byte therm_ReadBit()
{
byte bit=0;
THERM_OUTPUT(); // set pin as output
THERM_LOW(); // pull pin low for 1uS
_delay_us(1);
THERM_INPUT(); // release pin & wait 14 uS
_delay_us(14);
if (THERM_READ()) bit=1; // read pin value
_delay_us(45); // wait rest of 60uS period
return bit;
}
byte therm_Reset()
{
byte i;
THERM_OUTPUT(); // set pin as output
THERM_LOW(); // pull pin low for 480uS
_delay_us(480);
THERM_INPUT(); // set pin as input
_delay_us(60); // wait for 60uS
i = THERM_READ(); // get pin value
_delay_us(420); // wait for rest of 480uS period
return i;
}
//
// Read the 40 bit data stream from the DHT 22
// Store the results in private member data to be read by public member functions
//
int dht22_read(float *temperature, float *humidity) {
// uint8_t bitmask = _bitmask;
//volatile uint8_t *reg asm("r30") = _baseReg;
uint8_t retryCount;
uint8_t bitTimes[DHT22_DATA_BIT_COUNT];
int currentHumidity;
int currentTemperature;
uint8_t checkSum, csPart1, csPart2, csPart3, csPart4;
int i;
currentHumidity = 0;
currentTemperature = 0;
checkSum = 0;
//return currentTime;
for(i = 0; i < DHT22_DATA_BIT_COUNT; i++) {
bitTimes[i] = 0;
}
// Pin needs to start HIGH, wait until it is HIGH with a timeout
//cli();
THERM_INPUT_MODE();
//sei();
retryCount = 0;
do {
if (retryCount > 125)
return DHT_BUS_HUNG;
retryCount++;
_delay_us(2);
} while (!THERM_READ());
// Send the activate pulse
//cli();
THERM_LOW();
THERM_OUTPUT_MODE(); // Output Low
//sei();
_delay_us(1100); // 1.1 ms
//cli();
THERM_INPUT_MODE(); // Switch back to input so pin can float
//sei();
// Find the start of the ACK Pulse
retryCount = 0;
do {
if (retryCount > 25) //(Spec is 20 to 40 us, 25*2 == 50 us)
return DHT_ERROR_NOT_PRESENT;
retryCount++;
_delay_us(2);
} while (!THERM_READ());
// Find the end of the ACK Pulse
retryCount = 0;
do {
if (retryCount > 50) //(Spec is 80 us, 50*2 == 100 us)
return DHT_ERROR_ACK_TOO_LONG;
retryCount++;
_delay_us(2);
} while (THERM_READ());
// Read the 40 bit data stream
for (i = 0; i < DHT22_DATA_BIT_COUNT; i++) {
// Find the start of the sync pulse
retryCount = 0;
do {
if (retryCount > 35) //(Spec is 50 us, 35*2 == 70 us)
return DHT_ERROR_SYNC_TIMEOUT;
retryCount++;
_delay_us(2);
// Show activity on TX LED
PORTD &= ~_BV(PD5);
} while (!THERM_READ());
// Measure the width of the data pulse
retryCount = 0;
do {
if (retryCount > 50) //(Spec is 80 us, 50*2 == 100 us)
return DHT_ERROR_DATA_TIMEOUT;
retryCount++;
_delay_us(2);
// Show activity on TX LED
PORTD &= ~_BV(PD5);
} while (THERM_READ());
bitTimes[i] = retryCount;
}
// Now bitTimes have the number of retries (us *2)
// that were needed to find the end of each data bit
// Spec: 0 is 26 to 28 us
// Spec: 1 is 70 us
// bitTimes[x] <= 11 is a 0
// bitTimes[x] > 11 is a 1
// Note: the bits are offset by one from the data sheet, not sure why
for (i = 0; i < 16; i++) {
if (bitTimes[i + 1] > 11)
currentHumidity |= (1 << (15 - i));
}
for (i = 0; i < 16; i++) {
if (bitTimes[i + 17] > 11)
currentTemperature |= (1 << (15 - i));
}
for (i = 0; i < 8; i++) {
if (bitTimes[i + 33] > 11)
checkSum |= (1 << (7 - i));
}
*humidity = ((float)(currentHumidity & 0x7FFF)) / 10.0;
if(currentTemperature & 0x8000) {
// Below zero, non standard way of encoding negative numbers!
currentTemperature &= 0x7FFF;
*temperature = ((float)currentTemperature / 10.0) * -1.0;
} else {
*temperature = (float)currentTemperature / 10.0;
}
csPart1 = currentHumidity >> 8;
csPart2 = currentHumidity & 0xFF;
csPart3 = currentTemperature >> 8;
csPart4 = currentTemperature & 0xFF;
if (checkSum == ((csPart1 + csPart2 + csPart3 + csPart4) & 0xFF)) {
//*humidity = 10;
return DHT_ERROR_NONE;
}
//*humidity = 20;
return DHT_ERROR_CHECKSUM;
}
