Jordan Ford / Mbed 2 deprecated CapSense

Measure capacitances by counting rising edges of a 555 astable oscillator.

Dependencies:   4DGL-uLCD-SE mbed

capSense.h@0:292d0c987fe3, 2014-03-24 (annotated)

Committer:
jford38
Date:
Mon Mar 24 19:47:55 2014 +0000
Revision:
0:292d0c987fe3
Capacitive Sensing using 555 astable oscillator

Who changed what in which revision?

UserRevisionLine numberNew contents of line
jford38 0:292d0c987fe3 1 #ifndef CAP_SENSE_H
jford38 0:292d0c987fe3 2 #define CAP_SENSE_H
jford38 0:292d0c987fe3 3
jford38 0:292d0c987fe3 4 #include "mbed.h"
jford38 0:292d0c987fe3 5
jford38 0:292d0c987fe3 6 class CapSense {
jford38 0:292d0c987fe3 7
jford38 0:292d0c987fe3 8 public:
jford38 0:292d0c987fe3 9 int _Ra;
jford38 0:292d0c987fe3 10 int _Rb;
jford38 0:292d0c987fe3 11 int _Period;
jford38 0:292d0c987fe3 12
jford38 0:292d0c987fe3 13 CapSense(int, int, int, PinName);
jford38 0:292d0c987fe3 14 ~CapSense();
jford38 0:292d0c987fe3 15 float measure();
jford38 0:292d0c987fe3 16
jford38 0:292d0c987fe3 17 //private:
jford38 0:292d0c987fe3 18 volatile int _count;
jford38 0:292d0c987fe3 19 volatile float _partial;
jford38 0:292d0c987fe3 20 float _coeff;
jford38 0:292d0c987fe3 21
jford38 0:292d0c987fe3 22 void atInterrupt();
jford38 0:292d0c987fe3 23
jford38 0:292d0c987fe3 24 Timer _t;
jford38 0:292d0c987fe3 25 InterruptIn* _event;
jford38 0:292d0c987fe3 26 };
jford38 0:292d0c987fe3 27
jford38 0:292d0c987fe3 28 Serial pc(USBTX, USBRX);
jford38 0:292d0c987fe3 29
jford38 0:292d0c987fe3 30 CapSense::CapSense(int Ra, int Rb, int Period, PinName pIn) {
jford38 0:292d0c987fe3 31 _Ra = Ra;
jford38 0:292d0c987fe3 32 _Rb = Rb;
jford38 0:292d0c987fe3 33 _Period = Period;
jford38 0:292d0c987fe3 34 _event = new InterruptIn(pIn);
jford38 0:292d0c987fe3 35
jford38 0:292d0c987fe3 36 _coeff = (_Ra*_Rb)/(float)(_Ra+_Rb) * log( (float)(_Rb-2*_Ra)/(2*_Rb-_Ra) );
jford38 0:292d0c987fe3 37 }
jford38 0:292d0c987fe3 38
jford38 0:292d0c987fe3 39 CapSense::~CapSense() {
jford38 0:292d0c987fe3 40 delete _event;
jford38 0:292d0c987fe3 41 }
jford38 0:292d0c987fe3 42
jford38 0:292d0c987fe3 43 void CapSense::atInterrupt(void) {
jford38 0:292d0c987fe3 44 static float lastTime = 1;
jford38 0:292d0c987fe3 45 float time = _t.read_us();
jford38 0:292d0c987fe3 46 _t.stop();
jford38 0:292d0c987fe3 47 _t.reset();
jford38 0:292d0c987fe3 48 _partial = (time < lastTime) ? time/lastTime : 1;
jford38 0:292d0c987fe3 49 _count++;
jford38 0:292d0c987fe3 50 lastTime = time;
jford38 0:292d0c987fe3 51 _t.start();
jford38 0:292d0c987fe3 52 }
jford38 0:292d0c987fe3 53
jford38 0:292d0c987fe3 54 float CapSense::measure() {
jford38 0:292d0c987fe3 55 _event->rise(this, &CapSense::atInterrupt);
jford38 0:292d0c987fe3 56
jford38 0:292d0c987fe3 57 _count = 0;
jford38 0:292d0c987fe3 58 _partial = 0;
jford38 0:292d0c987fe3 59 wait_us(_Period);
jford38 0:292d0c987fe3 60 float read = _count + _partial;
jford38 0:292d0c987fe3 61
jford38 0:292d0c987fe3 62 _event->rise(NULL);
jford38 0:292d0c987fe3 63 _t.stop();
jford38 0:292d0c987fe3 64 return (float)_Period / ((.693*_Ra + _coeff) * read);
jford38 0:292d0c987fe3 65 }
jford38 0:292d0c987fe3 66
jford38 0:292d0c987fe3 67 #endif