int DHT::readData()
{
int err = ERROR_NONE;
Timer tmr;
DigitalInOut data_pin(_pin);
// We make sure we are the only ones
// reading data right now.
_mutex.lock();
// BUFFER TO RECEIVE
uint8_t cnt = 7;
uint8_t idx = 0;
tmr.stop();
tmr.reset();
// EMPTY BUFFER
for(int i=0; i< 5; i++) DHT_data[i] = 0;
// REQUEST SAMPLE
data_pin.output();
data_pin.write(0);
wait_ms(18);
data_pin.write(1);
wait_us(40);
data_pin.input();
// ACKNOWLEDGE or TIMEOUT
unsigned int loopCnt = 10000;
while(!data_pin.read())if(!loopCnt--)
{
_mutex.unlock();
return ERROR_DATA_TIMEOUT;
}
loopCnt = 10000;
while(data_pin.read())if(!loopCnt--)
{
_mutex.unlock();
return ERROR_DATA_TIMEOUT;
}
// READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT
for(int i=0; i<40; i++){
loopCnt = 10000;
while(!data_pin.read())if(loopCnt-- == 0)
{
_mutex.unlock();
return ERROR_DATA_TIMEOUT;
}
//unsigned long t = micros();
tmr.start();
loopCnt = 10000;
while(data_pin.read())if(!loopCnt--)
{
_mutex.unlock();
return ERROR_DATA_TIMEOUT;
}
if(tmr.read_us() > 40) DHT_data[idx] |= (1 << cnt);
tmr.stop();
tmr.reset();
if(cnt == 0){ // next byte?
cnt = 7; // restart at MSB
idx++; // next byte!
}else cnt--;
}
// WRITE TO RIGHT VARS
uint8_t sum = (DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3]) & 0xFF;
if(DHT_data[4] != sum)
{
_mutex.unlock();
return ERROR_CHECKSUM;
}
_lastTemperature= CalcTemperature();
_lastHumidity= CalcHumidity();
_mutex.unlock();
return err;
}
eError DHT::readData()
{
uint8_t i = 0, j = 0, b = 0, data_valid = 0;
uint32_t bit_value[DHT_DATA_BIT_COUNT] = {0};
eError err = ERROR_NONE;
//time_t currentTime = time(NULL);
DigitalInOut DHT_io(_pin);
// IO must be in hi state to start
if (ERROR_NONE != stall(DHT_io, 0, 250))
{
return BUS_BUSY;
}
// start the transfer
DHT_io.output();
DHT_io = 0;
// only 500uS for DHT22 but 18ms for DHT11
(_DHTtype == 22) ? wait_ms(18) : wait(1);
DHT_io = 1;
wait_us(30);
DHT_io.input();
// wait till the sensor grabs the bus
if (ERROR_NONE != stall(DHT_io, 1, 40))
{
return ERROR_NOT_PRESENT;
}
// sensor should signal low 80us and then hi 80us
if (ERROR_NONE != stall(DHT_io, 0, 100))
{
return ERROR_SYNC_TIMEOUT;
}
if (ERROR_NONE != stall(DHT_io, 1, 100))
{
return ERROR_NO_PATIENCE;
}
// capture the data
for (i = 0; i < 5; i++)
{
for (j = 0; j < 8; j++)
{
if (ERROR_NONE != stall(DHT_io, 0, 75))
{
return ERROR_DATA_TIMEOUT;
}
// logic 0 is 28us max, 1 is 70us
wait_us(40);
bit_value[i * 8 + j] = DHT_io;
if (ERROR_NONE != stall(DHT_io, 1, 50))
{
return ERROR_DATA_TIMEOUT;
}
}
}
// store the data
for (i = 0; i < 5; i++)
{
b = 0;
for (j = 0; j < 8; j++)
{
if (bit_value[i * 8 + j] == 1)
{
b |= (1 << (7 - j));
}
}
DHT_data[i] = b;
}
// uncomment to see the checksum error if it exists
//printf(" 0x%02x + 0x%02x + 0x%02x + 0x%02x = 0x%02x \n", DHT_data[0], DHT_data[1], DHT_data[2], DHT_data[3], DHT_data[4]);
data_valid = DHT_data[0] + DHT_data[1] + DHT_data[2] + DHT_data[3];
if (DHT_data[4] == data_valid)
{
//_lastReadTime = currentTime;
_lastTemperature = CalcTemperature();
_lastHumidity = CalcHumidity();
}
else
{
err = ERROR_CHECKSUM;
}
return err;
}
