Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 10/05/2014 04:19, Chris Albertson wrote: On Fri, May 9, 2014 at 10:46 AM, Tony tn...@toneh.demon.co.uk wrote: But isn't that only supported by 'timing' GPS modules that allow you to specify the location? But they are rather more expensive than the common navigation type modules - are there sub $15 modules that support that single-satellite timing feature? With a $15 budget. I think you are limited to the old Motorola Oncore type. The UT+ sells for about $15 on eBay. There are two versions of the UT. Get the timing one. These aren't to bad. The PPS one sigma error is about 50ns and the UT runs on 5 volts. The newer MT+ version is better but at least $30. Unfortunately they use way too much power - 800mW maximum compared to 50mW for a UBLOX MAX-7c which are around $15. It also is specified at 50ns rms, 99% 100ns. It appears that most, if not all, the timing type modules are higher power as well as more expensive; unless anyone has any better suggestions it looks like I'll have to stick to navigation type modules. Does it make sense to place thermal insolation on a TCXO? It does on an OCXO because there is a thermostat inside the device and the thermal insulation will help the OCXO maintain a constant temperature. But a TCXO will just run hotter. I think all you need is a box to keep drafts and direct sunlight off the TCXO. The insulation won't make much difference to the overall temperature excursions of the TCXO but that doesn't matter because the timing is continually corrected by the GPS; it will however significantly reduce the rate of change of temperature thus reducing the timing errors during holdovers when GPS is temporarily unavailable. I might need to allocate some of the budget for spikes on the antenna to prevent pidgeons perching on it! Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 10/05/2014 15:15, Attila Kinali wrote: On Fri, 09 May 2014 18:46:05 +0100 Tony tn...@toneh.demon.co.uk wrote: Quite a remarkable datasheet for a low cost part - I've not found any other low cost oscillator with either of those specifications, and even some (most?) of the OXCO don't specify the freq/temp slope. I'm quite sure the manufacturers have this data, but they do not readily publish it because it is not tested for and thus not guaranteed. Ie the manufacturers want to prevent someone from taking that data, constructing some specs in their mind and blaming the manufacturer when the circuit fails because the part didn't meet the specs. Absolutely - which is why I was surprised to see those specs in the datasheet (on Digikey's site). And why I wasn't surprised that I couldn't find that version of the datasheet anywhere else including the manufacturer's own website. Usually the manufacturers are quite happy to share that data if you ask nicely. Attila Kinali Yes , but that isn't much help unless you have a lot of of clout with the manufacturer, like the Apples of this world, or you are able to take on the risk that the parts will meet your needs and can buy all the the parts you're going to need in one go. The manufacturer won't guarantee any data that isn't in the datasheet and worse they can change the design or manufacturing process at any time; the part would still meet the published specs but all other characteristics could change considerably. Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On Mon, May 12, 2014 at 3:03 AM, Tony tn...@toneh.demon.co.uk wrote: Unfortunately they use way too much power - 800mW maximum compared to 50mW for a UBLOX MAX-7c which are around $15. It also is specified at 50ns rms, 99% 100ns. It appears that most, if not all, the timing type modules are higher power as well as more expensive; unless anyone has any better suggestions it looks like I'll have to stick to navigation type modules. I think they use more power because a timing mode GPS is used at a fixed location and so is likely to have AC mains power available and if a backup battery is needed it can be a large gell cell type More likely its lower power needs is because the uBlox tech is 10+ years more recent than the old Motorola stuff. -- Björn ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Unfortunately they use way too much power - 800mW maximum compared to 50mW for a UBLOX MAX-7c which are around $15. It also is specified at 50ns rms, 99% 100ns. It appears that most, if not all, the timing type modules are higher power as well as more expensive; unless anyone has any better suggestions it looks like I'll have to stick to navigation type modules. Have you looked at any of the Furuno modules? There is the Furuno GT-8036 on eBay for $20 each which is a M12 timing clone (both physical and software communication). It is spec'ed at 58mA... http://furunogps.us.com/docs/GT8036-Brochure.pdf Better than an old UT+ and a little cheaper (and faster shipping) than the M12+T from China. If you are looking at direct from manufacturer, their latest model is the GT-8536 (but still a M12 clone)... I have no idea what the price would be. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On Fri, May 9, 2014 at 10:46 AM, Tony tn...@toneh.demon.co.uk wrote: But isn't that only supported by 'timing' GPS modules that allow you to specify the location? But they are rather more expensive than the common navigation type modules - are there sub $15 modules that support that single-satellite timing feature? With a $15 budget. I think you are limited to the old Motorola Oncore type. The UT+ sells for about $15 on eBay. There are two versions of the UT. Get the timing one. These aren't to bad. The PPS one sigma error is about 50ns and the UT runs on 5 volts. The newer MT+ version is better but at least $30. Does it make sense to place thermal insolation on a TCXO? It does on an OCXO because there is a thermostat inside the device and the thermal insulation will help the OCXO maintain a constant temperature. But a TCXO will just run hotter. I think all you need is a box to keep drafts and direct sunlight off the TCXO. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On Fri, 09 May 2014 18:46:05 +0100 Tony tn...@toneh.demon.co.uk wrote: Quite a remarkable datasheet for a low cost part - I've not found any other low cost oscillator with either of those specifications, and even some (most?) of the OXCO don't specify the freq/temp slope. I'm quite sure the manufacturers have this data, but they do not readily publish it because it is not tested for and thus not guaranteed. Ie the manufacturers want to prevent someone from taking that data, constructing some specs in their mind and blaming the manufacturer when the circuit fails because the part didn't meet the specs. Usually the manufacturers are quite happy to share that data if you ask nicely. Attila Kinali -- I pity people who can't find laughter or at least some bit of amusement in the little doings of the day. I believe I could find something ridiculous even in the saddest moment, if necessary. It has nothing to do with being superficial. It's a matter of joy in life. -- Sophie Scholl ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 06/05/2014 02:24, Chris Albertson wrote: On Mon, May 5, 2014 at 6:55 AM, Tony tn...@toneh.demon.co.uk wrote: Yes - that is exactly what I intended. The problem though is maintaining sufficient accuracy during periods when the GPS clock is unavailable or unreliable (perhaps due to local interference), but I don't have any handle on how long that may be or how often it occurs. Clearly there are no absolute guarantees - eg. the GPS selective availability could be turned on again in exceptional circumstances, so I accept that 100ns accuracy can't be absolutely guaranteed. I assumed you were making these measurements at a fixed location.You don't loose GPS signal often. Onece you have the antenna in a location that works it continues to work, most of the time. Drop outs are rare in a fixed system after you gt it working.It's different in a moving vehicle. Thanks Chris - that's just the information I was looking for. Yes it would be at a fixed location; it wouldn't be a problem checking that it had good reception during installation. The question then is, in the experience of users of GPS timing references, for a decent but low cost receiver with a reasonably well sited antenna and assuming there is no significant interference, how long and how frequently is time synchronisation lost? If for example it's only 2 or 3 seconds every few weeks, then there isn't much of a problem. If 5 minute outages occur every few days then the holdover performance of the local oscillator is much more critical. As said above, once it works it pretty much continues