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Diff: MAX31865.cpp
- Revision:
- 0:ae18c7b91185
- Child:
- 1:175f5c2f8d15
diff -r 000000000000 -r ae18c7b91185 MAX31865.cpp
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/MAX31865.cpp Sun Aug 14 05:09:52 2016 +0000
@@ -0,0 +1,227 @@
+/**************************************************************************
+ * Arduino driver library for the MAX31865.
+ *
+ * Copyright (C) 2015 Ole Wolf <wolf@blazingangles.com>
+ *
+ *
+ * Wire the circuit as follows, assuming that level converters have been
+ * added for the 3.3V signals:
+ *
+ * Arduino Uno --> MAX31865
+ * ------------------------------------
+ * CS: any available pin --> CS
+ * MOSI: pin 11 --> SDI (mandatory for hardware SPI)
+ * MISO: pin 12 --> SDO (mandatory for hardware SPI)
+ * SCK: pin 13 --> SCLK (mandatory for hardware SPI)
+ *
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+**************************************************************************/
+
+//#include <Arduino.h>
+//#include <SPI.h>
+#include <MAX31865.h>
+#include "mbed.h"
+
+/**
+ * The constructor for the MAX31865_RTD class registers the CS pin and
+ * configures it as an output.
+ *
+ * @param [in] cs_pin Arduino pin selected for the CS signal.
+ */
+MAX31865_RTD::MAX31865_RTD( ptd_type type,PinName mosi, PinName miso, PinName sclk, PinName nss)
+ :spi( mosi, miso, sclk ),
+ nss( nss )
+
+
+{
+ /* Set the type of PTD. */
+ this->type = type;
+
+ spi.format(8,3);
+ spi.frequency(1000000);
+
+ //nss = 1;
+ /* CS pin for the SPI device. */
+ //this->cs_pin = cs_pin;
+ //pinMode( this->cs_pin, OUTPUT );
+
+ /* Pull the CS pin high to avoid conflicts on SPI bus. */
+ //nss = 1;
+ //nss = type;
+}
+
+
+
+/**
+ * Configure the MAX31865. The parameters correspond to Table 2 in the MAX31865
+ * datasheet. The parameters are combined into a control bit-field that is stored
+ * internally in the class for later reconfiguration, as are the fault threshold values.
+ *
+ * @param [in] v_bias Vbias enabled (@a true) or disabled (@a false).
+ * @param [in] conversion_mode Conversion mode auto (@a true) or off (@a false).
+ * @param [in] one_shot 1-shot measurement enabled (@a true) or disabled (@a false).
+ * @param [in] three_wire 3-wire enabled (@a true) or 2-wire/4-wire (@a false).
+ * @param [in] fault_detection Fault detection cycle control (see Table 3 in the MAX31865
+ * datasheet).
+ * @param [in] fault_clear Fault status auto-clear (@a true) or manual clear (@a false).
+ * @param [in] filter_50hz 50 Hz filter enabled (@a true) or 60 Hz filter enabled
+ * (@a false).
+ * @param [in] low_threshold Low fault threshold.
+ * @param [in] high_threshold High fault threshold.
+*/
+void MAX31865_RTD::configure( bool v_bias, bool conversion_mode, bool one_shot,
+ bool three_wire, uint8_t fault_cycle, bool fault_clear,
+ bool filter_50hz, uint16_t low_threshold,
+ uint16_t high_threshold )
+{
+ uint8_t control_bits = 0;
+ nss = 1;
+ /* Assemble the control bit mask. */
+ control_bits |= ( v_bias ? 0x80 : 0 );
+ control_bits |= ( conversion_mode ? 0x40 : 0 );
+ control_bits |= ( one_shot ? 0x20 : 0 );
+ control_bits |= ( three_wire ? 0x10 : 0 );
+ control_bits |= fault_cycle & 0b00001100;
+ control_bits |= ( fault_clear ? 0x02 : 0 );
+ control_bits |= ( filter_50hz ? 0x01 : 0 );
+
+ /* Store the control bits and the fault threshold limits for reconfiguration
+ purposes. */
+ this->configuration_control_bits = control_bits;
+ this->configuration_low_threshold = low_threshold;
+ this->configuration_high_threshold = high_threshold;
+
+ /* Perform an initial "reconfiguration." */
+ reconfigure( );
+}
+
+
+
+/**
+ * Reconfigure the MAX31865 by writing the stored control bits and the stored fault
+ * threshold values back to the chip.
