. One decent reception every couple of days or even weeks will take care of your requirements. Even once a quarter would be good enough in most cases. Once you learn how your local XO is doing, you can apply that in the future. Note also that many WWVB chipsets are now global, meaning they will also receive signals from LF time services in Europe and Japan Ideally, the device would work anywhere, but WWVB (US 60 KHz), JJY (Japan 40 and 60 KHz), DCF (Germany 77.5 KHz), MSF (UK 60 KHz) only cover so much of the world. We're still missing sub equatorial Africa, western Asia, South America, Australia, Hawaii, and Alaska. Still, we can probably cover 80% of the world's population with what we can get. There are a few global VLF time receiver chips, notably those from C-max and MAS. They get three frequencies, usually chosen to be 40, 60, and 77.5 KHz. Due to the key fob size, we can't have a very large ferrite rod antenna so our sensitivity will be poor. It's not even clear we can get eastern US reliably. One wonders if you can build some sort of long term reception processing that would pick out the signal from the noise. Since you know what you *should* be getting, you can overlay multiple minutes of reception to cancel out the noise. I wonder how much processing that will take. Would it be possible to recover enough signal fro the noise to make VLF receivable worldwide? 3. GPS Receiver 4. GPS Time Receiver As many cell phones now include GPS receivers sizes and prices are dropping. But I'm guessing you are not going to meet your fob-size nor power specs with GPS (or other satellite nav systems). Actually, size and power are not the limiting factor. Consider this module: http://www.u-blox.com/products/lea_la.html Size wise, this will fit (we have one for another project, pretty awesome, about a postage stamp in lateral footprint). Power wise, using it once a week for one minute would use 43 mAH, or about 20% of a CR2032 coin cell (our preferred power source). We could get by with a solid time hit every two months. I don't care about the 1 pps output, just the NMEA date message. The real killer is cost. This module is probably $30 in qty ($70 in qty 1). Maybe, if we are very lucky, we could source something similar for $15 in very high volume. The WWVB style receiver is probably under $2. The concept is fairly price sensitive so we have to be under $5 total manufacturing cost. Now if only I could duty cycle the cost, then the GPS would cost me less than $0.01. :-) 5. Cellular Now if each brand of cell phone would just have a standardized 1PPS output connector you'd be all set. We've done a lot of work on embedded cellular. It's a mess building something that works everywhere or with everything. Do cell phones even know UTC or do they just know local time? It is important that a device in central time go off at the same UTC time as one in eastern time, not at the same numeric local time. 8. Other? 1) Look into an interface with Sirius/XM satellite radio. Hmmm. I'll research that. One imagines the chipset cost is on par with GPS, however, and may not have had the commodity development attached to it yet. 2) Or piggy-back on the existing paging networks. Too spotty, too much testing. Pagers are a dying service as cell phones take their business. 3) Lock onto the carrier of a high-power local AM or FM station. If these stations use Rb or GPSDO referenced carriers you'll get a long-term stable frequency for free. Only if I
RE: [time-nuts] Low cost synchronization
On Sat, 20 Aug 2005, Bill Hawkins wrote: Perhaps this is a means to coordinate an attack. Ah, the age of paranoia. Rest assured, the experiment's purpose is as far from that as possible. If you look at my requirements (accurate to a few seconds, lasts more than a year, low cost, built in thousands), I don't think that is consistent with enabling any evil purposes that you could not have done more easily some other way that already exists. -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Hi Mike: It may not be possible to get what you are asking for as a stand alone time keeper but I think could be done by periodically resetting. Using a radio signal for resetting has problems with the coverage area and/or power consumption. Maybe the resetting signal could be an audio time code optimized for this application. The user could call an 800 phone number and a microphone in the device would hear the code and reset. Or at a public meeting the audio code could be put on the P.A. system so all present would be synchronized. If the microphone can hear the beeper of another unit there might be a way to use a button on a unit to cause it to send it's audio time sync signal so