to work. With a very good antenna site (mine is on a 4 foot above the roof line with a 360 degree view of the sky) I've never had a loss of signal except as a test. But then I don't look for them either. If you do get a loss of signal then all that happens is my GPSDO controller never updates the local oscillator. It sticks at the last setting. So the drift depends on how good is the local oscillator. I have two. One is a $15 crystal. It can run for hours before I can detect any drift (I my case that is a few ns of phase drift) Certainly your example of 5 minutes per day of GPS outage would be no problem at all even for a moderate quality OCXO. My other oscillator is a Rubidium. It is the $40 FE-5680 from eBay and it can go for days with no GPS corrections (at the few ns level) That's interesting. What model is the $15 oscillator? Is it an OXCO? Unfortunately the power consumption of the OXCOs I've looked at are much too high at 1W. However this TCXO is both cheap and remarkably comprehensively specified: http://media.digikey.com/pdf/Data%20Sheets/NDK%20PDFs/NT2016SA-16.368000_MHZ-NTG1.pdf Its a 16.368MHz oscillator for less than $2 and uses 1.5mA . Unusually the data sheet specifies not only the max temperature stability at +/- .5ppm from -10 to +70C, but also the max frequency/temperature slope at +/- .05ppm/C . It also specifies short term stability at max 1ppb over .1s. Quite a remarkable datasheet for a low cost part - I've not found any other low cost oscillator with either of those specifications, and even some (most?) of the OXCO don't specify the freq/temp slope. Having said that, I can't find the same datasheet anywhere else - those on NDK's website are less comprehensive. Perhaps those on Digikey's site are out of date, NDK not wanting to guarantee those specs for such a low cost part. I intend to try one and see how it performs in a box, with some insulation, when moved into a sunny spot after being shaded for a while. What about in more difficult circumstances - eg. in urban environment with an antenna that has a restricted view of the sky? Not that I expect to operate in such circumstances but it would be interesting to get a feel for how good or bad timing is maintained in less favourable situations. It all depends on the quality of the oscillator. But again you would fiddle with the antenna until it worked as best it could then you don't se much change in a fixed location system. The other thing that saves you is that for timing at a fixed location the GPS only needs ONE satellite. With any reasonable setup yo are likely to have one sat visible at all times. But isn't that only supported by 'timing' GPS modules that allow you to specify the location? But they are rather more expensive than the common navigation type modules - are there sub $15 modules that support that single-satellite timing feature? Thanks, Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 03/05/2014 18:41, Tom Van Baak (lab) wrote: Tony, Chris, Bert, Since all you want is a 10 ns time stamp / data logger you do not need a GPSDO, or OCXO, or VCXO. The solution is cheap and very simple. Your GPS receiver provides a 1PPS to the microprocessor. Use a plain XO or TCXO; the frequency does not need to be accurate, just stable to about 1e-9 (many $1 xtals do this). Each second your code [re]computes the drift between the clock and GPS. You may average over 10 to 100 seconds if you wish. Even though your clock is off-time and off-frequency your software knows what the offset is. Therefore, you can simply adjust the time stamp reading by the current clock error. This software GPSDO gives equal or actually slightly better performance than a real GPDSO but it is much simpler: no DAC, no EFC, no OCXO, no VCXO, no PLL. /tvb (i5s) ___ Tom, Yes - that is exactly what I intended. The problem though is maintaining sufficient accuracy during periods when the GPS clock is unavailable or unreliable (perhaps due to local interference), but I don't have any handle on how long that may be or how often it occurs. Clearly there are no absolute guarantees - eg. the GPS selective availability could be turned on again in exceptional circumstances, so I accept that 100ns accuracy can't be absolutely guaranteed. The question then is, in the experience of users of GPS timing references, for a decent but low cost receiver with a reasonably well sited antenna and assuming there is no significant interference, how long and how frequently is time synchronisation lost? If for example it's only 2 or 3 seconds every few weeks, then there isn't much of a problem. If 5 minute outages occur every few days then the holdover performance of the local oscillator is much more critical. What about in more difficult circumstances - eg. in urban environment with an antenna that has a restricted view of the sky? Not that I expect to operate in such circumstances but it would be interesting to get a feel for how good or bad timing is maintained in less favourable situations. Thanks, Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
The data loggers will be continuously powered, in fixed locations and should have reasonably good views of the sky so the use of a low cost GPS module should be feasible. Hi Tony, Ah, now you are asking a completely different question. When you started this thread you didn't mention anything about reliability of GPS signal. Now you are talking about lost signals, holdover duration, urban canyons, local interference. That totally changes the problem. The first thing you need to do is replace fuzzy adjectives with hard numbers. In your paragraphs below you use words like sufficient accuracy, during periods, decent, low cost, reasonably well, no significant, etc. It is impossible to solve your problem until you create a specification using real numbers instead of words. This could be a $50 solution or a $500 solution or a $50,000 solution, depending on what those words mean. If you implement holdover, the choice of oscillator and packaging is completely determined by the holdover spec you have to meet -- what's the worst case duration, what's the ambient temperature variation, and how many nanoseconds or microseconds of error can you tolerate during holdover. Do you have any choice where these sensors will be placed? I mean, if there is restricted sky view or too much local interference what will you do. Can you accept or reject locations based on a 1-day or 2-week performance validation trial? How many sensors are being deployed? Is this a one-off project or something commercial? I think it might be best to tell the group exactly what your project is; you may get many useful suggestions. Maybe GPS is not the most robust solution. /tvb Tom, Yes - that is exactly what I intended. The problem though is maintaining sufficient accuracy during periods when the GPS clock is unavailable or unreliable (perhaps due to local interference), but I don't have any handle on how long that may be or how often it occurs. Clearly there are no absolute guarantees - eg. the GPS selective availability could be turned on again in exceptional circumstances, so I accept that 100ns accuracy can't be absolutely guaranteed. The question then is, in the experience of users of GPS timing references, for a decent but low cost receiver with a reasonably well sited antenna and assuming there is no significant interference, how long and how frequently is time synchronisation lost? If for example it's only 2 or 3 seconds every few weeks, then there isn't much of a problem. If 5 minute outages occur every few days then the holdover performance of the local oscillator is much more critical. What about in more difficult circumstances - eg. in urban environment with an antenna that has a restricted view of the sky? Not that I expect to operate in such circumstances but it would be interesting to get a feel for how good or bad timing is maintained in less favourable situations. Thanks, Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On Mon, 05 May 2014 14:55:20 +0100 Tony tn...