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;
+}
+