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LibrePilot/flight/PiOS/Common/pios_mpxv.c
Oleg Semyonov 285cad290b pios: common PIOS #ifdef guards
Conflicts:
	flight/PiOS/Common/pios_com.c
	flight/PiOS/Common/pios_mpu6000.c
2013-03-24 13:03:54 +02:00

91 lines
3.1 KiB
C

/**
******************************************************************************
* @addtogroup PIOS PIOS Core hardware abstraction layer
* @{
* @addtogroup PIOS_MPXV Functions
* @brief Hardware functions to deal with the DIYDrones airspeed kit, using MPXV*.
* This is a differential sensor, so the value returned is first converted into
* calibrated airspeed, using http://en.wikipedia.org/wiki/Calibrated_airspeed
* @{
*
* @file pios_mpxv.c
* @author The OpenPilot Team, http://www.openpilot.org Copyright (C) 2012.
* @brief ETASV3 Airspeed Sensor Driver
* @see The GNU Public License (GPL) Version 3
*
******************************************************************************/
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "pios.h"
#ifdef PIOS_INCLUDE_MPXV
#define A0 340.27f //speed of sound at standard sea level in [m/s]
#define P0 101.325f //static air pressure at standard sea level in kPa
#define POWER (2.0f/7.0f)
#include "pios_mpxv.h"
/*
* Reads ADC.
*/
uint16_t PIOS_MPXV_Measure(PIOS_MPXV_descriptor *desc)
{
if (desc)
return PIOS_ADC_PinGet(desc->airspeedADCPin);
return 0;
}
/*
*Returns zeroPoint so that the user can inspect the calibration vs. the sensor value
*/
uint16_t PIOS_MPXV_Calibrate(PIOS_MPXV_descriptor *desc,uint16_t measurement){
desc->calibrationSum += measurement;
desc->calibrationCount++;
desc->zeroPoint = (uint16_t)(((float)desc->calibrationSum) / desc->calibrationCount);
return desc->zeroPoint;
}
/*
* Reads the airspeed and returns CAS (calibrated airspeed) in the case of success.
* In the case of a failed read, returns -1.
*/
float PIOS_MPXV_CalcAirspeed(PIOS_MPXV_descriptor *desc,uint16_t measurement)
{
//Calculate dynamic pressure, as per docs
float Qc = 3.3f/4096.0f * (float)(measurement - desc->zeroPoint);
//Saturate Qc on the lower bound, in order to make sure we don't have negative airspeeds. No need
// to saturate on the upper bound, we'll handle that later with calibratedAirspeed.
if (Qc < 0) {
Qc=0;
}
//Compute calibrated airspeed, as per http://en.wikipedia.org/wiki/Calibrated_airspeed
float calibratedAirspeed = A0*sqrt(5.0f*(pow(Qc/P0+1.0f,POWER)-1.0f));
//Upper bound airspeed. No need to lower bound it, that comes from Qc
if (calibratedAirspeed > desc->maxSpeed) { //in [m/s]
calibratedAirspeed=desc->maxSpeed;
}
return calibratedAirspeed;
}
#endif /* PIOS_INCLUDE_MPXV */