@toneh.demon.co.uk wrote: On 03/05/2014 18:41, Tom Van Baak (lab) wrote: Tony, Chris, Bert, Since all you want is a 10 ns time stamp / data logger you do not need a GPSDO, or OCXO, or VCXO. The solution is cheap and very simple. Your GPS receiver provides a 1PPS to the microprocessor. Use a plain XO or TCXO; the frequency does not need to be accurate, just stable to about 1e-9 (many $1 xtals do this). Each second your code [re]computes the drift between the clock and GPS. You may average over 10 to 100 seconds if you wish. Even though your clock is off-time and off-frequency your software knows what the offset is. Therefore, you can simply adjust the time stamp reading by the current clock error. This software GPSDO gives equal or actually slightly better performance than a real GPDSO but it is much simpler: no DAC, no EFC, no OCXO, no VCXO, no PLL. /tvb (i5s) ___ Tom, Yes - that is exactly what I intended. The problem though is maintaining sufficient accuracy during periods when the GPS clock is unavailable or unreliable (perhaps due to local interference), but I don't have any handle on how long that may be or how often it occurs. Clearly there are no absolute guarantees - eg. the GPS selective availability could be turned on again in exceptional circumstances, so I accept that 100ns accuracy can't be absolutely guaranteed. The question then is, in the experience of users of GPS timing references, for a decent but low cost receiver with a reasonably well sited antenna and assuming there is no significant interference, how long and how frequently is time synchronisation lost? If for example it's only 2 or 3 seconds every few weeks, then there isn't much of a problem. If 5 minute outages occur every few days then the holdover performance of the local oscillator is much more critical. What about in more difficult circumstances - eg. in urban environment with an antenna that has a restricted view of the sky? Not that I expect to operate in such circumstances but it would be interesting to get a feel for how good or bad timing is maintained in less favourable situations. Thanks, Tony H The maintenance of time between loss of GPS is why so many time references hit the surplus market. The hold over specs got to the point where they had to go to a rubidium reference. We should be up to our arm pits in Symetricoms, Trimble, etc, but I presume the stuff got crushed. I snagged two new old stock GPSDO (crystal based) from a cellular tech. At least the Chinese sold their references on ebay. Having second sourced products over the years, it is often easier just to take a published spec for an item and start from there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On Mon, May 5, 2014 at 6:55 AM, Tony tn...@toneh.demon.co.uk wrote: Yes - that is exactly what I intended. The problem though is maintaining sufficient accuracy during periods when the GPS clock is unavailable or unreliable (perhaps due to local interference), but I don't have any handle on how long that may be or how often it occurs. Clearly there are no absolute guarantees - eg. the GPS selective availability could be turned on again in exceptional circumstances, so I accept that 100ns accuracy can't be absolutely guaranteed. I assumed you were making these measurements at a fixed location.You don't loose GPS signal often. Onece you have the antenna in a location that works it continues to work, most of the time. Drop outs are rare in a fixed system after you gt it working.It's different in a moving vehicle. The question then is, in the experience of users of GPS timing references, for a decent but low cost receiver with a reasonably well sited antenna and assuming there is no significant interference, how long and how frequently is time synchronisation lost? If for example it's only 2 or 3 seconds every few weeks, then there isn't much of a problem. If 5 minute outages occur every few days then the holdover performance of the local oscillator is much more critical. As said above, once it works it pretty much continues to work. With a very good antenna site (mine is on a 4 foot above the roof line with a 360 degree view of the sky) I've never had a loss of signal except as a test. But then I don't look for them either. If you do get a loss of signal then all that happens is my GPSDO controller never updates the local oscillator. It sticks at the last setting. So the drift depends on how good is the local oscillator. I have two. One is a $15 crystal. It can run for hours before I can detect any drift (I my case that is a few ns of phase drift) Certainly your example of 5 minutes per day of GPS outage would be no problem at all even for a moderate quality OCXO. My other oscillator is a Rubidium. It is the $40 FE-5680 from eBay and it can go for days with no GPS corrections (at the few ns level) What about in more difficult circumstances - eg. in urban environment with an antenna that has a restricted view of the sky? Not that I expect to operate in such circumstances but it would be interesting to get a feel for how good or bad timing is maintained in less favourable situations. It all depends on the quality of the oscillator. But again you would fiddle with the antenna until it worked as best it could then you don't se much change in a fixed location system. The other thing that saves you is that for timing at a fixed location the GPS only needs ONE satellite. With any reasonable setup yo are likely to have one sat visible at all times. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 03/05/2014 02:07, Edesio Costa e Silva wrote: Welcome! Take a look at NavSpark from SkyTraq (http://www.skytraq.com.tw/). They had an Indiegogo (https://www.indiegogo.com/projects/navspark-arduino-compatible-with-gps-gnss-receiver) campaign recently and should deliver real soon now. The NavSpark chip has an trigger pin for time capture, a feature suggested by a fellow time-nut and a 100 MHz clock. Edésio Wow, that is very interesting - especially at under $18 including a powerful micro. Looks hard to beat, but would have preferred an ARM chip rather than SPARK. Can't have everything I guess! Tony ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 5/2/14, 7:07 PM, Tony wrote: On 03/05/2014 02:07, Edesio Costa e Silva wrote: Welcome! Take a look at NavSpark from SkyTraq (http://www.skytraq.com.tw/). They had an Indiegogo (https://www.indiegogo.com/projects/navspark-arduino-compatible-with-gps-gnss-receiver) campaign recently and should deliver real soon now. The NavSpark chip has an trigger pin for time capture, a feature suggested by a fellow time-nut and a 100 MHz clock. Edésio Wow, that is very interesting - especially at under $18 including a powerful micro. Looks hard to beat, but would have preferred an ARM chip rather than SPARK. Can't have everything I guess! THey probably did that because the LEON3 SPARC core is free (developed by Jiri Gaisler and Sandi Habinc for ESTEC, originally). I've done a lot with that SPARC: in fact I have one flying in space on the ISS right now as a software radio (which can do GPS, as a matter of interest). As soon as the GPS receiver software has the 1pps output, I'll be building a sort of GPSDO (TCXO driving an NCO, with NCO phase increment driven by corrections derived from GPS). There's a good tool chain for the SPARC (GCC), and Aeroflex Gaisler AB has a mailing list that provides support for questions (even if you're using the free open source cores). Gaisler also has a huge library of open source peripherals that you can integrate with the LEON core. If you want FPGA testbed code and real support, beyond the bare sources and documentation, you do need to pay for a license, but it's fairly reasonable ($5-10k, as I recall) if you're developing a product. There's also a good open source RTOS available (RTEMS) if you need that; THere's a variety of Linuxes also available for the SPARC V8, although it's definitely not a plug and play. It would be interesting to know what options on the LEON3 the NavSpark implements (e.g. FPU, etc.). The LEON3 (at least in some flavors) has a very cool debug support unit (DSU) which can do things like breakpoints on memory access to specific locations, instruction logging on a trigger, etc. The DSU can be accessed via serial port and/or JTAG and/or other interfaces. It's all GDB compatible, of course. I'd guess that writing C code for the SPARC is not much different than writing C code for the ARM. Ditto for ASM code. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Looks like this is all you'd need for most timing projects. Just add your favorite OCXO and some wire. The SPARC (not Spark) is actually a step up from ARM. It was developed by Sun Microsystems (now Oracle) it is optimized for things like fast context switching, multi tasking and so on, all the things done by operating systems. The Sparc V8 does 128 bit floating point, (quad precision) I wonder if 200Kb RAM is enough to run an older version of SunOS? (a BSD variant.) Are these shipping yet? On Fri, May 2, 2014 at 7:07 PM, Tony tn...