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

[Ben Laurie]

On 3 January 2017 at 21:33, Helge Walle <address@hidden> wrote:
> Thank you Pascal,
>
> The GPS I am testing now (on the photo) was bought a few years ago.
> I had a look at the Drotek NEO-M8N, and it seems very interesting.
> It is some time now since I invested in a new GPS, maybe this should be the
> one to buy and try.

u-blox 8 is a nice advance over 6. :-)

>
> Helge.
>
>
> 2017-01-03 21:53 GMT+01:00 Pascal Fust <address@hidden>:
>>
>> Hi everybody,
>>
>> I'm gonna add my 5 cents, as I was recently testing different arrangements
>> with a KroozSD and a new Drotek Neo-M8N.
>> After trying to get fixes with a Neo-M6 without much success, I was so
>> surprised about the improvement by the new u-blox GPS module. The identical
>> arrangement resulted in fast and precise fixes.
>> On my tricopter, I could even put the GPS just on top of the FC, using the
>> GPS shield from Drotek, and I got perfect GPS readings.
>> In my new fix-wing aircraft, however, I experienced interference of the FC
>> with the GPS at close distance without the shield. Moving the GPS ~30
>> centimeters away from the FC solved all GPS problems. The proximity of the
>> (433MHz) telemetry module did not cause any trouble so far.
>>
>> Regards, Pascal
>>
>>
>>
>> 2017-01-03 21:20 GMT+01:00 Prof. Dr.-Ing. Heinrich Warmers
>> <address@hidden>:
>>>
>>> Hi Helge,
>>> i think the helix antenna must be in the vertical position.
>>> The antenna is to near to the telemetry antenna.
>>> Please put the telemetry module  near the in the ventilation hole in  the
>>> back side of the fuselage.
>>> This is better for the RC-reciever as for the GPS-module.
>>> The transceiver Antenna has to be  much away as possible  from the
>>> receiver antennas GPS- and RC- receivers.
>>>
>>> regards Heinrich
>>>
>>>
>>>
>>> Am 03.01.2017 18:57, schrieb Helge Walle:
>>>
>>> Thank you for your kind reply and good advice, Heinrich.
>>>
>>> On the attached photo, the location of the autopilot is not easy to
>>> change. But this is a project under construction and all the other paparazzi
>>> components can be moved to other locations in the plane.
>>>
>>> The RC receiver is placed 2-3cm in front of the Lisa/M. And the XBee is
>>> approx 8-9cm in front of the RC receiver. Opinions on this are very welcome.
>>>
>>> The wiring shown is not permanent, and things look a bit messy at the
>>> moment  :-|
>>>
>>> If I lengthen the GPS cable I can make room for the unit at the front of
>>> the vehicle. Maybe it will help... and I have some ferrite rings that I can
>>> use. But I want to test this before I cut into the foam.
>>>
>>> Still, not knowing for certain the origin of the noise, and whether it is
>>> carried by wire or through air, is a bit frustrating. I tried some
>>> measurements with my 50MHz oscilloscope, but could not reveal anything
>>> useful.
>>>
>>> To try and get more knowledge about how the noise is transmitted, I would
>>> like to make a galvanic isolated link between the GPS and the board (for
>>> testing only). The easiest way to achieve this (i think) is to use opto
>>> isolators for RX and TX, and, a separate battery for the GPS.
>>>
>>> Thanks,
>>> Helge.
>>>
>>>
>>>
>>>
>>>
>>> 2017-01-03 10:32 GMT+01:00 Prof. Dr.-Ing. Heinrich Warmers
>>> <address@hidden>:
>>>>
>>>>
>>>> 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?
>>>>
>>>> Thanks,
>>>> Helge.
>>>>
>>>>
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