Potentiometer.cpp

00001 #include <stdio.h>
00002 #include "rtos.h"
00003 #include "Potentiometer.h"
00004 #include "SmartRestConf.h"
00005 #include "logging.h"
00006 
00007 // Cutoff for avoiding sending similar sensor data.
00008 #define THRESHOLD_PERCENT_ANA 0.02
00009 // Timeout for forcing a sending even if  readings are similar [seconds]
00010 #define TIME_LIMIT_ANA 900
00011 
00012 AnalogIn analog1(A0);
00013 AnalogIn analog2(A1);
00014 
00015 static inline bool valueChanged(float *V0, float *V1)
00016 {
00017         if (abs(V0[0]-V1[0]) <= abs(V0[0])*THRESHOLD_PERCENT_ANA &&
00018             abs(V0[1]-V1[1]) <= abs(V0[1])*THRESHOLD_PERCENT_ANA)
00019                 return false;
00020         else
00021                 return true;
00022 }
00023 
00024 int Potentiometer::read(char *buf, size_t maxLen, char *status, size_t num)
00025 {
00026         static const char *fmt = "107,%ld,%f,%f\r\n";
00027         float data[2] = {0, 0};
00028         float min[2] = {100, 100};
00029         float max[2] = {0, 0};
00030         // multiple sampling for data smoothing
00031         const unsigned short N = 20;
00032         for (unsigned short i = 0; i < N; ++i) {
00033                 float d0 = (float)analog1*100;
00034                 float d1 = (float)analog2*100;
00035                 data[0] += d0;
00036                 data[1] += d1;
00037                 min[0] = min[0] <= d0 ? min[0] : d0;
00038                 min[1] = min[1] <= d1 ? min[1] : d1;
00039                 max[0] = max[0] >= d0 ? max[0] : d0;
00040                 max[1] = max[1] >= d1 ? max[1] : d1;
00041                 Thread::wait(10);
00042         }
00043         data[0] = (data[0]-min[0]-max[0]) / (N-2);
00044         data[1] = (data[1]-min[1]-max[1]) / (N-2);
00045 
00046         float t_interval = timer.read();
00047         if (!valueChanged(oldValues, data) && t_interval < TIME_LIMIT_ANA) {
00048                 return 0;
00049         }
00050 
00051         size_t l = snprintf(buf, maxLen, fmt, deviceID, data[0], data[1]);
00052         if (status) {
00053                 snprintf(status, num, "Send Poti %.1f,%.1f", data[0], data[1]);
00054         }
00055         oldValues[0] = data[0];
00056         oldValues[1] = data[1];
00057         timer.reset();
00058         return l;
00059 }