Penn Electric / LinearAnalogSensor

This library is designed to work with devices like the LM335 temperature sensor. There are only two requirements for compatibility: 1) The device must be a sensor device that has an analog voltage output. 2) The physical quantity measured must vary linearly with the analog voltage. It uses a median filter to remove unwanted noise from ADC readings. The number of samples in the filter can be specified as an argument, as well as calibration points or a linear multiplier and coefficient.

LinearAnalogSensor.cpp@0:78eeca1c1944, 2013-08-07 (annotated)

Committer:
PennElectric
Date:
Wed Aug 07 19:37:12 2013 +0000
Revision:
0:78eeca1c1944
Recent update with the names changed and variable number of samples.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
PennElectric 0:78eeca1c1944 1 /* Copyright (c) <2012> <P. Patel>, MIT License
PennElectric 0:78eeca1c1944 2 *
PennElectric 0:78eeca1c1944 3 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
PennElectric 0:78eeca1c1944 4 * and associated documentation files (the "Software"), to deal in the Software without restriction,
PennElectric 0:78eeca1c1944 5 * including without limitation the rights to use, copy, modify, merge, publish, distribute,
PennElectric 0:78eeca1c1944 6 * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
PennElectric 0:78eeca1c1944 7 * furnished to do so, subject to the following conditions:
PennElectric 0:78eeca1c1944 8 *
PennElectric 0:78eeca1c1944 9 * The above copyright notice and this permission notice shall be included in all copies or
PennElectric 0:78eeca1c1944 10 * substantial portions of the Software.
PennElectric 0:78eeca1c1944 11 *
PennElectric 0:78eeca1c1944 12 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
PennElectric 0:78eeca1c1944 13 * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
PennElectric 0:78eeca1c1944 14 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
PennElectric 0:78eeca1c1944 15 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
PennElectric 0:78eeca1c1944 16 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
PennElectric 0:78eeca1c1944 17 */
PennElectric 0:78eeca1c1944 18
PennElectric 0:78eeca1c1944 19 // --------------------- Median Filtered Linear Temperature Sensor Reader ----------------------------
PennElectric 0:78eeca1c1944 20
PennElectric 0:78eeca1c1944 21 #include "LinearAnalogSensor.h"
PennElectric 0:78eeca1c1944 22 #include "mbed.h"
PennElectric 0:78eeca1c1944 23
PennElectric 0:78eeca1c1944 24 // Constructor using two calibration points to define linear multiplier and offset
PennElectric 0:78eeca1c1944 25 LinearAnalogSensor::LinearAnalogSensor(PinName pin, int numSamples, float temp1, unsigned short read1, float temp2, unsigned short read2):_pin(pin) {
PennElectric 0:78eeca1c1944 26 _reading = 0.0; // Zero the temperature
PennElectric 0:78eeca1c1944 27 _multiplier = (temp2 - temp1) / (read2 - read1); // Calculate multiplier as slope
PennElectric 0:78eeca1c1944 28 _offset = temp1 - (_multiplier * read1); // Calculate offset
PennElectric 0:78eeca1c1944 29 _numSamples = numSamples;
PennElectric 0:78eeca1c1944 30 _arr = new unsigned short[numSamples];
PennElectric 0:78eeca1c1944 31 }
PennElectric 0:78eeca1c1944 32 // Constructor using user defined multiplier and offset
PennElectric 0:78eeca1c1944 33 LinearAnalogSensor::LinearAnalogSensor(PinName pin, int numSamples, float multiplier, float offset):_pin(pin) {
PennElectric 0:78eeca1c1944 34 _reading = 0.0; // Zero the temperature
PennElectric 0:78eeca1c1944 35 _multiplier = multiplier; // Set multiplier
PennElectric 0:78eeca1c1944 36 _offset = offset; // Set offset
PennElectric 0:78eeca1c1944 37 _numSamples = numSamples;
PennElectric 0:78eeca1c1944 38 _arr = new unsigned short[numSamples];
PennElectric 0:78eeca1c1944 39 }
PennElectric 0:78eeca1c1944 40
PennElectric 0:78eeca1c1944 41 // Populates an array with temperature readings, sorts, and returns median
PennElectric 0:78eeca1c1944 42 float LinearAnalogSensor::read() {
PennElectric 0:78eeca1c1944 43 memset(_arr, 0, _numSamples * sizeof(unsigned short));
PennElectric 0:78eeca1c1944 44 _arr[0] = _pin.read_u16();
PennElectric 0:78eeca1c1944 45 for (int i = 1; i < _numSamples; i++) {
PennElectric 0:78eeca1c1944 46 _arr[i] = _pin.read_u16();
PennElectric 0:78eeca1c1944 47 unsigned short tmp = _arr[i];
PennElectric 0:78eeca1c1944 48 int j;
PennElectric 0:78eeca1c1944 49 for (j = i - 1; j >= 0; j--) {
PennElectric 0:78eeca1c1944 50 if (tmp>=_arr[j]) break;
PennElectric 0:78eeca1c1944 51 _arr[j + 1] = _arr[j];
PennElectric 0:78eeca1c1944 52 }
PennElectric 0:78eeca1c1944 53 _arr[j + 1] = tmp;
PennElectric 0:78eeca1c1944 54 }
PennElectric 0:78eeca1c1944 55 if (_numSamples % 2 == 0) {
PennElectric 0:78eeca1c1944 56 _reading = (((_arr[_numSamples >> 1] + _arr[(_numSamples >> 1) - 1]) / (2.0)) * _multiplier) + _offset;
PennElectric 0:78eeca1c1944 57 }
PennElectric 0:78eeca1c1944 58 if (_numSamples % 2 == 1) {
PennElectric 0:78eeca1c1944 59 _reading = (_arr[_numSamples >> 1] * _multiplier) + _offset;
PennElectric 0:78eeca1c1944 60 }
PennElectric 0:78eeca1c1944 61 return _reading;
PennElectric 0:78eeca1c1944 62 }
PennElectric 0:78eeca1c1944 63 // Returns last calculated temperature value
PennElectric 0:78eeca1c1944 64 float LinearAnalogSensor::getLast() {
PennElectric 0:78eeca1c1944 65 return _reading;
PennElectric 0:78eeca1c1944 66 }