Diff: MPL115A1.cpp

Revision:

0:f8ee2a5e377a

Child:

1:b2adf1b62898

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MPL115A1.cpp	Tue Apr 17 07:44:48 2012 +0000
@@ -0,0 +1,221 @@
+/* mbed MPL115A1 (Barometric Pressure Sensor) Library
+ *
+ * This code is based on application notes and
+ * Sparkfun example code, written by Jim Lindblom <jim at sparkfun.com>
+ *
+ * Copyright (c) 2012 Mitja Kleider
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// TODO: support shutdown pin
+
+
+#include "MPL115A1.h"
+
+MPL115A1::MPL115A1(SPI& spi, PinName ncs) : _spi(spi), _cs(ncs)
+{
+    _cs = 1;
+    // sdn = 1; // sensor on
+    
+    // SCL idle low, sample data on rising edge
+    _spi.format(8, 0); // 8bit, POL 0, PHA 0
+    _spi.frequency(1000000); // 1MHz
+}
+
+void MPL115A1::write_register(uint8_t address, char data)
+{
+    //write any data byte to any single address
+    //adds a 0 to the MSB of the address byte (WRITE mode)
+
+    address &= 0x7F;
+
+    _cs = 0;
+    wait_ms(1);
+    _spi.write(address);
+    wait_ms(1);
+    _spi.write(data);
+    wait_ms(1);
+    _cs = 1;
+}
+
+char MPL115A1::read_register(uint8_t address)
+{
+    // returns the contents of any 1 byte register from any address
+    // sets the MSB for every address byte (READ mode)
+
+    char byte;
+
+    address |= 0x80;
+
+    _cs = 0;
+    _spi.write(address);
+    byte = _spi.write(0x00);
+    _cs = 1;
+
+    return byte;
+}
+
+float MPL115A1::readPressure()
+{
+    // read pressure, temperature and coefficients, calculate and return absolute pressure [kPa]
+
+    write_register(MPL115A1_STARTBOTH, 0x00); // start temperature and pressure conversions
+    wait_ms(10); // AN: data is typically ready after 3ms, DS for both: max. 1ms
+    
+    // read raw pressure
+    uiPH = read_register(MPL115A1_PRESH);
+    uiPL = read_register(MPL115A1_PRESL);
+    uiTH = read_register(MPL115A1_TEMPH);
+    uiTL = read_register(MPL115A1_TEMPL);
+    
+    uiPadc = (unsigned int) uiPH << 8;
+    uiPadc += (unsigned int) uiPL & 0x00FF;
+    uiTadc = (unsigned int) uiTH << 8;
+    uiTadc += (unsigned int) uiTL & 0x00FF;
+    
+    // read coefficients, put into 16-bit Variables
+    // a0, pressure offset coefficient
+    sia0MSB = read_register(MPL115A1_A0MSB);
+    sia0LSB = read_register(MPL115A1_A0LSB);
+    sia0 = (signed int) sia0MSB << 8;
+    sia0 += (signed int) sia0LSB & 0x00FF;
+    
+    // b1, pressure sensitivity coefficient
+    sib1MSB = read_register(MPL115A1_B1MSB);
+    sib1LSB = read_register(MPL115A1_B1LSB);
+    sib1 = (signed int) sib1MSB << 8;
+    sib1 += (signed int) sib1LSB & 0x00FF;
+    
+    // b2, 1st order temperature offset coefficient (TCO)
+    sib2MSB = read_register(MPL115A1_B2MSB);
+    sib2LSB = read_register(MPL115A1_B2LSB);
+    sib2 = (signed int) sib2MSB << 8;
+    sib2 += (signed int) sib2LSB & 0x00FF;
+    
+    // c12, temperature sensitivity coefficient (TCS)
+    sic12MSB = read_register(MPL115A1_C12MSB);
+    sic12LSB = read_register(MPL115A1_C12LSB);
+    sic12 = (signed int) sic12MSB << 8;
+    sic12 += (signed int) sic12LSB & 0x00FF;
+    
+    // c11, pressure linearity (2nd order) coefficient
+    sic11MSB = read_register(MPL115A1_C11MSB);
