dht22_pic24hj

/* Delay function for up to 4552ms at 7.37Mhz FOSC */
void wait_ms(unsigned int wait) {
    float tick = 0;
    unsigned int loopValue = 0;
    T1CON = 0x0030;     // Set prescaler for T1 to 256
    tick = 69*1e-6;      // Calculate tick for given FOSC
    wait = wait * 1e-3;
    loopValue = (unsigned int) ( wait / tick );
    TMR1 = 0;           // Clear T1 registers
    _TON = 1;           // Start T1
    while (TMR1 < loopValue);   // Delay for @wait
    _TON = 0;           // Stop T1
}

/* Delay function for up to 142276us at 7.37Mhz FOSC*/
void wait_us(unsigned int wait) {
    float tick = 0;
    unsigned int loopValue = 0;
    T1CON = 0x0010;     // Set prescaler for T1 to 8
    tick = 2*1e-6;      // Calculate tick for given FOSC
    wait = wait * 1e-6;
    loopValue = (unsigned int) ( wait / tick );
    TMR1 = 0;           // Clear T1 registers
    _TON = 1;           // Start T1
    while (TMR1 < loopValue);   // Delay for @wait
    _TON = 0;           // Stop T1
}

/* Function to start T1 */
void startTimer() {
    TMR1 = 0;           // Clear T1 registers
    _T1IP = 0x01;       // Set T1 interrupt priority lvl
    _T1IF = 0;          // Clear T1 interrupt flag
    _T1IE = 1;          // Enable T1 interrupt
    T1Flag = 0;         // Flag for T1 overflow
    T1CON = 0x8010;     // Set prescaler for T1 to 8 and start T1
}

/* Stop T1 and calculate the signal time. Returns signal time in us. */
unsigned int stopTimer() {
    unsigned int sigTime = 0, TMRValue = 0;
    float tick;
    TMRValue = TMR1;       // Save current T1 register value
    _TON = 0;               // Stop T1
    T1Flag = 0;             // Flag for T1 overflow
    tick = 2;               // Calculate tick for given FOSC
    sigTime = (unsigned int) (TMRValue * tick);
    return sigTime;
}

/* Initalises communication with the sensor */
void sendStartSignal() {
    BUSHIGH;             // Set logical bus state to high
    WRITE;              // Bus pin as output
    BUSLOW;              // Set logical bus state to low
    wait_ms(20);        // Wait for at least 18ms
    BUSHIGH;            // Set logical bus state to high
    wait_us(39);        // Wait for at least 20us
    READ;               // Bus pin as input
}

/* Listen on the bus for sensor start signal */
unsigned char waitForSensor() {
    startTimer();       // Start T1 to determine sensor start signal time
    while (!DATADHT && !T1Flag);   // Sensor pulls bus low for ~80us
    if (T1Flag) {
        stopTimer();
        return 0;
    }
    else {
        while (DATADHT && !T1Flag);    // Sensor pulls bus high for ~80us
        if (T1Flag) {
            stopTimer();
            PutsXLCD("hier");
            return 0;
        }
        else {
            unsigned int time = stopTimer();    // Stop timer
            if (time >= 160 && !T1Flag)
                return 1;
            else
                return 0;
        }
    }
}