@toneh.demon.co.uk wrote: On 03/05/2014 02:07, Edesio Costa e Silva wrote: Welcome! Take a look at NavSpark from SkyTraq (http://www.skytraq.com.tw/). They had an Indiegogo (https://www.indiegogo.com/projects/navspark-arduino- compatible-with-gps-gnss-receiver) campaign recently and should deliver real soon now. The NavSpark chip has an trigger pin for time capture, a feature suggested by a fellow time-nut and a 100 MHz clock. Edésio Wow, that is very interesting - especially at under $18 including a powerful micro. Looks hard to beat, but would have preferred an ARM chip rather than SPARK. Can't have everything I guess! Tony ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 5/4/14, 8:40 AM, Chris Albertson wrote: Looks like this is all you'd need for most timing projects. Just add your favorite OCXO and some wire. The SPARC (not Spark) is actually a step up from ARM. It was developed by Sun Microsystems (now Oracle) it is optimized for things like fast context switching, multi tasking and so on, all the things done by operating systems. The Sparc V8 does 128 bit floating point, (quad precision) I wonder if 200Kb RAM is enough to run an older version of SunOS? (a BSD variant.) Not all SPARC V8s have FPU: the SPARC spec has a lot of flexibilty in implmentation: a lot of if you want X, then it has to do the following things in the following way, but it's optional http://www.gaisler.com/index.php/products/processors/leon3 There's multiprocessor versions. Versions with and without cache, versions with and without FPU, etc. If you want a POSIX compliant OS, then RTEMS will definitely fit in 200kbytes. Don't know about all the other options. I've never heard of a SunOS implementation on LEON, but there's a lot of weird stuff out there. You do want to make sure that whatever you use is reasonably complete and of a reasonably recent version (or at least one you're real familiar with). There are a fair number of one-off ports of some OS or another to the LEON, but which don't have any continuing support, bug fixes, or users to contribute. Imagine a grad student doing their thesis on An implementation of RSX-11M supervisor mode on the LEON3-MP... they get enough done to demonstrate that it works, and they graduate, and who has a bunch of RSX-11M software anyway. Are these shipping yet? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Moin, On Fri, 02 May 2014 23:54:25 +0100 Tony tn...@toneh.demon.co.uk wrote: I'm considering designing and building some dataloggers, probably ARM Cortex based (eg. STM32F4xx), which record the time of infrequent events, preferably to better than 100ns and if possible better than 50nS. The data loggers will be continuously powered, in fixed locations and should have reasonably good views of the sky so the use of a low cost GPS module should be feasible. I believe it shouldn't be too difficult to resolve the PPS timing to +/- 5ns or better with a 100MHz+ microcontroller clock, but obviously jitter would add to the error requiring the GPS to be better than perhaps 90ns or so worst case. if i'm not mistaken the c/c units of the STM32F4xx run at half main clock, ie 84MHz max. That would give you a resolution of 12ns. If you run of a VCXO and can stear the average PPS to lie at the border between two bins, ie that half of the time the PPS is higher, half of the time lower, then you should be able to get a bit better than 12ns. Inevitably cost and power constraints apply - ideally the GPS would cost less than $20 (in quantities of 100), and $15 would be good, but it doesn't seem easy to find very lost cost receivers with timing outputs that are properly specified, presumably because of the relative market volumes. The power consumption of most timing receivers also seem to be higher than navigation units - eg. the Trimble SMT-x spec is 100mA compared to the ADAfruit MTK3339-based module which draws 20mA (but they are a bit too expensive at $24 apiece). You can try the LEA modules from u-blox. Single piece they are available from ebay. You can get them from u-blox directly too. But you have to buy a couple at once otherwise you pay way too much. IIRC prices get reasonable from 20 pieces upward. Even the non-timing modules have usually PPS specified to be better than 100ns. This also raises questions about the short term stability of the microcontroller oscillator required to maintain sufficient accuracy when GPS timing is temporarily lost for some reason - but how long would that need to be? 30s? 5 minutes? 30 minutes? An OCXO or a Stratum-3 TXCO would be too expensive, but oscillator manufacturers don't seem to publish short term frequency stability specifications for low cost/low power oscillators, and finding such information isn't easy. Can anyone point to figures for a typical non-TXCO low cost oscillator, 10 or 16MHz? Have a look at John Vig's crystal oscillator tutorial to get an understanding of the different effects that affect the oscillator. As mentioned already temperature should be your first concern. I did find this study, http://tf.nist.gov/general/pdf/2276.pdf, measuring the stability of some low cost quartz wristwatches which gives some interesting data of 20 to 65ppb Allan deviation over 100s. That, but a 32kHz oscillator might give rise to jitter problems when multiplied up to a suitable frequency. The frequency does not affect the jitter as much as you think. It's more the Q of the oscillator that determines the close in phase noise. But as you are using a uC, the phase noise will be dominated by the PLL and VCO in the uC itself more than the one of the external oscillator. Also, the phase noise induced jitter is negligible compared to other effects when you are time stamping (a good oscillator gives you a jitter of 10ps, much below the ~10ns you can measure). Some oscillator datasheets specify Allan deviation values, but I guess what I need for estimating worst case timestamp error during holdover periods are actually MTIE values. Is there any way to estimate the latter from Allan deviations specs? Would an ADev of 65 x 10^-9 over 100s imply up to 6.5us of error after 100s? Under the assumption of no other environmental changes, yes. But on the order of 100s, temperature becomes significant for the accuracy you want to acheive. You either have to compensate it in the oscillator (using a TXCO) or correct it in software by measuring the temperature yourself. Alternatively, you can try to keep the quartz temperature within +/-1°C using some heating element. (it does not need to be a full OCXO) Also keep in mind that the ADEV values is the statistical variation of the signal. ie it represents a 1 sigma value. As a normal distribution is assumed, your error is unbounded (not actually true). If you are sensitive to maximum error, you should work with a 3 to 6 sigma value instead of with the ADEV value directly. Also note: ADEV changes with integration time and its value cannot easily be extrapolated, in general. You can take certain assumptions as to what kind of effect takes place in which time scale and apply its slope, but that's at most a rough guess. For more information on this topic see Phase Noise and Frequency Stability in Oscillators by Enrico Rubiola. HTH Attila Kinali -- I
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Hi Well some of us still have RSX-11M (and RSTS/E) code floating around ….. Bob On May 4, 2014, at 12:30 PM, Jim Lux jim...@earthlink.net wrote: On 5/4/14, 8:40 AM, Chris Albertson wrote: Looks like this is all you'd need for most timing projects. Just add your favorite OCXO and some wire. The SPARC (not Spark) is actually a step up from ARM. It was developed by Sun Microsystems (now Oracle) it is optimized for things like fast context switching, multi tasking and so on, all the things done by operating systems. The Sparc V8 does 128 bit floating point, (quad precision) I wonder if 200Kb RAM is enough to run an older version of SunOS? (a BSD variant.) Not all SPARC V8s have FPU: the SPARC spec has a lot of flexibilty in implmentation: a lot of if you want X, then it has to do the following things in the following way, but it's optional http://www.gaisler.com/index.php/products/processors/leon3 There's multiprocessor versions. Versions with and without cache, versions with and without FPU, etc. If you want a POSIX compliant OS, then RTEMS will definitely fit in 200kbytes. Don't know about all the other options. I've never heard of a SunOS implementation on LEON, but there's a lot of weird stuff out there. You do want to make sure that whatever you use is reasonably complete and of a reasonably recent version (or at least one you're real familiar with). There are a fair number of one-off ports of some OS or another to the LEON, but which don't have any continuing support, bug fixes, or users to contribute. Imagine a grad student doing their thesis on An implementation of RSX-11M supervisor mode on the LEON3-MP... they get enough done to demonstrate that it works, and they graduate, and who has a bunch of RSX-11M software anyway. Are these shipping yet? