MOON_HUMTEMP.cpp

00001 #include "Moon_HUMTEMP.h"
00002  
00003 HTU21D::HTU21D(PinName sda, PinName scl) {
00004  
00005     i2c_ = new I2C(sda, scl);
00006     //400KHz, as specified by the datasheet.
00007     i2c_->frequency(400000);
00008  
00009  
00010  
00011 }
00012  
00013 int HTU21D::sampleTemp_cel(void) {
00014  
00015     char tx[1];
00016     char rx[2];
00017  
00018     tx[0] = TRIGGER_TEMP_MEASURE; // Triggers a temperature measure by feeding correct opcode.
00019     i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1);
00020     wait_ms(50); // Per datasheet, wait long enough for device to sample temperature
00021     
00022     // Reads triggered measure
00023     i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2);
00024     wait_ms(1);
00025     
00026     // Algorithm from datasheet to compute temperature.
00027     unsigned int rawTemperature = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1];
00028     rawTemperature &= 0xFFFC;
00029  
00030     float tempTemperature = rawTemperature / (float)65536; //2^16 = 65536
00031     float realTemperature = -46.85 + (175.72 * tempTemperature); //From page 14
00032  
00033     return (int)realTemperature;
00034  
00035 }
00036  
00037 int HTU21D::sampleTemp_fah(void){
00038     int Temp_Original = sampleTemp_cel();
00039     int fah_temp = Temp_Original * 1.8 + 32;
00040     
00041     return fah_temp;
00042 }
00043  
00044 int HTU21D::sampleTemp_kel(void){
00045     int Temp_Original = sampleTemp_cel();
00046     int kel_temp = Temp_Original + 274;
00047     
00048     return kel_temp;
00049     
00050     
00051 }
00052  
00053 int HTU21D:: sample_Humid(void) {
00054  
00055     char tx[1];
00056     char rx[2];
00057  
00058  
00059     tx[0] = TRIGGER_HUMD_MEASURE; // Triggers a humidity measure by feeding correct opcode.
00060     i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1);
00061     wait_ms(16); // Per datasheet, wait long enough for device to sample humidity
00062     
00063     // Reads triggered measure
00064     i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2);
00065     wait_ms(1);
00066     
00067     //Algorithm from datasheet.
00068     unsigned int rawHumidity = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1];
00069  
00070     rawHumidity &= 0xFFFC; //Zero out the status bits but keep them in place
00071     
00072     //Given the raw humidity data, calculate the actual relative humidity
00073     float tempRH = rawHumidity / (float)65536; //2^16 = 65536
00074     float rh = -6 + (125 * tempRH); //From page 14
00075  
00076  
00077     return (int)rh;
00078  
00079 }
00080  
00081