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Which GPS Modules Save Settings?

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Bruce

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I am interested in sending GPS data from a rocket to the ground.

I have noticed that some GPS modules will save settings and some won't. I use u-center to change things like the sample rate and which sentences to output. My M9N GPS saves the settings just fine. After a power cycle or even after a couple of days, the settings remain. But an M8Q GPS does not save the settings even though it looks like it is.

Is there a list somewhere that tells which GPS modules save the configuration and which don't?
 

Reinhard

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Is there a battery or supercap on the M9N module that you're using? This would explain why it keeps its settings.
How long does it take for those systems to get their first fix after powering them up? If the M9N is much faster (typ. seconds instead of minutes) then there is some energy storage involved.
You can also check the u-blox documentation wether your modules are flash or ROM based.

Reinhard
 

ksaves2

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I discovered the cheaper versions of a GPS chipset usually don't allow one to change many of the settings through the manufacturer's setup program. They are "hobbled" versions of their pricier counterparts. As I recalled back when I was doing a lot of this, a $20.00 version of a GPS chip was limited as opposed to the "full range" $125.00 version which might just differ by one designated letter or number. This was some time ago mind you and prices for full featured chipsets have probably dropped somewhat.
Holee guacamole. Just did a search and found this: https://www.beyondlogic.org/fsa03/
Specs are pretty good, tiny unit and that antenna is for GPS reception. Just the module so would have to be wired into an Rf module to transmit the data.
Incidentally, I dorked an Eggfinder tracker by dropping it and the GPS receiver snapped clean off the base. For fun I took it out of the junk door as I acquired a fancy dancy desoldering station. I have a quadrifilar GPS chipset that runs off the same power as the EggFinder and I just had to solder 3 wires. Two for "+" and "-" (power) and one wire for the signal "out" of the GPS to the signal "in" of the broken EggFinder. Eureka, it works! Still does last time I tried it.
Oh the reason I was trying to get into a particular GPS chipset's setup program was I wanted to make a comment statement that would go out over the transmitted NMEA sentences that would have my Ham callsign, KC9LDH, which would make it perfectly legal for me to use the unit on the ham bands. The GPS stat sheet said it was totally doable but I found out I couldn't program the "cheaper" version of the chipset to do it. That area was grayed out in the setup program. Tried a couple of other cheap GPS chipsets and same issue. They were not full featured.
I was trying to come up with a cheap disposable tracker and having to buy a $125.00 full featured GPS chipset spoiled that quest.
Launch a rocket high enough or far enough and even though one has a GPS tracker, it's no guarantee you'll get it back. Yes the odds are much greater especially if one can track on a live map but everyone knows that "shoot" happens. I can attest to as one of my early Beeline GPS trackers died in a core sampled rocket. Didn't need the tracker to find it. Ouch!
Kurt
 

gtg738w

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Are you actually saving the config after you send the new settings? That is a separate step in uCenter. As Reinhard said, the M9 module you have may have a battery backup. If that’s the case, removing power won’t actually cause a restart to clear the config.
 

Bruce

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I click on "send" at the bottom in u-center to save the settings. Then I choose "CFG (Configuration)" and "send" to save the configuration. Is there another step that I'm missing?

Most of the GPS modules that I have seen have a little battery on them. I assume that's for the BBR Battery Backed RAM. Is that memory only for saving the coldstart info? I have measured the voltage of the battery on several GPSs and it varies widely. It seems like the battery only lasts for a few days.

Why don't GPSs use flash memory instead of BBR?
 

gtg738w

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I click on "send" at the bottom in u-center to save the settings. Then I choose "CFG (Configuration)" and "send" to save the configuration. Is there another step that I'm missing?

Most of the GPS modules that I have seen have a little battery on them. I assume that's for the BBR Battery Backed RAM. Is that memory only for saving the coldstart info? I have measured the voltage of the battery on several GPSs and it varies widely. It seems like the battery only lasts for a few days.

Why don't GPSs use flash memory instead of BBR?
Which modules are you using? Some include flash, some don't. The data sheets will tell you for sure. The module is just the GNSS chip plus a variety of peripherals depending on the config. There are lots of different combinations available, it's not a difference of M8 vs M9. The battery is required to run the clock. The engine requires accurate time for a fix and the orbital data will only tell you what's visible if you know what time it is. The precise orbital data is only good for a few hours so there is not much use in having a battery that will last for weeks or months. u-blox does have the AssistNow Autonomous service that will extrapolate orbits to aid the search but it still needs to download the current data before you can get a fix.
 

ksaves2

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I click on "send" at the bottom in u-center to save the settings. Then I choose "CFG (Configuration)" and "send" to save the configuration. Is there another step that I'm missing?

