PSE530.cpp

00001 #include "mbed.h"
00002 #include "PSE530.h"
00003 
00004 /**
00005  * SMC PSE530 pressure sensor
00006  * analog output 1.0V - 5.0V
00007  * 1.0V : 0
00008  * 5.0V : 1MPa
00009  * (at 0.6V : -0.1MPa)
00010  * Our sensor I/F converts 0-5V to 0-3V
00011  * So we suppose V = Analog Float Value : Pressure
00012  * 0.6V = 0.2 : 0
00013  * 3.0V = 1.0 : 1MPa
00014  */
00015  
00016  /**
00017   * conversion from Pa to kgf/cm2
00018   * 98,066.5 Pa = 1 kgf/cm2
00019   * 1 Pa = 1 / 98066.6 kgf/cm2
00020   */
00021 
00022 PSE530::PSE530(AnalogIn *ain)
00023 {
00024     _ain = ain ;
00025 }
00026 
00027 PSE530::~PSE530(void) 
00028 {
00029     if (_ain) {
00030         delete _ain ;
00031     }
00032 }
00033 
00034 /**
00035  * On FRDM-KL25Z ADC's AREF is about 3.28V
00036  * Where the converted pressure output is 0 to 3.21V
00037  * So we must map ADC output 0 to 3.21/3.28 as full scale
00038  * 
00039  * Then according to the datasheet of PSE530
00040  * when full range is 0V to 5V
00041  * 1V is 0 and 5V is 1MPa which is converted to
00042  * 0.642/3.28 to 3.21/3.28 ~ 0.195731 to 0.9786585.
00043  * The linear equation of
00044  * y = a x + b
00045  * 0 = a * 0.195731 + b
00046  * 1 = a * 0.978658 + b
00047  * results a = 1.277, b = -0.250
00048  */
00049 float PSE530::getPressure(void)
00050 {
00051     float coef_A = 1.277 ;
00052     float coef_B = -0.250 ;
00053     float av = 0.0 ;
00054     float value = 0.0 ;
00055     av = coef_A * _ain->read() + coef_B ;
00056 //    printf("Pressure ADC = %.4f\n", av) ;
00057     value = 1000000 * av  ; /* 1MPa at 1.0 */
00058     value = value / 98066.5 ; /* Pa -> kgf/cm2 */
00059     return( value ) ;
00060 }