[Paparazzi-devel] STM32 and GPS reception.

[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?

Thanks,

Helge.