I'm looking for a GPS module to use with my Arduino Uno project, and I'm looking for any & all suggestions you may have. Ideally, I'm looking for a receiver that is able to:
acquire a GPS signal very quickly (within ~10 sec) upon initial power-up regardless from when it was last powered up (thus, hot-start capable with the use of a coin battery perhaps)
has an external antenna connector (for attaching an active external antenna)
Based on your experiences, what GPS receivers would you recommend? I'm aware of the Ultimate GPS (Adafruit), but I'm looking for other (similar) alternatives.
acquire a GPS signal very quickly (within ~10 sec) upon initial power-up regardless from when it was last powered up (thus, hot-start capable with the use of a coin battery perhaps)
Not possible. The satellite's orbits are constantly changing, so the battery backed data are good for only a period of time. The data rate from the satellites is very low (takes several minutes for a complete almanac message to be sent) and if the GPS unit doesn't already have a good idea which satellites are in the sky, it has to wait until enough have been completely identified and accurately located before calculating the position. You may have to wait up to 15 minutes for a completely cold "factory" start. Time to first fix - Wikipedia
Edit: Of the many I've used, I'm happy with the following battery backed Locosys module, which in the best case can get a fix in well under 10 seconds after turn on. It does not have an external antenna connector: http://www.pololu.com/product/2138
Thanks for the suggestions... I guess that I'm looking for something that is performing similar to the Locosys model you mentioned.
So, I realize that maybe I should "restate" my question to "which GPS receivers exist that have a relatively fast satellite acquisition?
Has anyone used the Ublox Neo-6M? It looks like it has an external antenna adaptor, and also a coin battery attached to it. I wonder what the sat acquisition time is for this model...
I don't think you are paying attention to what Jremington just said. Fancy new technology is not going to get around the fact that
it takes time to acquire 12 satelites. If anyone has fast gps equipment it is the military, but how fast, they're not saying. Fifteen seconds just sounds redicuous. It's more like a minute or more at the very least.
AFAIK some GPS can do a fast start but they require an upload of an ephemeris of the satellites' orbit from a PC/mobile device. This update is available by subscription but I don't know how much they cost. Uploading the ephemeris means that the GPS receiver does not have to wait until it has downloaded the ephemeris from the satellites thereby speeding up the acquisition of the birds and locking on.
A battery backup, such as in the Adafruit Ultimate GPS, allows retention of the recently received ephemeris but it isn't accurate for very long and may not contain info on all possible satellites. When you start up the GPS a few minutes or hours later the data is still good and the GPS can fix very quickly. Once that data is out of date you have to wait again.
In some circumstances, yes. It all depends upon which birds it was seeing when it was shutdown and which birds are visible when it is powered up again.
I have had my Adafruit Ultimate GPS sometimes obtain a lock after 10 seconds when it has been off for several hours - with external antenna connected.
I have used 4 of these and just received a "7" but have not tested.
Warm start in under 30 seconds, typically 10-15 seconds.
The 6M are available for under $17 delivered, I love 'em but I am only using the RMC$ sentences and I hacked Ladyada's lib lots! http://www.ebay.com/itm/181293242043
Thanks Pete & Ray for your very helpful feedback! This really helped me in narrow down the options...
Ray, it sounds like the 6M or even the Max-7 might be just what I am looking for. Could you tell me specifically which model of the 6M you are using (maybe there is a link in Ebay from which I could order one)? And also, I was wondering... what is your take on the Max-7? From what I read it seems to be an improved version of the ublox-6, but I don't have either so I'm not sure if this is the case...
Both work identically with the exception that one has the detachable antenna. Of course, the detachable antenna can be replaced with an active antenna design, if desired. But today's passive patch antennas seem to offer very good performance and also compact space - IMO.
Ray... this is awesome! It definitely looks like the RYG25AI (U-blox 6M) is what I am looking for.
One last quick question... can this GPS be powered using 5v? In the specs, it says that it operates with voltages between 3.5-5.5v, but just wanted to confirm this.
Btw, cool article you sent me about the GPS clock!
can this GPS be powered using 5v? In the specs, it says that it operates with voltages between 3.5-5.5v, but just wanted to confirm this.
Well, I can confirm that the two in the links provided are 3.3V; See attachment.
But, one should never assume with these inexpensive off-shore products. If you order a 6M you will get a 6M because they want more for the 7M, but the U-blox module is 3.3V and the regulator is on the breakout board. This is where things get iffy ... breakout boards come and go and there are lots of theories as to why this happens, but a common one is that the breakouts are produced 'off-shift' during a non-inventory run. My personal experience has been very good, but please do not assume and always double-check your board to ensure the regulator is physically on the board!
If you absolutely must have things the way a picture on eBay looks, it is best not to use eBay - rather, go to Sparkfun or Adafruit or Newark or Jameco or one of the power-web sellers.
thank you so much for your invaluable advice... I just placed an order for the Ublox-7 to see how that works out. I was able to confirm with the vendor that it will take 5v (hopefully the item I get will indeed do so... as you said, you never know ). Just in case I will check to make sure the regulator is indeed in the board, per your recommendation.
Thank you so much for your very valuable words of advice... it really helps for guys like me that are starting to learn about all the different GPS "flavors" out there
). Just in case I will check to make sure the regulator is indeed in the board, per your recommendation.