![](/media/cache/img/default_profile.jpg.50x50_q85.jpg)
Smart
Diff: HTU21D.cpp
- Revision:
- 0:69293b19ee19
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/HTU21D.cpp Wed Feb 28 16:34:40 2018 +0000 @@ -0,0 +1,83 @@ +// EE 4391 Senior Design +// Professor Hinkle and Dr. Compeau +// @author Team Eta +// Texas State University + +// @section DESCRIPTION +// HTU21D Humidity and Temperature sensor. +// Datasheet, specs, and information: +// https://cdn.sparkfun.com/assets/6/a/8/e/f/525778d4757b7f50398b4567.pdf + + +#include "HTU21D.h" + +HTU21D::HTU21D(PinName sda, PinName scl) { + + i2c_ = new I2C(sda, scl); + //400KHz, as specified by the datasheet page 3. + i2c_->frequency(400000); +} + +int HTU21D::sample_ctemp(void) { + + char tx[1]; + char rx[2]; + + tx[0] = TRIGGER_TEMP_MEASURE; // Triggers a temperature measure by feeding correct opcode. + i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1); + wait_ms(50); // Per datasheet, wait long enough for device to sample temperature + + // Reads triggered measure + i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2); + wait_ms(1); + + // Algorithm from datasheet to compute temperature. + unsigned int rawTemperature = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1]; + rawTemperature &= 0xFFFC; + + float tempTemperature = rawTemperature / (float)65536; //2^16 = 65536 + float realTemperature = -46.85 + (175.72 * tempTemperature); //From page 14 + + return (int)realTemperature; +} + +int HTU21D::sample_ftemp(void){ + int temptemp = sample_ctemp(); + int ftemp = temptemp * 1.8 + 32; //Change this value to fit our Hexiwear or adjut temperature calibration -- "16" used to be "32" + + return ftemp; +} + +int HTU21D::sample_ktemp(void){ + int temptemp = sample_ctemp(); + int ktemp = temptemp + 274; + + return ktemp; +} + +int HTU21D::sample_humid(void) { + + char tx[1]; + char rx[2]; + + + tx[0] = TRIGGER_HUMD_MEASURE; // Triggers a humidity measure by feeding correct opcode. + i2c_->write((HTU21D_I2C_ADDRESS << 1) & 0xFE, tx, 1); + wait_ms(16); // Per datasheet, wait long enough for device to sample humidity + + // Reads triggered measure + i2c_->read((HTU21D_I2C_ADDRESS << 1) | 0x01, rx, 2); + wait_ms(1); + + //Algorithm from datasheet. + unsigned int rawHumidity = ((unsigned int) rx[0] << 8) | (unsigned int) rx[1]; + + rawHumidity &= 0xFFFC; //Zero out the status bits but keep them in place + + //Given the raw humidity data, calculate the actual relative humidity + float tempRH = rawHumidity / (float)65536; //2^16 = 65536 + float rh = 20 + (125 * tempRH); //From page 14 --- "20" used to be "-6" + + return (int)rh; +} +