other nearby units would sync to it. The device could learn it's aging rate at each reset and so change the divisor number to match the current aging rate. After sync the device might emit beeps or Morse code telling the user how far off it was allowing the user to gauge how often they need to resync. A TCXO should work for this. Have Fun, Brooke Clarke, N6GCE -- w/Java http://www.PRC68.com w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com Mike Ciholas wrote: Hi, I have a challenging research project to build thousands, perhaps millions, of devices that maintain mutual synchronization. The devices need to be low cost (under $20 retail, $8 manufacturing), small in size (key chain fob), and low power (operate at least 18 months on a battery). Synchronization ideally needs to be within a second or two over a year but there is some leeway to trade cost for performance here up to perhaps 10 seconds of variation per year. Ideally, the device works anywhere in the world but we may have to limit it to North America. 1. Crystal Modeling First idea was to get stable 32.768KHz watch crystals, perform a factory initial calibration, and use a temperature sensor to correct for the crystal temp curve. This idea is the cheapest, simplest, works everywhere, and uses the lowest power. Initial tolerance on the crystals is +/- 20 ppm (I've not found better in commodity parts), which equates to +/- 10 minutes a year, clearly unacceptable. I suspect that if I did an initial factory calibration and tracked temperature, I might improve this to +/- 2 ppm much like Maxim did with this part: http://pdfserv.maxim-ic.com/en/ds/DS32kHz.pdf But even so, +/- 1 minute per year is not really good enough. I suspect getting to a few seconds (+/- 0.1ppm) is unrealistic with any algorithm one can come up with. The base physics is simply not that predictable. 2. WWVB Receiver A second idea is to provide some external reference and the most logical choice is WWVB as used in several wrist watches. A little more cost but manageable. We've dissected several wrist watches and found they use a small ferrite antenna. The reception performance is spotty, however. I was unable to lock at work (lots of equipment) but did well at home (electrically quiet). If we go to the NE tip of Maine, that's twice as far from WWVB as we are here, so I wonder if the watch will ever pick up the signal. The saving grace is that the device needs to get the signal only sporadically, once a week or even once a month would do it since we can feed that back into correcting the local crystal. The negatives are that such a device is limited to the US and nearby, and it may have poor performance in many locales due to weak signals, local interference, and the small antenna rod we are limited to due to size (less than 1 inch). It does cost more, maybe $1-2 more in production quantity. Right now, this seems like the best option available to us. There are similar time broadcasting stations in Europe and China. We could build a unit that works in those regions, either as different models, or as a unit with multiple receivers. Still not global, but perhaps covering 50% of the world's population? 3. GPS Receiver A more precise external reference, use a GPS receiver. This gets us global coverage and is very precise. Uses a lot of power, so we would only activate it very briefly and not very often (once a week perhaps) to save battery. Major issue here is cost. Best I can do for an OEM module is around $25 in qty which busts the budget severely. It also has similar problems of being used in a place with no sky visibility. Size can be a problem in the cheaper modules. Some modules are quite small: http://www.u-blox.com/products/lea_la.html Cute, huh? 4. GPS Time Receiver This is fantasy land. I don't need the 100ns time reference, all I need is something good to one second or so. In this case, it seems possible to receive only 1 satellite, decode the digital data, and extract the time. It would be off by the variation in pseudo range which can't be corrected for. But I don't care about that level of accuracy. The question is, if you
RE: [time-nuts] Low cost synchronization