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 5/4/14, 10:07 AM, Bob Camp wrote: Hi Well some of us still have RSX-11M (and RSTS/E) code floating around ….. B As do I, but the stuff I'd actually reuse is pretty OS independent (signal processing code in FORTRAN, and in reality, I'd most likely rewrite it anyway.) I suspect you'll probably not be wanting to port something OS dependent to a SPARC to build a GPSDO... Then again this is time-nuts, with the emphasis on nuts. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On Sun, May 4, 2014 at 5:40 PM, Chris Albertson albertson.ch...@gmail.com wrote: Looks like this is all you'd need for most timing projects. Just add your favorite OCXO and some wire. The SPARC (not Spark) is actually a step up from ARM. It was developed by Sun Microsystems (now Oracle) it is optimized for things like fast context switching, multi tasking and so on, all the things done by operating systems. The Sparc V8 does 128 bit floating point, (quad precision) I wonder if 200Kb RAM is enough to run an older version of SunOS? (a BSD variant.) In a previous life, I worked as Unix sysadmin at university. We had several old Sun3 (motorola 68020 based) and a few Sparcstation based on Sparc. The first SunOS I worked with was 4.1.1U1 and the last 4.1.4. I remember even the 68020 were a bit unhappy with 4Mbytes of RAM but I can't recall if it was a kernel requirement or just the userland stuff we needed to run on them. Probably NetBSD can be a more recent and configurable option for embedded sparcs. best regards Frank ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
These guys claim IEEE-754 FPU. But this is not the board to use for a Posix-like OS. For that you'd want disk controller, networking and so on. The big advantage of this thing is that it has an Arduino compatible boot loader and pinout so it drops into that environment which is VERY easy for many people to use. It has a very short learning curve. You can't say that about other embedded Sparc. SPARC, ARM or AVR should not matter to people who are using the Arduino IDE, All they see is the same C++ like environment and a small set of library functions. Not all SPARC V8s have FPU: the SPARC spec has a lot of flexibilty in implmentation: a lot of if you want X, then it has to do the following things in the following way, but it's optional http://www.gaisler.com/index.php/products/processors/leon3 There's multiprocessor versions. Versions with and without cache, versions with and without FPU, etc. If you want a POSIX compliant OS, then RTEMS will definitely fit in 200kbytes. Don't know about all the other options. I've never heard of a SunOS implementation on LEON, but there's a lot of weird stuff out there. You do want to make sure that whatever you use is reasonably complete and of a reasonably recent version (or at least one you're real familiar with). There are a fair number of one-off ports of some OS or another to the LEON, but which don't have any continuing support, bug fixes, or users to contribute. Imagine a grad student doing their thesis on An implementation of RSX-11M supervisor mode on the LEON3-MP... they get enough done to demonstrate that it works, and they graduate, and who has a bunch of RSX-11M software anyway. Are these shipping yet? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Hi Well I do have those Sparc machines sitting over in the shed ….. I suspect hauling over the CRT monitor to go with it would be a bit of a pain. I doubt I would win the “low power GPSDO of the year” award with it. Like it or not, once you get to 64 bit math, the “this versus that” hardware questions matter less and less on a GPSDO. The world is awash in CPU’s that will do what you need to do. The real issue is software / firmware. Since GPSDO’s were not a real big deal back in the 70’s and early 80’, there probably isn’t a lot of native GPSDO code for PDP-11’s or SPARC’s. Bob On May 4, 2014, at 1:34 PM, Jim Lux jim...@earthlink.net wrote: On 5/4/14, 10:07 AM, Bob Camp wrote: Hi Well some of us still have RSX-11M (and RSTS/E) code floating around ….. B As do I, but the stuff I'd actually reuse is pretty OS independent (signal processing code in FORTRAN, and in reality, I'd most likely rewrite it anyway.) I suspect you'll probably not be wanting to port something OS dependent to a SPARC to build a GPSDO... Then again this is time-nuts, with the emphasis on nuts. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 5/4/14, 11:38 AM, Chris Albertson wrote: These guys claim IEEE-754 FPU. But this is not the board to use for a Posix-like OS. For that you'd want disk controller, networking and so on. Ah, so they did include the FPU: that's handy. Actually, an in-ram file system, along with a decent threading model, queues, and so forth, even with no disk and networking, is still useful. The fact that you can test your code by compiling and running it in a linux environment is quite helpful. The big advantage of this thing is that it has an Arduino compatible boot loader and pinout so it drops into that environment which is VERY easy for many people to use. It has a very short learning curve. You can't say that about other embedded Sparc. Very much so. SPARC, ARM or AVR should not matter to people who are using the Arduino IDE, All they see is the same C++ like environment and a small set of library functions. And that's pretty cool. But, since we have a bunch of GPS based precision navigation/orbit determination code we're developing that runs on a SPARC V8, (so we've dealt with all the potential numerical idiosyncracies), we might be able to do an inexpensive port of Real Time Gipsy to this platform. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 5/4/14, 11:44 AM, Bob Camp wrote: Hi Well I do have those Sparc machines sitting over in the shed ….. I suspect hauling over the CRT monitor to go with it would be a bit of a pain. I doubt I would win the “low power GPSDO of the year” award with it. Like it or not, once you get to 64 bit math, the “this versus that” hardware questions matter less and less on a GPSDO. The world is awash in CPU’s that will do what you need to do. The real issue is software / firmware. Since GPSDO’s were not a real big deal back in the 70’s and early 80’, there probably isn’t a lot of native GPSDO code for PDP-11’s or SPARC’s. One thing I've learned over the last few years is that while they're all called SPARC, and have similar instruction sets and architectures, they're not that identical. For the most part, as you say, you don't care: you're writing in C or C++, and it's 32 bit math, so it's almost processor independent. In any case, there *is* native GPS receiver code for SPARCs, but it's not from the 70s and 80s. It's from this year and last. And it's probably not releasable in general. But at least it's an existence proof that it can be done. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
I am not advertising for DX but I have bought 4 with good results and their units have a 5 V regulator on it. Some have even a TTL to RS converter on board. Bert Kehren In a message dated 5/2/2014 11:40:47 P.M. Eastern Daylight Time, tn...@toneh.demon.co.uk writes: On 03/05/2014 00:59, ewkeh...@aol.com wrote: Welcome to the nuts Tony Thanks, Bert. You are not specifying exactly how accurate time has to be but in my book and based on tests the most reasonable priced GPS with 1 pps is a Ublox 6M that you can get with antenna for less than $ 22 antenna included from _www.DX.com_ (http://www.DX.com) . They have volume discount. Shipping is very slow but included. They seem to be presently out of the 1 pps version but all ublox units have a 1 pps output and I use with and without and all I do is solder a wire to pin 3. Bert Kehren As I said in my first post I'd like to achieve an accuracy of better than 100ns - or 50ns if possible at reasonable cost. I had come across the Ublox 6M when I was looking earlier, but I misunderstood the data sheet and thought it was only the expensive ($135) LEA/NEO-6T versions which provided timing. Definitely worth a closer look - the NEO-6M is specced at 30ns RMS which is good enough. The power consumption is a little higher than I would have liked at 37mA/3V, but still rather less than others. Thanks, Tony ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Tony There seem to be many variables. Cost, power, how many, overall stability etc. Most likely you will find that the GPS module is not the most expensive part but the VCXO. It also makes a large difference if it is one off or a larger volume is needed. You can always find a bargain, and maybe a close out sale but if you have to look at a continuous supply the picture changes dramatically and also the design. Bert Kehren In a message dated 5/2/2014 11:40:47 P.M. Eastern Daylight Time, tn...