mn
Thermistor.cpp
- Committer:
- unix_guru
- Date:
- 2016-03-09
- Revision:
- 0:000a8be2414d
- Child:
- 2:ee3997416bcc
File content as of revision 0:000a8be2414d:
/* * Thermistor Temperature library * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include "mbed.h" #include "Thermistor.h" Thermistor::Thermistor(PinName pin) : _pin(pin) { // _pin(pin) means pass pin to the AnalogIn constructor init(); } void Thermistor::init() { ThermistorNominal = THERMISTORNOMINAL; TemperatureNominal = TEMPERATURENOMINAL; BCoefficient = BCOEFFICIENT; SeriesResistor = SERIESRESISTOR; } // This is the workhorse routine that calculates the temperature // using the Steinhart-Hart equation for thermistors // https://en.wikipedia.org/wiki/Steinhart%E2%80%93Hart_equation float Thermistor::get_temperature() { float temperature =0, resistance =0; float steinhart =0; double a=0; int smooth = 5; // Number of samples to smooth for(int i=0;i<smooth;i++) { a += _pin.read_u16(); // Read 16bit Analog value } a = a/smooth; // Get average of samples // pc.printf("Raw Analog Value for Thermistor = %d\r\n",a); /* Calculate the resistance of the thermistor from analog votage read. */ resistance = (float) SeriesResistor / ((65536.0 / a) - 1); // pc.printf("Resistance for Thermistor = %f\r\n",resistance); steinhart = resistance / ThermistorNominal; // (R/Ro) steinhart = log(steinhart); // ln(R/Ro) steinhart /= BCoefficient; // 1/B * ln(R/Ro) steinhart += 1.0 / (TemperatureNominal + 273.15); // + (1/To) steinhart = 1.0 / steinhart; // Invert temperature = steinhart - 273.15; // convert to C return temperature; } void Thermistor::set_ThermistorNominal(float thermnom) { ThermistorNominal = thermnom; } void Thermistor::set_TemperatureNominal(float tempnom){ TemperatureNominal = tempnom; } void Thermistor::set_BCoefficient(float bcoefficient){ BCoefficient = bcoefficient; } void Thermistor::set_SeriesResistor(float resistor){ SeriesResistor = resistor; }