On Sat, 20 Aug 2005, Bill Hawkins wrote: Perhaps this is a means to coordinate an attack. And Mike Ciholas replied, Ah, the age of paranoia. Rest assured, the experiment's purpose is as far from that as possible. Well, no, not so much the age of paranoia as the age of extreme self-interest and no empathy for others. This leads to too many liars with public exposure, followed by erosion of trust. When a salesman says Trust me ... these days, it is best to walk away. Trust is the basis for civilization. It is sad to see it replaced by paranoid behavior as people learn not to trust other people. Mike, I've no reason to believe that you are lying, but you have withheld information. OTOH, if you did tell us the reason for these ticking key fobs, how would that differ from an email from someone who's money is trapped in Africa unless I help out? I mean, besides the fact that you aren't asking for money, although you could profit. Then too, your client could have misrepresented their purpose. I apologize if my creative mind has caused you any distress. It has caused me some distress as I try to work out what the fobs are for. Given the size of your market and the high probability of some religious or New Age significance, I'll never know until I see them for sale, if they go public. Regards, Bill Hawkins ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Mike - I've spent a fair amount of time looking in to this as part of my Internet testbed. At the moment, I have about 25 nodes using EndRun's CDMA time receivers ($1k-ish each), so I've been very interested in cheaper solutions, for obvious reasons. I assume that the devices of which you're speaking are standalone items? Something like a sensor deployment, possibly networked? Knowing more about how you actually plan on using these would help a bit. For example, if they're networked within particular regions, that gives you an easy way to synch to within milliseconds. WWVB: Are you going to be deploying inside buildings? Buildings with electronics and UPSes? If so, be very careful. Most cheap WWVB watches and clocks don't work very well on the east coast, from my experience. I poked around at a few in my old lab in Boston, and they were a no-go. Your analysis of GPS seems correct. You can probably build a $50 GPS time receiver to synch to milliseconds, but not much cheaper. On the other hand, as the 911 location requirements for cell phones expand, this may change. But not yet. Atomic reference: I'd say no chance in the next 5+ years. Local stable crystal: Actually, you could make it more than stable enough, but it would exceed your power requirements, because you'd probably fall back to an oven controlled oscillator. There goes your battery. But why did you try your initial experiments with 32.768Khz watch crystals? You're much more likely to find a good, solid 10Mhz reference with an SC cut TCXO. For instance, that maxim IC you mentioned has +- 2ppm, which is really quite awful by instrumentation standards. Compare to this one: http://www.bdelectronic.com/frequency/oscillatorTCXO.html .3ppm tempco, +- 1ppm/year. They don't show their overall allen deviation curves, but you get the idea - it'll be within 1ppm by the end of the year, and since that aging will probably happen over time, I'd guess it would probably get you something like 10 seconds within a year. Or something like: http://www.vectron.com/products/tcxo/tc140.pdf (... which is probably expensive, but which you can get in 0.2 ppm accuracy vs. temperature and 2ppm/10 years). Another option you may have just eliminated on principle: Internet synchronization. Very easy to keep synched to within a few hundred ms. (Internet can also be replaced by ACTS telephone, or your favorite other technology). Very limited in where you can deploy if you want outdoor deployment. WWVB and its kin may well be your best bet, _if_ you can hear them enough places. -Dave On Aug 18, 2005, at 1:29 PM, Mike Ciholas wrote: Hi, I have a challenging research project to build thousands, perhaps millions, of devices that maintain mutual synchronization. The devices need to be low cost (under $20 retail, $8 manufacturing), small in size (key chain fob), and low power (operate at least 18 months on a battery). Synchronization ideally needs to be within a second or two over a year but there is some leeway to trade cost for performance here up to perhaps 10 seconds of variation per year. Ideally, the device works anywhere in the world but we may have to limit it to North America. 1. Crystal Modeling First idea was to get stable 32.768KHz watch crystals, perform a factory initial calibration, and use a temperature sensor to correct for the crystal temp curve. This idea is the cheapest, simplest, works everywhere, and uses the lowest power. Initial tolerance on the crystals is +/- 20 ppm (I've not found better in commodity parts), which equates to +/- 10 minutes a year, clearly unacceptable. I suspect that if I did an initial factory calibration and tracked temperature, I might improve this to +/- 2 ppm much like Maxim did with this part: http://pdfserv.maxim-ic.com/en/ds/DS32kHz.pdf But even so, +/- 1 minute per year is not really good enough. I suspect getting to a few seconds (+/- 0.1ppm) is unrealistic with any algorithm one can come up with. The base physics is simply not that predictable. 