pressuresensor.cpp

00001 /* Copyright (c) 2017 Philippe Kalaf, MIT License
00002  *
00003  * Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
00004  * and associated documentation files (the "Software"), to deal in the Software without restriction, 
00005  * including without limitation the rights to use, copy, modify, merge, publish, distribute, 
00006  * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
00007  * furnished to do so, subject to the following conditions:
00008  *
00009  * The above copyright notice and this permission notice shall be included in all copies or 
00010  * substantial portions of the Software.
00011  *
00012  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING 
00013  * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
00014  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, 
00015  * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
00016  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
00017  */
00018 
00019 /* Analog output pressure sensor driver */
00020 #include "pressuresensor.h"
00021 
00022 PressureSensor::PressureSensor(PinName pin) : 
00023                                 _input(pin),
00024                                 _worker_thread(osPriorityNormal, 256)
00025 {
00026     _worker_thread.start(callback(this, &PressureSensor::_worker));
00027 }
00028 
00029 // returns pressure in bar
00030 float PressureSensor::read_bars()
00031 {
00032     return float(read_pa())/100000;
00033 }
00034 
00035 // returns pressure in Pa, 100000 Pa = 1 bar
00036 // avoids float calculations for 
00037 int PressureSensor::read_pa()
00038 {
00039     // sensor provides linear voltage between 0.5V to 5V representing 0 to 20 bars
00040     // 0.5V to 3.3V <-> 0 bar to 12.44 bar
00041     // read_u16 should return a value between 9930 and 65535 representing 0.5 to 3.3V
00042     // measurements show a range between 10300 and 60000 respresenting 0.5 to 3.3V
00043     // each 3995 represents 100000 Pa (1 bar) -> each unit represents 25 Pa
00044     // measurements show the 0.5V value at around 10300
00045     int pressure_pascal = (_input.read_u16() - 10300);
00046     pressure_pascal = (pressure_pascal * 25);
00047 
00048     return pressure_pascal;
00049 } 
00050 
00051 void PressureSensor::_worker()
00052 {
00053     while(true)
00054     {
00055         if(_read_count != -1)
00056         {
00057             _read_count++;
00058             // keep calculating average
00059             _average_pressure = ( _average_pressure * (_read_count-1) 
00060                     + read_pa() )
00061                 /_read_count;
00062         }
00063 
00064         ThisThread::sleep_for(200);
00065     }
00066 }
00067 
00068 void PressureSensor::start_count()
00069 {
00070     _read_count = 0;
00071     _average_pressure = 0;
00072 }
00073 
00074 float PressureSensor::stop_count()
00075 {
00076     _read_count = -1;
00077     return float(_average_pressure) / 100000;
00078 }