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Re: [Paparazzi-devel] STM32 and GPS reception.

From: Prof. Dr.-Ing. Heinrich Warmers
Subject: Re: [Paparazzi-devel] STM32 and GPS reception.
Date: Tue, 03 Jan 2017 10:32:25 +0100
User-agent: Mozilla/5.0 (Windows NT 5.0; rv:12.0) Gecko/20120428 Thunderbird/12.0.1

Hi Helge Walle,

we know at a long time period that the STM32 has much more  noise than the LPC2148.
The periphery on the LPC2148 works only with 8MHz the core with 60 MHz.
Therefore we fly the wing aircraft only with the old Twog and Tiny13.
The Tiny13 is the best but has an old GPS module.
With the NARZE 32  (STM32103) i hat many problems wit the GPS  I get only a fix when i use a lage distance 40cm away from the autopilot pcb.
Try the following:
 1. use ferrite rings for all wires from and to the autopilot PCB.
 2. capsule the autopilot  with aluminium film
 3. keep the GPS module far away from the telemetrie antenna and the motor electronic.
 4. If you use plan antenna keep a balsa wood plate covert with aluminium film under the GPS module (after that we hat 3dB more).
 5. Use a GPS module with active filter between the antenna an the receiver. A club member  make   a new  GPS module with   the Neo8  and a filter an had often an error below 1m. 

The last point use a lower periphery clock for the STM32. This take a lot of work.
If you have 6 satellite revived (38dB and more)  there is no problem in Norway.

Please send me photos of you aircraft and the wireing.

regards Heinrich


Am 02.01.2017 18:17, schrieb Helge Walle:
Hello paparazzi community, and happy new year!

Lately I have been trying to get a satisfactory GPS reception with my STM32 based autopilots, but without success. The two STM32 based boards I have, are a Lisa/M v2.0 and one Elle0. In addition I have an old Twog (LPC2148) to compare with. I have three different GPS's from different vendors, all Ublox5 or Ublox6. The one used most for testing is an Ublox5 receiver with Sarantel antenna (bought from PPZUAV).

I am not sure if the reception quality is influenced by me living 62 degrees north (Norway).

When I connect my GPS receivers to either the Twog or my PC, the fix happens very quickly, and I get approx 6m accuracy outdoors. And, most important, the results are consistent.

When I connect the same GPS's to the STM32 boards, the reception is noticeably worse, not consistent, and it may take several minutes to get a fix, even outdoors.

I tried longer leads, up to 1m. Reception got better, but by far not as good as with the Twog or a PC. Also I tried ferrite rings with better, but not good results. Longer leads combined with ferrite rings brought things close to ok. But then again my plane is small...

I am planning on connecting the GPS via an optical coupler, or even try a wireless connection to see if the interference is reduced. This would anyway be just for testing because of the added complexity. I am not sure if the interference is carried through the connection leads, or via air or both. Does anyone know this?

Searching the net, I found a forum where it was claimed that the interference has something to do with cyclic reading of the STM32 flash. However I cannot confirm this myself.

Shielding of the board is something I hesitate to try, because it makes everything more difficult when connecting and disconnecthing peripherals.

Before I continue with this, does anyone have any knowledge that would help? There is a thread on the mailing list from 2012, but I couldn't find anything very helpful there.

Are there any settings on the STM32F1/4 that could be helpful in reducing the noise?


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