@toneh.demon.co.uk writes: On 03/05/2014 00:59, ewkeh...@aol.com wrote: Welcome to the nuts Tony Thanks, Bert. You are not specifying exactly how accurate time has to be but in my book and based on tests the most reasonable priced GPS with 1 pps is a Ublox 6M that you can get with antenna for less than $ 22 antenna included from _www.DX.com_ (http://www.DX.com) . They have volume discount. Shipping is very slow but included. They seem to be presently out of the 1 pps version but all ublox units have a 1 pps output and I use with and without and all I do is solder a wire to pin 3. Bert Kehren As I said in my first post I'd like to achieve an accuracy of better than 100ns - or 50ns if possible at reasonable cost. I had come across the Ublox 6M when I was looking earlier, but I misunderstood the data sheet and thought it was only the expensive ($135) LEA/NEO-6T versions which provided timing. Definitely worth a closer look - the NEO-6M is specced at 30ns RMS which is good enough. The power consumption is a little higher than I would have liked at 37mA/3V, but still rather less than others. Thanks, Tony ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Tony, Chris, Bert, Since all you want is a 10 ns time stamp / data logger you do not need a GPSDO, or OCXO, or VCXO. The solution is cheap and very simple. Your GPS receiver provides a 1PPS to the microprocessor. Use a plain XO or TCXO; the frequency does not need to be accurate, just stable to about 1e-9 (many $1 xtals do this). Each second your code [re]computes the drift between the clock and GPS. You may average over 10 to 100 seconds if you wish. Even though your clock is off-time and off-frequency your software knows what the offset is. Therefore, you can simply adjust the time stamp reading by the current clock error. This software GPSDO gives equal or actually slightly better performance than a real GPDSO but it is much simpler: no DAC, no EFC, no OCXO, no VCXO, no PLL. /tvb (i5s) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On Sat, 03 May 2014 02:38:07 +0100 Tony tn...@toneh.demon.co.uk wrote: On 03/05/2014 00:59, ewkeh...@aol.com wrote: Welcome to the nuts Tony Thanks, Bert. You are not specifying exactly how accurate time has to be but in my book and based on tests the most reasonable priced GPS with 1 pps is a Ublox 6M that you can get with antenna for less than $ 22 antenna included from _www.DX.com_ (http://www.DX.com) . They have volume discount. Shipping is very slow but included. They seem to be presently out of the 1 pps version but all ublox units have a 1 pps output and I use with and without and all I do is solder a wire to pin 3. Bert Kehren As I said in my first post I'd like to achieve an accuracy of better than 100ns - or 50ns if possible at reasonable cost. I had come across the Ublox 6M when I was looking earlier, but I misunderstood the data sheet and thought it was only the expensive ($135) LEA/NEO-6T versions which provided timing. Definitely worth a closer look - the NEO-6M is specced at 30ns RMS which is good enough. The power consumption is a little higher than I would have liked at 37mA/3V, but still rather less than others. Thanks, Tony ___ I hope I'm not getting to philosophical here, but isn't the time stamp accuracy measured between receivers? That is, if I have two GPSDO, they are guarenteed to be within X amount of time from each other. Or do you consider a time stamp to be absolute? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Low cost GPS module for 100ns timestamping error
Hi, I'm new here so please be gentle! I'm considering designing and building some dataloggers, probably ARM Cortex based (eg. STM32F4xx), which record the time of infrequent events, preferably to better than 100ns and if possible better than 50nS. The data loggers will be continuously powered, in fixed locations and should have reasonably good views of the sky so the use of a low cost GPS module should be feasible. I believe it shouldn't be too difficult to resolve the PPS timing to +/- 5ns or better with a 100MHz+ microcontroller clock, but obviously jitter would add to the error requiring the GPS to be better than perhaps 90ns or so worst case. Inevitably cost and power constraints apply - ideally the GPS would cost less than $20 (in quantities of 100), and $15 would be good, but it doesn't seem easy to find very lost cost receivers with timing outputs that are properly specified, presumably because of the relative market volumes. The power consumption of most timing receivers also seem to be higher than navigation units - eg. the Trimble SMT-x spec is 100mA compared to the ADAfruit MTK3339-based module which draws 20mA (but they are a bit too expensive at $24 apiece). There are several cheap modules that have PPS outputs but no accuracy specification; it's possible that these could be used with sufficient averaging/filtering of the PPS output. Actually repeatability is the important requirement rather than accuracy as they could be calibrated. Perhaps even a PPS o/p is not absolutely necessary - could the NEMA output timing be used given enough averaging and a sufficiently stable oscillator? Compromising the timing accuracy requirement a bit to say 150ns may be acceptable if the GPS device is cheap enough. I understand that the PPS outputs of some cheap modules sometimes become ill-behaved, but in this application the time stamp can be adjusted (or anomalous clocks ignored) post-event if necessary to correct for temporary disturbances. This also raises questions about the short term stability of the microcontroller oscillator required to maintain sufficient accuracy when GPS timing is temporarily lost for some reason - but how long would that need to be? 30s? 5 minutes? 30 minutes? An OCXO or a Stratum-3 TXCO would be too expensive, but oscillator manufacturers don't seem to publish short term frequency stability specifications for low cost/low power oscillators, and finding such information isn't easy. Can anyone point to figures for a typical non-TXCO low cost oscillator, 10 or 16MHz? I did find this study, http://tf.nist.gov/general/pdf/2276.pdf, measuring the stability of some low cost quartz wristwatches which gives some interesting data of 20 to 65ppb Allan deviation over 100s. That, but a 32kHz oscillator might give rise to jitter problems when multiplied up to a suitable frequency. Some oscillator datasheets specify Allan deviation values, but I guess what I need for estimating worst case timestamp error during holdover periods are actually MTIE values. Is there any way to estimate the latter from Allan deviations specs? Would an ADev of 65 x 10^-9 over 100s imply up to 6.5us of error after 100s? Any thoughts? Thanks, Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
tn...@toneh.demon.co.uk said: Can anyone point to figures for a typical non-TXCO low cost oscillator, 10 or 16MHz? In general, low cost oscillators make pretty good thermometers. I think you have a much better chance of getting good results if you are willing to post-process the data. I suggest you get one of the GPS units you are considering and collect some data. That will answer many of your questions and probably raise a few more. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Welcome to the nuts Tony You are not specifying exactly how accurate time has to be but in my book and based on tests the most reasonable priced GPS with 1 pps is a Ublox 6M that you can get with antenna for less than $ 22 antenna included from _www.DX.com_ (http://www.DX.com) . They have volume discount. Shipping is very slow but included. They seem to be presently out of the 1 pps version but all ublox units have a 1 pps output and I use with and without and all I do is solder a wire to pin 3. Bert Kehren In a message dated 5/2/2014 7:02:57 P.M. Eastern Daylight Time, tn...