flight/modules/Airspeed/baro_airspeed_ms4525do.c

   1 /**
   2  ******************************************************************************
   3  * @addtogroup OpenPilotModules OpenPilot Modules
   4  * @{
   5  * @addtogroup AirspeedModule Airspeed Module
   6  * @brief Communicate with airspeed sensors and return values
   7  * @{
   8  *
   9  * @file       baro_airspeed_ms4525do.c
  10  * @author     The OpenPilot Team, http://www.openpilot.org Copyright (C) 2014.
  11  * @brief      Airspeed module, handles temperature and pressure readings from MS4525DO
  12  *
  13  * @see        The GNU Public License (GPL) Version 3
  14  *
  15  *****************************************************************************/
  16 /*
  17  * This program is free software; you can redistribute it and/or modify
  18  * it under the terms of the GNU General Public License as published by
  19  * the Free Software Foundation; either version 3 of the License, or
  20  * (at your option) any later version.
  21  *
  22  * This program is distributed in the hope that it will be useful, but
  23  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  24  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  25  * for more details.
  26  *
  27  * You should have received a copy of the GNU General Public License along
  28  * with this program; if not, write to the Free Software Foundation, Inc.,
  29  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  30  */
  31
  32 /**
  33  * Output object: BaroAirspeed
  34  *
  35  * This module will periodically update the value of the BaroAirspeed object.
  36  *
  37  */
  38
  39 #include "openpilot.h"
  40 #include "hwsettings.h"
  41 #include "airspeedsettings.h"
  42 #include "airspeedsensor.h" // object that will be updated by the module
  43 #include "airspeedalarm.h"
  44
  45 #if defined(PIOS_INCLUDE_MS4525DO)
  46
  47 #define CALIBRATION_IDLE_MS  0              // Time to wait before calibrating, in [ms]
  48 #define CALIBRATION_COUNT_MS 4000 // Time to spend calibrating, in [ms]
  49 #define FILTER_SHIFT         5                      // Barry Dorr filter parameter k
  50
  51 #define P0                   101325.0f           // standard pressure
  52 #define CCEXPONENT           0.2857142857f       // exponent of compressibility correction 2/7
  53 #define CASFACTOR            760.8802669f        // sqrt(5) * speed of sound at standard
  54 #define TASFACTOR            0.05891022589f      // 1/sqrt(T0)
  55
  56 // Private types
  57
  58 // Private functions definitions
  59
  60 // Private variables
  61 static uint16_t calibrationCount = 0;
  62 static uint32_t filter_reg = 0; // Barry Dorr filter register
  63
  64 void baro_airspeedGetMS4525DO(AirspeedSensorData *airspeedSensor, AirspeedSettingsData *airspeedSettings)
  65 {
  66     uint16_t values[2];
  67
  68     // Read sensor
  69     int8_t retVal = PIOS_MS4525DO_Read(values);
  70
  71     // check for errors
  72     if (retVal != 0) {
  73         airspeedSensor->SensorValue            = -1;
  74         airspeedSensor->SensorValueTemperature = -1;
  75         airspeedSensor->SensorConnected        = AIRSPEEDSENSOR_SENSORCONNECTED_FALSE;
  76         airspeedSensor->CalibratedAirspeed     = 0;
  77         AirspeedAlarm(SYSTEMALARMS_ALARM_ERROR);
  78         return;
  79     }
  80
  81     airspeedSensor->SensorValue = values[0];
  82     airspeedSensor->SensorValueTemperature = values[1];
  83
  84     // only calibrate if no stored calibration is available
  85     if (!airspeedSettings->ZeroPoint) {
  86         // Calibrate sensor by averaging zero point value
  87         if (calibrationCount <= CALIBRATION_IDLE_MS / airspeedSettings->SamplePeriod) {
  88             calibrationCount++;
  89             filter_reg = (airspeedSensor->SensorValue << FILTER_SHIFT);
  90             AirspeedAlarm(SYSTEMALARMS_ALARM_WARNING);
  91             return;
  92         } else if (calibrationCount <= (CALIBRATION_IDLE_MS + CALIBRATION_COUNT_MS) / airspeedSettings->SamplePeriod) {
  93             calibrationCount++;
  94             // update filter register
  95             filter_reg = filter_reg - (filter_reg >> FILTER_SHIFT) + airspeedSensor->SensorValue;
  96
  97             if (calibrationCount > (CALIBRATION_IDLE_MS + CALIBRATION_COUNT_MS) / airspeedSettings->SamplePeriod) {
  98                 // Scale output for unity gain.
  99                 airspeedSettings->ZeroPoint = (uint16_t)(filter_reg >> FILTER_SHIFT);
 100
 101                 AirspeedSettingsZeroPointSet(&airspeedSettings->ZeroPoint);
 102                 calibrationCount = 0;
 103             }
 104             AirspeedAlarm(SYSTEMALARMS_ALARM_WARNING);
 105             return;
 106         }
 107     }
 108
 109     /*  Compute airspeed
 110         assume sensor is A Type and has a range of 1 psi, i.e. Pmin=-1.0 psi and Pmax=1.0 psi
 111         Datasheet pressure: output = 0.8 * 16383 / (Pmax-Pmin) * (P - Pmin) + 0.1 * 16383
 112         Inversion: P = (10*output - 81915)/65532 in psi
 113         1 psi = 6894,757293168 Pa
 114         P = (10*output - 81915)*0.1052120688 in Pa
 115         Datasheet temperature: output = (T+50)*2047 / 200
 116         Inversion: T = (200*out - 102350)/2047 in C
 117         T = (200*out - 102350)/2047 + 273.15 in K
 118      */
 119     const float dP = (10 * (int32_t)(airspeedSensor->SensorValue - airspeedSettings->ZeroPoint)) * 0.1052120688f;
 120     const float T  = (float)(200 * (int32_t)airspeedSensor->SensorValueTemperature - 102350) / 2047 + 273.15f;
 121
 122     airspeedSensor->DifferentialPressure = dP;
 123     airspeedSensor->Temperature = T;
 124     // CAS  = Csound * sqrt( 5 *( (dP/P0 +1)^(2/7) - 1) )
 125     // TAS  = Csound * sqrt( 5 T/T0 *( (dP/P0 +1)^(2/7) - 1) )
 126     // where Csound = 340.276 m/s at standard condition T0=288.15 K and P0 = 101315 Pa
 127     airspeedSensor->CalibratedAirspeed = airspeedSettings->Scale * CASFACTOR * sqrtf(powf(fabsf(dP) / P0 + 1.0f, CCEXPONENT) - 1.0f);
 128     airspeedSensor->TrueAirspeed = airspeedSensor->CalibratedAirspeed * TASFACTOR * sqrtf(T);
 129     airspeedSensor->SensorConnected    = AIRSPEEDSENSOR_SENSORCONNECTED_TRUE;
 130     // everything is fine so set ALARM_OK
 131     AirspeedAlarm(SYSTEMALARMS_ALARM_OK);
 132 }
 133
 134 #endif /* if defined(PIOS_INCLUDE_MS4525DO) */
 135
 136 /**
 137  * @}
 138  * @}
 139  */