add low pass filter to meas airspeed driver including logging of filtered value

src/drivers/meas_airspeed/meas_airspeed.cpp

@@ -79,6 +79,8 @@
 #include <systemlib/param/param.h>
 #include <systemlib/perf_counter.h>
 
+#include <mathlib/math/filter/LowPassFilter2p.hpp>
+
 #include <drivers/drv_airspeed.h>
 #include <drivers/drv_hrt.h>
 
@@ -99,6 +101,8 @@
 #define ADDR_READ_MR			0x00	/* write to this address to start conversion */
 
 /* Measurement rate is 100Hz */
+#define MEAS_RATE 100.0f
+#define MEAS_DRIVER_FILTER_FREQ 3.0f
 #define CONVERSION_INTERVAL	(1000000 / 100)	/* microseconds */
 
 class MEASAirspeed : public Airspeed
@@ -116,6 +120,7 @@ protected:
 	virtual int	measure();
 	virtual int	collect();
 
+	math::LowPassFilter2p	_filter;
 };
 
 /*
@@ -124,7 +129,8 @@ protected:
 extern "C" __EXPORT int meas_airspeed_main(int argc, char *argv[]);
 
 MEASAirspeed::MEASAirspeed(int bus, int address, const char* path) : Airspeed(bus, address,
-			CONVERSION_INTERVAL, path)
+			CONVERSION_INTERVAL, path),
+			_filter(MEAS_RATE, MEAS_DRIVER_FILTER_FREQ)
 {
 
 }
@@ -208,6 +214,7 @@ MEASAirspeed::collect()
         report.error_count = perf_event_count(_comms_errors);
 	report.temperature = temperature;
 	report.differential_pressure_pa = diff_press_pa;
+	report.differential_pressure_filtered_pa =  _filter.apply(diff_press_pa);
 	report.voltage = 0;
 	report.max_differential_pressure_pa = _max_differential_pressure_pa;
 

src/modules/sdlog2/sdlog2.c

@@ -1142,6 +1142,7 @@ int sdlog2_thread_main(int argc, char *argv[])
 					log_msg.body.log_SENS.baro_alt = buf.sensor.baro_alt_meter;
 					log_msg.body.log_SENS.baro_temp = buf.sensor.baro_temp_celcius;
 					log_msg.body.log_SENS.diff_pres = buf.sensor.differential_pressure_pa;
+					log_msg.body.log_SENS.diff_pres_filtered = buf.sensor.differential_pressure_filtered_pa;
 					LOGBUFFER_WRITE_AND_COUNT(SENS);
 				}
 			}

src/modules/sdlog2/sdlog2_messages.h

@@ -92,6 +92,7 @@ struct log_SENS_s {
 	float baro_alt;
 	float baro_temp;
 	float diff_pres;
+	float diff_pres_filtered;
 };
 
 /* --- LPOS - LOCAL POSITION --- */
@@ -306,7 +307,7 @@ static const struct log_format_s log_formats[] = {
 	LOG_FORMAT(ATT, "fffffffff", "Roll,Pitch,Yaw,RollRate,PitchRate,YawRate,GX,GY,GZ"),
 	LOG_FORMAT(ATSP, "ffff", "RollSP,PitchSP,YawSP,ThrustSP"),
 	LOG_FORMAT(IMU, "fffffffff", "AccX,AccY,AccZ,GyroX,GyroY,GyroZ,MagX,MagY,MagZ"),
-	LOG_FORMAT(SENS, "ffff", "BaroPres,BaroAlt,BaroTemp,DiffPres"),
+	LOG_FORMAT(SENS, "ffff", "BaroPres,BaroAlt,BaroTemp,DiffPres,DiffPresFilt"),
 	LOG_FORMAT(LPOS, "ffffffLLfBBB", "X,Y,Z,VX,VY,VZ,RefLat,RefLon,RefAlt,XYFlags,ZFlags,Landed"),
 	LOG_FORMAT(LPSP, "ffff", "X,Y,Z,Yaw"),
 	LOG_FORMAT(GPS, "QBffLLfffff", "GPSTime,FixType,EPH,EPV,Lat,Lon,Alt,VelN,VelE,VelD,Cog"),

src/modules/sensors/sensors.cpp

@@ -1028,6 +1028,7 @@ Sensors::diff_pres_poll(struct sensor_combined_s &raw)
 		orb_copy(ORB_ID(differential_pressure), _diff_pres_sub, &_diff_pres);
 
 		raw.differential_pressure_pa = _diff_pres.differential_pressure_pa;
+		raw.differential_pressure_filtered_pa = _diff_pres.differential_pressure_filtered_pa;
 		raw.differential_pressure_counter++;
 
 		_airspeed.indicated_airspeed_m_s = calc_indicated_airspeed(_diff_pres.differential_pressure_pa);

src/modules/uORB/topics/differential_pressure.h

@@ -54,8 +54,9 @@
 struct differential_pressure_s {
 	uint64_t	timestamp;			/**< microseconds since system boot, needed to integrate */
 	uint64_t	error_count;
-	float	differential_pressure_pa;	/**< Differential pressure reading */
+	float	differential_pressure_pa;		/**< Differential pressure reading */
-	float	max_differential_pressure_pa;	/**< Maximum differential pressure reading */
+	float	differential_pressure_filtered_pa;	/**< Low pass filtered differential pressure reading */
+	float	max_differential_pressure_pa;		/**< Maximum differential pressure reading */
 	float		voltage;			/**< Voltage from analog airspeed sensors (voltage divider already compensated) */
 	float		temperature;			/**< Temperature provided by sensor */
 

src/modules/uORB/topics/sensor_combined.h

@@ -103,8 +103,9 @@ struct sensor_combined_s {
 	float mcu_temp_celcius;			/**< Internal temperature measurement of MCU */
 	uint32_t baro_counter;			/**< Number of raw baro measurements taken        */
 
-	float differential_pressure_pa;				/**< Airspeed sensor differential pressure                  */ 
+	float differential_pressure_pa;		/**< Airspeed sensor differential pressure           */
-	uint32_t differential_pressure_counter;		/**< Number of raw differential pressure measurements taken */
+	float differential_pressure_filtered_pa;	/**< Low pass filtered airspeed sensor differential pressure reading */
+	uint32_t differential_pressure_counter;	/**< Number of raw differential pressure measurements taken */
 };
 
 /**