Diff: capSense.h

Revision:

0:8b2d83f469fa

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/capSense.h	Thu Jun 25 00:26:16 2015 +0000
@@ -0,0 +1,67 @@
+#ifndef CAP_SENSE_H
+#define CAP_SENSE_H
+
+#include "mbed.h"
+
+class CapSense {
+    
+    public:
+        int _Ra;
+        int _Rb;
+        int _Period;
+        
+        CapSense(int, int, int, PinName);
+        ~CapSense();
+        float measure();
+    
+    //private:
+        volatile int _count;
+        volatile float _partial;  
+        float _coeff; 
+        
+        void atInterrupt(); 
+    
+        Timer _t;
+        InterruptIn* _event;
+};
+
+//Serial pc(USBTX, USBRX);
+
+CapSense::CapSense(int Ra, int Rb, int Period, PinName pIn) {
+    _Ra = Ra;
+    _Rb = Rb;
+    _Period = Period;
+    _event = new InterruptIn(pIn);
+    
+    _coeff = (_Ra*_Rb)/(float)(_Ra+_Rb) * log( (float)(_Rb-2*_Ra)/(2*_Rb-_Ra) );
+}
+
+CapSense::~CapSense() {
+    delete _event;    
+}
+
+void CapSense::atInterrupt(void) {
+    static float lastTime = 1;
+    float time = _t.read_us();
+    _t.stop();
+    _t.reset();
+    _partial = (time < lastTime) ? time/lastTime : 1;
+    _count++;
+    lastTime = time;
+    _t.start();
+}
+
+float CapSense::measure() {
+    _event->rise(this, &CapSense::atInterrupt);
+    
+    _count = 0;
+    _partial = 0;
+    wait_us(_Period);
+    float read = _count + _partial; 
+    
+    _event->rise(NULL);
+    _t.stop();
+    return (float)_Period / ((.693*_Ra + _coeff) * read); 
+}
+
+#endif
\ No newline at end of file