2. WWVB Receiver A second idea is to provide some external reference and the most logical choice is WWVB as used in several wrist watches. A little more cost but manageable. We've dissected several wrist watches and found they use a small ferrite antenna. The reception performance is spotty, however. I was unable to lock at work (lots of equipment) but did well at home (electrically quiet). If we go to the NE tip of Maine, that's twice as far from WWVB as we are here, so I wonder if the watch will ever pick up the signal. The saving grace is that the device needs to get the signal only sporadically, once a week or even once a month would do it since we can feed that back into correcting the local crystal. The negatives are that such a device is limited to the US and nearby, and it may have poor performance in many locales due to weak signals, local
Re: [time-nuts] Low cost synchronization
David Andersen wrote: Local stable crystal: Actually, you could make it more than stable enough, but it would exceed your power requirements, because you'd probably fall back to an oven controlled oscillator. There goes your battery. But why did you try your initial experiments with 32.768Khz watch crystals? You're much more likely to find a good, solid 10Mhz reference with an SC cut TCXO. For instance, that maxim IC you mentioned has +- 2ppm, which is really quite awful by instrumentation standards. Compare to this one: http://www.bdelectronic.com/frequency/oscillatorTCXO.html .3ppm tempco, +- 1ppm/year. They don't show their overall allen deviation curves, but you get the idea - it'll be within 1ppm by the end of the year, and since that aging will probably happen over time, I'd guess it would probably get you something like 10 seconds within a year. Or something like: http://www.vectron.com/products/tcxo/tc140.pdf (... which is probably expensive, but which you can get in 0.2 ppm accuracy vs. temperature and 2ppm/10 years). -Dave Dave, The requirement that you seem to have missed is the 18 month battery lifetime. A 10 MHz oscillator is a couple milliapmeres, so it won't do the trick. The watch crystal needs only about 10 microamperes to oscillate. Mike, The 32K crystal may be usable, but you'd have to put some effort into the design to get the temp compensation tuned to the particular crystal, and you'd have to grade the crystals for tempco in the mfg stage. That might be doable in quantity, if you come up with the right sort of computerized test fixture in an oven. I have built a few nixie tube wristwatches using the cheap 32KHz crystals, so I have direct experience in this matter. (Has anyone else on this list built an electronic wristwatch?) Getting the crystal adjusted to 1ppm is not too hard. You'd have to temperature compensate it to get to 0.1 ppm, and that would be limited to perhaps 10C-30C temperature range. It's a lot easier to compensate the crystal if it's worn on the wrist rather than sitting in a car, since a person's wrist is essentially an oven. The real world has ridiculous temperature extremes - don't even think about stabilizing a crystal used outdoors unless it's thermally connected to a human. You should be able to evaluate the feasibility of using a compensated crystal based on the above. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
A couple of points here. Yes, a 10MHz oscillator will severely blast the budget - power wise. But you should remember that 10MHz is also not actually a good frequency for temperature coefficient of crystals - except for SOME SC cut types. Generally speaking the zero tempco rollover frequency for many SC's and most AT's is between 4.5 and 5.5MHz. You can actually get very good tempco's by running two oscillators either 500kHz or 1MHz apart and mixing them. Mounted in a thermal mass but without an oven they will oven give better than TCXO and moderate oven type performance. Real time temperature compensation is actually quite common. In several radio applications I have designed systems using two techniques. 1.. Have the manufacturer supply AT crystals with carefully controlled cut angles - for a given cut angle the tempco will not vary much. Then use a simple compensation table based on angle. 