@toneh.demon.co.uk writes: Hi, I'm new here so please be gentle! I'm considering designing and building some dataloggers, probably ARM Cortex based (eg. STM32F4xx), which record the time of infrequent events, preferably to better than 100ns and if possible better than 50nS. The data loggers will be continuously powered, in fixed locations and should have reasonably good views of the sky so the use of a low cost GPS module should be feasible. I believe it shouldn't be too difficult to resolve the PPS timing to +/- 5ns or better with a 100MHz+ microcontroller clock, but obviously jitter would add to the error requiring the GPS to be better than perhaps 90ns or so worst case. Inevitably cost and power constraints apply - ideally the GPS would cost less than $20 (in quantities of 100), and $15 would be good, but it doesn't seem easy to find very lost cost receivers with timing outputs that are properly specified, presumably because of the relative market volumes. The power consumption of most timing receivers also seem to be higher than navigation units - eg. the Trimble SMT-x spec is 100mA compared to the ADAfruit MTK3339-based module which draws 20mA (but they are a bit too expensive at $24 apiece). There are several cheap modules that have PPS outputs but no accuracy specification; it's possible that these could be used with sufficient averaging/filtering of the PPS output. Actually repeatability is the important requirement rather than accuracy as they could be calibrated. Perhaps even a PPS o/p is not absolutely necessary - could the NEMA output timing be used given enough averaging and a sufficiently stable oscillator? Compromising the timing accuracy requirement a bit to say 150ns may be acceptable if the GPS device is cheap enough. I understand that the PPS outputs of some cheap modules sometimes become ill-behaved, but in this application the time stamp can be adjusted (or anomalous clocks ignored) post-event if necessary to correct for temporary disturbances. This also raises questions about the short term stability of the microcontroller oscillator required to maintain sufficient accuracy when GPS timing is temporarily lost for some reason - but how long would that need to be? 30s? 5 minutes? 30 minutes? An OCXO or a Stratum-3 TXCO would be too expensive, but oscillator manufacturers don't seem to publish short term frequency stability specifications for low cost/low power oscillators, and finding such information isn't easy. Can anyone point to figures for a typical non-TXCO low cost oscillator, 10 or 16MHz? I did find this study, http://tf.nist.gov/general/pdf/2276.pdf, measuring the stability of some low cost quartz wristwatches which gives some interesting data of 20 to 65ppb Allan deviation over 100s. That, but a 32kHz oscillator might give rise to jitter problems when multiplied up to a suitable frequency. Some oscillator datasheets specify Allan deviation values, but I guess what I need for estimating worst case timestamp error during holdover periods are actually MTIE values. Is there any way to estimate the latter from Allan deviations specs? Would an ADev of 65 x 10^-9 over 100s imply up to 6.5us of error after 100s? Any thoughts? Thanks, Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
Welcome! Take a look at NavSpark from SkyTraq (http://www.skytraq.com.tw/). They had an Indiegogo (https://www.indiegogo.com/projects/navspark-arduino-compatible-with-gps-gnss-receiver) campaign recently and should deliver real soon now. The NavSpark chip has an trigger pin for time capture, a feature suggested by a fellow time-nut and a 100 MHz clock. Edésio On Fri, May 02, 2014 at 07:59:14PM -0400, ewkeh...@aol.com wrote: Welcome to the nuts Tony You are not specifying exactly how accurate time has to be but in my book and based on tests the most reasonable priced GPS with 1 pps is a Ublox 6M that you can get with antenna for less than $ 22 antenna included from _www.DX.com_ (http://www.DX.com) . They have volume discount. Shipping is very slow but included. They seem to be presently out of the 1 pps version but all ublox units have a 1 pps output and I use with and without and all I do is solder a wire to pin 3. Bert Kehren In a message dated 5/2/2014 7:02:57 P.M. Eastern Daylight Time, tn...@toneh.demon.co.uk writes: Hi, I'm new here so please be gentle! I'm considering designing and building some dataloggers, probably ARM Cortex based (eg. STM32F4xx), which record the time of infrequent events, preferably to better than 100ns and if possible better than 50nS. The data loggers will be continuously powered, in fixed locations and should have reasonably good views of the sky so the use of a low cost GPS module should be feasible. I believe it shouldn't be too difficult to resolve the PPS timing to +/- 5ns or better with a 100MHz+ microcontroller clock, but obviously jitter would add to the error requiring the GPS to be better than perhaps 90ns or so worst case. Inevitably cost and power constraints apply - ideally the GPS would cost less than $20 (in quantities of 100), and $15 would be good, but it doesn't seem easy to find very lost cost receivers with timing outputs that are properly specified, presumably because of the relative market volumes. The power consumption of most timing receivers also seem to be higher than navigation units - eg. the Trimble SMT-x spec is 100mA compared to the ADAfruit MTK3339-based module which draws 20mA (but they are a bit too expensive at $24 apiece). There are several cheap modules that have PPS outputs but no accuracy specification; it's possible that these could be used with sufficient averaging/filtering of the PPS output. Actually repeatability is the important requirement rather than accuracy as they could be calibrated. Perhaps even a PPS o/p is not absolutely necessary - could the NEMA output timing be used given enough averaging and a sufficiently stable oscillator? Compromising the timing accuracy requirement a bit to say 150ns may be acceptable if the GPS device is cheap enough. I understand that the PPS outputs of some cheap modules sometimes become ill-behaved, but in this application the time stamp can be adjusted (or anomalous clocks ignored) post-event if necessary to correct for temporary disturbances. This also raises questions about the short term stability of the microcontroller oscillator required to maintain sufficient accuracy when GPS timing is temporarily lost for some reason - but how long would that need to be? 30s? 5 minutes? 30 minutes? An OCXO or a Stratum-3 TXCO would be too expensive, but oscillator manufacturers don't seem to publish short term frequency stability specifications for low cost/low power oscillators, and finding such information isn't easy. Can anyone point to figures for a typical non-TXCO low cost oscillator, 10 or 16MHz? I did find this study, http://tf.nist.gov/general/pdf/2276.pdf, measuring the stability of some low cost quartz wristwatches which gives some interesting data of 20 to 65ppb Allan deviation over 100s. That, but a 32kHz oscillator might give rise to jitter problems when multiplied up to a suitable frequency. Some oscillator datasheets specify Allan deviation values, but I guess what I need for estimating worst case timestamp error during holdover periods are actually MTIE values. Is there any way to estimate the latter from Allan deviations specs? Would an ADev of 65 x 10^-9 over 100s imply up to 6.5us of error after 100s? Any thoughts? Thanks, Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 03/05/2014 00:48, Hal Murray wrote: tn...@toneh.demon.co.uk said: Can anyone point to figures for a typical non-TXCO low cost oscillator, 10 or 16MHz? In general, low cost oscillators make pretty good thermometers. True, but it's short term stability that matters here - over 10s of seconds the temperature shouldn't change much - especially if a bit of insulation is used around the oscillator. I think you have a much better chance of getting good results if you are willing to post-process the data. I'm not sure I understand this - I need to record the time that an event occurs so I need an accurate time reference. What can I store to post-process? The time reference drift and jitter relative to the local oscillator before and after the event? I suggest you get one of the GPS units you are considering and collect some data. That will answer many of your questions and probably raise a few more. Well yes, but that will cost time and money - I was hoping to get some recommendations/suggestions from people who have some experience with low cost GPS modules, so as to narrow the field down a bit before experimenting myself. Thanks, Tony ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
On 03/05/2014 00:59, ewkeh...@aol.com wrote: Welcome to the nuts Tony Thanks, Bert. You are not specifying exactly how accurate time has to be but in my book and based on tests the most reasonable priced GPS with 1 pps is a Ublox 6M that you can get with antenna for less than $ 22 antenna included from _www.DX.com_ (http://www.DX.com) . They have volume discount. Shipping is very slow but included. They seem to be presently out of the 1 pps version but all ublox units have a 1 pps output and I use with and without and all I do is solder a wire to pin 3. Bert Kehren As I said in my first post I'd like to achieve an accuracy of better than 100ns - or 50ns if possible at reasonable cost. I had come across the Ublox 6M when I was looking earlier, but I misunderstood the data sheet and thought it was only the expensive ($135) LEA/NEO-6T versions which provided timing. Definitely worth a closer look - the NEO-6M is specced at 30ns RMS which is good enough. The power consumption is a little higher than I would have liked at 37mA/3V, but still rather less than others. Thanks, Tony ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Low cost GPS module for 100ns timestamping error
