SHT2x.cpp

/*
  SHT2x - A Humidity Library for Arduino.

  Supported Sensor modules:
    SHT21-Breakout Module - http://www.moderndevice.com/products/sht21-humidity-sensor
	SHT2x-Breakout Module - http://www.misenso.com/products/001
	
  Created by Christopher Ladden at Modern Device on December 2009.
  Modified by Paul Badger March 2010
  
  Modified by www.misenso.com on October 2011:
	- code optimisation
	- compatibility with Arduino 1.0
  
  Modified by Patrick Thompson
	- Added NON Blocking Functions
  
  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <inttypes.h>
#include "wire.h"
#include "Arduino.h"
#include "SHT2x.h"

uint8_t ReadingStatus = SHT2X_Status::eReady;

/******************************************************************************
 * Global Functions
 ******************************************************************************/

/**********************************************************
 * GetHumidity
 *  Gets the current humidity from the sensor.
 *
 * @return float - The relative humidity in %RH
 **********************************************************/
float SHT2xClass::GetHumidity()
{
	float result = readSensor(eRHumidityHoldCmd);
	
	return (-6.0 + 125.0 / 65536.0 * (float)(readSensor(result)));
}


/**********************************************************
 * StartSensorRead
 *  SensorToRead = Which Sensor to Start Reading
 *	Starts A Sensor Read
 * @return uint8_t - Code to Look for Errors 1 = Success
 **********************************************************/
uint8_t SHT2xClass::StartSensorRead(uint8_t SensorToRead)
{
	uint8_t returnCode = 0;
	if (ReadingStatus == SHT2X_Status::eReady)
	{
		ReadingStatus = SensorToRead;
		Wire.beginTransmission(eSHT2xAddress);
		if (SensorToRead == SHT2X_Status::eTempature)
		{
			Wire.write(eTempNoHoldCmd);					
			
		}
		if (SensorToRead == SHT2X_Status::eHumidity)
		{
			Wire.write(eRHumidityNoHoldCmd);
		}
		Wire.endTransmission();               	
		delayMicroseconds(20);
		returnCode = 1;
	}
	return returnCode;
}

/**********************************************************
 * SensorDataReady
 *  Checks to see if sensor data is ready
 *
 * @return bool - True if Ready to read data
 **********************************************************/
bool SHT2xClass::SensorDataReady()
{
	bool result = false;
	if (ReadingStatus > 0)
	{
		if (Wire.requestFrom(eSHT2xAddress,3) >= 3)
		{
			result = true;
		}
	}
	return result;
}


/**********************************************************
 * ReadSensorData
 *  Reads incoming Sensor Data and returns it;
 *
 * @return uint8_t = Sensor that was read 
  **********************************************************/
uint8_t SHT2xClass::ReadSensorData(float* result)
{
	uint8_t returnCode = ReadingStatus;
	uint16_t rawData;
	rawData = ((Wire.read()) << 8);
	rawData += Wire.read();
	rawData &= ~0x0003;   // clear two low bits (status bits)
	if (ReadingStatus == SHT2X_Status::eHumidity)
	{
		*result = (-6.0 + 125.0 / 65536.0 * (float)(rawData));
	}
	if (ReadingStatus == SHT2X_Status::eTempature)
	{
		*result = (-46.85 + 175.72 / 65536.0 * (float)(rawData));
	}
	ReadingStatus = SHT2X_Status::eReady;
	return returnCode;
}


/**********************************************************
 * GetTemperature
 *  Gets the current temperature from the sensor.
 *
 * @return float - The temperature in Deg C
 **********************************************************/
float SHT2xClass::GetTemperature()
{
	float result = (readSensor(eTempHoldCmd));

	return (-46.85 + 175.72 / 65536.0 * (float)(result));
}


/******************************************************************************
 * Private Functions
 ******************************************************************************/

uint16_t SHT2xClass::readSensor(uint8_t command)
{
    uint16_t result;

    Wire.beginTransmission(eSHT2xAddress);	//begin
    Wire.write(command);					//send the pointer location
    delay(100);
    Wire.endTransmission();               	//end

    Wire.requestFrom(eSHT2xAddress, 3);
    while(Wire.available() < 3) {
      ; //wait
    }

    //Store the result
    result = ((Wire.read()) << 8);
    result += Wire.read();
	result &= ~0x0003;   // clear two low bits (status bits)
    return result;
}


SHT2xClass SHT2x;