2.. Learn the crystal characteristics. In a couple of chamber runs measure the characteristics of each crystal. You probably only need to do 20 temperatures to cover -10 to +60C. Work out the slope and using some nice interpolation algorithm work out a correction table. Then voltage control the Xtal osc to keep the frequency on target. #2 works well enough that a pretty standard crystal will deliver TCXO or better performance because very few TCXO's use active compensation. But really, can we fit all of this ins key fob? Nope! I suspect in the best research tradition the OP needs to look at WHY his application demands synchronization at this sort of level. In one project where my client initially asked for timing accuracy of this order, we found that we could collect data with timestamps and temperatures, and when we looked at the logger and the data we could measure the offset for a particular logger and then back correct the timestamps on the data. In that case we used a correction system like #1 above, but we had something like 150x50x10mm to work in, not a key fob! John At 02:18 PM 8/18/2005, you wrote: David Andersen wrote: Local stable crystal: Actually, you could make it more than stable enough, but it would exceed your power requirements, because you'd probably fall back to an oven controlled oscillator. There goes your battery. But why did you try your initial experiments with 32.768Khz watch crystals? You're much more likely to find a good, solid 10Mhz reference with an SC cut TCXO. For instance, that maxim IC you mentioned has +- 2ppm, which is really quite awful by instrumentation standards. Compare to this one: http://www.bdelectronic.com/frequency/oscillatorTCXO.html .3ppm tempco, +- 1ppm/year. They don't show their overall allen deviation curves, but you get the idea - it'll be within 1ppm by the end of the year, and since that aging will probably happen over time, I'd guess it would probably get you something like 10 seconds within a year. Or something like: http://www.vectron.com/products/tcxo/tc140.pdf (... which is probably expensive, but which you can get in 0.2 ppm accuracy vs. temperature and 2ppm/10 years). -Dave Dave, The requirement that you seem to have missed is the 18 month battery lifetime. A 10 MHz oscillator is a couple milliapmeres, so it won't do the trick. The watch crystal needs only about 10 microamperes to oscillate. Mike, The 32K crystal may be usable, but you'd have to put some effort into the design to get the temp compensation tuned to the particular crystal, and you'd have to grade the crystals for tempco in the mfg stage. That might be doable in quantity, if you come up with the right sort of computerized test fixture in an oven. I have built a few nixie tube wristwatches using the cheap 32KHz crystals, so I have direct experience in this matter. (Has anyone else on this list built an electronic wristwatch?) Getting the crystal adjusted to 1ppm is not too hard. You'd have to temperature compensate it to get to 0.1 ppm, and that would be limited to perhaps 10C-30C temperature range. It's a lot easier to compensate the crystal if it's worn on the wrist rather than sitting in a car, since a person's wrist is essentially an oven. The real world has ridiculous temperature extremes - don't even think about stabilizing a crystal used outdoors unless it's thermally connected to a human. You should be able to evaluate the feasibility of using a compensated crystal based on the above. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
On Thu, 18 Aug 2005, David Andersen wrote: I assume that the devices of which you're speaking are standalone items? Something like a sensor deployment, possibly networked? Knowing more about how you actually plan on using these would help a bit. Yes, it would. The devices are part of a social experiment and are meant to be carried by humans. The devices, at preprogrammed times, signal the human with an audio signal. We want all the devices to create this signal simultaneously, which means something on the order of a few seconds variation among all the units anywhere in the world. There is no network, no display, no user interface, zip. A key fob would be ideal and low cost is critical. Most cheap WWVB watches and clocks don't work very well on the east coast, from my experience. I poked around at a few in my old lab in Boston, and they were a no-go. Yes, this is my worry. Switching power supplies in the vicinity seem to be the determining factor in how well these systems work. Local stable crystal: Actually, you could make it more than stable enough, but it would exceed your power requirements, because you'd probably fall back to an oven controlled oscillator. There goes your battery. It is important to note that we don't need an *accurate* time reference, we need s *stable* one. That means we're happy to correct, in software, a crystal that is running 10ppm slow *if* it holds that error throughout it's life. We can build adjustments into the software, so no need to pull, tweak, or PLL to some arbitrary