The Neo-6M based module (Crius CN-06) is available from HobbyKing for $20 (sometimes on sale for $16). You do have to add the wire to access the 1PPS signal. In my testing, I prefer it over the Adafruit Ultimate GPS. The Neo-6M seemed to a a little more sensitive (could get reliable lock and tracking sitting on the floor of a 2 story stucco house (stucco over wire mesh) away from any windows and did not have issues with reporting fixes of a rather stationary antenna - the Adafruit module would fake a fixed position if it was not moving). I did a little testing of the 1PPS output and it seemed to be quite good. My application was mainly driven by the desire to calculate the range and bearing between two units spaced 100 feet to a couple of miles (using an Xbee radio link). I could move a unit in a circle a couple of feet radius around another one and get good range/bearing info... not too shabby for a $20 hockey puck. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
here is what I'd do Get a decent OCXO (ovenized crystal oscillator and control it with your GPS. Don't worry if the GPS's PPS is 50ns or 5ns. You are going to be averaging these for a while.Basically you build a GPSDO.These have become very easy to make. I have one I made for about $8 and it has not gained or lost 100ns in weeks. Next get a second uP, not the one controlling the GPSDO. let your GPSDO 10MHz output drive this uP's counter and have the thing your are timing connect to the pin that will capture the counter. This is done in HARDWARE.The pin can cause the hardware counter to be captured to a register. So the software need not be real time The counter is ALSO captured by the 1 PPS from the gps.This way you capture both the one second tick and your event. You log the number of counts past the second. You can use ARM processors but I'm doing this with an Arduino cone I got on eBay for under $4. You do not need much CPU power as all the real time stuff is done in the uP's peripheral hardware. The uP only has to send the data over a link or log it so an SD memory card. even the 8-bit AVR is faster than I need for that. On Fri, May 2, 2014 at 3:54 PM, Tony tn...@toneh.demon.co.uk wrote: Hi, I'm new here so please be gentle! I'm considering designing and building some dataloggers, probably ARM Cortex based (eg. STM32F4xx), which record the time of infrequent events, preferably to better than 100ns and if possible better than 50nS. The data loggers will be continuously powered, in fixed locations and should have reasonably good views of the sky so the use of a low cost GPS module should be feasible. I believe it shouldn't be too difficult to resolve the PPS timing to +/- 5ns or better with a 100MHz+ microcontroller clock, but obviously jitter would add to the error requiring the GPS to be better than perhaps 90ns or so worst case. Inevitably cost and power constraints apply - ideally the GPS would cost less than $20 (in quantities of 100), and $15 would be good, but it doesn't seem easy to find very lost cost receivers with timing outputs that are properly specified, presumably because of the relative market volumes. The power consumption of most timing receivers also seem to be higher than navigation units - eg. the Trimble SMT-x spec is 100mA compared to the ADAfruit MTK3339-based module which draws 20mA (but they are a bit too expensive at $24 apiece). There are several cheap modules that have PPS outputs but no accuracy specification; it's possible that these could be used with sufficient averaging/filtering of the PPS output. Actually repeatability is the important requirement rather than accuracy as they could be calibrated. Perhaps even a PPS o/p is not absolutely necessary - could the NEMA output timing be used given enough averaging and a sufficiently stable oscillator? Compromising the timing accuracy requirement a bit to say 150ns may be acceptable if the GPS device is cheap enough. I understand that the PPS outputs of some cheap modules sometimes become ill-behaved, but in this application the time stamp can be adjusted (or anomalous clocks ignored) post-event if necessary to correct for temporary disturbances. This also raises questions about the short term stability of the microcontroller oscillator required to maintain sufficient accuracy when GPS timing is temporarily lost for some reason - but how long would that need to be? 30s? 5 minutes? 30 minutes? An OCXO or a Stratum-3 TXCO would be too expensive, but oscillator manufacturers don't seem to publish short term frequency stability specifications for low cost/low power oscillators, and finding such information isn't easy. Can anyone point to figures for a typical non-TXCO low cost oscillator, 10 or 16MHz? I did find this study, http://tf.nist.gov/general/pdf/2276.pdf, measuring the stability of some low cost quartz wristwatches which gives some interesting data of 20 to 65ppb Allan deviation over 100s. That, but a 32kHz oscillator might give rise to jitter problems when multiplied up to a suitable frequency. Some oscillator datasheets specify Allan deviation values, but I guess what I need for estimating worst case timestamp error during holdover periods are actually MTIE values. Is there any way to estimate the latter from Allan deviations specs? Would an ADev of 65 x 10^-9 over 100s imply up to 6.5us of error after 100s? Any thoughts? Thanks, Tony H ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
tn...@toneh.demon.co.uk said: In general, low cost oscillators make pretty good thermometers. True, but it's short term stability that matters here - over 10s of seconds the temperature shouldn't change much - especially if a bit of insulation is used around the oscillator. Ballpark is 1 PPM per degree C. That's 1 microsecond/second. You are interested in low ns, so you have to at least think about temperature changes. Will your box be outdoors in the sun? What happens when a big black cloud comes over? I'm not sure I understand this - I need to record the time that an event occurs so I need an accurate time reference. What can I store to post-process? The time reference drift and jitter relative to the local oscillator before and after the event? I was assuming that you would capture the time of your events and also the time of several/many PPS events surrounding your events. By time, I mean the counter value from the counter/timer module. I'm not familiar with the chip you are interested in, but the ARM SOC chips I've worked with have a switching matrix between the input pins and their collection of IO modules. I would try to set things up so the PPS signal can be used by both counters. (maybe using 2 pins) The idea is to switch the event counter to the PPS signal to find the offset between the counters. You also have to monitor the serial port so you can label the time of a PPS pulse and/or do sawtooth correction. You also need status info. How good is the fix? ... What are you going to do if/when the GPS fades out? (or gets confused by multipath) One of the reasons to collect some data is so you know what happens just before and/or just after your GPS unit decides it can't get a good fix. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Low cost GPS module for 100ns timestamping error
-Original Message- From: Tony [] I'm considering designing and building some dataloggers, probably ARM Cortex based (eg. STM32F4xx), which record the time of infrequent events, preferably to better than 100ns and if possible better than 50nS. The data loggers will be continuously powered, in fixed locations and should have reasonably good views of the sky so the use of a low cost GPS module should be feasible. I believe it shouldn't be too difficult to resolve the PPS timing to +/- 5ns or better with a 100MHz+ microcontroller clock, but obviously jitter would add to the error requiring the GPS to be better than perhaps 90ns or so worst case. [] === The MAX-7Q has a TCXO and works well as a PPS source. https://www.u-blox.com/en/gps-modules/pvt-modules/max-7.html or perhaps the MAX-M8Q but I've not played with one of those. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
