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/* 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. |
*/ |
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// TODO: support shutdown pin |
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#include "MPL115A1.h" |
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MPL115A1::MPL115A1(SPI& spi, PinName ncs) : _spi(spi), _cs(ncs) |
{ |
_cs = 1; |
// sdn = 1; // sensor on |
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// SCL idle low, sample data on rising edge |
_spi.format(8, 0); // 8bit, POL 0, PHA 0 |
_spi.frequency(1000000); // 1MHz |
} |
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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) |
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address &= 0x7F; |
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_cs = 0; |
wait_ms(1); |
_spi.write(address); |
wait_ms(1); |
_spi.write(data); |
wait_ms(1); |
_cs = 1; |
} |
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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) |
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char byte; |
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address |= 0x80; |
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_cs = 0; |
_spi.write(address); |
byte = _spi.write(0x00); |
_cs = 1; |
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return byte; |
} |
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float MPL115A1::readPressure() |
{ |
// read pressure, temperature and coefficients, calculate and return absolute pressure [kPa] |
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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 |
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// read raw pressure |
uiPH = read_register(MPL115A1_PRESH); |
uiPL = read_register(MPL115A1_PRESL); |
uiTH = read_register(MPL115A1_TEMPH); |
uiTL = read_register(MPL115A1_TEMPL); |
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uiPadc = (unsigned int) uiPH << 8; |
uiPadc += (unsigned int) uiPL & 0x00FF; |
uiTadc = (unsigned int) uiTH << 8; |
uiTadc += (unsigned int) uiTL & 0x00FF; |
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// 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; |
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// b1, pressure sensitivity coefficient |
sib1MSB = read_register(MPL115A1_B1MSB); |
sib1LSB = read_register(MPL115A1_B1LSB); |
sib1 = (signed int) sib1MSB << 8; |
sib1 += (signed int) sib1LSB & 0x00FF; |
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// 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; |
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// 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; |
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// 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; |
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// 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; |
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// Coefficient 9 equation compensation |
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// 10bit stored in 16bit, shift right |
uiPadc = uiPadc >> 6; |
uiTadc = uiTadc >> 6; |
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// Step 1: c11x1 = c11 * Padc |
lt1 = (signed long) sic11; |
lt2 = (signed long) uiPadc; |
lt3 = lt1*lt2; |
si_c11x1 = (signed long) lt3; |
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// Step 2: a11 = b1 + c11x1 |
lt1 = ((signed long)sib1)<<14; |
lt2 = (signed long) si_c11x1; |
lt3 = lt1 + lt2; |
si_a11 = (signed long)(lt3>>14); |
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// Step 3: c12x2 = c12 * Tadc |
lt1 = (signed long) sic12; |
lt2 = (signed long) uiTadc; |
lt3 = lt1*lt2; |
si_c12x2 = (signed long)lt3; |
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// 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; |
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// Step 5: c22x2 = c22*Tadc |
lt1 = (signed long)sic22; |
lt2 = (signed long)uiTadc; |
lt3 = lt1 * lt2; |
si_c22x2 = (signed long)(lt3); |
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// 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); |
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// Step 7: a1x1 = a1 * Padc |
lt1 = (signed long)si_a1; |
lt2 = (signed long)uiPadc; |
lt3 = lt1*lt2; |
si_a1x1 = (signed long)(lt3); |
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// Step 8: y1 = a0 + a1x1 |
lt1 = ((signed long)sia0<<10); |
lt2 = (signed long)si_a1x1; |
lt3 = lt1+lt2; |
si_y1 = ((signed long)lt3>>10); |
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// Step 9: a2x2 = a2 * Tadc |
lt1 = (signed long)si_a2; |
lt2 = (signed long)uiTadc; |
lt3 = lt1*lt2; |
si_a2x2 = (signed long)(lt3); |
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// Step 10: pComp = y1 + a2x2 |
lt1 = ((signed long)si_y1<<10); |
lt2 = (signed long)si_a2x2; |
lt3 = lt1+lt2; |
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// Fixed point result with rounding |
//siPcomp = ((signed int)lt3>>13); |
siPcomp = lt3/8192; |
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// 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; |
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return decPcomp; |
} |
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float MPL115A1::readTemperature() |
{ |
// read, calculate and return temperature |
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write_register(MPL115A1_STARTTEMP, 0x00); // start temperature conversion |
wait_ms(10); // AN: data is typically ready after 3ms, DS for temp: max. 0.7ms |
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// read raw temperature |
uiTH = read_register(MPL115A1_TEMPH); |
uiTL = read_register(MPL115A1_TEMPL); |
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uiTadc = (unsigned int) uiTH << 8; |
uiTadc += (unsigned int) uiTL & 0x00FF; |
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// 10bit stored in 16bit, shift right |
uiTadc = uiTadc >> 6; |
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// Tadc is 472 counts at 25degC, -5.35 counts/degC |
// return ((float)uiTadc - 472.0)/(-5.35) + 25 |
return (605.75-uiTadc)*0.186916; |
} |