Most of the GPS modules that I have seen have a little battery on them. I assume that's for the BBR Battery Backed RAM. Is that memory only for saving the coldstart info? I have measured the voltage of the battery on several GPSs and it varies widely. It seems like the battery only lasts for a few days.

Why don't GPSs use flash memory instead of BBR?
No you are likely not missing anything. If you are using a "cheaper" version of a chipset it won't take your inputs on that option.

When I was messing with the 3DR radios with a GPS I was totally hobbled in that I couldn't get my Ham radio callsign into a comment line on the GPS setup. I had everything connected up right, I could change things like units and such and it just wouldn't allow me to put a comment line in. I would have had to spend a lot more money for the full featured chipset. I didn't want to do that so gave up.

If you are using a cheap(er) version of a GPS chipset, bear in mind it might still be hobbled about its' full capabilities.

I found that out the hard way but I didn't waste much money in the quest. In fact I kind'a enjoyed it. I got an early "cheap" chipset with American (GPS) and Russian (Glonass) capability simultaneously and was blown away with a mapping GPS program I was using. A bad guy could have stuck a missile or a bomb right through the back picture window of my house if they were using this technology. Of course the "gubbermints" have better access to stuff than we peons do! ;)

Kurt
 

Bruce

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Which modules are you using? Some include flash, some don't. The data sheets will tell you for sure. The module is just the GNSS chip plus a variety of peripherals depending on the config. There are lots of different combinations available, it's not a difference of M8 vs M9. The battery is required to run the clock.
The modules that I am using are the NEO-M9N and the NEO-M8N. From my observations, the M9 saves the configuration settings, but the M8 doesn't.

This u-blox Line Card says that both the NEO-M9N and NEO-M8N have programmable flash memory. What am I missing?

Programmable.jpg
 

gtg738w

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My M9N GPS saves the settings just fine. After a power cycle or even after a couple of days, the settings remain. But an M8Q GPS does not save the settings even though it looks like it is.
Your first message said M8Q. If you are using the M8N, does it reply with an ACK after the save command? It *should* work.
 

Bruce

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I now realize that the M8Q does not have the ability to save settings, but the M8N should.

Can you explain a bit about the ACK? I'm using u-center to save the settings to both the M9N which saves fine and the M8N which doesn't. I don't see "ACK" anywhere in u-center with either of them, but I'm probably just missing it. Where exactly do I look?
 

gtg738w

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If you open a packet console you can see exactly what u-center is exchanging with the module. If you send a UBX-CFG-CFG and the module can comply, it will respond with UBX ACK-ACK. If it can't comply or the request was invalid, it should respond with UBX-ACK-NAK.

config.PNG
 

ksaves2

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If you open a packet console you can see exactly what u-center is exchanging with the module. If you send a UBX-CFG-CFG and the module can comply, it will respond with UBX ACK-ACK. If it can't comply or the request was invalid, it should respond with UBX-ACK-NAK.

View attachment 448085
Well shoot, I haven't worked with this stuff for a few years but I learned something useful and interesting from the above exchange. Thanks. Hope to get back to flying soon but being widowed for the past two years means I do all the domestic chores/cooking now and not as much time for building. I refuse to live on fast/junk food and got my cooking chops back pretty quickly after my spouse passed. I didn't get married until I was just about 32 and took care of myself for quite a few years before that. Thanks Mom.
Kurt :)
 

Bruce

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If you open a packet console you can see exactly what u-center is exchanging with the module. If you send a UBX-CFG-CFG and the module can comply, it will respond with UBX ACK-ACK. If it can't comply or the request was invalid, it should respond with UBX-ACK-NAK.

View attachment 448085
With the M8N, u-center does indeed respond with UBX ACK-ACK successfully and the settings are saved. Power cycle the GPS and everything works fine with the new settings. But the next day, the settings are lost and it's back to defaults...
 

SparkyVTFlyer

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With the M8N, u-center does indeed respond with UBX ACK-ACK successfully and the settings are saved. Power cycle the GPS and everything works fine with the new settings. But the next day, the settings are lost and it's back to defaults...
I noticed the same thing on the M8N a few years ago. I finally gave up and used a micro controller to program the settings over serial at startup. Its not too hard, and you can get the hex sentences right from U-Center.

Another note, the M8N and M8Q have very different update rates. The M8N can do a maximum of 5 updates per second on two GNSS systems, where the M8Q can do 10, for a total of 10 and 20 updates per second respectively. The M9N can do 25 updates per second across 4 GNSS systems - thats 100 updates per second! Holy smokes! I can't wait until I try that one out!
 

Reinhard

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With the M8N, u-center does indeed respond with UBX ACK-ACK successfully and the settings are saved. Power cycle the GPS and everything works fine with the new settings. But the next day, the settings are lost and it's back to defaults...
This means you particular module contains a capacitor instead of a battery. You can usually replace it with a battery (requires some rework).

Reinhard
 
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