frequency. But why did you try your initial experiments with 32.768Khz watch crystals? Power. A CR1620 battery is 75mAH and a CR2032 is 225 mAH. For 18 months, this is 6uA or 17uA average current draw. The only thing that can meet that is a low KHz crystal. You're much more likely to find a good, solid 10Mhz reference with an SC cut TCXO. For instance, that maxim IC you mentioned has +- 2ppm, which is really quite awful by instrumentation standards. Compare to this one: http://www.bdelectronic.com/frequency/oscillatorTCXO.html .3ppm tempco, +- 1ppm/year. One idea is to keep the TCXO off most of the time, turn it on and let it stabilize, then compare it to the low power crystal. Make an adjustment based on that. But, I suspect the constant on/off will affect the TCXO poorly, and you miss most of the low power crystal variations (temperature, shock, etc). So this doesn't seem possible. I'd also guess these TCXOs are $10 in qty. Lastly, +/- 1ppm is +/- 30 seconds per year which is still not really good enough. Another option you may have just eliminated on principle: Internet synchronization. Technically, this works really well. The concept we had for this was a USB key fob. Plug it in to an Internet connected computer and capture the time. The device could also have a super cap on board for power, charge it from the USB slot, and you don't need a battery. I was thinking this would be an ideal concept with all sorts of flexibility. The sync operation would not need to be done too often, perhaps once every 90 days, so limited access is okay as long as it occurs often enough. However, there are issues. Namely that the USB device would need software on the computer to make the connection and that the experiment wants to be as accessible to people as possible, even those which have no access to a computer. A possible compromise was suggested: build a GPS time module with USB ports on it that serves the role of the time provider. This would replace or augment the PC. This complicated the experiment as well but provided a way for unconnected or distant people to sync up. It would only work well if people using the device are grouped which may not be compatible with the experiment's goals. WWVB and its kin may well be your best bet, _if_ you can hear them enough places. Yes, so far that is the leading candidate. Maybe if we all chipped in a $0.01 each ($3M total), they can get the power up to 1MW? That would probably get world wide coverage (and cook nearby hot dogs... :-). -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Low cost synchronization
Are the subjects all within major metro areas? I wonder if the TV stations are sending usable time codes in their blanking intervals these days. -- john, KE5FX ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
On Thu, 18 Aug 2005, David Forbes wrote: The 32K crystal may be usable, but you'd have to put some effort into the design to get the temp compensation tuned to the particular crystal, and you'd have to grade the crystals for tempco in the mfg stage. That might be doable in quantity, if you come up with the right sort of computerized test fixture in an oven. All of the temp compensation can be in software and after the fact. I don't need the crystal tweaked, I just need to know what numerical corrections I need to apply to the counter. Thus it becomes zero electronics (besides some temp sensor) and only software. I have built a few nixie tube wristwatches using the cheap 32KHz crystals, so I have direct experience in this matter. (Has anyone else on this list built an electronic wristwatch?) Getting the crystal adjusted to 1ppm is not too hard. You'd have to temperature compensate it to get to 0.1 ppm, and that would be limited to perhaps 10C-30C temperature range. You give me more hope than I had previously. I understand how to capture the initial tolerance (operate the device at the factory and record the variation in internal memory). I know how to correct the temperature curve (the parabolic deviation away from 25C). But I am left with aging as a concern. Most of these crystals claim aging to be +/- 3ppm the first year. That's +/- 1.5 minutes for a year which is unacceptable. Maybe crystals from one batch all age the same, maybe they age based on shock/vibration (which will vary from unit to unit). I just don't know. Here is an example datasheet: http://www.ecsxtal.com/pdf/ecs-3x8.pdf It's a lot easier to compensate the crystal if it's worn on the wrist rather than sitting in a car, since a person's wrist is essentially an oven. The real world has ridiculous temperature extremes - don't even think about stabilizing a crystal used outdoors unless it's thermally connected to a human. Just like someone who leaves their watch in the car on a sunny day, I can't be sure the device will be in a temperature stable environment. The best I can do is try to model the temperature effect and correct for it. Hence the temp curve in the datasheet. Tracking it to within +/- 0.1ppm seems tough. You should be able to evaluate the feasibility of using a compensated crystal based on the above. Yes, I think it is going to be possible to achieve +/- 1.0ppm. I think +/- 0.5ppm can be done with some hard work. I don't think +/- 0.1ppm (+/- 3 seconds/year) is realistic. -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