+    sic11LSB = read_register(MPL115A1_C11LSB);
+    sic11 = (signed int) sic11MSB << 8;
+    sic11 += (signed int) sic11LSB & 0x00FF;
+    
+    // c22, 2nd order temperature offset coefficient
+    sic22MSB = read_register(MPL115A1_C22MSB);
+    sic22LSB = read_register(MPL115A1_C22LSB);
+    sic22 = (signed int) sic22MSB << 8;
+    sic22 += (signed int) sic22LSB & 0x00FF;
+    
+    // Coefficient 9 equation compensation
+    
+    // 10bit stored in 16bit, shift right
+    uiPadc = uiPadc >> 6;
+    uiTadc = uiTadc >> 6;
+    
+    // Step 1: c11x1 = c11 * Padc
+    lt1 = (signed long) sic11;
+    lt2 = (signed long) uiPadc;
+    lt3 = lt1*lt2;
+    si_c11x1 = (signed long) lt3;
+    
+    // Step 2: a11 = b1 + c11x1
+    lt1 = ((signed long)sib1)<<14;
+    lt2 = (signed long) si_c11x1;
+    lt3 = lt1 + lt2;
+    si_a11 = (signed long)(lt3>>14);
+    
+    // Step 3: c12x2 = c12 * Tadc
+    lt1 = (signed long) sic12;
+    lt2 = (signed long) uiTadc;
+    lt3 = lt1*lt2;
+    si_c12x2 = (signed long)lt3;
+    
+    // Step 4: a1 = a11 + c12x2
+    lt1 = ((signed long)si_a11<<11);
+    lt2 = (signed long)si_c12x2;
+    lt3 = lt1 + lt2;
+    si_a1 = (signed long) lt3>>11;
+    
+    // Step 5: c22x2 = c22*Tadc
+    lt1 = (signed long)sic22;
+    lt2 = (signed long)uiTadc;
+    lt3 = lt1 * lt2;
+    si_c22x2 = (signed long)(lt3);
+    
+    // Step 6: a2 = b2 + c22x2
+    lt1 = ((signed long)sib2<<15);
+    lt2 = ((signed long)si_c22x2>1);
+    lt3 = lt1+lt2;
+    si_a2 = ((signed long)lt3>>16);
+    
+    // Step 7: a1x1 = a1 * Padc
+    lt1 = (signed long)si_a1;
+    lt2 = (signed long)uiPadc;
+    lt3 = lt1*lt2;
+    si_a1x1 = (signed long)(lt3);
+    
+    // Step 8: y1 = a0 + a1x1
+    lt1 = ((signed long)sia0<<10);
+    lt2 = (signed long)si_a1x1;
+    lt3 = lt1+lt2;
+    si_y1 = ((signed long)lt3>>10);
+    
+    // Step 9: a2x2 = a2 * Tadc
+    lt1 = (signed long)si_a2;
+    lt2 = (signed long)uiTadc;
+    lt3 = lt1*lt2;
+    si_a2x2 = (signed long)(lt3);
+    
+    // Step 10: pComp = y1 + a2x2
+    lt1 = ((signed long)si_y1<<10);
+    lt2 = (signed long)si_a2x2;
+    lt3 = lt1+lt2;
+    
+    // Fixed point result with rounding
+    //siPcomp = ((signed int)lt3>>13);
+    siPcomp = lt3/8192;
+    
+    // decPcomp is defined as a floating point number
+    // Conversion to decimal value from 1023 ADC count value
+    // ADC counts are 0 to 1023, pressure is 50 to 115kPa respectively
+    decPcomp = ((65.0/1023.0)*siPcomp)+50;
+    
+    return decPcomp;
+}
+
+float MPL115A1::readTemperature()
+{
+    // read, calculate and return temperature
+
+    write_register(MPL115A1_STARTTEMP, 0x00); // start temperature conversion
+    wait_ms(10); // AN: data is typically ready after 3ms, DS for temp: max. 0.7ms
+    
+    // read raw temperature
+    uiTH = read_register(MPL115A1_TEMPH);
+    uiTL = read_register(MPL115A1_TEMPL);
+    
+    uiTadc = (unsigned int) uiTH << 8;
+    uiTadc += (unsigned int) uiTL & 0x00FF;
+    
+    // 10bit stored in 16bit, shift right
+    uiTadc = uiTadc >> 6;
+    
+    // Tadc is 472 counts at 25degC, -5.35 counts/degC
+    // return ((float)uiTadc - 472.0)/(-5.35) + 25
+    return (605.75-uiTadc)/5.35;
+}
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