LinearTempSensor.cpp

00001 /* mbed Linear Temperature Sensor library
00002  * Supports Microchip MCP9700/9701, National Semiconductor LM35
00003  *
00004  * Written by Todotani, Nov 22 2010
00005  */
00006 
00007 #include "LinearTempSensor.h"
00008 
00009 LinearTempSensor::LinearTempSensor(PinName ain, int N, SensorType type):
00010         // Initialize private variables using Initialization Lists
00011         // _ain(ain) is equivalent to _ain = new AnalogIn(ain)
00012         // _sample(N) is equivalent to _sample = N
00013         _ain(ain), _samples(N), _type(type) {
00014     sampleBuffer = (float *)malloc(sizeof(float) * _samples);
00015     sampleCount = 0;
00016     index       = 0;
00017     Vref        = 3300;
00018     bufferNotFilled = true;
00019 
00020     // Set constants to calculate temperature from sensor value
00021     switch (_type) {
00022         case LM35:
00023             V0 = 0.0f;
00024             Tc = 10.0f;
00025             break;
00026       case MCP9701:
00027             V0 = 400.0f;
00028             Tc = 19.5f;
00029             break;
00030       case MCP9700:
00031        default:
00032             V0 = 500.0f;
00033             Tc = 10.0f;
00034     }
00035     
00036     for (int i = 0; i < _samples; i++)
00037         sampleBuffer[i] = 0.0f;
00038 }
00039 
00040 
00041 LinearTempSensor::~LinearTempSensor() {
00042     free(sampleBuffer);
00043 }
00044 
00045 
00046 float LinearTempSensor::Sense() {
00047     float val;
00048 
00049     val = _ain * Vref;
00050     sampleBuffer[index] = val;
00051     //printf("Index:%d  ", index);    // Debug print
00052     if ( ++index >= _samples )
00053         index = 0;
00054 
00055     if ( bufferNotFilled && (sampleCount == _samples) ) {
00056         bufferNotFilled = false;
00057     }
00058     //printf("flag:%d  ", bufferNotFilled);   // Debug print
00059     sampleCount++;
00060 
00061     return val;
00062 }
00063 
00064 
00065 float LinearTempSensor::GetAverageTemp() {
00066     float sum = 0;
00067     int i, numberOfsumples;
00068 
00069     if (sampleCount == 0)
00070         return 0;
00071 
00072     if (bufferNotFilled) {
00073         // In case number of samples less than buffer lenght
00074         for (i = 0; i < sampleCount; i++) {
00075             sum += sampleBuffer[i];
00076         }
00077         numberOfsumples = sampleCount;
00078     } else {
00079         // In case buffer is filled
00080         for (i = 0; i < _samples; i++) {
00081             sum += sampleBuffer[i];
00082         }
00083         numberOfsumples = _samples;
00084     }
00085 
00086     return ((sum / numberOfsumples) - V0) / Tc;    //  Temp = (Vout - V0) / Tc
00087 }
00088 
00089 
00090 float LinearTempSensor::GetLatestTemp() {
00091     return (sampleBuffer[(sampleCount-1)%_samples] - V0) / Tc;
00092 }