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Re: [Paparazzi-devel] BMP085 sensor

From: Prof. Dr.-Ing. Heinrich Warmers
Subject: Re: [Paparazzi-devel] BMP085 sensor
Date: Wed, 03 Aug 2011 13:28:43 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; de-DE; rv:1.4) Gecko/20030619 Netscape/7.1 (ax)

i see the same fast changes of the pressure sensor.
If no GPS fix is given, the altitude estimator_z is well filtered  but  when GPS has a fix this is not true.
I can not  find the call of  the estimator  with the GPS altitude. But there must be one.
One other problem is that the GPS altitude  has the basis MSL and the altitude of the pressure sensor ground level.
The variance of the GPS altitude is in the range of +-20m.
Thanks for any help,


Helge Walle schrieb:


I have studied baro_bmp.c trying to find the reason why readings from the BMP085 sensor seems to wander in steps of up to +/- 0.5 hPa around “center”. This amounts to approx +/- 4m at sea level. No luck so far, however.

The program selects a high resolution setting of the sensor. As far as the BMP085 datasheet goes I would expect values in the SENSOR_SYNC_SEND message to have a higher resolution. I want to look more at this, but a few questions arise.

In .../var/<my_aircraft>/generated/modules.h there is this code:

static inline void modules_init(void) {
static inline void modules_periodic_task(void) {
   static uint8_t i7; i7++; if (i7>=7) i7=0;
   if (i7 == 0) {
static inline void modules_event_task(void) {

I suppose this code is based on .../conf/modules/baro_bmp.xml. But what is the effect of i7 and how/where is it generated?
It looks to me as if baro_bmp_event() is run 8 times as often as baro_bmp_periodic(). Is this correct?

Could someone please explain a little about this?

Thanks for any help,


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