Ada Fruit GPS Ultimate Breakout Board for PineA64
#11
(09-02-2016, 10:06 AM)MarkHaysHarris777 Wrote: The VBAT is absolutely necessary for real-life practical use of this gps unit... otherwise boot-up and acquisition of fix can take anywhere from 15 minutes to a couple of hours !

15 minutes to a couple of hours? But the datasheet says that a cold start acquisition typically takes 35 second (and so does the adafruit overview)! Now, since it says typically, I could see you padding it out to say... 1 minute, but not 15 minutes to hours? I have the exact same breakout from Adafruit, and with the battery removed, it can lock on in just under 30 seconds when in open sky on a clear day.

   

Perhaps this is this when you're running the on-board ceramic antenna and are using it indoors? As those numbers would make sense then, as its much harder to acquire a signal... even then, it can be touch and go if you get a lock at all or not.
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#12
(09-02-2016, 10:05 PM)pfeerick Wrote:
(09-02-2016, 10:06 AM)MarkHaysHarris777 Wrote: The VBAT is absolutely necessary for real-life practical use of this gps unit... otherwise boot-up and acquisition of fix can take anywhere from 15 minutes to a couple of hours !

15 minutes to a couple of hours? But the datasheet says that a cold start acquisition typically takes 35 second (and so does the adafruit overview)! Now, since it says typically, I could see you padding it out to say... 1 minute, but not 15 minutes to hours? I have the exact same breakout from Adafruit, and with the battery removed, it can lock on in just under 30 seconds when in open sky on a clear day.

Perhaps this is this when you're running the on-board ceramic antenna and are using it indoors? As those numbers would make sense then, as its much harder to acquire a signal... even then, it can be touch and go if you get a lock at all or not.

This is one of those times, pfeerick, when you make absolutely no sense what-so-ever.

... you are arguing against my empirical evidence and experience.  Acquisition depends not only on an open sky, but also on the periods of the satellites in that sky.  I am an expert in tracking those satellites.  Under some ideal conditions I have had my gps receiver obtain a fix from cold boot in 30 seconds;  however, it is 'usually' on the order of 10 to 15 minutes !  ... and funny this should come up now, yesterday my receiver (because of atmospheric conditions and the actual positions of the satellites in orbit) did not obtain a 3D fix for almost 2.5 hours !  It bobbled in and out of 2D fix with less than 3 satellites in view with a good signal.  This happens infrequently, but it does happen.  The point of having the backup battery is that the acquisition times to 3D fix are 'usually' cut in half and sometimes reduced to just a couple of minutes , and in many cases just 30 seconds. The ratings get confused because most testing assumes best conditions, and a backup battery in place. 

pfeerick, this is science not opinion; I'm not interested in arguing about it either. Put a battery on your gps or not.  I choose to, and it works for me. You are free to take my expert advice or not... or like we say in the forums-- YMMV
marcushh777    Cool

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#13
(09-02-2016, 10:21 PM)MarkHaysHarris777 Wrote: ... you are arguing against my empirical evidence and experience.  

pfeerick, this is science not opinion; I'm not interested in arguing about it either. Put a battery on your gps or not.  I choose to, and it works for me. You are free to take my expert advice or not...  or like we say in the forums-- YMMV

Do NOT confuse a question as to where you get the information for a statement you make as being an argument against your 'empirical evidence and experience'.

I didn't start going on about how I've used multiple different GPS chipsets, starting with the EM-406 which really did take 2-3 minutes to get a lock, and doesn't have any memory backup. I have been using them for several years for position hold and automated waypoint navigation of both model aircraft and multi-rotors, so know how they behave with different environments.

So there is absolutely no need steam-roller other forum members simply because they asked you where you got the information from. Especially when if you consider the question was in relation to acquisition time, and if you want, I'll upload the video I took showing the MTK3388 acquiring a position fix in under 30 seconds with no battery backup to demonstrate that what i have said makes absolutely no sense what-so-ever.

btw, whilst I highly recommend the Adafruit Ultimate GPS Breakout due to their excellent quality products, guides and support, since it is US$40 + postage, if you want a GPS unit that is much more sensitive, is just as easy to use, and has a very comprehensive datasheet and protocol guide, you can't go past the uBlox NEO-7. They aren't the newest GPS chipset in the uBlox range, but at AU$15-16 (inc. postage!) on eBay, you can't got wrong with them. They come with a ceramic antenna, and have the uFL an external GPS 'mouse' (antenna). You can use them like most other GPS chips in Serial NMEA mode, or can use the proprietary (but open) UBX binary protocol, making it possible to write some very efficient GPS processing code.
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#14
Addendum:  GPS Made Easy  by  Lawrence and Alex Letham:

https://www.amazon.com/GPS-Made-Easy-Pos...1594851034

Letham's book GPS Made Easy: Using Global Positioning Systems Outdoors  5th Ed  is the primary source for understanding the use of GPS receivers in the wild; used by experts, and highly recommended by experts. 

This book is my favorite GPS book;  if you can afford only one, this is it !



