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Topic: GPS Display Time Standard (Read 5692 times) previous topic - next topic

GPS Display Time Standard

Hi All,

I'm currently working on a couple of clock projects, and I wanted to have a reasonably accurate time standard to set them, so I put together this quick project, a GPS Display/Time Standard.

[attachment=0]

This board uses a GlobalSat EM-406 GPS engine, a PIC 16F689 MCU, and an 8x2 LCD display. The board is intended to be powered externally for stand-alone operation, or by the attached clock. Time data is output to the clock via a 4 pin MTA connector. The firmware will display the number of "locked" satellites on power up, and then revert to time display mode as soon as a valid position/time is received. Time display can be in 12H or 24H format, and a programmable UTC offset can be set to display "local" time if desired.

This project is not intended for ultimate time setting accuracy, but should deliver sub-second (< 1 second) accuracy, which is good enough for my needs.

John

Re: GPS Display Time Standard

Reply #1
Ahh the clock project; as 'standard' as the LED matrix and the accelerometer electronics projects. Its like everyone who starts in electronics will always start by making those 3 projects. Although myself; I have never had interest in LED toys, accelerometers, or clocks; i jumped direct to digital communications; thats my interest :3

But this seems a bit more interesting then a standard clock project; its a serious clock project!
So what is this really for? let me understand this a bit better..

from what I read (correct me if im wrong) you are not using this as the actual time keeping mechanism within your new to be clock projects but a bases to set those clock projects? and perhaps ensure accuracy? Very neat; can you explain how you will use this device to do that? Does it somhow connect to your clock and monitor the time difference between the two for x amount of time or something? That would be a great tool for people who enjoy making clocks. If its not for that then what is it for? besides telling you the time :3

My co-worker did somthing similar; he is designing a nixy tube clock (ah the nixy tube; almost fits inline with the 'standards' above; I also never had interest in the nixy tube). So at the stage now he has finished the PCB and all the electronically workings; so he can properly control the nixies and all that good stuff; now hes just perfecting the firmware. So what he did was create a program on his PC (hes a software programmer by trade) that interconnected to his clock. So his clock; every x amount of time will send something like this through UART:

24:00:000
<0xFF>

So what it does is; it tells his application that the clock will be exactly 24:00 right when the next bit comes; so then his application will then grab the time from one of those government time servers; and he lets this run 24/7 for the last few months. At some point he will hit the 'compile' button on his program and it will spit out all the results and generate abunch of variables for him; offset and drift being the most important im sure...

But yeah; I was very impressed by his techniques in building his clocks (which he will sell on ebay i guess is the plan. apparently they sell pretty good with a good markup on ebay). So I think it would be super neat to perform that same kind of information gathering on an embedded design; then you could just hook it up to a wall-wart or whatever and stick it away in some closet for a few months; take it one out day and export the results to a PC. no need to have some application running 24/7 with the risk of crashing; or risk of the PC turning off and so on... Everything stored to EEPROM or somthing.. That would be a really neat project!

Does anyone know which is more accurate? VS: GPS; PC Time server; or one of those microwave time deal-o's (if thats not the GPS method).

Re: GPS Display Time Standard

Reply #2
there's only one serious problem in dealing with GPS, and that's getting signal inside the apartment/house. For e.g. inside my appt I can't get lock from any satellite, and I tried more then 20 different gps receivers, some with huge antenna's. Everything else is fairly simple to implement.

@brent, gps uses particle fountain data from ground station combined with local atomic clock so it's super accurate, pc time server is eventually linked to particle fountain but it has it's short-cumming so it's good for showing time, nothing else.

Re: GPS Display Time Standard

Reply #3
[quote author="arhi"][sup:][/sup:]
@brent, gps uses particle fountain data from ground station combined with local atomic clock so it's super accurate, pc time server is eventually linked to particle fountain but it has it's short-cumming so it's good for showing time, nothing else.[/quote]

well; whats the difference? if its accurate?

Re: GPS Display Time Standard

Reply #4
[quote author="BrentBXR"] whats the difference? if its accurate?[/quote]

If you just need to show time ntpd is cheapest option no doubt. If you need stable oscillator ntpd is not precise enough for governing it. Also, if you need to time precise events (microseconds) again ntpd is not precise enough. With GPS you can govern an oscillator so for e.g. you can make ovenized xtal (not at all complex to DIY) and then govern it with GPS where every 100-200 seconds (or every 24 hours) you make checks and changes to the oven driver getting the output "perfectly true"

Re: GPS Display Time Standard

Reply #5
Hi All,

Here is a photo of the completed GPS Display Time Standard I intend to use for setting a variety of clock projects I've made, or am working on. This GPS module, the GlobalSat EM-406, has excellent sensitivity as I've been able to lock onto the necessary satellites inside my home without any difficulty!

[attachment=0]

John

Re: GPS Display Time Standard

Reply #6
Nice build! Is the time constantly pulled from the GPS, or do you use it to update a RTC occasionally?
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Re: GPS Display Time Standard

Reply #7
Is it possible to see circuit of GPS Display Time Standard?