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GARMIN doesn't know the date

S

spuds

Member
It could be the humidity, but then again is there a problem with Garmin GPS 296? I have seen this posted before, but I am looking for a list of occurrences to send Garmin. I know of several GPS 296's that do not remember the date from one week to the next. I've heard of all sorts of baloney about system resets, software updates, etc from Garmin. They don't do any good. I've seen the 296's go back in time!

If this has happenned to you, please respond. I'll write the letter to Garmin.


Spuds
 
My 296 will loose it's date & time too, if sitting idle. But once it captures and tracks the satellites, it's right on "exact" time and date.

edit: I just turned it on, since it's been off since Christmas, when I timed an atomic clock/ weather station; that I got as a gift. It now says Dec. 25th, 2007 & 9:05 PM, when it's really Jan. 3rd, 8:35 PM.

This has never bothered me at all. I just took it outside, and once it locked on, it's perfect time again. Right down to the millisecond. Perhaps even more!

L.Adamson
 
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It has happened to my 276C many times (the 276C is the marine version of the 296). It's always after the unit has set for a few months. The cure is always to let the unit find itself and then charge it from a wall outlet for a few hours. This is true even though the unit indicates that the batteries are fully charged. Once it's charged, the unit keeps time for months. You might see if the same thing happens with the 296.

Guy
 
In fact, I wouldn't be surprised if these GPS's don't even contain software for time keeping; because they are just too precise, when picking up the GPS satellite fix. I don't see much point in a built in clock, that ends up a few seconds or minutes off, like most time pieces eventually do.

But then, I just second guessing here.

edit: Okay, I just read the "charging" reply....
will check it out.

L.Adamson
 
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Prediction...

L.Adamson said:
In fact, I wouldn't be surprised if these GPS's don't even contain software for time keeping; because they are just too precise, when picking up the GPS satellite fix. I don't see much point in a built in clock, that ends up a few seconds or minutes off, like most time pieces eventually do.

But then, I just second guessing here.

edit: Okay, I just read the "charging" reply....
will check it out.

L.Adamson
Click to expand...

I think it needs it's internal clock for satellite prediction after it sits.

If it "knows" time, date and location it can lock in faster when switched on. If not, it just takes longer to lock up....

gil A
 
It needs precise satellite location prediction (which requires exact time) to calculate it's location from the satellite signals - but each satellite signal carries a time stamp as well. When you turn the unit on, even if it thinks it is in the middle of last week/month/year, as soon as it wakes up and receives that first satellite signal with a current timestamp it will reset the internal clock to that timestamp, providing the unit with the correct current prediction locations for the birds.

I would not be surprised to find there is a small battery-driven clock circuit inside the unit that could go dead, causing it to lose the current time if it's been down for a while - but I would be VERY surprised if anyone could show that the time stays incorrect after the unit has a chance to hook up to the constellation of birds overhead. That would result in a location that either could not be computed, or could be randomly anywhere in 3-dimensionial earth-centered space.
 
GPS inernal clock

In the hangar, (no GPS signal), go to main menu. Note the date and time; turn it off. Without taking it out of the hangar, turn it on again an hour later. Did the time change on the main menu page without a sattelite update? It should have, because without knowing the date and time, it does not know which sattalites to find. Mine used to always know the date and time; now it doesn't. The battery is OK because I can run it on battery and it will eventually find itself. I am aware that the sattalites send their own time signals for navigation. I am asking whether the unit knows the time after a week in the hangar.
 
spuds said:
In the hangar, (no GPS signal), go to main menu. Note the date and time; turn it off. Without taking it out of the hangar, turn it on again an hour later. Did the time change on the main menu page without a satellite update? It should have, because without knowing the date and time, it does not know which satellites to find. Mine used to always know the date and time; now it doesn't. The battery is OK because I can run it on battery and it will eventually find itself. I am aware that the satellites send their own time signals for navigation. I am asking whether the unit knows the time after a week in the hangar.
Click to expand...

I just turned my 296 back on, after sitting for two days since this thread started. It still had the date of Jan. 3rd, same as when it was turned off.

I have now put it on the window ledge inside my office, where it just picked up enough satellites to update it's position. The Garmin manual states, that once the unit picks up enough satellites to get a position fix, then it will update to the exact location, as well as the date and time. And sure enough, my 296 just updated to atomic time, as it always has.

From what I read so far, the 296 manual doesn't get to specific about date and time. But one thing for certain, is that GPS does not need to store the correct date and time to get a location fix. From what I've read, this info comes from the orbiting satellites , which get their timing from atomic clocks.

L.Adamson
 
GPSMAP 296 Unit Software

I don't own a 296 so can't comment on your specific clock issue.

However, in surfing the Garmin website today, it lists new unit software for the GPSMAP 296 (Ver. 5.30 as of Jan 02, 2008).
 
Without current and correct time, the unit has no idea where or when it is - but the first sat signal it receives (long before it has enough satellites to calculate a position) will carry the current time and reset the clock internally - so from that point on it knows the constellation positions via it's orbit prediction algorithms. The unit does not need to know where the birds are in the sky on initial power up to receive the signal with the timestamp - it only needs that to compute it's location, which it can ONLY do after it receives signals containing the timestamp that allows it to predict the constellation positions.

The internal clock only needs to be precise to a few parts in a million, something easily done with cheap quartz oscillators, since it will get updated rather frequently from the orbiting satellites.
 
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