On Thu, 18 Aug 2005, Chuck Harris wrote: Phase lock the crystal to the 50/60 Hz powerline? The signal seems to be ubiquitous. I considered that. There are many problems: The person with the device may move from one place to another and may pick up anyone of three possible phases of power or different utilities (they are sync'ed?). In this case, it may become hard to constantly watch your phase and adjust. At best, you can make short temporal measurements based on stable signals and use that to look at you local crystal. But, on short time scales, the 60Hz wave has poor stability. It is controlled well on longer time scales (witness all the clocks using it), but we can't assure a stable environment to measure that against. 60Hz is also very low frequency. I wasn't sure I could pick it up reliably despite all my experience getting it when I don't want it! Worth thinking about, though (says the man with a 250KV three phase trunk outside his building...) -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
On Thu, 18 Aug 2005, buehl wrote: The 1 Hz difference leads to the problems of 'is it +1 or -1; I can deal with this with a digital counter. You will always know if A is ahead of B or not. Or at zero, there is no output to count. Yes, this is a problem. Perhaps it is better to make sure the crystals are different, like 32KHz and 38KHz. But still, is the difference between them stable to 0.1ppm? I'm skeptical (otherwise everyone would do it this way), but I'd be happy for it to be so! Does anyone in the group have expertise in forced aging of crystals. In the 'good old days' before precision trimmed parts, we commonly 'aged' parts with temperature cycles and voltage cycles to get past all the first year variations. This gave long term stability as well as sorting out all the early life failures of parts. Would take care of the 'first year drift' variable. If it is a simple bake, that we can do. But if it more complex than that, the manufacturing cost might exceed other solutions. I was thinking we would build the PCB (which goes through a reflow heat cycle), then bake the end result at 100C or something for an hour. But this was just speculation on my part that it would help with long term aging. I guess I would find out in a year... :-( -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Phase lock the crystal to the 50/60 Hz powerline? The signal seems to be ubiquitous. Not sure if this would work to the level you need. See: http://www.leapsecond.com/pages/mains/ /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
- Original Message - From: Mike Ciholas [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 19, 2005 7:34 AM Subject: Re: [time-nuts] Low cost synchronization Yes, it would. The devices are part of a social experiment and are meant to be carried by humans. The devices, at preprogrammed times, signal the human with an audio signal. We want all the devices to create this signal simultaneously, which means something on the order of a few seconds variation among all the units anywhere in the world. Mike While a fascinating engineering challenge, I fail to see the need for such accurate timing, given the typically wide ranging timeframe for human response to similar signals -eg cell phones ringing, etc. Or is it enough for the user to merely be aware of the audible prompt? Is it possible to elaborate? Regards Dave Brown, NZ -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.10.12/77 - Release Date: 18/08/2005 ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
Yes, it would. The devices are part of a social experiment and are meant to be carried by humans. Speaking of social experiments. I thought I had a reasonable idea as to what a GPS 1PPS is used for - until I read this: http://home.connection.com/~louis/globalchimes/proposal.htm Regards, Kiwi Geoff. http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
