#define DHT11_PIN 0 // define anlog port 0

byte read_dht11_dat()
{
byte i = 0;
byte result=0;
for(i=0; i< 8; i++)
{
while(!(PINC & _BV(DHT11_PIN)))
{}; // wait forever until anlog input port 0 is '1' (NOTICE: PINC reads all the analog input ports
//and _BV(X) is the macro operation which pull up positon 'X'to '1' and the rest positions to '0'. it is equivalent to 1<
delayMicroseconds(30);
if(PINC & _BV(DHT11_PIN)) //if analog input port 0 is still '1' after 30 us
result |=(1<<(7-i)); //this position is 1
while((PINC & _BV(DHT11_PIN))); // wait '1' finish
}
return result;
}


void setup()
{
DDRC |= _BV(DHT11_PIN); //let analog port 0 be output port
PORTC |= _BV(DHT11_PIN); //let the initial value of this port be '1'
Serial.begin(9600);
Serial.println("Ready");
}

void loop()
{
byte dht11_dat[5];
byte dht11_in;
byte i;// start condition

PORTC &= ~_BV(DHT11_PIN); // 1. pull-down i/o pin for 18ms
delay(18);
PORTC |= _BV(DHT11_PIN); // 2. pull-up i/o pin for 40ms
delayMicroseconds(1);
DDRC &= ~_BV(DHT11_PIN); //let analog port 0 be input port
delayMicroseconds(40);

dht11_in = PINC & _BV(DHT11_PIN); // read only the input port 0
if(dht11_in)
{
Serial.println("dht11 start condition 1 not met"); // wait for DHT response signal: LOW
delay(1000);
return;
}
delayMicroseconds(80);
dht11_in = PINC & _BV(DHT11_PIN); //
if(!dht11_in)
{
Serial.println("dht11 start condition 2 not met"); //wair for second response signal:HIGH
return;
}

delayMicroseconds(80);// now ready for data reception
for (i=0; i<5; i++)
{ dht11_dat[i] = read_dht11_dat();} //recieved 40 bits data. Details are described in datasheet

DDRC |= _BV(DHT11_PIN); //let analog port 0 be output port after all the data have been received
PORTC |= _BV(DHT11_PIN); //let the value of this port be '1' after all the data have been received
byte dht11_check_sum = dht11_dat[0]+dht11_dat[1]+dht11_dat[2]+dht11_dat[3];// check check_sum
if(dht11_dat[4]!= dht11_check_sum)
{
Serial.println("DHT11 checksum error");
}
Serial.print("Current humdity = ");
Serial.print(dht11_dat[0], DEC);
Serial.print(".");
Serial.print(dht11_dat[1], DEC);
Serial.print("% ");
Serial.print("temperature = ");
Serial.print(dht11_dat[2], DEC);
Serial.print(".");
Serial.print(dht11_dat[3], DEC);
Serial.println("C ");
delay(2000); //fresh time
}