UBlox LEA-5T receiver and Ublox U-center timing is out - Page 1
Forum section: electronics / general

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 05:03:20 pm
content: as the heading says, I have a ublox lea-5t receiver and it is running on ublox U-center, I have 9 satellites locked, the long and lat co ordinates are right but the time is UTC as it should be yet it is an hour behind actual time, any one got a clue how to sort this out , the manual is as much use as a dog with no bark or tail.

author: linux-works
author_rank: Super Contributor
timestamp: September 28, 2015, 05:08:04 pm
content: gps does not know (or care) about local time or timezones.you have to do that yourself. that's why processors are connected to gps systems. they take the DST offsets and local offsets into account.

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 05:10:11 pm
content: Ok, but how ?. I cant find any way of doing it

author: Stupid Beard
author_rank: Regular Contributor
timestamp: September 28, 2015, 05:22:14 pm
content: What, specifically, are you trying to do? Are you trying to setup an NTP server with the GPS as the primary reference? Or are you just connecting it to your computer for a bit of a play around? Or something else?What I'm getting at is you are probably asking the wrong question, and setting the GPS device to report in something other than UTC is almost certainly the wrong thing to be doing and is asking for trouble.

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 05:26:29 pm
content: I am merely playing about at the moment, but it annoys me it is not synched with my pc or that I cant find any way of changing the time to my pc clock

author: nfmax
author_rank: Super Contributor
timestamp: September 28, 2015, 05:35:19 pm
content: You need to synchronise your PC clock to the GPS receiver. Then your PC will give you local time, since Windows knows about time zones, but the clock will be locked to the time received by the U-Blox. To do this, the best software to use is ntp. David Taylor has a load of information on how to do his on many systems, including Windows:http://www.satsignal.eu/ntp/index.html. Once it's set up, it operates automatically, and can keep not only the PC but also any other computers such as routers, Raspberry Pi's etc., on your local network synchronised to within a few microseconds, or better with some effort.

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 05:37:37 pm
content: Ok I will take a look at that, I have tried to use trimble studio to reset the ublox receiver as well but it just says the receiver wont accept it.

author: Stupid Beard
author_rank: Regular Contributor
timestamp: September 28, 2015, 05:45:56 pm
content: Quote from: Deathwish on September 28, 2015, 05:26:29 pmI just checked the protocol reference for it and it looks like you can't change the time zone that it reports in. I have the datasheet and protocol reference for the LEA.5T if you need them.

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 06:00:24 pm
content: Quote from: Stupid Beard on September 28, 2015, 05:45:56 pmPlease and thank you.

author: Stupid Beard
author_rank: Regular Contributor
timestamp: September 28, 2015, 06:04:58 pm
content: Quote from: Deathwish on September 28, 2015, 06:00:24 pmThey were too big to attach, so I shoved them on my dropbox here:DatasheetProtocol Specification

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 06:09:55 pm
content: thank you.

author: Stupid Beard
author_rank: Regular Contributor
timestamp: September 28, 2015, 06:10:49 pm
content: No worries mate

author: linux-works
author_rank: Super Contributor
timestamp: September 28, 2015, 06:22:06 pm
content: as you can see, the gps will only report gmt time. any shifts from there, its up to your software (everything other than gps module) to do.now, you can usually set pc's clock to EITHER gmt time OR local time. see if there is some way to directly set via gmt/utc. I know that in unix I can set the 'cmos clock' to either local or utc time.utc is less problematic for clocks as there is no daylight nonsense time, no time zones, its just pure constant time. its an absolute reference. the lesson is to keep clocks set to gmt/utc and its the 'user presentation' layer that has the job of mapping utc to whatever local format and offset is needed.I have written some code (arduino) that does time stuff. I learned this lesson myselfI tried setting 'cmos time' (so to speak) to be local time and it was just a mess. setting it to gmt time and then keeping a DST offset table (search on timezone.h for arduino) was the right solution.one hack might be to run a script (even python) that gets the gps utc time from your module, does the right offset and calls the 'set system cmos clock' routine with that data. it could be done, if there is not some native windows way of doing it. on linux, it would be trivial, and in fact, you simply run 'ntpd' and it knows about timezones and gps modules and so on.one of my rasp. pi boxes is JUST an ntp/gps timeserver. it uses a ublox 6m module, iirc, and it gets access to the 1pps pulsing led, feeds that into the linux kernel and you end up with a very very accurate timeserver. you can then point windows at THAT (I do) and it will Just Plain Work(tm). that might be another solution for you. its known to work and I use it myself. you edit the time setting in win7 (for example) and instead of time.windows.com, you point it to your IP address on your home LAN (the box that is the rasp. pi system with the ublox connected to IT).

