No fix on u-blox neo 6m

External hardware connected to the STM32 board
jucordero
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No fix on u-blox neo 6m

Post by jucordero » Fri Oct 28, 2016 6:13 pm

Hi

I purchased a couple maple-mini clones from ebay in order to test their capabilities and see if they could replace my Teensy on some finished and ongoing projects. I managed to program them quite easily (Thanks to all of you!).

Hooked up a cheap GPS module (u-blox neo 6m) and I'm having a lot of trouble making it getting a fix. The wiring and serial connection are working as I see the incoming data in the serial monitor. Also, I'm getting a fix almost instantaneously in the Teensy and a NANO.
I have tried to replicate the same conditions on the other boards, but it seems like the only ones which are not working properly are the maple clones.

At first I thought it could be a power issue, as the VCC line is not that smooth as on the Teensy. But the same issue is observed by powering it from Vin. Tried with a 3.3 voltage regulator but even that seems to fail.

Right now I'm running out of ideas. Does any of you know what could be happening?

Thanks!

stevestrong
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Re: No fix on u-blox neo 6m

Post by stevestrong » Fri Oct 28, 2016 6:51 pm

What exactly is not working? Which serial interface are you using?

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RogerClark
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Re: No fix on u-blox neo 6m

Post by RogerClark » Fri Oct 28, 2016 8:11 pm

You need to separate out the changes and test them individually in a scientific way.

E.g. if you think the problem is power supply noise or instability, then power the GPS from the Maple but connect the Serial data lines to the AVR ( and also connect their GND together)

Also try holding the Maple mini in reset in another test in this config.

Then do it the other way, e.g perhaps power from the Teensy, but data to the Maple mini

Or power the GPS from a battery and only connect serial plus gnd to the Maple mini

Perhaps also consider RF noise, e.g. power and data to AVR but also run the Maple mini to generate noise

jucordero
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Re: No fix on u-blox neo 6m

Post by jucordero » Sat Oct 29, 2016 4:36 am

Hi Steve and Roger, sorry for the poor description.

These devices use USART. I'm using Serial1.
The reported NMEA sentences show no information regarding time/date or any position. They do appear in the correct format, but the info between the delimiters is just a bunch of invalid data (9999 or similar, typical default numbers I guess) or no data at all. This changes as soon as I power it using the Teensy, keeping the data line on the maple and grounding them together as Roger suggested. That is why I first thought it was a power related issue.

I've estimated the current output with the module on and have not seen anything higher than 100mA.

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RogerClark
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Re: No fix on u-blox neo 6m

Post by RogerClark » Sat Oct 29, 2016 4:46 am

The voltage regulators on some Maple mini and generic STM32 boards are very low quality

I'd recommend if you need 3.3V to power it (rather than 5V) then use a different source of 3.3V.

Next you'd need to see if the data that the Maple mini thinks is garbage is really garbage or its its interpretation of valid data.

There is nothing to stop you connecting a USB to Serial adaptor RX input to the RX input of the Maple mini and look at the data that appears on both, to determine if the data is corrupt or not

stevestrong
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Re: No fix on u-blox neo 6m

Post by stevestrong » Sat Oct 29, 2016 9:37 am

As Roger indicated, try separate 3.3V power supply for that module.
How do you inspect the serial data comming out of the module? On PC with the serial monitor? Can you show the hw connection on a picture?

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ddrown
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Re: No fix on u-blox neo 6m

Post by ddrown » Sat Oct 29, 2016 4:23 pm

jucordero wrote:Hi Steve and Roger, sorry for the poor description.

These devices use USART. I'm using Serial1.
The reported NMEA sentences show no information regarding time/date or any position. They do appear in the correct format, but the info between the delimiters is just a bunch of invalid data (9999 or similar, typical default numbers I guess) or no data at all. This changes as soon as I power it using the Teensy, keeping the data line on the maple and grounding them together as Roger suggested. That is why I first thought it was a power related issue.

I've estimated the current output with the module on and have not seen anything higher than 100mA.
How does the SNR from the GSV http://www.gpsinformation.org/dale/nmea.htm#GSV message compare?

Are you using an external GPS antenna or a built in one?

Are you testing the modules in the same spot? Signal strength can vary dramatically from place to place

jucordero
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Re: No fix on u-blox neo 6m

Post by jucordero » Sun Oct 30, 2016 10:08 pm

Hi again!

Thank you all for your replies.

Steve: I'm inspecting data directly in the serial monitor, by printing all data received by the serial port.

Here is an example of the typical incoming data:

Code: Select all

$GPRMC,215449.00,V,,,,,,,301016,,,N*77
$GPVTG,,,,,,,,,N*30
$GPGGA,215449.00,,,,,0,00,99.99,,,,,,*69
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30
$GPGSV,2,1,05,03,,,21,15,,,18,20,,,22,22,,,28*7A
$GPGSV,2,2,05,31,,,30*7D
$GPGLL,,,,,215449.00,V,N*45
which are the normal NMEA sentences.

I'm thinking that this is indeed a power issue since powering the module from the teensy and retrieving data in the maple seems to work with no flaws.
Is it possible to change the on-board regulator? Has anyone done it before?

ddrown: The SNR is certainly lower than the example you gave me, around 25, but the same values do give me a fix in the rest of the boards.

I'll look at other ways for powering the module.
Thank you guys!

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ahull
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Re: No fix on u-blox neo 6m

Post by ahull » Sun Oct 30, 2016 10:44 pm

An oscilloscope on the power input to the GPS module might provide some clues, you may simply need a few more decoupling capacitors or shorter leads.
- Andy Hull -

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ddrown
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Re: No fix on u-blox neo 6m

Post by ddrown » Mon Oct 31, 2016 9:42 pm

jucordero wrote: Here is an example of the typical incoming data:

Code: Select all

$GPRMC,215449.00,V,,,,,,,301016,,,N*77
$GPVTG,,,,,,,,,N*30
$GPGGA,215449.00,,,,,0,00,99.99,,,,,,*69
$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30
$GPGSV,2,1,05,03,,,21,15,,,18,20,,,22,22,,,28*7A
$GPGSV,2,2,05,31,,,30*7D
$GPGLL,,,,,215449.00,V,N*45
Ok, so in that short example you have:

1. GPS knows the current date and time (so it has a signal)
2. GPS is showing multiple satellites (so it has multiple signals)
3. GPS doesn't know where it is (satellites have no relative position info, and the other position fields are empty)
4. GPS doesn't have a lock (see #3)
5. GPS doesn't have many satellites with strong (greater than 25dB) signals

Here's a comparison set of GSVs:

Code: Select all

$GPGSV,3,1,10,21,65,144,27,18,60,022,34,10,48,321,25,32,47,240,29*73
$GPGSV,3,2,10,24,38,075,36,27,27,285,18,14,21,229,20,20,18,085,22*7E
$GPGSV,3,3,10,15,15,047,32,08,06,318,21*7D
From this output, it currently has 6 satellites over 25 dB SNR: #21, #18, #10, #32, #24, #15 I'm using an external antenna but it's just sitting inside on a window sill.

SNR has two components: the noise and the signal strength. An external antenna can help the signal strength. Moving the GPS module away from noise is another option.

Modules can lock with weaker signals (20dB+ sometimes, 10dB+ rarely), but it's less likely. Having 3 satellites over 25dB SNR is a good start.

Keep in mind that these satellites are moving very quickly and orbit the earth roughly every 12 hours. If you don't have a good signal now, you might have a better one in a few minutes.

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