lib_SHT25.cpp

00001 /** SHT25 class
00002 *
00003 * @purpose       library for SHT25 humidity and temperature sensor
00004 *
00005 * Use to get temperature and humidity
00006 *
00007 * https://www.sensirion.com/products/humidity-sensor/
00008 *
00009 * Example:
00010 * @code
00011 * #include "lib_SHT25.h"
00012 * 
00013 * SHT25  sensor(I2C_SDA, I2C_SCL);
00014 * 
00015 * int main()
00016 * {
00017 *     while(1)
00018 *     {
00019 *         sensor.waitSafeHeat();
00020 *         float temperature = sensor.getTemperature(), humidity = sensor.getHumidity();
00021 *         printf("\r\ntemperature = %6.2f%cC -|- humidity = %6.2f%%RH", temperature, 248, humidity);
00022 *         sensor.waitSafeHeat();
00023 *         sensor.getData(&temperature, &humidity);
00024 *         printf("\r\ntemperature = %6.2f%cC -|- humidity = %6.2f%%RH", temperature, 248, humidity);
00025 *     }
00026 * }
00027 * @endcode
00028 * @file          lib_SHT25.cpp
00029 * @date          Jun 2018
00030 * @author        Yannic Simon
00031 */
00032 #include "lib_SHT25.h"
00033 
00034 SHT25::SHT25(PinName sda, PinName scl, enum_sht_prec precision, int frequency) : _i2c(sda, scl)
00035 {
00036     _i2c.frequency((frequency<=400e3)?frequency:400e3);
00037     setPrecision(precision);
00038     _temperature = _humidity = NAN;
00039     _selfHeatTemperature = _selfHeatHumidity = false;
00040     _t.attach(callback(this, &SHT25::keepSafeTemperature), SHT_SELF_HEATING);
00041     _h.attach(callback(this, &SHT25::keepSafeHumidity), SHT_SELF_HEATING);
00042 }
00043 
00044 void SHT25::getData(float *tempC, float *relHumidity)
00045 {
00046     if(_selfHeatTemperature && _selfHeatHumidity) readData();
00047     *tempC = _temperature;
00048     *relHumidity = _humidity;
00049 }
00050 
00051 void SHT25::readData(void)
00052 {
00053     _temperature = readTemperature();
00054     _humidity = readHumidity();
00055 }
00056 
00057 float SHT25::getTemperature(void)
00058 {
00059     if(_selfHeatTemperature) _temperature = readTemperature();
00060     return _temperature;
00061 }
00062 
00063 float SHT25::readTemperature(void) // if I2C Freezing go down PullUp resistor to 2K or slow frequency
00064 {
00065     char cmd[] = {SHT_TRIG_TEMP_NHOLD}, rx[] = {0xFF, 0xFF, 0xFF};
00066     _selfHeatTemperature = false;
00067     _t.attach(callback(this, &SHT25::keepSafeTemperature), SHT_SELF_HEATING);
00068     if(!_i2c.write(SHT_I2C_ADDR, cmd, 1))
00069     {
00070         SHT_WAIT(66);
00071         int ack = _i2c.read(SHT_I2C_ADDR, rx, 3);
00072         if(ack)
00073         {
00074             SHT_WAIT(19);
00075             ack = _i2c.read(SHT_I2C_ADDR, rx, 3);    
00076         }
00077         return ack?NAN:-46.85f + 175.72f * ((((rx[0] << 8) | rx[1]) & 0xFFFC) / 65536.0f);
00078     }
00079     return NAN;
00080 }
00081 
00082 float SHT25::getHumidity(void)
00083 {
00084     if(_selfHeatHumidity) _humidity = readHumidity();
00085     return _humidity;
00086 }
00087 
00088 float SHT25::readHumidity(void) // if I2C Freezing go down PullUp resistor to 2K or slow frequency
00089 {
00090     char cmd[] = {SHT_TRIG_RH_NHOLD}, rx[] = {0xFF, 0xFF, 0xFF};
00091     _selfHeatHumidity = false;
00092     _h.attach(callback(this, &SHT25::keepSafeHumidity), SHT_SELF_HEATING);
00093     if(!_i2c.write(SHT_I2C_ADDR, cmd, 1))
00094     {
00095         SHT_WAIT(29);
00096         int ack = _i2c.read(SHT_I2C_ADDR, rx, 3);
00097         return ack?NAN:-6.0f + 125.0f * ((((rx[0] << 8) | rx[1]) & 0xFFFC) / 65536.0f);
00098     }
00099     return NAN;
00100 }
00101 
00102 bool SHT25::setPrecision(const enum_sht_prec precision)
00103 {
00104     char cmd[] = {SHT_WRITE_REG_USER, precision};
00105     return !_i2c.write(SHT_I2C_ADDR, cmd, 2, false);
00106 }
00107 
00108 bool SHT25::softReset()
00109 {
00110     char cmd[] = {SHT_SOFT_RESET};
00111     return !_i2c.write(SHT_I2C_ADDR, cmd, 1, false);
00112 }
00113 
00114 void SHT25::waitSafeHeat(void)
00115 {
00116     while(!_selfHeatTemperature || !_selfHeatHumidity) __NOP();
00117 }
00118 
00119 void SHT25::keepSafeTemperature(void)
00120 {
00121     _selfHeatTemperature = true;
00122 }
00123 
00124 void SHT25::keepSafeHumidity(void)
00125 {
00126     _selfHeatHumidity = true;
00127 }