Diff: sensors/PSE530.cpp

Revision:

0:774324cbc5a6

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sensors/PSE530.cpp	Fri Mar 02 07:56:09 2018 +0000
@@ -0,0 +1,60 @@
+#include "mbed.h"
+#include "PSE530.h"
+
+/**
+ * SMC PSE530 pressure sensor
+ * analog output 1.0V - 5.0V
+ * 1.0V : 0
+ * 5.0V : 1MPa
+ * (at 0.6V : -0.1MPa)
+ * Our sensor I/F converts 0-5V to 0-3V
+ * So we suppose V = Analog Float Value : Pressure
+ * 0.6V = 0.2 : 0
+ * 3.0V = 1.0 : 1MPa
+ */
+ 
+ /**
+  * conversion from Pa to kgf/cm2
+  * 98,066.5 Pa = 1 kgf/cm2
+  * 1 Pa = 1 / 98066.6 kgf/cm2
+  */
+
+PSE530::PSE530(AnalogIn *ain)
+{
+    _ain = ain ;
+}
+
+PSE530::~PSE530(void) 
+{
+    if (_ain) {
+        delete _ain ;
+    }
+}
+
+/**
+ * On FRDM-KL25Z ADC's AREF is about 3.28V
+ * Where the converted pressure output is 0 to 3.21V
+ * So we must map ADC output 0 to 3.21/3.28 as full scale
+ * 
+ * Then according to the datasheet of PSE530
+ * when full range is 0V to 5V
+ * 1V is 0 and 5V is 1MPa which is converted to
+ * 0.642/3.28 to 3.21/3.28 ~ 0.195731 to 0.9786585.
+ * The linear equation of
+ * y = a x + b
+ * 0 = a * 0.195731 + b
+ * 1 = a * 0.978658 + b
+ * results a = 1.277, b = -0.250
+ */
+float PSE530::getPressure(void)
+{
+    float coef_A = 1.277 ;
+    float coef_B = -0.250 ;
+    float av = 0.0 ;
+    float value = 0.0 ;
+    av = coef_A * _ain->read() + coef_B ;
+//    printf("Pressure ADC = %.4f\n", av) ;
+    value = 1000000 * av  ; /* 1MPa at 1.0 */
+    value = value / 98066.5 ; /* Pa -> kgf/cm2 */
+    return( value ) ;
+}