Jhon Plantikow
User a frequecy of response using LM555 in circuit to mensure the capacitor unit
Revision 0:8b2d83f469fa, committed 2015-06-25
- Comitter:
- jhon309
- Date:
- Thu Jun 25 00:26:16 2015 +0000
- Commit message:
- .
Changed in this revision
diff -r 000000000000 -r 8b2d83f469fa capSense.h
--- /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
diff -r 000000000000 -r 8b2d83f469fa main.cpp
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp Thu Jun 25 00:26:16 2015 +0000
@@ -0,0 +1,21 @@
+#include "mbed.h"
+#include "capSense.h"
+#include <ctype.h>
+
+
+#define RA 51000 // ohms
+#define RB 22000 // ohms
+#define PERIOD 2000000 //us
+
+
+Serial pc(SERIAL_TX, SERIAL_RX);
+CapSense cap(RA, RB, PERIOD, PB_9);
+
+int main()
+{
+ while(1)
+ {
+ float capacitance = cap.measure();
+ pc.printf("%.4f#%.2f\n", capacitance,(float)cap._count/1.999);
+ }
+}
\ No newline at end of file
diff -r 000000000000 -r 8b2d83f469fa mbed.bld --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/mbed.bld Thu Jun 25 00:26:16 2015 +0000 @@ -0,0 +1,1 @@ +http://mbed.org/users/mbed_official/code/mbed/builds/7cff1c4259d7 \ No newline at end of file