I ordered my 'active mode' external antennae and adapter for the ada fruit ultimate gps breakout board.  I will be posting my pics and testing data here in a few days.  This active antennae system is extremely sensitive and recommended for GPS use indoors, or in the cabin of a plane, boat, or  shack...

PS.  We have solved the battery clip problem.  If you solder the battery clip to the breakout board do so only  at the edges of the clip, and then coat the clip edges with a generous blob of 30 minute epoxy resin to each clip tab.



The following table of data is a cut|paste view of the output from the GPS codes I have posted here. I thought I might make a small explanation of the output; although, it should be self explanatory, but if you're new to gps receivers then a little explanation can go a long ways.



time: 095319.000   date: 040916   N: 4402.4399   W: 09226.0817   El: 367.8 M

    sats: 07   type: GPS fix   mode: Auto 3D  >3 SVs used

                  SVn: ('El', 'Azi', 'dB')
               ----------------------------
                   23: ('58', '186', '29')
                   26: ('21', '055', '30')
                   08: ('37', '159', '29')
                   09: ('67', '258', '22')
                   27: ('50', '108', '28')
                   07: ('40', '296', '27')
                   16: ('49', '050', '32')

time: 095319.000   date: 040916   N: 4402.4399   W: 09226.0817   El: 367.8 M




The time(s) above are UTC (Greenwich time, Coordinated Universal Time).  In this case 9 hours 53 minutes 19.000 seconds.  The date is September the 4th, 2016 and the location is 44 degrees 2.4399 minutes N. lattitude, and 92 degrees 26.0817 minutes W. longitude.  The elevation above sea level for this auto gps 3D fix is 367.8 meters.

The table shows that greater than three(3) satellites were used to compute the auto 3D gps fix. Seven(7) satellites are in view each with a relative signal strength of between 22dB and 32dB. For each SVn numbered on the left, there are three numbers (elevation, azimuth, and signal dB). The elevation of each satellite up above the horizon is in degrees, with 90 being directly overhead. The azimuth (or bearing) is in degrees around clockwise from North (which is Azi 0 or 360; 90 is East, 180 is South, 270 is West). So, in the table above satellite (23) is 58 degrees 'up' above the horizon, and 186 degrees around clockwise from North... or almost directly South. 

Each of the satellites may be positioned on a circular sky-chart and tracked over time. Its fun, and easy, as long as you have some tool to parse out the satellite information from the NMEA sentences; that is what my codes presented in this thread accomplish-- the output of which is displayed above.
marcushh777    Cool

please join us for a chat @  irc.pine64.xyz:6667   or ssl  irc.pine64.xyz:6697

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#15
   

My active antennae arrived today with at least one undamaged and functional u.fl to SMA adapter pigtail. The active antennae draws 10ma from the ada fruit ultimate gps breakout board and immediately gives the receiver an instant 20dB gain over the built-in ceramic antennae. 

The active end (not shown , in the ceiling) is magnetic so that it can be fastened easily to the top of a moving vehicle. The other end of the 5M cable is attached to the receiver by way of a u.fl to SMA connector ( which I had to fiddle with because the pigtail was designed to be male or female ) and the receiver detects the antennae presence and automatically goes into active mode. One of the optional NMEA sentences tells you whether the active antennae is currently being used, and if there are any shorts or problems.

I noticed immediately that the relative signal strength of all SVn increased dramatically ( most of them into the high 30(s) or mid to high 40(s);  within just a few seconds of being plugged in the receiver stabilized with 10 SVn in view and the receiver went into Differential GPS Fix. This is the first time I've seen my receiver in differential mode. The lat., long., and el., readings stabilized to within +|- (1) in the last place and remained stable. 

I'm spoilt now... the active antennae is a must-have especially for indoor use, or inside a vehicle.
marcushh777    Cool

please join us for a chat @  irc.pine64.xyz:6667   or ssl  irc.pine64.xyz:6697

( I regret that I am not able to respond to personal messages;  let's meet on irc! )
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#16
time: 220413.000   date: 070916   N: 4402.4389   W: 09226.0827   El: 367.4 M

    sats: 10   type: Differential GPS fix   mode: Auto 3D  >3 SVs used

                  SVn: ('El', 'Azi', 'dB')
               ----------------------------
                   15: ('46', '161', '41')
                   13: ('50', '107', '46')
                   18: ('24', '246', '30')
                   20: ('77', '273', '23')
                   05: ('41', '057', '40')
                   21: ('44', '299', '41')
                   02: ('14', '108', '29')
                   26: ('13', '299', '22')
                   29: ('63', '205', '35')
                   16: ('09', '326', '14')

time: 220413.000   date: 070916   N: 4402.4389   W: 09226.0827   El: 367.4 M
marcushh777    Cool

please join us for a chat @  irc.pine64.xyz:6667   or ssl  irc.pine64.xyz:6697

( I regret that I am not able to respond to personal messages;  let's meet on irc! )
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#17
Nice writeup Mark. Can you sticky this thread also, as it shows the serial bus being used. Can you also edit it to indicate which pins you've connected the GPS to... I've having to guess that you plugged the GPS TX into Pin 10, etc... [Image: wink.png] And you wouldn't want me to blow up a GPS module now, would you? [Image: tongue.png]
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