Diff: SHT40.cpp

Revision:

0:c46b3e0a8c2b

Child:

1:c6381a3f2d9a

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/SHT40.cpp	Mon Feb 07 15:08:07 2022 +0000
@@ -0,0 +1,85 @@
+/**
+ * @author Andrew Reed 
+ * 
+ * Freeware --
+ * simple driver hacked together by hardware engineer, definite scope for 
+ * improvement by someone who knows waht they are doing.
+ *
+ * @section DESCRIPTION
+ *
+ * SHT40 i2c Humidity and Temperature sensor.
+ *
+ * Datasheet, specs, and information:
+ *
+ * https://www.adafruit.com/product/4885
+ */
+
+/**
+ * Includes
+ */
+#include "SHT40.h"
+
+SHT40::SHT40(PinName sda, PinName scl) {
+
+    i2c_ = new I2C(sda, scl);
+    //400KHz, as specified by the datasheet.
+    i2c_->frequency(I2C_SPEED_FAST);
+
+
+
+}
+
+int SHT40::tempC(void) {
+
+    char txBuff[2];
+    char rxBuff[6];
+
+    txBuff[0] = SHT4x_NOHEAT_HIGHPRECISION; // Triggers a temperature measure by feeding correct opcode.
+    txBuff[1] = SHT4x_NOHEAT_HIGHPRECISION >> 8;
+    i2c_->write((SHT40_I2C_ADDRESS << 1) & 0xFE, txBuff, 2);
+    thread_sleep_for(50); // Per datasheet, wait long enough for device to sample temperature
+    
+    // Reads triggered measure
+    i2c_->read((SHT40_I2C_ADDRESS << 1) | 0x01, rxBuff, 6);
+    thread_sleep_for(1);
+    
+    // Algorithm from arduino sht4x.h to compute temperature.
+    unsigned int rawTemperature = ((unsigned int) rxBuff[0] << 8) | (unsigned int) rxBuff[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 SHT40::relHumid(void) {
+
+    char txBuff[2];
+    char rxBuff[6];
+
+
+    txBuff[0] = SHT4x_NOHEAT_HIGHPRECISION; // send command.
+    txBuff[1] = SHT4x_NOHEAT_HIGHPRECISION >> 8;
+    i2c_->write((SHT40_I2C_ADDRESS << 1) & 0xFE, txBuff, 2);
+    thread_sleep_for(16); // delay to sample humidity
+    
+    // Reads measurement
+    i2c_->read((SHT40_I2C_ADDRESS << 1) | 0x01, rxBuff, 6);
+    thread_sleep_for(1);
+    
+    //Algorithm from sht4x.h.
+    unsigned int rawHumidity = ((unsigned int) rxBuff[3] << 8) | (unsigned int) rxBuff[4];
+
+    rawHumidity &= 0xFFFC; //Zero out the status bits but keep them in place
+    
+    //Convert to relative humidity
+    float RH = rawHumidity / (float)65536; // two bytes worth to float
+    float rh = -6 + (125 * RH); // adjustment values as per sht4x.h
+    rh = min(max(rh, (float)0.0), (float)100.0);
+
+
+    return (int)rh;
+
+}
+