+ */
+void MAX31865_RTD::reconfigure( )
+{
+ /* Write the configuration to the MAX31865. */
+ nss = 0;
+ // wait_us(100);
+ spi.write( 0x80 );
+ spi.write( this->configuration_control_bits );
+ nss = 1;
+
+ /* Write the threshold values. */
+ nss = 0;
+ // wait_us(100);
+ spi.write( 0x83 );
+ spi.write( ( this->configuration_high_threshold >> 8 ) & 0x00ff );
+ spi.write( this->configuration_high_threshold & 0x00ff );
+ spi.write( ( this->configuration_low_threshold >> 8 ) & 0x00ff );
+ spi.write( this->configuration_low_threshold & 0x00ff );
+ nss = 1;
+
+}
+
+
+
+/**
+ * Apply the Callendar-Van Dusen equation to convert the RTD resistance
+ * to temperature:
+ *
+ * \f[
+ * t=\frac{-A\pm \sqrt{A^2-4B\left(1-\frac{R_t}{R_0}\right)}}{2B}
+ * \f],
+ *
+ * where
+ *
+ * \f$A\f$ and \f$B\f$ are the RTD coefficients, \f$R_t\f$ is the current
+ * resistance of the RTD, and \f$R_0\f$ is the resistance of the RTD at 0
+ * degrees Celcius.
+ *
+ * For more information on measuring with an RTD, see:
+ * <http://newton.ex.ac.uk/teaching/CDHW/Sensors/an046.pdf>.
+ *
+ * @param [in] resistance The measured RTD resistance.
+ * @return Temperature in degrees Celcius.
+ */
+double MAX31865_RTD::temperature( ) const
+{
+ static const double a2 = 2.0 * RTD_B;
+ static const double b_sq = RTD_A * RTD_A;
+
+ const double rtd_resistance =
+ ( this->type == RTD_PT100 ) ? RTD_RESISTANCE_PT100 : RTD_RESISTANCE_PT1000;
+
+ double c = 1.0 - resistance( ) / rtd_resistance;
+ double D = b_sq - 2.0 * a2 * c;
+ double temperature_deg_C = ( -RTD_A + sqrt( D ) ) / a2;
+
+ return( temperature_deg_C );
+}
+
+
+
+/**
+ * Read all settings and measurements from the MAX31865 and store them
+ * internally in the class.
+ *
+ * @return Fault status byte
+ */
+uint8_t MAX31865_RTD::read_all( )
+{
+ uint16_t combined_bytes;
+
+ /* Start the read operation. */
+ nss = 0;
+ /* Tell the MAX31865 that we want to read, starting at register 0. */
+ spi.write( 0x00 );
+
+ /* Read the MAX31865 registers in the following order:
+ Configuration
+ RTD
+ High Fault Threshold
+ Low Fault Threshold
+ Fault Status */
+
+ this->measured_configuration = spi.write( 0x00 );
+
+ combined_bytes = spi.write( 0x00 ) << 8;
+ combined_bytes |= spi.write( 0x00 );
+ this->measured_resistance = combined_bytes >> 1;
+
+ combined_bytes = spi.write( 0x00 ) << 8;
+ combined_bytes |= spi.write( 0x00 );
+ this->measured_high_threshold = combined_bytes >> 1;
+
+ combined_bytes = spi.write( 0x00 ) << 8;
+ combined_bytes |= spi.write( 0x00 );
+ this->measured_low_threshold = combined_bytes >> 1;
+
+ this->measured_status = spi.write( 0x00 );
+
+ nss = 1;
+
+ /* Reset the configuration if the measured resistance is
+ zero or a fault occurred. */
+ if( ( this->measured_resistance == 0 )
+ || ( this->measured_status != 0 ) )
+ {
+ reconfigure( );
+ }
+
+ return( status( ) );
+}
+
+