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 06:32:52 pm
content: If I cant sort it I am reverting to some old fashioned wild west justice, gonna shoot it with a .357 ( actually its a hammer but hey ho )

author: Stupid Beard
author_rank: Regular Contributor
timestamp: September 28, 2015, 06:39:39 pm
content: Quote from: linux-works on September 28, 2015, 06:22:06 pmWithout wanting to detract from your point, which is generally correct, it is worth pointing out the UTC is not an absolute reference. It still has leap seconds to worry about. If you want an absolute reference then you have to use TAI.GPS time itself is based on UTC as it was in 1980, and as such is a constant offset from TAI. The offset from UTC varies depending on how many leap seconds have been added. The GPS satellites send UTC offset messages so that receivers can correct their offset and report in UTC.Time is one of those things that everyone thinks is simple but it is in fact fraught with many caveats and issues. The only guarantee is that if you write time handling code yourself, there is an extremely high probability that you have screwed it up in some way that will bite you eventually even if it appears to work now.Quote from: Deathwish on September 28, 2015, 06:32:52 pmSet your clock to UTC, then they will matchDaylight savings is a load of bollocks anyway.

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 06:52:07 pm
content: Yeah i agree with the DST thing but it's what everything including shitebay uses and it is kinda standard isnt it. if only churchill et al had never started that mess up I would be happy.

author: Stupid Beard
author_rank: Regular Contributor
timestamp: September 28, 2015, 07:02:39 pm
content: Quote from: Deathwish on September 28, 2015, 06:52:07 pmI work from home and keep strange hours, so I revel in shunning conventional standards of time. I think next year I will be boycotting daylight savings altogether.

author: linux-works
author_rank: Super Contributor
timestamp: September 28, 2015, 07:13:24 pm
content: techie stuffhttp://playground.arduino.cc/Code/TimeI use the timezone library from them and its already worked out. I get gps time from my ublox, and if the timezone 'to and from' tables are setup right you simply use them and you magically get local time. it should work automatically as dst changes since it marks the day and time of the 'edge' eventon the rasp pi board its even easier since unix handles the local stuff and ntpd has built in modes for gps serial devices. you install gpds, ntpd and if you care about the led pulse events, you run a patched linux kernel and send in the led via some digital wire (gpio). from then on, that 'appliance' just does the right thing and it reports proper ntp time. windows can sync to ntp servers and so that's the best solution.if you are up for taking a rasp pi board and interfacing the ublox, I'm happy to help with that.my box, fwiw:the ublox module (just a small simple easy to deal with module) is in blue and has a backup battery on it as well as an external u.fl antenna wire. there's other stuff going on inside that box (lol) but you'd only need the pi board (far right) and the ublox module. there are quite a few articles about how to get a rasp pi to be an NTP server that uses gps.

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 08:18:30 pm
content: Too much hard work for me that, I dont even know why I got this thing, it just looked cool. I don't even understand sat stuff either, I was hoping I could shove it in a box, interface it with some sort of display and get it to tell me the time and co-ordinates on the display. maybe even use the 1pps outputs for something else as well.Now where did I put my hammer..

author: linux-works
author_rank: Super Contributor
timestamp: September 28, 2015, 08:40:07 pm
content: this was not a heathkit, lol!DIY means you are doing more than just 'paint by numbers'.oh well.

author: Deathwish
author_rank: Unknown
timestamp: September 28, 2015, 08:43:53 pm
content: heathkit, isnt he the fella from wuthering heights ?.One day when i have finished one of my projects ( looks across at his drawer set and thinks "hmm, yeah" ) I will start something I have no doubt. I seem to be forever waiting for parts to finish something or other.

author: linux-works
author_rank: Super Contributor
timestamp: September 28, 2015, 08:57:59 pm
content: Quote from: Deathwish on September 28, 2015, 08:43:53 pmnah, its a crunchy candy bar. not sure who you are thinking of.lol

author: Deathwish
author_rank: Unknown
timestamp: September 29, 2015, 08:53:03 pm
content: This thing is funny, Tesco superstore will be charging me rent soon because according to it I have been wandering about inside the store since I ran it up yesterday