HTU21D.cpp

00001 // @author Alex Lipford
00002 // Georgia Institute of Technology 
00003 // ECE 4180 Embeded Systems Design
00004 // Professor Hamblen
00005 // 10/19/2014
00006  
00007 // @section LICENSE
00008 // ----------------------------------------------------------------------------
00009 // "THE BEER-WARE LICENSE" (Revision 42):
00010 // <alexlipford@gmail.com> wrote this file. As long as you retain this notice you
00011 // can do whatever you want with this stuff. If we meet some day, and you think
00012 // this stuff is worth it, you can buy me a beer in return.
00013 // ----------------------------------------------------------------------------
00014 
00015 // @section DESCRIPTION
00016 // HTU21D Humidity and Temperature sensor.
00017 // Datasheet, specs, and information:
00018 // https://www.sparkfun.com/products/12064
00019 
00020 
00021 #include "HTU21D.h"
00022 
00023 HTU21D::HTU21D(PinName sda, PinName scl) {
00024 
00025     i2c_ = new I2C(sda, scl);
00026     //400KHz, as specified by the datasheet.
00027     i2c_->frequency(400000);
00028 }
00029 
00030 int HTU21D::sample_ctemp(void) {
00031 
00032     char tx[1];
00033     char rx[2];
00034 
00035     tx[0] = TRIGGER_TEMP_MEASURE; // Triggers a temperature measure by feeding correct opcode.
00036     i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1);
00037     wait_ms(50); // Per datasheet, wait long enough for device to sample temperature
00038     
00039     // Reads triggered measure
00040     i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2);
00041     wait_ms(1);
00042     
00043     // Algorithm from datasheet to compute temperature.
00044     unsigned int rawTemperature = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1];
00045     rawTemperature &= 0xFFFC;
00046 
00047     float tempTemperature = rawTemperature / (float)65536; //2^16 = 65536
00048     float realTemperature = -46.85 + (175.72 * tempTemperature); //From page 14
00049 
00050     return (int)realTemperature;
00051 }
00052 
00053 int HTU21D::sample_ftemp(void){
00054     int temptemp = sample_ctemp();
00055     int ftemp = temptemp * 1.8 + 32;
00056     
00057     return ftemp;
00058 }
00059 
00060 int HTU21D::sample_ktemp(void){
00061     int temptemp = sample_ctemp();
00062     int ktemp = temptemp + 274;
00063     
00064     return ktemp;
00065 }
00066 
00067 int HTU21D::sample_humid(void) {
00068 
00069     char tx[1];
00070     char rx[2];
00071 
00072 
00073     tx[0] = TRIGGER_HUMD_MEASURE; // Triggers a humidity measure by feeding correct opcode.
00074     i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1);
00075     wait_ms(16); // Per datasheet, wait long enough for device to sample humidity
00076     
00077     // Reads triggered measure
00078     i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2);
00079     wait_ms(1);
00080     
00081     //Algorithm from datasheet.
00082     unsigned int rawHumidity = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1];
00083 
00084     rawHumidity &= 0xFFFC; //Zero out the status bits but keep them in place
00085     
00086     //Given the raw humidity data, calculate the actual relative humidity
00087     float tempRH = rawHumidity / (float)65536; //2^16 = 65536
00088     float rh = -6 + (125 * tempRH); //From page 14
00089 
00090     return (int)rh;
00091 }
00092