No fix on u-blox neo 6m

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

Post by RogerClark » Sat Jun 10, 2017 10:32 pm

I dont think you should need to go to these lengths, but recently I have been using some 1W 5V DC to DC isolators, to prevent CPU noise getting into the audio input of HiFi amplifiers.

They are fairly inexpensive, I think about $2 each, and provide complete galvanic isolation, and are good at getting rid of high frequency noise. ( however they may not get rid of terrible hum)

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

Post by Pito » Sun Jun 11, 2017 9:11 am

There could be an issue with BP's oscillator harmonics. The ~21st harmonic of the 72MHz may jam the GPS receiver.
As an experiment, try to change the BP's clock, what happens.
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ilf
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Re: No fix on u-blox neo 6m

Post by ilf » Mon Jun 12, 2017 5:41 pm

Hi. In reverse order. I'll change to 48 Mhz, to see if that will have some effect (I'm using a ST-LINK to upload and I'm using Serial3 for serial).

I'll look into the DC to DC isolators, hopefully those could help, if I can get my hands on those soon enough.

Btw, here are the pictures of the setup. Essentially I have the same on another breadboard but with Pro Mini, and the same setup works.
https://www.dropbox.com/sh/usmsbtvekcj1 ... W9APa?dl=0


Sidenote, I'm also having problems with my LoRa module and the LMIC, but that is a problem for another day. I'm using the modified version of LMIC by Tomtor, but I'll ping him directly for ideas on the email from github, although I suppose the issues might be related to the one I have with the GPS.

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Re: No fix on u-blox neo 6m

Post by ilf » Tue Jun 13, 2017 1:31 pm

OK, I tried with 48 Mhz. That didn't help but I still think it's not a RF problem, because as I mentioned, as long as the GPS is connected to either the GND or any of the RX/TX pins on the Blue Pill, the GPS doesn't work. This is when the Blue PIll is not even powered. Again I repeat, the MCU is not powered.

As I mentioned, if the RX/TX pins are connected from the GPS to the Blue Pill, this causes the power pin of the Blue Pill to blink too. Again the Blue Pill is not connected to either GND or Vcc.

I'm using 3.3 external LDO to power he devices btw.

I wonder, could the GPS breakout board be the problem, as I think it is 3.3/5V tolerant, could the level shifting cause problems?

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

Post by Pito » Tue Jun 13, 2017 1:51 pm

Is the GPS 5V device?? Are the GPS's TX/RX 5V logic?
If yes then you are powering the BP via the internal BPs clamp diodes from the GPS's TX/RX pins as they are 5V idle.
Put 1k (or 2k2 or 3k3 or 4k7) resistors in series with Tx and Rx:
BP TX ------[1k]------ GPS RX
BP RX ------[1k]------ GPS TX
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ilf
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Re: No fix on u-blox neo 6m

Post by ilf » Tue Jun 13, 2017 3:38 pm

This is a 5V tolerant device. It is one of the so called Neo-6M GPS from the Chinese manuf. Actually it has the exact same LDO as the one on the Blue Pill. I tried with 2k2 in series with TX/RX. Same situation. If I connect this device with the exact same setup on another breadboard with ProMini (8V/3.3) everything works. The GPS works if connected to USB-to-serial converter. Once I connect it to the Blue Pill (GND/RX/TX) the GPS goes crazy. Seems the only pin that does not affect it is Vcc. And this is when connecting to a Blue Pill that is not even powered on.

The only thing I haven't tested is to connect the GPS directly to the Blue Pill without the breadboard. *The breadboard is OK, as the 10DOF is working fine on the I2C.

Completely stunned by this situation. I know there is communication between the GPS and the Blue Pill, but the data is corrupted for some reason. The serials on the blue pill are fine, tested them with serial to USB and the GPS is ok, again USB to serial. Also GPS to Arduino is fine. I'm getting frustrated as I'm trying to build a POC, but I would like to use HW Serials and the AVRs don't have enough (except the Mega, which I don't have around currently)

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

Post by Pito » Tue Jun 13, 2017 7:21 pm

If I connect this device with the exact same setup on another breadboard
BTW, there are breadboards which do not have continual GND and VCC rails, you must use jumpers. Just an idea when all is the same but only the breadboards change..
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Re: No fix on u-blox neo 6m

Post by zmemw16 » Tue Jun 13, 2017 8:56 pm

+1

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

Post by RogerClark » Tue Jun 13, 2017 9:36 pm

I think you should try without the breadboard, its a nest of various lengths of hundreds of wires, all capacitively coupled together.

Use a single ground, put RF chokes in both ground and supply to the BP, keep wires short. If necessary, shield the BP inside a aluminium foil box.

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Re: No fix on u-blox neo 6m

Post by ilf » Wed Jun 14, 2017 1:08 pm

Hi Roger and all,

Just coming back to report back. I basically discarded the breadboard, connected the GPS directly with jumper wires to the Blue Pill and everything works pretty nice. Then connected the 10 DOF IMU to the I2C, both working fine.

On that note, I can confirm that TinyGPS++ works nice on the Blue Pill, also NeoGPS works pretty nice too in NMEA mode.

Now let's see if I'll be able to make the InAir9B work. I connected it to another Blue Pill, and I just started debugging.

Thank you all for the support. Sidenote I always hated breadboards, but when prototyping with a lot of sensors it's usually handy.

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