On Fri, 19 Aug 2005, Geoff wrote: Speaking of social experiments. I thought I had a reasonable idea as to what a GPS 1PPS is used for - until I read this: http://home.connection.com/~louis/globalchimes/proposal.htm Interesting. This isn't our application, but it shares many of the same traits. -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
On Fri, 19 Aug 2005, Poul-Henning Kamp wrote: 2. WWVB Receiver This is probably the most feasible means. Yes, I concur for at least the US. A 60KHz will get us US, something in England, and Japan (decoding software needs to be different, but not the radio parts). Maybe that's good enough. The company used to be called Temic, not sure if they are still called that. I've found two: http://www.mas-oy.com/archive/da9180.pdf This looks like the winning solution. Here is the TEMIC: http://www.ortodoxism.ro/datasheets/Temic/mXyzuryv.pdf This seems to not be as well supported. If anybody knows any more, please let me know. I have disassembled several WWVB watches. Of course, they are all COB (chip on board), but just from the chip dimensions, I know the chips they use (and the WWVB part seems to be separate from the watch logic otherwise) aren't either one of the above. Strange. Must be a high volume bare die house somewhere that is doing this. Our concept might well benefit from COB due to our volumes (10,000, perhaps millions). -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Low cost synchronization
From: Mike Ciholas [EMAIL PROTECTED] Subject: [time-nuts] Low cost synchronization Date: Thu, 18 Aug 2005 12:29:40 -0500 (CDT) Message-ID: [EMAIL PROTECTED] Hi Mike, 4. GPS Time Receiver This is fantasy land. I don't need the 100ns time reference, all I need is something good to one second or so. In this case, it seems possible to receive only 1 satellite, decode the digital data, and extract the time. It would be off by the variation in pseudo range which can't be corrected for. But I don't care about that level of accuracy. The question is, if you don't have to track multiple satellites and don't need to recover the pseudo range accurately, can you build a wickedly cheaper GPS time receiver? My expectation is no. You probably can get down to maybe half if you are very diligent, which still puts me out of the budget plus has a ridiculous high NRE. Unless this already exists, anyone? I have some VHDL code lying around... but no, I think it will effectively be hard to beat the integration level of modern receivers. The E911 work as well as wish for small portable receivers has forced integration to go further. On principle of doing a single- receiver GPS that will work. The first line of analogue receivers where 1-channel receivers multiplexing between satelites. Checkout the GPS chips again. 5. Cellular We've done extensive work with embedded cell phone modules. These modules are most often used for wireless remote monitoring and transport digital data. They do get the time from the cell system. Again, cost is a major issue. An OEM cell module runs over $65 in qty so this idea is sunk. It would also suffer from lack of global and local coverage. It is a shifting buissness and in longterm you may be toast. 6. TV Stations TV stations broadcast a time signal that VCRs/DVRs use for clock setting. Again, lack of global or even regional coverage. Some TV stations, annoyingly, broadcast the wrong time, too. Cost is probably high, but this idea was rejected before this was investigated. Also, the analogue signal is hitting the deck as ATSC and DVB enters. Sad but true. However, if you listen to ATSC or DVB pilot-tones ;O) 7. Atomic Reference Still research, but NIST has a small scale atomic reference: http://www.nist.gov/public_affairs/releases/miniclock.htm Unfortunately, not ready for commercial apps, probably will be too expensive, and it uses too much power. The best I could do on power is to power it up periodically and adjust the local crystal to it which integrates long term error. Small physics package does not say anything about the electronics package ;O) Cheers, Magnus ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Low cost synchronization
So, does it have to handle leap seconds? ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
RE: [time-nuts] Low cost synchronization
On Thu, 18 Aug 2005, Bill Hawkins wrote: So, does it have to handle leap seconds? Hmnm, interesting question. Obviously if we track WWVB, it can. The important part is that the units stay synchronized. So if all of them miss the leap second, that is okay. This would be the case if we had only an internal reference. Absolute accuracy is not an issue. -- Mike Ciholas(812) 476-2721 x101 CIHOLAS Enterprises (812) 476-2881 fax 255 S. Garvin St, Suite B [EMAIL PROTECTED] Evansville, IN 47713http://www.ciholas.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
