SparkFun_RHT03.cpp

/*	SparkFunRHT03.cpp
	Jim Lindblom <jim@sparkfun.com>
	August 31, 2015
    
    Ported to Arduino by Shawn Hymel
    October 28, 2016
	https://github.com/sparkfun/SparkFun_RHT03_Arduino_Library
	
	This is the main source file for the SparkFunRHT03 Arduino
	library.
	
	Development environment specifics:
	Arduino IDE v1.6.5
	Distributed as-is; no warranty is given. 
*/

#include "SparkFun_RHT03.h"

RHT03::RHT03()
{
}

void RHT03::begin(int dataPin)
{
    _dataPin = dataPin;
    pinMode(_dataPin, INPUT_PULLUP);
}

float RHT03::tempC()
{
    return (float) _temperature / 10.0;
}

float RHT03::tempF()
{
    return (tempC() * 9.0 / 5.0 + 32.0);
}

float RHT03::humidity()
{
    return (float) _humidity / 10.0;
}

int RHT03::update()
{
    unsigned long marks[41] = {0};
    unsigned long stops[40] = {0};
    unsigned int highTime, lowTime;
    byte dataBytes[5] = {0};
    
    noInterrupts();
    
    // Begin state: input HIGH
    pinMode(_dataPin, INPUT_PULLUP);
    delay(100);
    // Start signal: host sets data low, waits 1 ms, then pulls back up, wait 20-40us
    pinMode(_dataPin, OUTPUT);
    digitalWrite(_dataPin, LOW);
    delay(2); // Wait 1 ms minimum
    pinMode(_dataPin, INPUT_PULLUP);
    delayMicroseconds(20);
    // Sensor should pull data pin low 80us, then pull back up
    if (! waitForRHT(LOW, 1000) )
        return errorExit(0);
    if (! waitForRHT(HIGH, 1000) )
        return errorExit(0);
    
    // Sensor transmits 40 bytes (16 rh, 16 temp, 8 checksum)
    // Each byte starts with a ~50us LOW then a HIGH pulse. The duration of the
    // HIGH pulse determines the value of the bit.
    // LOW: 26-28us (<LOW duration)
    // HIGH: 70us (>LOW duration)
    for (int i=0; i<40; i++)
    {
        if (! waitForRHT(LOW, 1000) )
            return errorExit(-i);
        marks[i] = micros();
        if (! waitForRHT(HIGH, 1000) )
            return errorExit(-i);
        stops[i] = micros();
    }
    if (! waitForRHT(LOW, 1000) )
        return errorExit(-41);
    marks[40] = micros();
    
    interrupts();
    
    for (int i=0; i<40; i++)
    {
        lowTime = stops[i] - marks[i];
        highTime = marks[i + 1] - stops[i];
        if (highTime > lowTime)
        {
            dataBytes[i/8] |= (1<<(7 - i%8));
        }
    }
    
    if (checksum(dataBytes[CHECKSUM], dataBytes, 4))
    {
        _humidity = ((uint16_t) dataBytes[HUMIDITY_H] << 8) | dataBytes[HUMIDITY_L];
        _temperature = ((uint16_t) dataBytes[TEMP_H] << 8) | dataBytes[TEMP_L];
        return 1;
    }
    else
    {
        return -43;
    }
}

bool RHT03::checksum(byte check, byte * data, unsigned int datalen)
{
    byte sum = 0;
    for (int i=0; i<datalen; i++)
    {
        sum = sum + data[i];
    }
    if (sum == check)
        return true;
    
    return false;
}

int RHT03::errorExit(int code)
{
    interrupts();
    return code;
}

bool RHT03::waitForRHT(int pinState, unsigned int timeout)
{
    unsigned int counter = 0;
    while ((digitalRead(_dataPin) != pinState) && (counter++ < timeout))
        delayMicroseconds(1);
    
    if (counter >= timeout)
        return false;
    else
        return true;
}