Dear Zainul, Thanks for your kind explanation. This makes me clear about why I couldn't achieve an accuracy better than 100ms-order with a conventional GPS receiver (e.g., Garmin **) alone. (Actually I already tried to synchronize clocks using GPS receivers, but was disappointed with the performance. :) )
Thanks again for you help. Best regards, Jinkyu Zainul M Charbiwala wrote: > Hi Jinkyu, > > If you want to go the GPS way, and have a scenario where a good GPS > signal is available to you, you could use the PPS signal that is > provided by most GPS receivers. > > This is a pulse-per-second signal, the edge for which is guaranteed to > have a jitter no less than 1us (typically). To get the event time > stamp in microsecond numbers however, you should wire the PPS signal > to a hardware counter that runs off a decently calibrated high > frequency crystal. You can then get event timestamps by reading the > absolute time in seconds from the GPS and the fractional part in > microseconds from the hardware counter. > > If you're adventurous, you could design (or use) a frequency > multiplier that uses a PLL to lock a low-stability high-frequency 1MHz > clock to the high-stability low-frequency 1Hz PPS signal. This will > result in (ideally) a high-stability high-frequency clock that you can > then wire to a counter. > > > Hope that helps, > > Zainul. > > On Sat, Aug 15, 2009 at 7:39 AM, Jinkyu Koo<[email protected]> wrote: > >> Thanks for the comments, Alan and Thomas. >> >> Wiring or powerful amplifier would be a good solution. >> However, in my scenario, distance between two nodes sometimes reaches >> several tens of miles, >> which makes it difficult to use such an approach. >> >> So I am wondering if there is any equipment that can measure the time of >> event in micro-second order precision, >> and can be synchronized with some standard clock. >> For example, I imagines a device made by mixing an oscilloscope and >> GPS-receiver :) >> If I can secure two such devices, I will be free from physical distance. >> >> Thanks, >> Jinkyu >> >> Alan Marchiori wrote: >> >>> On Fri, Aug 14, 2009 at 11:19 AM, Thomas Schmid<[email protected]> >>> wrote: >>> >>> >>>> No, what Jinkyu tires to do is to evaluate the precision of FTSP over >>>> a whole network. One possibility would be to have your beacon node use >>>> a power amplifier like this one: >>>> >>>> http://focus.ti.com/docs/prod/folders/print/cc2591.html >>>> >>>> This would extend the range of your beacon compared to other nodes, >>>> increasing the probability that more nodes will hear it. However, >>>> depending on your distances and the accuracies that you look at, you >>>> might want to incorporate time of flight into your precision >>>> measurements. >>>> >>>> Cheers, >>>> >>>> Thomas >>>> >>>> >>> I see; you could also use some form of backchannel communication for >>> syncornization. Possibly even just a wire supplying a 1 pulse per >>> second tied to an interrupt input. >>> _______________________________________________ >>> Tinyos-help mailing list >>> [email protected] >>> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >>> >>> >> -- >> Ph.D. Student >> School of Electrical and Computer Engineering >> Purdue University, West Lafayette >> >> Office: EE338 & MSEE280 >> Cell: 1-765-337-1704 >> E-mail: [email protected] >> >> >> _______________________________________________ >> Tinyos-help mailing list >> [email protected] >> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >> >> -- Ph.D. Student School of Electrical and Computer Engineering Purdue University, West Lafayette Office: EE338 & MSEE280 Cell: 1-765-337-1704 E-mail: [email protected] _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
